Analysis of the "nurse-tree effect" of exotic shelter trees on the growth of the indigenous Podocarpus falcatus in an Ethiopian montane forest

Analysis o he “nu se- ee e ec “ o exo ic shel e ees on he g ow h o he indigenous Podoca pus alca us in an E hiopian mon ane o es Disse a ion Zu E langung des Dok o g ades de Fakul ä Biologie, Chemie und Geowissenscha en de Uni e si ä Bay eu h o geleg on Simone S obl Bay eu h, im Augus 2011 II Die o liegende A bei wu de in de Zei on Mä z 2005 bis Augus 2011 un e de Lei ung on P o . D . D . h.c. E win Beck am Leh s uhl ü P lanzenphysiologie ange e ig . Die Un e suchungen anden im Rahmen de DFG-P ojek e “Regene a ion in an E hiopian mon ane o es wi h special emphasis on ee biology and nu se- ee unc ions“ und “Coexis ence o di e en unc ional ypes o indigenous ees o he Munessa Fo es , E hiopia: Ca bon, wa e and nu ien ela ions” s a und wu den du ch Mi el de Deu schen Fo schungsgemeinscha ge ö de (DFG BE 473 35/2 und DFG BE 47339/1). Volls ändige Abd uck de on de Fakul ä ü Biologie, Chemie und Geowissenscha en de Uni e si ä Bay eu h genehmig en Disse a ion zu E langung des akademischen G ades eines Dok o s de Na u wissenscha en (D . e . na .). Disse a ion einge eich am: 16. Augus 2011 Zulassung du ch die P ü ungskommission: 29. Sep embe 2011 Wissenscha liches Kolloquium: 13. Feb ua 2012 Am ie ende Dekanin: P o . D . Bea e Lohne P ü ungsausschuss: P o . D . D . h.c. E win Beck (E s gu ach e ) PD D . G ego Aas (Zwei gu ach e ) P o . D . Kon ad De ne P o . D . Be ina Engelb ech P o . D . Ge ha d Gebaue (Vo si z) III Folgende Ve ö en lichungen sind im Zei aum diese A bei en s anden: S obl S, Fe ene M, Beck E (2011) Analysis o he “shel e ee-e ec ” o na u al and exo ic o es canopies on he g ow h o young Podoca pus alca us ees in sou he n E hiopia. T ees - S uc u e and Func ion 25: 769-783 K epkowski J, B aeuning A, Geb eki s os A, S obl S (2011) Cambial g ow h dynamics and clima ic con ol o di e en ee li e o ms in opical moun ain o es in E hiopia. T ees-S uc u e and Func ion 25:59-70 Con en I Con en I Lis o igu es IV Lis o ables VIII 1 In oduc ion 1 1.1 Fo es s in E hiopia 1 1.2 The Munessa-Shashamene Fo es 1 1.3 Impac o exo ic ee plan a ion on he en i onmen and he eju ena ion o indigenous ees 3 1.4 The “nu se- ee e ec ” 4 1.5 Aim o he s udy 6 1.6 Ou each o he s udy 7 2 Ma e ial and me hods 9 2.1 S udy a ea 9 2.2 Clima e o he esea ch a ea 10 2.3 Geology and soils 11 2.4 In es iga ed ees 12 2.4.1 Podoca pus alca us 12 2.4.2 Pinus pa ula 12 2.4.3 Eucalyp us saligna 13 2.5 Resea ch si es and plo s 13 2.5.1 The s uc u e o he h ee o es s, as e lec ed by he in es iga ed plo s 18 2.5.2 Heigh , dbh and p ojec ed c own a ea o he saplings 20 2.5.3 Heigh , dbh and p ojec ed c own a ea o he shel e - ees 21 2.6 Mic oclima e 21 2.6.1 Sub-canopy mic oclima es 22 2.7 Measu emen o sap low 23 2.7.1 Hea dissipa ion me hod (G anie ) 23 2.7.2 Sap low measu emen 24 2.7.3 Calcula ion o sap low 25 2.7.4 Iden i ica ion o sap wood a ea 26 2.7.5 Calib a ion o sap low senso s 26 2.8 Gas exchange 27 2.8.1 P inciple o he Walz po ome e 27 2.8.2 Measu emen o pho osyn hesis 28 2.9 The δ 13 C iso ope a io 29 2.10 S a is ical analysis 30 3 Resul s 31 Con en II 3.1 G ow h 31 3.2 Soil-bo n ac o s o po en ial e ec s on g ow h 32 3.3 Clima e and sub-canopy mic oclima e o he plo s 32 3.3.1 The e ec s o he di e en canopies on he sub-canopy mic oclima es 32 3.3.1.1 Tempe a u e 32 3.3.1.2 Wa e apou p essu e de ici (VPD) and ela i e humidi y 33 3.3.1.3 Th ough all 35 3.3.1.4 Pho osyn he ic ac i e adia ion (PAR) 36 3.3.2 Ve ical g adien s in he sub-canopy mic oclima es summa ized o e he yea 38 3.3.2.1 Tempe a u e, ela i e humidi y and VPD 38 3.3.2.2 Pho osyn he ic ac i e adia ion 38 3.3.3 Daily cou ses o mic oclima e ac o s e ealed by mean hou ly alues 39 3.3.3.1 Diu nal cou se o ai empe a u e and VPD– examples o d y and ainy season days a he saplings le el 39 3.3.3.2 Daily cou se o PAR a saplings le el – examples o d y and ainy season days 41 3.3.4 Daily a e ages and sums, espec i ely, o he a iables o he unde s o ey mic oclima es 43 3.4 Pho osyn hesis 44 3.4.1 In es iga ion o ac o s in luencing CO 2 ne up ake 44 3.4.1.1 In luence o clima e ac o s 44 3.4.1.2 Ligh sa u a ion 45 3.4.1.3 Expe imen al simula ion o he in luence o sun lecks on pho osyn he ic ne CO 2 up ake 46 3.4.2 Sun lecks 48 3.4.2.1 E ec o he numbe and equency o sun lecks on he daily ne CO 2 up ake 48 3.4.2.2 Classi ica ion o he h ee sub-canopy ligh clima es by ligh in ensi y and empo al sha es o ligh in ensi y classes 49 3.4.2.3 The ole o sun lecks in he daily CO 2 up ake 52 3.4.3 Daily accumula ed PAR and ca bon gain 52 3.4.4 Co ela ion be ween PAR, CO 2 ne up ake and s oma al conduc ance 54 3.5 CO 2 ne up ake o he Podoca pus alca us shel e - ee in compa ison o he saplings 55 Con en III 3.5.1 Ligh esponse cu e 56 3.5.2 Diu nal cou ses o ne CO 2 up ake and PAR 56 3.5.3 Ca bon gain 57 3.6 Sap low 57 3.6.1 Diu nal cou ses o sap low o he Podoca pus alca us saplings as ela ed o VPD unde he di e en canopies 58 3.6.2 Daily sums o sap low o he Podoca pus alca us saplings in he di e en si es on example days in he ainy and d y season 61 3.6.3 Sap low o he shel e - ees 62 3.6.4 Daily sums o sap low o he Podoca pus saplings and shel e - ees 67 3.6.5 T anspi a ion e sus sap low 68 3.7 Ca bon iso opes (δ 13 C) o he lea es o he Podoca pus alca us saplings and nu se- ees 70 4 Discussion 72 4.1 Ve i ica ion o he shel e - ee e ec on he g ow h o Podoca pus saplings 72 4.2 In luence o clima e ac o s on he pe o mance and wa e ela ions o he Podoca pus saplings 74 4.2.1 Tempe a u es and VPD 75 4.2.2 Th ough all 75 4.2.3 Sub-canopy ligh ela ions (PAR) 76 4.2.4 S oma al esponses o mic oclima e ac o s and e ec s on CO 2 up ake 77 4.2.5 E ec o PAR on ca bon up ake 78 4.2.5.1 Ligh esponse cu es 78 4.2.5.2 Ligh lecks 79 4.2.6 E ec o sun lecks and di use PAR on ca bon up ake 80 4.2.7 Wa e ela ions - supply and consump ion 82 4.3 Conclusion 85 5 Summa y 86 6 Zusammen assung 90 7 Li e a u e 95 8 Acknowledgemen 105 Con en IV Lis o igu es Figu e 1: Ma u e Podoca pus alca us a he edge o he na u al o es , wi h he ypical s em g ow h wi h pe iphe al s ands occu ing in olde ees. Fo an es ima ion o he size compa e he pe son a he base o he s em. 3 Figu e 2: Eucalyp us plan a ion abou one yea a e clea - elling. Cen e o he backg ound: Some Eucalyp us ees we e excep ed om he elling ac ion. Backg ound igh : A Podoca pus “mo he ee” p o iding he seeds. Middle and o eg ound: Podoca pus saplings a e emo al o he coppiced Eucalyp us ees. 6 Figu e 3: E hiopia and he loca ion o he s udy a ea. A: Map o A ica wi h E hiopia (black hemmed) (sa elli e o hog aphic map: NASA), B: physical map o E hiopia, cen al E hiopian i alley (A si egion) ma ked by a black ec angle (sa elli e map E hiopia: Wikimedia), C: Sa elli e image o he esea ch a ea “Kuke” in he Munessa-Shashamene Fo es , wi h na u al o es and plan a ions o exo ic ee species (Google Ea h). Due o he came a angle o he image no h is o ien ed o he lowe side o he pic u e. 10 Figu e 4: Wal e - ype clima e diag am o he esea ch a ea (eigh yea a e ages 2001 o 2009 a Kuke ield s a ion). 11 Figu e 5: A: Na u al o es wi h medium size Podoca pus alca us (cen e) and B: Podoca pus sapling (wi h ed ape) in he na u al o es in he plo 1a. 14 Figu e 6: Unde s o ey o an abou 40 yea s old Pinus pa ula plan a ion wi h many Podoca pus saplings (PF). 15 Figu e 7: View in o an Eucalyp us saligna plan a ion wi h 3 Podoca pus saplings (PF) g owing in he unde s o ey. 16 Figu e 8: S uc u e o he in es iga ed plo s. Ve ical p ojec ion o he c own a eas o he in es iga ed Podoca pus alca us saplings/ eele s (black ci cles) and o he shel e (o ange ci cles) ees in he h ee plo s. A: Plo in he na u al o es , wi h an a ea o 52 m 2 , B: Plo in he Pinus plan a ion, 102 m 2 , C: Plo in he Eucalyp us plan a ion, 103 m 2 ; P: Podoca pus alca us, Pi Pinus pa ula, E: Eucalyp us saligna, T o he ee species; b own lines: ences. 19 Figu e 9: Ske ch o mic oclima e s a ion moun ed on he sca old and he posi ion o he senso s. RH/T senso s o ela i e humidi y and ai empe a u e, PAR senso , L global adia ion senso , RC h ough all collec o , DL da a logge , PF Podoca pus alca us sapling. 22 Figu e 10: A: PAR, global adia ion, empe a u e and ela i e humidi y senso s on op o he sca olds, B Unde s o ey s a ion wi h senso s o PAR, global adia ion, empe a u e, ela i e humidi y, and h ough all collec o ; C sca old in he Eucalyp us plan a ion. 23 Figu e 11: A: P inciple o sap low measu emen s wi h he G anie me hod (Mo ze 2003), B Sap low measu emen in he na u al o es on a Podoca pus alca us (nu se- ee) wi h adia ion p o ec ion o aluminium oil and cons an powe supply, in he backg ound he senso s o he mic oclima e s a ion. 24 Figu e 12: Calib a ion o he G anie sap low senso s o Podoca pus (dbh 9.5 cm). Dashed line: heo e ical co ela ion acco ding o G anie (G anie 1985). 27 Con en V Figu e 13: A: P inciple o he GFS-3000 po ome e in he CO 2 con olled mode (Walz 2005, modi ied ske ch), B: Measu emen o pho osyn hesis o a Podoca pus alca us sapling in he Pinus plo . 28 Figu e 14: Mon hly ela i e g ow h a es ( adial g ow h a dbh) o Podoca pus saplings a he h ee si es measu ed o e wo yea s (Ap il 2005 o Ma ch 2007). Di e en lowe case le e s indica e s a is ically signi ican di e ences. RGR was in es iga ed wi h he linea mixed e ec model, wi h he plo s as ixed ac o s and he indi idual ees and numbe s o measu emen s as andom ac o s. 31 Figu e 15: Mon hly means o he ai empe a u es 1.5 m abo e g ound in he h ee o es plo s (NF: na u al o es , ES: Eucalyp us saligna plan a ion and PP: Pinus pa ula plan a ion and o he e e ence s a ion ou side he o es (2 m). Due o he a ailabili y o only 2 mic oclima e s a ions con inuous eadings a e only o he na u al o es plo . The second mic oclima e s a ion was s a ed in No embe 2005 and was pe iodically mo ed be ween he 2 o he si es. Thus, da a se s om he plo s in he Pinus and he Eucalyp us plan a ions a e p incipally no con inuous. Be ween July and Oc obe 2006, bo h mic oclima e s a ions in he o es si es had addi ionally echnical p oblems. 33 Figu e 16: Mon hly means o VPD ( eco ded 1.5 m abo e g ound le el) in he h ee o es plo s (NF: na u al o es , PP: Pinus pa ula plan a ion, ES: Eucalyp us saligna plan a ion) and o he e e ence s a ion ou side he o es (2 m abo e g ound). Wi h espec o gaps in he da a se s e e o he legend o Figu e 15. 34 Figu e 17: Mon hly means o he ela i e humidi y 1.5 m abo e g ound le el in he h ee o es plo s (NF: na u al o es , PP: Pinus pa ula plan a ion, ES Eucalyp us saligna plan a ion) and o he e e ence s a ion a he esea ch s a ion (2 m abo e g ound). Wi h espec o he gaps in he da a e e o he legend o Figu e 15. 35 Figu e 18: Mon hly means o h ough all in he h ee o es ypes as compa ed o he (mon hly) p ecipi a ion ou side he o es . Be ween July and Oc obe 2006 ( ainy season), he mic oclima e s a ion in he na u al o es (NF) had a echnical p oblem and in Sep embe and Oc obe 2006 also he ain gauge o he second mic oclima e s a ion which was s a ed in No embe 2005, ailed. 36 Figu e 19: Mon hly a e age o he daily sums o he sola adia ion 1.5 m abo e g ound le el in he h ee o es plo s and o he e e ence s a ion ou side he o es (2 m). Fo gaps in he da a se s e e o he legend o Figu e 15. 37 Figu e 20: Visualiza ion o g adien s o mon hly means o he daily sums o pho osyn he ic ac i e adia ion (PAR) be ween he unde s o ey a saplings (a 1.5 m) and he sub-canopy le els (be ween 10 and 12 m abo e g ound). 39 Figu e 21: Daily cou ses o hou ly means o ai empe a u e in he h ee o es ypes a saplings le el. A: In he na u al o es and in he Pinus plan a ion on a ainy day (July 3, 2006). B: In he na u al o es and in he Eucalyp us plan a ion on a ainy day (June 2, 2006). C: In he na u al o es and in he Pinus plan a ion on a sunny day (No embe 8, 2005). D: In he na u al o es and in he Eucalyp us plan a ion on a sunny day (Ma ch 8, 2006). 40 Figu e 22: Daily cou ses o mean hou ly VPD in he h ee o es s a saplings le el. A: In he na u al o es and in he Pinus plan a ion on a ainy day (July 3, 2006). Con en VI B: In he na u al o es and in he Eucalyp us plan a ion on a ainy day (June 2, 2006). C: In he na u al o es and in he Pinus plan a ion on a sunny day (No embe 8, 2005). D: In he na u al o es and in he Eucalyp us plan a ion on a sunny day (Ma ch 8, 2006). 41 Figu e 23: Daily cou ses o mean hou ly pho osyn he ic ac i e adia ion (PAR) in he h ee o es ypes a saplings le el. A: In he na u al o es and in he Pinus plan a ion on a ainy day (July 3, 2006). B: In he na u al o es and in he Eucalyp us plan a ion on a ainy day (June 2, 2006). C: In he na u al o es and in he Pinus plan a ion on a sunny day (No embe 8, 2005). D: In he na u al o es and in he Eucalyp us plan a ion on a sunny day (Ma ch 8, 2006). 42 Figu e 24: Co ela ion be ween di e en PAR in ensi ies and CO 2 ne up ake unde ambien condi ions, i.e. a ying empe a u e and ela i e humidi y. Each da a poin shows he mean alue (± SE) o CO 2 ne up ake when el. humidi y changed be ween 22 and 66%, and he empe a u e be ween 15 and 32 °C. The quad a ic model g aph is based on he pa ame e es ima es o he quad a ic model gi en in Table 5 44 Figu e 25: Ligh (PAR) esponse cu es o pho osyn he ic CO 2 ne up ake by lea es o Podoca pus saplings g owing unde he canopies o he na u al o es (A), o Pinus pa ula (B), Eucalyp us saligna (C) and wi hou shel e in an open si e (D). Da a show mean alues o wo o i e saplings pe si e wi h 3 epe i ions pe lea (± S.E.) 46 Figu e 26: Analysis o he ligh leck e ec on pho osyn he ic CO 2 up ake by wo a i icial ligh condi ions, p o iding he same amoun s o PAR o e an iden ical ime- span. PAR p o ided as cons an pho on lux densi y o 83 µmol m -2 s -1 (A), PAR p o ided as in e mi en ligh lecks o 30 s a an in ensi y o 200 o 400 µmol m -2 s -1 supe imposed on a basic in ensi y o 40 µmol m -2 s -1 (B). The in e al be ween he indi idual ligh lecks was 60 s. 47 Figu e 27: Pe cen age o daily PAR (A) a he saplings’ le el, and (B) ime spans ( ela i e o he daily ligh pe iod) o PAR inpu a he di e en si es, sepa a ed in o di e en ligh in ensi ies o 0 - 40 (di use ligh , blue), 40-70 (g een), 70 - 100 ( ed), 100 - 500 (yellow), 500 - 1000 (da k ed) and > 1000 (o ange) µmol m -2 s -1 . 49 Figu e 28: Daily cou ses o CO 2 ne up ake (A), o s oma al conduc ance (g s ) and anspi a ion (E) by Podoca pus saplings, and o PAR and ai empe a u e on a sunny day (24. No . 2006) in he na u al o es (a, b); on a sunny day (12. Dec. 2006) in he Pinus plan a ion (c, d); and on a cloudy day wi h some d izzle (20. Ma ch 2006) in he Eucalyp us plan a ion (e, ). To al sums o CO 2 ne up ake: 36.4 (a), 34.7 (c) and 48.0 (e) mmol m -2 d -1 ; o al sums o PAR: 1.5 (a), 4.7 (c) and 2.5 (e) mol m -2 d -1 . 51 Figu e 29: Pho osyn he ic ligh esponse cu e o lea es o a Podoca pus alca us shel e - ee in he na u al o es . Da a show mean alues o i e ligh esponse cu es ± S.E. 56 Figu e 30: Diu nal cou se o ne CO 2 up ake as ela ed o PAR o lea es om o he sun-c own o he Podoca pus alca us shel e - ee in he na u al o es on a sunny day in he ainy season (May 31, 2006). 57 Figu e 31: Rela ion be ween sap low and VPD in he na u al o es . Diu nal cou ses o sap low o a small Podoca pus alca us ee (dbh 8.7 cm) and o VPD. A: cloudy day (June 1, 2006) and B: d y season’s day (Janua y 22, 2007). 59 1 In oduc ion 4 plan a ions o Cup essus lusi anica in Eas A ica. Eucalyp us is plan ed e e ywhe e in E hiopia and such plan a ions a e epo ed o damage he ecosys em due o he high demand o wa e and nu ien s o he ees (Poo e 1985) and because he lea es, ba k and oo s elease allelopa hic subs ances which inhibi he g ow h o a g ound ege a ion (Lisanewo k and Michelsen 1993; Michelsen 1993). Needles o coni e ous species, such as pine, con ain high concen a ions o a oma ic and acidic low molecula compounds which a e eleased upon li e decomposi ion in o he soil (Fe nandez e al. 2006) and may hus acidi y he uppe soil ho izons which ha bou a high p opo ion o he ine oo s. Fu he mo e li e decomposi ion and nu ien elease is inhibi ed by an acid milieu, and ca ionic nu ien s a e leached om he soil in o he g ound wa e , especially in egions wi h high p ecipi a ion (Poo e 1985; Flo ence 1986; Yi daw 2001). Conside ing he en i onmen al de e io a ion caused by mono onous plan a ions o he commonly used exo ic ees he chance o indigenous woody plan s o ge a oo hold and eju ena e na u ally in hose plan a ions appea s o be e y small. Howe e , such judgemen s equi e mo e de ailed conside a ion. 1.4 The “nu se- ee e ec ” Recen s udies demons a ed a po en ial o exo ic ee plan a ions o p omo e he egene a ion o opical indigenous ee species (Pa o a 1992; Pa o a 1995; Fimbel and Fimbel 1996; Ha ing on and Ewel 1997; Keenan e al. 1997; Obe hause 1997; Ash on e al. 1998; O samo 1998; Lemenih 2006; Kasenene 2007; Selwyn and Ganesan 2009). Depending on he o me ege a ion, he clima e, and he exo ic ee species used o a o es a ion o e o es a ion, posi i e o nega i e e ec s on soil hyd ology (Hube e al. 2008; Li le e al. 2009), soil physical and chemical p ope ies (Binkley and Resh 1999), li e und nu ien u no e (B asell and Sinclai 1983; Lisanewo k and Michelsen 1993) and soil ca bon s ocks (Guo and Gi o d 2002) p e ail. Monocul u es o as g owing exo ic species change dynamics o soil p ocesses usually mo e han plan a ions o slowly g owing ees (Li le e al. 2009). Regene a ion o o es s o indigenous ees unde he shel e o exo ic ees, e.g. a ious species o Pinus and Eucalyp us, has been s udied in many egions, especially in Cen al Ame ica (Pa o a 1995; Hagga e al. 1997; Mon agnini 2001; Healey and Ga a 2003; Cusack and Mon agnini 2004) and E hiopia (Pohjonen and Pukkala 1990; Michelsen 1993; Senbe a e al. 2002; Lemenih e al. 2004; Yi daw and Luukkanen 2004; Lemenih and Teke ay 2005). Enhanced g ow h o young indigenous ees unde he canopy o an exo ic 1 In oduc ion 5 plan a ion has been e med he “nu se- ee e ec ” (Ha dwick e al. 1997; O samo 1998; San iago-Ga cia e al. 2008). Excep in he in e io o e y dense plan a ions o Cup essus lusi anica, na u al egene a ion o indigenous ee species, in pa icula o Podoca pus alca us, has been obse ed o a ious ex en s in he plan a ions o he Munessa-Shashamene Fo es . This phenomenon has been add essed in se e al pape s on he ecophysiology o he espec i e indigenous and exo ic ee species (Fe ene and Feleke 2001; Feye a e al. 2002; Lue ge e al. 2003; Fe ene and Beck 2004; F i zsche e al. 2006). Su p isingly, he Pinus pa ula and Eucalyp us saligna plan a ions ha bou a dense hough une enly dis ibu ed popula ion o Podoca pus saplings han he na u al o es , i he a eas a e no oo a om a seed p oducing Podoca pus ee (Tes aye e al. 2010). E en mo e unexpec ed was he obse a ion ha he saplings appa en ly pe o m simila o e en be e in he plan a ions han unde he na u al canopy (Tadele 2004). Podoca pus alca us is known as a yea ound seeding ee (Tes aye e al. 2010) whose seedlings and saplings a e nei he b owsed by ca le and wildli e no se e ely a acked by insec s. A su i al a e o 90% o he Podoca pus seedlings was eco ded benea h he canopy o shel e - ees, whe eas in ull ligh and wi hou shel e only 55% su i ed. A e ec ui men o he seedlings, ela i e g ow h a es we e highes unde mode a e ligh (Tes aye 2008; Gi ma e al. 2010). Howe e , when a big Podoca pus ee begins o o e op he canopy o he o he shel e - ees he lea es o i s c own mus ully adap o he in ense opical ligh in ensi ies. Such adap a ion could ake place al eady on he saplings s age, because a e clea - elling o he exo ic shel e - ees he Podoca pus saplings immedia ely eac ed wi h enhanced g ow h con e ing he plan a ion in o a close- o-na u e o es which is domina ed by Podoca pus (Figu e 2). 1 In oduc ion 6 Figu e 2: Eucalyp us plan a ion abou one yea a e clea - elling. Cen e o he backg ound: Some Eucalyp us ees we e excep ed om he elling ac ion. Backg ound igh : A Podoca pus “mo he ee” p o iding he seeds. Middle and o eg ound: Podoca pus saplings a e emo al o he coppiced Eucalyp us ees. 1.5 Aim o he s udy The easons o he “nu se- ee e ec ” a e unknown as a e he ex en s o he e ec unde di e en shel e s. In he esea ch a ea o he Munessa-Shashamene o es soils (Ashag ie e al. 2005) and he clima e condi ions a e simila . The e o e he idea came up ha di e ences in he mic oclima e unde he a ious canopies a e esponsible o he di e ences in g ow h o he indigenous saplings. Majo ecophysiologically ele an componen s o such mic oclima e a e humidi y and ligh (Chazdon and Fe che 1984). Bo h ac o s con ol ca bon gain by a ec ing s oma al conduc ance and pho osyn hesis. E ec s o he s uc u e o he canopy on he in ensi ies o di use adia ion and he empo al pa e ns o sun lecks a e ob ious (Chazdon and Pea cy 1986a; Pea cy 1990; Chazdon and Pea cy 1991; Lemenih e al. 2004; Leakey e al. 2005). The e o e he hypo hesis is pu o wa d ha a ying pa e ns o i adiance and di e en con ibu ions o sun lecks o he o al pho osyn he ic ac i e adia ion (PAR) eaching he unde s o ey ep esen he main ac o s o he pe o mance and g ow h o he Podoca pus alca us saplings unde he shel e o he na u al o es and exo ic ee 1 In oduc ion 7 monocul u es. O he ac o s can be empe a u e and humidi y, which, howe e , may no di e e y much be ween he a ious neighbou ing o es ypes. The hypo hesis is supplemen ed by he assump ion ha compe i ion o soil wa e be ween he saplings and he shel e - ees is negligible. The speci ic objec i es o his s udy we e (I) o e i y he “nu se- ee e ec ” o he exo ic ee plan a ions in compa ison wi h he na u al o es , (II) o cha ac e ize he di e en ligh condi ions on he basis o daily and seasonal pa e ns o PAR wi h ega d o pho osyn he ic ca bon up ake by he P. alca us saplings, (III) o examine he e ec s o o he en i onmen al a iables on pho osyn hesis, and (IV) o ge insigh in he wa e ela ions o he saplings in compa ison o hose o he shel e - ees. Resea ch plo s we e es ablished in he na u al o es as con ol and in a Pinus pa ula and a Eucalyp us saligna plan a ion. Ecological and physiological ai s we e eco ded du ing d y and we seasons o e a pe iod o 2 yea s and inally co ela ed wi h g ow h o he saplings. 1.6 Ou each o he s udy In he Munessa o es he plan a ions a e ha es ed by clea - elling. Whe eas Cup essus lusi anica p oduces a huge amoun o iable seeds om which he nex gene a ion o he plan a ion de elops, Pinus pa ula and Eucalyp us o es s, al hough ample p oducing cones and ui s, espec i ely, mus be eplan ed, because ge mina ion o he seeds is poo . Acco ding o he a ailable in o ma ion egula o a ion be ween he ee species a e clea - elling o a plan a ion is no common. Taking ad an age o he “nu se- ee e ec ”, o a ion would be possible be ween he exo ic monocul u e and a Podoca pus o es , which con ains also some o he indigenous b oadlea woody species. Up o he p esen ime such o a ion, depending on acciden al seed inpu , may no be wo hwhile om he iewpoin o o es y. Howe e , allowing small g o es o Podoca pus in exo ic ee plan a ions would back up su i al o he aluable indigenous ee species in he egion while simul aneously main ain a sou ce o iable seeds o a sys ema ic o a ion be ween he exo ic and he indigenous species. Such mode o o es managemen may 1 In oduc ion 8 g ea ly p o i om he shel e - ee e ec by which g ow h o Podoca pus ju eniles is conside ably accele a ed. Podoca pus alca us is in g ea demand because o i s s aigh s em and he quali y o i s wood which is highe han ha o Pinus pa ula. G ow h o young ees is ela i ely as and he ees mus be ha es ed be o e he onse o he di e en ial ac i i y o he cambium which esul s in he ypical pe iphe al s ands o old Podoca pus ees (Figu e 1). The only disad an age o his kind o o es managemen is he ha es o he shel e - ees which mus be pe o med in a way by which he Podoca pus saplings a e no hea ily damaged. This is no a p oblem in he Eucalyp us plan a ion which is anyway coppiced om ime o ime, bu may be a p oblem in a Pinus plan a ion. Howe e , also he e he economic su plus p o i should balance he highe cos s o ha es ing. 2 Ma e ial and me hods 9 2 Ma e ial and me hods 2.1 S udy a ea E hiopia a he “Ho n o A ica” (Figu e 3 A) is bo de ed by ou d y coun ies, namely E i ea in he No h, Djibou i and Somalia in he Eas , Kenya in he Sou h whe eas in he Wes a humid a ea con inues in o he Sudan. E hiopia’s size is abou 1.1 million km², and i is inhabi ed by abou 70 million people (FAO 2007). The opog aphy is ema kably di e se, anging om 120 m below sea le el in he Danakil dep ession o moun ainous egions well abo e 4000 m a.s.l. in he no he n Semien and he sou he n Bale Moun ains. Two- hi ds o he land a ea a e upland pla eaus, and 50% o he coun y is abo e 1200 m a.s.l. The highland complex o moun ains and pla eaus is incised by he G ea Ri Valley, which ex ends om he sou hwes o no heas o he coun y. As a consequence o i s geog aphical posi ion and i s opology, E hiopia’s landscapes comp ise se e al clima e egions and ecological zones: Dese s along he eas e n bo de , opical o es in he sou hwes and la ge a omon ane and a oalpine egions in he no he n and he sou h-eas e n pa s o he coun y (Figu e 3 B). The p esen s udy was ealized in he Munessa-Shashamene Fo es (7°13’ N 38°37’ E), which is a mon ainous a ea in he A si egion on he eas e n esca pmen o he cen al E hiopian Ri Valley, wi h an al i udinal ange o he o es be ween 1900 and 3200 m a.s.l. The a ea o abou 23,000 ha (Sil ano a 1996) comp ises pa ches o na u al o es , a semi-d y e e g een a omon ane o es , and plan a ions o cyp ess (Cup essus lusi anica), eucalyp s (mainly Eucalyp us saligna and globulus) and pines (Pinus pa ula), and small c op ields and pas u es. The ee densi y o he exo ic plan a ions s a s wi h app oxima ely 1600 - 2500 ees pe hec a e; a e hinning a inal ee densi y o 500 - 600 ees pe hec a e emains. The whole a ea is unde he adminis a ion and managemen o he Munessa- Shashamene In eg a ed S a e Fo es y De elopmen and U iliza ion P ojec . The in es iga ed plo s o he p esen s udy a e loca ed in an a ea, locally known as “Kuke”, o 2280 m al i ude. Kuke is a o es clea ing whe e a esea ch s a ion has been es ablished in 2004 (Figu e 3 C). 2 Ma e ial and me hods 10 Figu e 3: E hiopia and he loca ion o he s udy a ea. A: Map o A ica wi h E hiopia (black hemmed) (sa elli e o hog aphic map: NASA), B: physical map o E hiopia, cen al E hiopian i alley (A si egion) ma ked by a black ec angle (sa elli e map E hiopia: Wikimedia), C: Sa elli e image o he esea ch a ea “Kuke” in he Munessa-Shashamene Fo es , wi h na u al o es and plan a ions o exo ic ee species (Google Ea h). Due o he came a angle o he image no h is o ien ed o he lowe side o he pic u e. 2.2 Clima e o he esea ch a ea The e e ence clima e s a ion a Kuke was es ablished in 2001 on he clea ing close o he esea ch s a ion. The a e age annual ain all is 1144 mm and he mean annual empe a u e is 15 °C, bo h eco ded om 2001 o 2009 (Figu e 4). In 2006, when mos measu emen s we e made, annual ain all (1413 mm) was highe han he a e age om 2001 o 2009 (1144 mm, Figu e 4). The small ains came ea ly in ha yea (Ma ch and Ap il) and con inued in o he main ainy season om Augus o Oc obe . Also he amoun o p ecipi a ion in he main ainy season was conside able highe han he annual a e age, wi h a maximum in July (296 mm s. an a e age o 179 mm). I espec i e o he hea y ain all in 2006, he annual mean o he ai empe a u e (measu ed 2 m abo e g ound le el) did no di e om he eigh yea s a e age. Mon hly a e ages and daily cou ses o impo an mic oclima e pa ame e s a e shown oge he wi h o he da a in he esul s sec ion. Eucalyp us plan a ion Pinus plan a ion Na u al o es Cup essus plan a ion Resea ch s a ion C A 200 m N “Kuke” 2280 m B 2 Ma e ial and me hods 11 Figu e 4: Wal e - ype clima e diag am o he esea ch a ea (eigh yea a e ages 2001 o 2009 a Kuke ield s a ion). 2.3 Geology and soils The s udy a ea is a pa o he g ea lake egion o he main E hiopian Ri Valley, si ua ed eas o he h ee g ea lakes Langano, Shalla and Abia a. The c es s o he moun ains o he eas e n esca pmen ange be ween 3200 and 4000 m al i ude. Like mos pa s o he E hiopian Ri Valley, he bed ock o his upland consis s o olcanic ma e ial om he Pliocene o ea ly Pleis ocene. Mos o he bed ock can be a ilia ed wi h he achy es (Ben enu i e al. 2002). The soils o he s udy a ea a 2280 m a.s.l. we e classi ied as Mollic Ni isols acco ding o he Wo ld Re e ence Base o Soil Resou ces (WRB 2007). They a e b ownish o eddish, ine- ex u ed bu well d ained wi h a high pe cen age o clay (o e 50%) (F i zsche e al. 2007). They a e ich in nu ien s, excep phospha e and he uppe ho izons a e sligh ly acidic (pH 6.3) (F i zsche e al. 2007). Mo e de ails o he soils in he Munessa-Shashamene egion a e gi en in ela ed s udies by soil scien is s wo king in his egion (F i zsche e al. 2006; F i zsche e al. 2007; F eie e al. 2010). mon hs J F M A M J J A S O N D P ecipi a ion [mm] 20 40 60 80 100 120 140 Tempe a u e [°C] 10 20 30 40 50 60 70 Kuke 2280 m [8] 15.0 °C 1144 mm 300 200 6.8 °C 2.7 °C 28.1 °C 23.0 °C 2 Ma e ial and me hods 12 2.4 In es iga ed ees 2.4.1 Podoca pus alca us Podoca pus alca us (Thunb.) R. B . ex Mi b. is he dominan indigenous ee species in he a omon ane Munessa-Shashamene Fo es . I is an e e g een gymnospe m and belongs o he Podoca paceae (F iis 1992). In he esea ch a ea i g ows up o 45 m high, wi h a co esponding s em diame e o 2 m. I s pale g ey o b own ba k, p oduces lakes o long i egula ec angles (Been je 1994). The lea es a e na ow, shiny da k g een, 2 - 6 cm long, g adually ape ing owa ds bo h ends; young lea es a e la ge and b igh e gi ing a g een lush (Bekele-Tesemma e al. 1993). P. alca us is a ap oo species (F i zsche e al. 2006). Seeds o Podoca pus a e dispe sed mainly by bi ds and wildli e (Teke ay 2011). P. alca us is ound a al i udes be ween 1500 and 2600 m a.s.l., and in a eas wi h an annual ain all be ween 700 and 1500 mm and an a e age empe a u e be ween 15 and 20 °C (F iis 1992). I is na i e o E hiopia, Bu undi, Democ a ic Republic o Congo, Kenya, Leso ho, Malawi, Mozambique, Rwanda, Sou h A ica, Sudan, Tanzania, and Uganda (Teke ay 2011) Te med he “Eas A ican yellow-wood” i p oduces a high-class so wood and is he e o e used o many pu poses like imbe , u ni u e and handic a s, while less aluable pa s se e as i ewood. Oil om he seeds is used o medical pu poses. 2.4.2 Pinus pa ula In he esea ch a ea Pinus pa ula (Schldl. e Cham.), a membe o he Pinaceae om Mexico, g ows abou 35 m high eaching a maximum diame e a b eas heigh o 1.2 m. The bole is s aigh and cylind ical, a ely o ked. The lea es g ow in ascicles o 3 and a e 15 o 25 cm long (O wa e al. 2009). The ba k o P. pa ula is cha ac e is ically eddish-o ange in young ees and g ey-b own and e ically idged in olde ees (Bekele-Tesemma e al. 1993). I is plan ed in an al i udinal ange be ween 1000 and 3000 m a.s.l. and equi es annual ain all be ween 1000 and 2000 mm and a mode a e empe a u e (O wa e al. 2009). Pinus pa ula was i s in oduced o Sou h A ica in 1907 (Nyoka 2003) and was men ioned in E hiopia a he u n o he 20 h cen u y (Nino 2009). P. pa ula is a as g owing ee, i s wood is sui able o imbe , pape and i ewood (Bekele-Tesemma e al. 1993). 2 Ma e ial and me hods 13 2.4.3 Eucalyp us saligna Eucalyp us saligna (Smi h) om he My aceae is a la ge e e g een ee, in E hiopia usually 40 - 50 m high, bu can each 60 - 70 m, wi h a s aigh unk and a s em diame e o up o 2 m (Bekele-Tesemma e al. 1993). The ba k on old unks is g ey o b ownish, ough wi h hick idges and peeling in s ipes. The lea es a e up o 20 cm and 3 cm wide, poin ed and cu ed. The colou o he uppe side is sil e y o g een, he lowe side is pale g een (Bekele-Tesemma e al. 1993). E. saligna is a as g owing and ligh demanding species which is adap ed o sub opical clima es wi h d y seasons o no mo e han 4 mon hs (O wa e al. 2009). I s al i udinal ange is om sea le el o 3100 m. I pe o ms bes on si es wi h 1400 o 1600 mm ain all (Pohjonen and Pukkala 1990). E. saligna is highly sui ed o sho - o a ion plan a ions, and coppicing is ecommended e e y 6 o 10 yea s o he p oduc ion o i ewood and pulpwood (O wa e al. 2009), bu due o he s aigh g ow h o he uncoppiced ee, i is sough o poles and pylons p oduc ion (Pohjonen and Pukkala 1990). E. saligna is na i e o Aus alia, bu g ows success ully in plan a ions in he opics and sub opics all o e he wo ld. Eucalyp us was in oduced o E hiopia a he end o he 19 h cen u y o accommoda e he high demand o i ewood o he g owing popula ion o Addis Ababa (Pohjonen and Pukkala 1990). Today, o e hal a million hec a es o Eucalyp us plan a ions a e es ablished in E hiopia (Dessie and E kossa 2011). 2.5 Resea ch si es and plo s In he h ee di e en o es ypes (na u al o es , Pinus plan a ion and Eucalyp us plan a ion, all a 2280 m a.s.l., see Figu e 3), si es we e selec ed whe e se e al Podoca pus saplings g ew in icini y and unde he ypical canopy o he so-called “nu se- ees”. The si ua ion in he selec ed plan a ion plo s was a i icial wi h ega d o he densi y and dis ance o he “nu se- ees” bu na u al as a as he loca ion, dis ance and age o he saplings we e conce ned. In he e e g een na u al o es , he canopy was composed o Podoca pus alca us and o he b oadlea e e g eens, mainly Syzygium guineense. The densi y o he saplings in he na u al o es was smalle han in he plan a ions. The e o e wo plo s we e selec ed in he na u al o es (Plo 1a and 1b, Figu e 5), one wi h a nu se- ee si ua ion o one adul Podoca pus ee and i e P. alca us saplings, and he o he wi h h ee medium size Podoca pus ees (Table 1 a). The second plo was al eady unde in es iga ion in he p e ious p ojec phase. Wooden 2 Ma e ial and me hods 20 Table 2: The canopy densi y o he h ee in es iga ed plo s. Pe cen co e was es ima ed om GIS A c iew da a. Si e Co e [%] Na u al o es 99 Pinus plan a ion Eucalyp us plan a ion 68 72 2.5.2 Heigh , dbh and p ojec ed c own a ea o he saplings All ees in he h ee di e en plo s we e iden i ied and he exac diame e a b eas heigh (dbh) was measu ed a he beginning o he s udy. The dbh o he Podoca pus alca us saplings and o he “nu se- ees” (Podoca pus alca us, Eucalyp us saligna and Pinus pa ula) we e measu ed e e y 3 mon hs. The heigh s o he Podoca pus alca us saplings we e measu ed e e y 3 mon hs wi h a olding ule, he heigh s o he nu se- ees we e measu ed a he beginning and he end o he s udy wi h a hypsome e (Fo es o Ve ex, Fo es o Ins umen AB, Sweden). The ex ensions o he c owns o all nu se- ees and Podoca pus alca us saplings we e measu ed a he beginning and he end o he s udy (Ap il 2005 and Feb ua y 2007). Measu emen s we e ca ied ou in ou di ec ions (No h, Eas , Sou h and Wes ) wi h a pe pendicula and a measu ing ape. F om he esul s o he measu emen s a map o he plo s wi h all ees and c owns was d awn and digi alized (GIS A c iew 3.1). Wi h he p og am he size o he c owns was calcula ed and p esen ed. A he beginning o he s udy he in es iga ed young Podoca pus ees in he na u al o es we e small wi h a diame e a b eas heigh (dbh) anging om 1.0 o 2.7 cm. T ee heigh s we e be ween 2.1 and 2.5 m, excep ee NF P4 wi h a dbh o 5.3 cm and a heigh o 4.7 m. In he Pinus plan a ion, he Podoca pus saplings we e sligh ly alle . Dbh anged om 1.5 o 5.2 cm, and heigh s om 0.8 o 5.1 m. Two Podoca pus saplings (Pin P6 and Pin P11) we e oo small o eaching b eas heigh . In he Eucalyp us si e, he young Podoca pus ees we e again alle wi h dbh be ween 2.1 o 8.7 cm and heigh s om 1.4 o 9.7 m. One Podoca pus sapling (E P5) was oo small o dbh measu emen . P ojec ed c own a eas o he Podoca pus saplings (Figu e 8), calcula ed wi h GIS A cView we e small in he na u al o es anging om 1.1 o 2.1 m², excep NF P4 wi h a 2 Ma e ial and me hods 21 size o 7.1 m². In he Pinus si e he c owns o he saplings anged be ween 0.6 and 5.3 m² and in he Eucalyp us si e om 1.0 o 16.2 m². 2.5.3 Heigh , dbh and p ojec ed c own a ea o he shel e - ees The na u al o es is domina ed by Podoca pus alca us, accompanied by Syzygium guineense, P unus a icana and C o on mac os achyus. In he plo only Podoca pus alca us was conside ed a shel e - ee o he saplings. Compa ed o he shel e - ees in he plan a ions, he Podoca pus shel e - ees we e much smalle , wi h a dbh be ween 10.4 and 21.6 cm and heigh s om 9.3 o 16.5 m. Pinus pa ula ees we e be ween 23 and 40 m all. S em diame e s o hese ees anged om 20.5 o 41.2 cm. In he Eucalyp us si e, mos o he ees had been coppiced once, only ES 3, ES 8 and ES 9 had hei o iginal size. The e o e, he diame e s a b eas heigh and he heigh s o he Eucalyp us saligna ees di e ed conside ably. Thei heigh s anged om 12.6 m (coppiced ee) o 40.7 m (non-coppiced ee) and hei dbh om 11.0 o 41.6 cm. C own a eas o he shel e - ees had a wide ange in all si es. The Podoca pus alca us shel e - ees had c own p ojec ion a eas be ween 6.7 and 31.7 m²; C own a eas o Pinus pa ula anged om 5.3 o 25.9 m². The bigges c owns we e hose o he Eucalyp us saligna ees anging om 6.9 o 44.5 m². He e, he g ea a ia ion was due o he p esence o coppiced and un ea ed ees. 2.6 Mic oclima e The a ea’s clima e and he mic oclima es unde he canopies o he shel e - ees we e moni o ed wi h h ee clima e s a ions. The e e ence clima e s a ion (Me os, Pessl Ins umen s, Weiz, Aus ia) inside he compound o he esea ch s a ion measu ed he clima e o he open a ea. Reco ds we e o ela i e humidi y, ai empe a u e, sola adia ion, b igh ness, lea we ness, wind speed, p ecipi a ion and soil empe a u e. The senso s we e ins alled in 2.0 m heigh , he ain collec o a 1.0 m heigh and he senso o soil empe a u e a 20 cm dep h. The s a ion was unning since 2001. The measu ing in e al by his s a ion as well as o he sub-canopy mic oclima e s a ions was en minu es and he alues we e a e aged o e one hou . 2 Ma e ial and me hods 22 2.6.1 Sub-canopy mic oclima es In o de o in es iga e he sub-canopy mic oclima e p o ided by he “nu se- ees” wo clima e s a ions (Thies Clima, Adol Thies GmbH & Co.KG, Gö ingen, Ge many), equipped wi h senso s o ela i e humidi y, ai empe a u e, sola adia ion, and pho osyn he ic ac i e adia ion we e moun ed on he sca olds. The ain gauge o measu ing h ough all was placed nex o he sca old 1 m abo e g ound. In he o he mic oclima e s a ion h ough all was measu ed wi h a ipping-bucke ain gauge and a HOBO E en Logge (Onse Compu e Co po a ion, Bou ne, MA, USA). The s a ion in he na u al o es was ope a ed pe manen ly; he o he clima e s a ion was pe iodically used in he Pinus and he Eucalyp us plo s. The senso s we e ins alled 1.2 ( h ough all collec o ) and 1.5 m (PAR, global adia ion, ai empe a u e and ela i e humidi y) abo e he g ound and a di e en heigh s on he sca olds (Figu e 9, Figu e 10). Ano he PAR senso was moun ed on he sca old a 7.0 m, he emaining senso s (PAR, global adia ion, ai empe a u e and ela i e humidi y we e exposed a ound he op pla o m o he sca old be ween 11 and 13 m, depending on he heigh o he sca old. Elec ici y was p o ided om 3 sola panels which we e moun ed on ou igge s om he op o he sca olds. Figu e 9: Ske ch o mic oclima e s a ion moun ed on he sca old and he posi ion o he senso s. RH/T senso s o ela i e humidi y and ai empe a u e, PAR senso , L global adia ion senso , RC h ough all collec o , DL da a logge , PF Podoca pus alca us sapling. 2 Ma e ial and me hods 23 Figu e 10: A: PAR, global adia ion, empe a u e and ela i e humidi y senso s on op o he sca olds, B Unde s o ey s a ion wi h senso s o PAR, global adia ion, empe a u e, ela i e humidi y, and h ough all collec o ; C sca old in he Eucalyp us plan a ion. 2.7 Measu emen o sap low Whole- ee anspi a ion can be measu ed ia quan i ica ion o he sap low h ough he xylem. Commonly he hea dissipa ion me hod (G anie 1985) is used o his pu pose. 2.7.1 Hea dissipa ion me hod (G anie ) The measu ing uni consis s o wo senso s which a e inse ed adially in a e ical dis ance o 10 cm in he s em. The Design o bo h senso s is iden ical wi h a leng h o 20 mm o 40 mm and a diame e o 2 mm. They consis o a cons an an hea ing coil a he ip and a coppe -cons an an he mos a elay. The uppe senso is hea ed wi h cons an cu en o 120 mA, he lowe one is used as a e e ence and has he same empe a u e as he ambien wood. Wa e low in he s em cools he hea ed senso . The change o i s empe a u e depends on he eloci y wa e lux, and is egis e ed by he da a logge as a ol age luc ua ion (40 µV = 1 °C). Because i is only he uppe senso which is (hea ed C A B 2 Ma e ial and me hods 24 and) cooled, he lowes sap low a es a e e lec ed by he maximum empe a u e di e ence (Figu e 11 A). Figu e 11: A: P inciple o sap low measu emen s wi h he G anie me hod (Mo ze 2003), B Sap low measu emen in he na u al o es on a Podoca pus alca us (nu se- ee) wi h adia ion p o ec ion o aluminium oil and cons an powe supply, in he backg ound he senso s o he mic oclima e s a ion. 2.7.2 Sap low measu emen Sap low measu emen s we e pe o med be ween Ma ch 2005 and Feb ua y 2007. Fou Podoca pus ees in he na u al o es we e in es iga ed o 101 days, 64 days in he ainy season and 39 in he d y season. In he Pinus si e, measu emen s we e ca ied ou on h ee Pinus nu se- ees and one Podoca pus sapling on 21 days, 18 days in he ainy season and 3 days in he d y season. In he Eucalyp us plan a ion, sap low was measu ed on 9 days in he ainy season and 3 days in he d y season, in o al 12 days, on i e Eucalyp us nu se- ees and one Podoca pus sapling. Each ee was equipped wi h h ee pai s o senso s (Heinz Kaupe , Bay eu h, Ge many), excep he Podoca pus sapling in he Pinus si e which was oo small in ci cum e ence; only one pai o senso s was ins alled he e. The h ee pai s o senso s we e placed equidis an ly on he ci cum e ence o he s em. Fo he ins alla ion o he senso s wo holes o 2.1 mm wid h we e d illed in he s em a b eas heigh in a e ical dis ance o 10 cm. The holes we e lined wi h aluminium ubes o p o ec he senso s and o wa an op imal hea exchange be ween he senso and he su ounding wood. Addi ionally silicone g ease was used o imp o e hea ansi ion B A 2 Ma e ial and me hods 25 be ween he senso and he aluminium ube. The senso s we e connec ed o a powe dis ibu ion box (Elec onics wo kshop o he Uni e si y o Bay eu h), a cons an powe supply (lead acid ba e y and sola panels, Con ad Elec onic, Hi schau, Ge many) and a da a logge (DL2E, Del a-T De ices, Camb idge, UK). Finally senso s we e ai - igh sealed wi h wax (Lau il Wundwachs, W. Neudo GmbH, Emme hal, Ge many) and w apped wi h se e al laye s o aluminium oil o p o ec he p obes agains ain and hea ing by sola adia ion (Figu e 11 B). Measu emen s we e aken e e y 30 seconds, and e e y en minu es he a e ages o 20 eadings we e s o ed in he da a logge . 2.7.3 Calcula ion o sap low Calcula ion o sap low was ia sap low densi y as sugges ed by G anie (G anie 1985) (Equa ions 1 and 2). Sap lux densi y ]mincmml[kJ 12b S−− ⋅⋅⋅α= (1) J S = Sap low densi y α = Coe icien (0.714) k = ela ion o hea ed and unhea ed p obe b = Scaling exponen (1.231)      − ∆ ∆ =1 T T k M (2) ∆T M = Maximum empe a u e di e ence be ween hea ed and e e ence p obe a sap low = 0 ∆T = Tempe a u e di e ence be ween hea ed and e e ence p obe Sap low is calcula ed by equa ion 3: ]minml[AJSF 1 SWS − ⋅⋅= (3) SF = Sap low J S = Sap low densi y A SW = Sap wood a ea 2 Ma e ial and me hods 26 2.7.4 Iden i ica ion o sap wood a ea Sap low densi y ela es o a no malized a ea (commonly 1 cm 2 ). In o de o calcula e he ac ual sap lux, sap low densi y mus be mul iplied wi h he conduc ing a ea o he s em, he so-called so - o sap wood. In he hea - o ha dwood, he conduc ing elemen s o he xylem a e plugged by yloses and hus canno con ibu e o wa e anspo . Fo he de e mina ion o he conduc ing a ea o he s ems, wood samples we e aken wi h an inc emen bo e (Suun o Oy, Vaan a, Finland). To lea e he in es iga ed ees undamaged wood samples we e aken om equi alen ees in he neighbou hood. In he d ill co es, he bo de line be ween he hea - and he sap wood could be mic oscopically ecognized o Eucalyp us by he lack o p esence o yloses. Fo he coni e s, he di e en colou (Podoca pus alca us) o he we and he d y pa (Pinus pa ula) o he sample delimi ed he sap wood a ea om he hea -wood. The sap wood a ea was simply calcula ed (equa ion 4) by HWCSSW AAA − = (4) A SW = Sap wood a ea A CS = C oss sec ion a ea A HW = Hea wood a ea F om he a io be ween sap wood a ea and c oss sec ion a ea o conspeci ic ees o di e en size a eg ession line was calcula ed, om which he sap wood a ea o o he han he examined indi iduals could be es ima ed. 2.7.5 Calib a ion o sap low senso s G anie (G anie 1985) has published a calib a ion cu e o he coe icien K o senso pai e sus ac ual sap low densi y. While K- alues o se e al ees i o he calib a ion cu e, no da a we e a ailable o Podoca pus alca us. The e o e a calib a ion expe imen was ca ied ou wi h a P. alca us ee om he na u al o es wi h a heigh o 9.5 m and a dbh o 10.2 cm. The s em o he ee was equipped wi h h ee sap low senso s o equilib a ion. A e h ee days he s em was cu 50 cm below and abo e he inse ed p obes. In he labo a o y he senso s we e ac i a ed by elec ical powe and connec ed o a da a logge , and he sec ion o he s em was i mly ixed upside down in a e ical posi ion. On he new op, a ube wi h he same diame e was moun ed, sealed 2 Ma e ial and me hods 27 wi h silicone and illed wi h wa e . A he lowe end o he s em sec ion wa e lux ou o he s em was eco ded wi h a balance while he da a logge egis e ed he empe a u e di e ence be ween he senso s. F om bo h da ase s a eg ession was p oduced (Figu e 12). Sap low (senso alue) [ml min -1 ] 0123456 Sap low (g a ime ic measu emen ) [ml min -1 ] 0 1 2 3 4 5 6 ² = 0.78 y = 1.2238 x + 1.3944 Figu e 12: Calib a ion o he G anie sap low senso s o Podoca pus (dbh 9.5 cm). Dashed line: heo e ical co ela ion acco ding o G anie (G anie 1985). 2.8 Gas exchange CO 2 ne gas exchange was measu ed wi h a Walz po ome e . 2.8.1 P inciple o he Walz po ome e Wi h he Walz po ome e (GFS-3000, Heinz Walz GmbH, E el ich, Ge many) gas exchange (CO 2 , H 2 O) o a lea was measu ed in a ious modes, unde na u al, ambien al condi ions, a a i icial ligh in ensi ies (ligh esponse cu e), a p ese CO 2 concen a ions and o he da kened lea (da k espi a ion). Since he Walz po ome e o he simila LICOR ins umen a e used wo ldwide, a de ailed desc ip ion o i s unc ion will no be p esen ed he e. I should, howe e , be men ioned ha wi h he po ome e also he s oma al conduc ance and om he simul aneously eco ded ela i e humidi y o VPD and he ai (o lea ) empe a u e, anspi a ion can be de e mined. A ske ch o he cons uc ion and unc ioning o he Walz po ome e is p o ided in Figu e 13 A. 2 Ma e ial and me hods 28 Figu e 13: A: P inciple o he GFS-3000 po ome e in he CO 2 con olled mode (Walz 2005, modi ied ske ch), B: Measu emen o pho osyn hesis o a Podoca pus alca us sapling in he Pinus plo . 2.8.2 Measu emen o pho osyn hesis Pho osyn hesis was measu ed in h ee campaigns om Sep embe o Decembe 2005 (end o ainy season and ea ly d y season), om Feb ua y o July 2006 (end o d y season and ainy season) and om No embe 2006 o Feb ua y 2007 (d y season a e an ex ended ainy season). Because one single Podoca pus lea is oo na ow o ill he opening o he senso head, 3 o 4 lea es, while s ill a ached o he wig we e pu oge he side by side o ill he ape u e o he cu e e. Tu ning he wig as a as possible in i s na u al posi ion, he a angemen was le o he en i e measu emen which commonly ook he whole ligh -pe iod o he day. Such daily cou ses o CO 2 ne up ake by he lea es o he Podoca pus saplings and he simul aneously measu ed mic oclima ic pa ame e s we e eco ded in he na u al o es (5 saplings, 16 days), in he Pinus si e (8 saplings, 22 days) and in he Eucalyp us si e (3 saplings, 21 days). Pho osyn hesis o he “nu se- ees” was measu ed on 9 days in he na u al o es (1 Podoca pus alca us), on 13 days wi h he Pinus (2 ees), and on 6 days a he Eucalyp us si e (1 Eucalyp us saligna ee). All measu emen s we e pe o med in he d y and he ainy season. B il e pump CO 2 abso be H 2 O con ol al e il e pump CO 2 injec o CO 2 ca idge CO 2 con ol al e mass low me e cu e e cou se il e il e cu e e H 2 O e e ence CO 2 e e ence cou se il e H 2 O sample humidi ie d ie 4 channel analyze CO 2 sample A ai 2 Ma e ial and me hods 29 In addi ion o he daily cou ses o pho osyn he ic CO 2 ne up ake o espi a o y elease, also ligh and CO 2 sa u a ion cu es o pho osyn hesis we e measu ed. Fo compa ison, some Podoca pus alca us ees g owing ou side a shel e we e also measu ed. These ees g ow in a young cyp ess plan a ion o which he ees we e abou 1 - 1.2 m high and hus lowe han he Podoca pus sapling. 2.9 The δ 13 C iso ope a io The measu emen o he δ 13 C iso ope a io o plan ma e ial allows an assessmen o he long- e m wa e ela ions o he plan unde he clima ic condi ions du ing he li e- ime o he espec i e plan o gan. The heo y o he 13 C disc imina ion analysis has been gene ally accep ed (Fa quha e al. 1989). Highe alues o he iso ope 13 C indica e less s oma al esis ance, i.e. gene ally mois e ambien al condi ions. A se o δ 13 C alues enclose he alues which a e ypical o C4- and C3-plan s, espec i ely, indica ing mois e o d ie long- e m condi ions. Lea samples o δ 13 C analysis we e collec ed in July 2006 om h ee Podoca pus saplings and om h ee nu se- ees o each si e. F om all ees and saplings, old and young lea es om di e en pa s o he c owns we e sampled and d ied. The δ 13 C iso ope a ios we e de e mined in he labo a o y o he Iso ope Biogeochemis y o he Bay eu h Cen e o Ecology and En i onmen al Resea ch wi h an iso ope a io mass spec ome e (IRMS, del a S, Finnigan MAT, B emen, Ge many). Ca bon iso ope a ios a e exp essed in ela ion o he PDB s anda d (Ehle inge e al. 1987). Ca bon iso ope a io: 1−= s s sR R δ (5) δ s = δ 13 C a io in he plan R s = δ 13 C Iso opic abundance in he plan R s = Mola abundance a ion o he s anda d ( 13 C/ 12 C) 3 Resul s 36 Figu e 18: Mon hly means o h ough all in he h ee o es ypes as compa ed o he (mon hly) p ecipi a ion ou side he o es . Be ween July and Oc obe 2006 ( ainy season), he mic oclima e s a ion in he na u al o es (NF) had a echnical p oblem and in Sep embe and Oc obe 2006 also he ain gauge o he second mic oclima e s a ion which was s a ed in No embe 2005, ailed. 3.3.1.4 Pho osyn he ic ac i e adia ion (PAR) Figu e 19 shows he mon hly a e ages o he mean daily sums o PAR ou side he o es and in he h ee si es. Ou side he o es , alues o PAR we e calcula ed om o al sola adia ion using he ac o = 0.46 (Rao 1984). Sub-canopy PAR was measu ed di ec ly wi h PAR senso s. The mon hly means o he e e ence s a ion ou side he o es we e be ween 17.2 and 40.8 mol m -2 d -1 , whe eas in he na u al o es and he plan a ions, only 0.8 o 3.4% o he o al i adia ion eached he le el o he saplings. Compa ed o he na u al o es , mean alues o PAR we e app oxima ely wo imes highe in he plan a ions. Seasonal di e ences o PAR on he indi idual si es we e signi ican ou side he o es , bu no o PAR unde he 3 canopies (Table 3). Da e Aug 05 Sep 05 Oc 05 No 05 Dez 05 Jan 06 Feb 06 Ma 06 Ap 06 May 06 Jun 06 Jul 06 Aug 06 Sep 06 Oc 06 No 06 Dez 06 Jan 07 Feb 07 P ecipi a ion / Th ough all [mm mon h -1 ] 0 10 20 30 50 100 150 200 250 300 350 Re e ence s a ion NF PP ES 3 Resul s 37 Figu e 19: Mon hly a e age o he daily sums o he sola adia ion 1.5 m abo e g ound le el in he h ee o es plo s and o he e e ence s a ion ou side he o es (2 m). Fo gaps in he da a se s e e o he legend o Figu e 15. Table 3: Clima e ac o s de e mined by he e e ence s a ion ou side he o es , and o he sub- canopy spaces o he h ee o es ypes. Numbe s ep esen mon hly means and s anda d e o s. Da a o Sola adia ion, PAR, VPD, p ecipi a ion and h ough all a e calcula ed om 19 mon hs ( e e ence s a ion), 15 mon hs (na u al o es ), 5 mon hs (Pinus plan a ion) and 6 mon hs (Eucalyp us plan a ion), espec i ely. Numbe s in b acke s show alues o he e e ence s a ion which di ec ly co espond o he espec i e measu ing pe iods. Lowe case le e s indica e signi ican di e ences be ween seasons and si es. Re e ence s a ion Na u al o es Pinus plan a ion Eucalyp us plan a ion Sola adia ion [mol m -2 d -1 ] Rainy season D y season 45.0 ±2.5 a 72.0 ±1.5 b PAR [mol m -2 d -1 ] Rainy season D y season 20.5 ± 1.1 a 33.0 ± 0.7 b 0.2 ± 0.01 c (21.2 ± 2.6) 0.2 ± 0.01 c (30.7 ± 1.9) no da a (20.5 ± 1.1) 0.9 ± 0.03 d (34.4 ± 0.9) 1.0 ± 0.2 d (24.4 ± 2.1) 0.8 ± 0.2 d (31.2 ± 1.0) VPD [hPa] Rainy season D y season 1.3 ± 0.4 a 4.2 ± 0.5 b 1.4 ± 0.3 a (1.7 ± 0.6) 4.3 ± 0.4 b (4.2 ± 0.5) no da a (1.3 ± 0.4) 5.0 ± 0.7 c (3.8 ± 0.7) 1.8 ± 0.4 a (2.9 ± 0.9) 4.0 ± 0.1 b (4.4 ± 0.9) P ecipi a ion [l mon h -1 ] and Th ough all [%] Rainy season D y season 148.6 ± 22.7 a 27.2 ± 10.3 b 53 ± 7 c % 34 ± 15 d % 56 ± 4 c % 32 ± 6 d % 54 ± 8 c % no da a 1 Mon hly means o PAR o he e e ence s a ion a e calcula ed om sola adia ion using a con e sion ac o o =0.46 (Rao 1984). Da e Aug 05 Sep 05 Oc 05 No 05 Dez 05 Jan 06 Feb 06 Ma 06 Ap 06 May 06 Jun 06 Jul 06 Aug 06 Sep 06 Oc 06 No 06 Dez 06 Jan 07 Feb 07 PAR [mol m - ² d -1 ] 0 1 2 20 40 60 e e ence s a ion NF PP ES 3 Resul s 38 3.3.2 Ve ical g adien s in he sub-canopy mic oclima es summa ized o e he yea 3.3.2.1 Tempe a u e, ela i e humidi y and VPD The g adien s o he componen s o he mic oclima e unde he canopies o he shel e - ees be ween he lowes b anches in 10 m (na u al o es ) o 12 m heigh (plan a ions) and he saplings le el a 1.5 m heigh we e eco ded wi h he senso s on he sca olds. Ai empe a u e dec eased by less han 1 °C (on a e age) owa ds he o es loo . Concomi an ly, ela i e humidi y inc eased up o 10% du ing he d y, and up o 5% du ing he ainy season. Acco dingly, mon hly means o VPD we e always highe a 10 o 12 m compa ed o he alues a saplings le el. Di e ences we e mo e p onounced in he ainy season when mean VPD alues a he op o he sca old we e up o 40 and 50% highe compa ed o he saplings le el in he Eucalyp us si e and he na u al o es , espec i ely. In he d y season, alues o VPD we e 27 and 20% lowe a saplings le el in he na u al o es and he Eucalyp us plan a ion, espec i ely, and only 7% lowe in he Pinus si e, as compa ed o he lowe side o he canopy. 3.3.2.2 Pho osyn he ic ac i e adia ion The s onges dec ease o PAR om he lowe side o he canopy o he saplings le el was obse ed in he na u al o es whe e he mean daily sum o PAR was 3.5 imes highe a he uppe (0.7 mol m -2 d -1 ) compa ed o he lowe le el (0.2 mol m -2 d -1 ) (Figu e 20). In he Pinus plan a ion, he dec ease was less p onounced, as 56% (0.9 mol m -2 d -1 ) o PAR measu ed immedia ely unde he canopy (1.6 mol m -2 d -1 ) eached he saplings. The espec i e dec ease o PAR unde he Eucalyp us canopy was in be ween he wo g adien s wi h 2.4 imes highe alues measu ed unde he canopy (1.9 mol m -2 d -1 ) compa ed o he saplings le el (0.8 mol m -2 d -1 ). I mus be kep in mind ha he canopy o he Eucalyp us plan a ion was in pa ly wo- ie ed, consis ing o he c owns o he uncoppiced and o he young Eucalyp us ees ha had eg own om he coppiced s umps. Benea h he old Eucalyp us indi iduals he i adia ion was usually highe as he e was only 1 c own. Due o his s uc u e he canopy o he Eucalyp us o es was pa chy and he g adien o PAR was no e e ywhe e he same. Ne e heless g ow h o he Podoca pus saplings unde all h ee shel e s lead hem in o a be e ligh clima e coun e ac ed by a educ ion o he ela i e humidi y o he ai . Since he g adien s in empe a u e und VPD we e less s eep han ha o PAR, he dec ease in humidi y did no ou weigh he posi i e e ec o he inc easing ligh in ensi y. 3 Resul s 39 Figu e 20: Visualiza ion o g adien s o mon hly means o he daily sums o pho osyn he ic ac i e adia ion (PAR) be ween he unde s o ey a saplings (a 1.5 m) and he sub-canopy le els (be ween 10 and 12 m abo e g ound). 3.3.3 Daily cou ses o mic oclima e ac o s e ealed by mean hou ly alues Because mon hly means equalize minima and maxima, and hus do no show di e ences in he ac ual alues du ing he day, diu nal cou ses o selec ed ypical days in he ainy and d y season shall be compa ed in he ollowing sec ion o a mo e de ailed di e en ia ion be ween sub-canopy spaces in he na u al o es and he plan a ions. Because only 2 mic oclima e s a ions we e a ailable in addi ion o he e e ence s a ion and one o hem was main ained in he na u al o es , da a om he same days could no be eco ded simul aneously in he wo plan a ions. 3.3.3.1 Diu nal cou se o ai empe a u e and VPD– examples o d y and ainy season days a he saplings le el In he cou se o a day, ai empe a u e in he plan a ions was only sligh ly highe compa ed o he na u al o es (Figu e 21). Daily luc ua ions o ai empe a u e we e less ob ious in he ainy season in all si es wi h alues anging be ween 13 °C in he ea ly mo ning and 20 °C in he a e noon (Figu e 21 A and B). Tempe a u es abo e 15 °C las ed be ween 6 and 8 hou s, maxima occu ed be ween 14:00 and 16:00 h. In he d y season, he daily a ia ions we e highe . A ound sun ise empe a u es d opped o 7 °C bu ose up o 24 °C a ound noon. (Figu e 21 C a nd D). Daily maxima we e eco ded 10-12 Na u al Fo es Pinus Si e Eucalyp us Si e 1.5 Heigh [m] 3 Resul s 40 be ween 15:00 and 16:00 h. Dec ease o ai empe a u es a e sunse was delayed by a ew hou s as compa ed o he si ua ion du ing he ainy season. Figu e 21: Daily cou ses o hou ly means o ai empe a u e in he h ee o es ypes a saplings le el. A: In he na u al o es and in he Pinus plan a ion on a ainy day (July 3, 2006). B: In he na u al o es and in he Eucalyp us plan a ion on a ainy day (June 2, 2006). C: In he na u al o es and in he Pinus plan a ion on a sunny day (No embe 8, 2005). D: In he na u al o es and in he Eucalyp us plan a ion on a sunny day (Ma ch 8, 2006). The daily cou se o VPD ollowed in gene al ha o he ai empe a u e sugges ing ha he o al amoun o wa e apou in he ai did no change e y much in he cou se o he day. VPD inc eased in he mo ning, a aining i s maximum be ween noon and 16:00 h and subsequen ly dec eased eaching i s minimum a ound 8:00 h, o as in he ainy season al eady sho ly a e sunse . While VPD app oached ze o du ing a ainy season nigh , i s ayed a he high in he d y season. This is no unexpec ed bu wo h men ioning wi h ega d o he s oma al beha iou desc ibed unde 3.4.4 (Co ela ion be ween PAR, CO 2 ne up ake and s oma al conduc ance). On ainy days VPD luc ua ed in a small ange be ween 0 and 1.2 hPa, while daily luc ua ions on sunny days we e abou h ee imes as much be ween 0.3 and 3.7 hPa. On a d y season day VPD in he Pinus plan a ion was up o 0.7 hPa highe han unde he canopy o he ime [h] 00 04 08 12 16 20 00 NF ES NF ES Tempe a u e [°C] 0 5 10 15 20 25 30 NF PP Rainy Season D y Season 00 04 08 12 16 20 0 5 10 15 20 25 NF PP D y Season Rainy Season A B CD 3 Resul s 41 na u al o es while on ainy days he di e ence was only 0.2 hPa. (Figu e 22 A & C). Unde he canopy o Eucalyp us (Figu e 22 B & D) VPD was only o a ew hou s in he a e noon highe han ha in he na u al o es , and he di e ences be ween he Eucalyp us plan a ion and he na u al o es on he whole we e smalle . Ne e heless, in gene al VPD was highe in he plan a ions han in he na u al o es (Figu e 22). Figu e 22: Daily cou ses o mean hou ly VPD in he h ee o es s a saplings le el. A: In he na u al o es and in he Pinus plan a ion on a ainy day (July 3, 2006). B: In he na u al o es and in he Eucalyp us plan a ion on a ainy day (June 2, 2006). C: In he na u al o es and in he Pinus plan a ion on a sunny day (No embe 8, 2005). D: In he na u al o es and in he Eucalyp us plan a ion on a sunny day (Ma ch 8, 2006). 3.3.3.2 Daily cou se o PAR a saplings le el – examples o d y and ainy season days Pho osyn he ic ac i e adia ion (PAR) was conside ably highe in he plan a ions compa ed o he na u al o es (Figu e 23). Unde he canopy o Pinus maximum daily lux a es o PAR we e up o 9 imes highe on a ainy day and up o 8 imes highe in he d y season, espec i ely (Figu e 23 A and C). Unde Eucalyp us, he co esponding a es o PAR we e up o 5 imes highe on a ainy, and up o 6 imes highe on a day in he d y season (Figu e 23 B and D). Maximum midday alues o PAR we e simila in 00 04 08 12 16 20 0 1 2 3 4 NF PP ime [h] 00 04 08 12 16 20 00 NF ES D y Season D y Season C D NF ES Rainy Season B VPD [hPa] 0 1 2 3 4 5 NF PP Rainy Season A 3 Resul s 42 bo h plan a ions on ainy days wi h 43 and 47 µmol m -2 s -1 in he Pinus and he Eucalyp us plan a ion, espec i ely (Figu e 23 A and B). In he d y season, highes midday alues we e abou wice as high (unde Pinus 105, unde Eucalyp us 80 µmol m - 2 s -1 (Figu e 23 C & D). The highes midday alues in he na u al o es we e only be ween 5 and 10 µmol m -2 s -1 on ainy (Figu e 23 A & B) and abou 13 and 14 µmol m -2 s -1 (Figu e 23 C and D) on sunny days. The daily cou ses o PAR show a simul aneous s a in he mo ning a ound 7:00 h o he Eucalyp us plan a ion and he na u al o es , whe eas, due o he mo e open canopy o he Pinus plan a ion, PAR ose one hou ea lie in bo h season (Figu e 23 A and C). Figu e 23: Daily cou ses o mean hou ly pho osyn he ic ac i e adia ion (PAR) in he h ee o es ypes a saplings le el. A: In he na u al o es and in he Pinus plan a ion on a ainy day (July 3, 2006). B: In he na u al o es and in he Eucalyp us plan a ion on a ainy day (June 2, 2006). C: In he na u al o es and in he Pinus plan a ion on a sunny day (No embe 8, 2005). D: In he na u al o es and in he Eucalyp us plan a ion on a sunny day (Ma ch 8, 2006). NF ES PAR [µmol m -2 s -1 ] 0 20 40 60 80 100 120 NF PP ime [h] 00 04 08 12 16 20 0 20 40 60 80 100 NF PP Rainy Season Rainy Season D y Season D y Season AB CD 00 04 08 12 16 20 00 NF ES 3 Resul s 43 3.3.4 Daily a e ages and sums, espec i ely, o he a iables o he unde s o ey mic oclima es A summa y o he daily cou ses o he mic oclima e a iables o he unde s o ey space, as p esen ed in Figu e 21 o Figu e 23 o he example days, is shown in Table 4. Daily sums a e gi en o PAR and h ough all, mean alues o ai empe a u e and VPD. PAR a he saplings’ le el was consis en ly highe in he plan a ions han in he na u al o es , i espec i e o he season. On he example days gi en in Table 4, PAR in he na u al o es was on a e age 16% o ha in he Pinus plan a ion and 23% o ha in he Eucalyp us plan a ion. Di e ences o he daily a e age in ai empe a u e and apou p essu e de ici be ween he si es we e negligible in he ainy season and only sligh ly mo e appa en in he d y season. In he Pinus plan a ion a saplings le el, daily mean empe a u e was 0.8 °C and a e aged VPD was 0.2 hPa highe han in he na u al o es . Unde Eucalyp us, a e aged daily empe a u e and VPD did no di e subs an ially om hose unde he na u al canopy. The daily sums o he h ough all showed compa able alues o he na u al o es and he Pinus plan a ion, whe eas in he Eucalyp us plan a ion, 40% o he h ough all, compa ed o he sums in he na u al o es , we e al eady aken away by e apo a ion and in e cep ion in he plan a ions. Table 4: Cha ac e iza ion o he sub-canopy mic oclima es o he h ee o es ypes. Daily a e ages ( empe a u e, VPD) and sums (PAR, h ough all) o he mic oclima e in he na u al o es (NF) and he plan a ions (PP and ES) on selec ed days in he d y and ainy season Rainy season (July 3, 2006) Rainy season (June 2, 2006) D y season (No 8, 2005) D y season (Ma ch 8, 2006) NF PP NF ES NF PP NF ES PAR [mol m -2 d -1 ] 0.14 1.02 0.15 0.71 0.23 1.29 0.29 1.15 Tempe a u e [°C] 15.2 15.5 14.3 14.5 13.4 14.2 17.7 17.9 VPD [hPa] 0.20 0.30 0.22 0.24 1.06 1.28 2.01 2.12 Th ough all [mm d -1 ] 9.7 9.2 11.3 6.8 3 Resul s 44 3.4 Pho osyn hesis 3.4.1 In es iga ion o ac o s in luencing CO 2 ne up ake 3.4.1.1 In luence o clima e ac o s To assess he impo ance o he di e en en i onmen al ac o s on pho osyn he ic ca bon gain, CO 2 ne up ake o a Podoca pus sapling was measu ed a ou di e en ligh le els (100, 500, 1000 and 1500 µmol m - ² s -1 ), unde d y season condi ions wi h ai empe a u e anging om 14.5 o 32 °C and ela i e humidi y anging om 22 o 66% and a VPD be ween 0.2 and 3.9 hPa (Figu e 24 ). PAR [µmol m -2 s -1 ] 100 500 1000 1500 CO2 ne up ake [µmol m -2 s -1 ] 0 1 2 3 4 Figu e 24: Co ela ion be ween di e en PAR in ensi ies and CO 2 ne up ake unde ambien condi ions, i.e. a ying empe a u e and ela i e humidi y. Each da a poin shows he mean alue (± SE) o CO 2 ne up ake when el. humidi y changed be ween 22 and 66%, and he empe a u e be ween 15 and 32 °C. The quad a ic model g aph is based on he pa ame e es ima es o he quad a ic model gi en in Table 5 Signi ican e ec s we e ound o PAR (F 1,154 = 375.39; p < 0.001) and ai empe a u e (F 1,154 = 19.04; p < 0.001), bu no o ela i e humidi y (Table 5). The e ec o PAR, which esul s in an op imum o CO 2 ne up ake be ween 500 and 1000 µmol m - ² s -1 (Table 5), explained 71% ( ² = 0.712) o he a ia ions o CO 2 ne up ake. When ela i e humidi y and ai empe a u e we e eplaced by VPD, he signi ican le els showed simila esul s. Bo h, PAR (F 1,154 = 321.51; p < 0.001) and VPD (F 1,154 = 14.53; p < 0.001), we e signi ican ly in luencing CO 2 ne up ake. Bo h clima e ac o s oge he explained 75% ( ² = 0.753) o he a ia ions o he ne CO 2 up ake, wi h a p opo ion o 3 Resul s 45 PAR o 71% and o VPD o 4%. The e we e no signi ican in e ac ions be ween he ac o s . Table 5: Examina ion o he signi icance o mic oclima e e ec s on pho osyn he ic CO 2 ne up ake by lea es o Podoca pus alca us saplings by he quad a ic model applied o ou le els o PAR and he anges o a ying H, VPD and empe a u e desc ibed abo e. DF F- alue p- alue PAR 1,154 375.39 < 0.001 (PAR)² 1,154 243.45 < 0.001 Rel. humidi y 1,154 0.22 0.64 Tempe a u e 1,154 19.04 < 0.001 VPD 1,154 14.53 < 0.001 3.4.1.2 Ligh sa u a ion Ligh esponse cu es o CO 2 ne up ake a ambien CO 2 concen a ion, cons an empe a u e and ela i e humidi y we e simila wi h lea es om he Podoca pus saplings unde all h ee canopy ypes (Figu e 25 A o C), bu he a es measu ed wi h saplings g owing ou side he shel e in he open a ea we e by 20% lowe (Figu e 25 D) a low ligh in ensi ies. A linea inc ease was obse ed up o 100 µmol PAR m -2 s -1 and ligh sa u a ion was achie ed be ween 1500 and 2000 µmol m -2 s -1 . Maximal a es o CO 2 ne up ake we e be ween 2.4 (lea es om saplings in he open si e) and 2.9 µmol m -2 s -1 (lea es o saplings in he Pinus si e). 3 Resul s 52 3.4.2.3 The ole o sun lecks in he daily CO 2 up ake Table 6 shows he di e ences be ween a ligh clima e wi h sun lecks and a i ual, equally dis ibu ed cons an ligh in ensi y. The daily accumula ed PAR and he daily ca bon up ake measu ed in he di e en si es unde cloudy and clea sky a e compa ed wi h an es ima ed daily ca bon gain, calcula ed om he a e age PAR in ensi y du ing he day and he co esponding CO 2 ne up ake calcula ed om he ligh esponse cu es (Figu e 25). The e iciency is calcula ed as pe cen age o he measu ed om he es ima ed CO 2 ne up ake. The highes e iciency, nea 100%, was eached in he Pinus plan a ion on cloudy days while on sunny days wi h highe PAR inpu , he e iciency was less eaching only 70%. In he na u al o es , he appa en e iciency did no di e conside ably be ween cloudy and sunny days, bu as unde Pinus i was highe unde cloudy condi ions (86% and 80% o cloudy and sunny days, espec i ely). E iciency o he ac ual PAR unde he canopy o Eucalyp us was also highe on cloudy days, bu in gene al he e iciencies we e much lowe wi h 72% and 53% o cloudy and sunny days, espec i ely. Table 6: Pho osyn he ic e iciency o he ac ual sub-canopy ligh clima e compa ed o a i ual cons an illumina ion wi h he same amoun s o PAR applied o e he same ime pe iod. Es ima ed daily CO 2 ne up ake was calcula ed using he ligh esponse cu es o CO 2 ne up ake shown in Figu e 25. Fo es / plan a ion Clima e condi ion Daily sum o PAR [mol m -2 d - 1 ] A e age PAR in ensi y [µmol m -2 s -1 ] Es ima ed daily CO 2 ne up ake [mmol m -2 d -1 ] Measu ed daily CO 2 ne up ake [mmol m -2 d - 1 ] Appa en e iciency o he ac ual adia ion [%] Na u al o es cloudy 1.40 40.3 32.1 27.5 86 sunny 1.63 48.0 35.3 28.3 80 Pinus plan a ion cloudy 1.56 45.7 34.1 33.0 97 sunny 2.04 59.8 39.5 27.8 70 Eucalyp us plan a ion cloudy 0.92 27.0 32.4 23.4 72 sunny 1.08 31.5 33.4 17.6 53 3.4.3 Daily accumula ed PAR and ca bon gain Daily amoun s o PAR eaching he indi idual di e ed be ween cloudy and sunny days and om si e o si e (Table 7). In he na u al o es he daily amoun s o PAR a ied om 450 o 2840 mmol m -2 d -1 wi h a mean alue (n = 8) o 1400 mmol m -2 d -1 o ainy condi ions and 1630 mmol m -2 d -1 o sunny days (n = 8). In he Pinus plan a ion, he span o he daily PAR sums was wide wi h co esponding alues be ween 430 and 3 Resul s 53 4730 mmol m -2 d -1 and a e ages o 1560 and 2050 mmol m -2 d -1 unde cloudy (n = 9) and sunny wea he condi ions (n = 13), espec i ely. In he Eucalyp us si e he spans o he daily amoun s o PAR we e compa able o hose o he na u al o es anging om 240 o 2680 mmol m -2 d -1 . Howe e , he mean alues we e conside ably lowe han in he na u al o es wi h 920 mmol m -2 d -1 unde cloudy sky (n = 8) and 1080 mmol m -2 d -1 unde sunny condi ions (n = 13). The numbe o daily sun lecks did no di e e y much on he h ee si es wi h a e age alues be ween 31 and 40. Depending on he wea he condi ion, i.e. cloudiness, he numbe as such could be e en highe on a cloudy han on a sunny day (Pinus si e). The du a ion o he indi idual sun lecks was simila ly depending on he cloud co e and usually longe sun lecks we e obse ed on sunny days. The pe cen age o daily accumula ed PAR esul ing om sun lecks was highes in he Pinus plan a ion i espec i e o he wea he condi ions (71% and 72% on cloudy and sunny days, espec i ely). In he Eucalyp us si e, sun lecks accoun ed o 40% o he daily PAR unde cloudy sky and 51% on sunny days. In he na u al o es , he sha e o PAR esul ing om sun lecks was sligh ly highe wi h 55% and 67% unde cloudy and sunny wea he condi ion, espec i ely. The alues o all pho osyn he ic measu emen s o Podoca pus saplings showed a signi ican ly lowe ca bon gain o he saplings in he Eucalyp us plan a ion compa ed o saplings in he na u al o es (p = 0.04) and he Pinus si e (p = 0.003) (Table 6), whe eas he di e ence be ween ca bon up ake by he saplings in he na u al o es and he Pinus plan a ion was s a is ically no signi ican . Likewise, he mean alues did no di e signi ican ly be ween cloudy and sunny days. In he Eucalyp us si e, he daily ca bon gains o he Podoca pus saplings anged be ween 4 o 38 mmol m -2 d -1 , and he daily a e ages di e ed unde cloudy (23 mmol m -2 d -1 ) and sunny wea he (18 mmol m -2 d -1 ). In acco dance wi h he daily sha e o sun lecks in accumula ed PAR, he pe cen age o he daily CO 2 up ake esul ing om sun lecks was lowes unde Eucalyp us and mo e CO 2 was assimila ed on sunny han on ainy days. In con as , in spi e o he highe sha e o sun lecks o he o al PAR, CO 2 up ake esul ing om sun lecks was highe unde cloudy sky han on sunny days in he o he wo o es si es. As could be expec ed om he high con ibu ion o sun lecks o he daily PAR, CO 2 up ake by he Podoca pus saplings, a ibu able o sun lecks, was highes in he Pinus plan a ion. 3 Resul s 54 Table 7: The sub-canopy ligh clima es o he 3 in es iga ed o es a eas and hei e ec s on pho osyn he ic CO 2 ne up ake. Wi h ega d o he ypical wea he si ua ions 2 classes o he daily accumula ed global adia ion we e de ined: 19 - 59 mol m -2 d -1 o cloudy days wi h d izzle, ypical o he we season and 60 - 82 mol m -2 d -1 o sunny days o he d y season. Means ± ±± ± S.E., di e en lowe case le e s indica e di e ences be ween he si es. Na u al o es Pinus plan a ion Eucalyp us plan a ion Numbe o analyzed daily cou ses 8 8 9 13 8 13 Wea he condi ion cloudy sunny cloudy sunny cloudy sunny Daily accumula ed PAR [mmol m -2 d -1 ] 1399 ab ± 306 1630 ab ± 309 1563 ab ± 185 2044 a ± 322 924 b ± 248 1080 b ± 195 Daily numbe s o sun lecks > 40 µmol m -2 s -1 31 a ± 4 39 a ± 4 40 a ± 2 33 a ± 3 35 a ± 5 35 a ± 4 Pe cen o daily accumula ed PAR esul ing om sun lecks > 40 µmol m -2 s -1 55 67 71 72 40 51 Daily CO 2 ne up ake [mmol m -2 d -1 ] 28 a ± 3 27 a ± 4 33 a ± 3 28 a ± 2 23 ab ± 4 18 b ± 3 Pe cen o daily CO2 ne up ake esul ing om sun lecks > 40 µmol m -2 s -1 41 38 62 48 27 31 3.4.4 Co ela ion be ween PAR, CO 2 ne up ake and s oma al conduc ance Table 8 shows he co ela ions be ween PAR and CO 2 ne up ake, be ween s oma al conduc ance and CO 2 ne up ake and be ween PAR and s oma al conduc ance. The ela ionship be ween PAR and assimila ion did no di e much be ween he si es. In gene al, he ela ionship was sligh ly be e be o e noon ( 2 = 0.57 o 0.65) compa ed o he a e noon alues ( 2 = 0.46 o 0.52) when s oma al conduc ance comes in o play. The co ela ion be ween s oma al conduc ance and CO 2 ne up ake di e s be ween he si es. The s onges co ela ion is ound in he na u al o es , whe e 46% o he assimila ion could be explained by s oma al conduc ance. Also in he Eucalyp us si e, he ela ion be ween he wo pa ame e s is s ill s ong wi h 2 = 0.38, whe eas in he Pinus plan a ion, he ela ion be ween he wo pa ame e s is no ha ob ious ( 2 = 0.29). In all si es, he co ela ion is conside ably s onge in he a e noon compa ed o he 3 Resul s 55 mo ning hou s. The co ela ion be ween PAR and s oma al conduc ance is ambiguous. The bes ela ion is ound in he Pinus plan a ion ( 2 = 0.28), he e he di e ence be ween mo ning and a e noon alues is only small. In he na u al o es he co ela ion is weak he a e noon ( 2 = 0.29), whe eas in he mo ning, no co ela ion was obse ed. In he Eucalyp us plan a ion, he co ela ion was e y weak du ing he whole day ( 2 = 0.13). Table 8: Co ela ion be ween pho osyn he ic ac i e adia ion and CO 2 ne up ake (PAR/A), be ween s oma al conduc ance and CO 2 ne up ake (g s /A), and be ween pho osyn he ic ac i e adia ion and s oma al conduc ance (PAR/g s ) o he saplings in he h ee di e en si es. Numbe s gi en a e co ela ion ac o s ( ²) be ween he da ase s o 17, 22 and 18 daily cou ses in he na u al o es , he Pinus and he Eucalyp us plan a ion, espec i ely, on he one hand (bold), and he h ee daily cou ses shown in Figu e 28 on he o he . n PAR/A [ ²] g s /A [ ²] PAR/g s [ ²] Na u al o es whole day mo ning (8:30-13:00) a e noon(13:00-18.00) Figu e 28 b mo ning Figu e 28 b a e noon 17 17 17 1 1 0.53 0.57 0.49 0.75 0.56 0.46 0.24 0.66 0.24 0.83 0.19 0.10 0.29 0.18 0.44 Pinus plan a ion whole day mo ning (8:30-13:00) a e noon(13:00-18.00) Figu e 28 d mo ning Figu e 28 d a e noon 22 22 22 1 1 0.56 0.61 0.52 0.78 0.57 0.29 0.33 0.58 0.46 0.76 0.28 0.27 0.33 0.16 0.60 Eucalyp us plan a ion whole day mo ning (8:30-13:00) a e noon(13:00-18.00) Figu e 28 mo ning Figu e 28 a e noon 18 18 18 1 1 0.56 0.65 0.46 0.75 0.50 0.38 0.22 0.51 0.66 0.67 0.13 0.12 0.15 0.56 0.32 3.5 CO 2 ne up ake o he Podoca pus alca us shel e - ee in compa ison o he saplings To show he di e ence be ween he young Podoca pus saplings and he ma u e ee, ligh sa u a ion cu es, he daily cou se o CO 2 ne up ake and he daily sums o ca bon gain in es iga ed. 3 Resul s 56 3.5.1 Ligh esponse cu e The ligh esponse cu e o lea es o a Podoca pus shel e - ee (Figu e 29) is e y simila o hose o he saplings in he di e en si es, and he maximum a e is only sligh ly highe eaching 4.0 µmol m -2 s -1 . The linea sec ion o he cu e (a low PAR in ensi ies) is e y s eep and sa u a ion s a ed a PAR alues o 750 µmol m -2 s -1 , as wi h lea es o he saplings. Figu e 29: Pho osyn he ic ligh esponse cu e o lea es o a Podoca pus alca us shel e - ee in he na u al o es . Da a show mean alues o i e ligh esponse cu es ± S.E. 3.5.2 Diu nal cou ses o ne CO 2 up ake and PAR CO 2 ne up ake o he 17 m high Podoca pus alca us shel e - ee was measu ed in he ou e pa o he sun c own (Figu e 30) on a d y day in he ainy season on May 31 in 2006. PAR alues abo e 400 µmol m -2 s -1 we e al eady eco ded in he mo ning a ound 9.00 h, ollowed by a con inuous up and down un il 14:45 h when he ligh in ensi y due o he inclina ion o he sun declined o a le el below 200 µmol m -2 s -1 . CO 2 ne up ake a es a ied be ween 1.5 and 2.3 µmol m -2 s -1 a mode a e and high ligh in ensi ies, espec i ely, and be ween 0.8 and 1.6 µmol m -2 s -1 in he a e noon a e 15:00 h. PAR [µmol m -2 s -1 ] 0 500 1000 1500 2000 CO 2 ne up ake [µmol m -2 s -1 ] 0 1 2 3 4 5 3 Resul s 57 ime o he day 08 09 10 11 12 13 14 15 16 17 18 Assimila ion [µmol m -2 s -1 ] 0 1 2 3 PAR [µmol m -2 s -1 ] 0 400 800 1200 Assimila ion PAR Figu e 30: Diu nal cou se o ne CO 2 up ake as ela ed o PAR o lea es om o he sun-c own o he Podoca pus alca us shel e - ee in he na u al o es on a sunny day in he ainy season (May 31, 2006). 3.5.3 Ca bon gain Daily ca bon gain o he Podoca pus shel e - ee was measu ed on 9 days in he sun c own a 12 m heigh unde d y (n = 4) and cloudy (n = 5) wea he condi ions. Daily accumula ed ca bon gain was be ween 8.0 o 61.0 mmol m -2 d -1 wi h a mean alue o 27.9 mmol m -2 d -1 . Respec i e daily PAR sums we e be ween 0.3 and 4.4 mol m -2 d -1 , wi h a mean alue o 1.9 mol m -2 d -1 . 3.6 Sap low Xylem sap low was measu ed on young Podoca pus alca us and on he shel e - ees. In addi ion o in o ma ion abou he wa e demand o he h ee ee species he ques ion o a po en ial compe i ion be ween he saplings and he adul shel e - ees was add essed. Un o una ely, he size o se e al o he Podoca pus saplings was oo small o using he G anie me hod; in he na u al o es he s ems o he saplings we e oo hin o sap low measu emen s. The e o e a bigge sapling wi h a dbh o 8.6 cm and a heigh o 7.6 m was selec ed. In he Eucalyp us si e, a Podoca pus alca us sapling o he same size (dbh 8.7 cm, 6.5 m) was used, whe eas he Podoca pus sapling in he Pinus plan a ion was smalle (dbh 5.1 cm, heigh 4.8 m). Sap low o he Podoca pus saplings and he shel e - ees was calcula ed om an equa ion de i ed om a calib a ion expe imen (see me hods sec ion: Calib a ion o sap low senso s). Sap low 3 Resul s 58 o Pinus and Eucalyp us was calcula ed om sap low densi y and sap wood a ea, which could be de e mined om c oss-sec ion o elled ees. Sap wood a ea was on a e age 41% o he o al s em a ea in Pinus, whe eas in Eucalyp us, sap wood a ea dec eased s ongly wi h inc easing ee diame e . Sap wood a ea o smalle ees was abou 50 % o he s em a ea, in he big Eucalyp us, he sap wood a ea was only 26% o he s em a ea. 3.6.1 Diu nal cou ses o sap low o he Podoca pus alca us saplings as ela ed o VPD unde he di e en canopies Diu nal cou ses o sap low o he Podoca pus sapling in he na u al o es a e shown o wo days o he ainy and he d y season (Figu e 31). On a cloudy day in he ainy season (Figu e 31 A), sap low s a ed la e in he mo ning a 10:00 h and ceased in he e ening a ound 21:30 h. Du ing he day, he cou se ollowed in gene al VPD bo h showing a small dep ession du ing noon. Ra es o sap low we e low eaching maximum alues o 17.3 ml min -1 . The co esponding VPD was 7.0 hPa. Du ing nigh ime, sap low was negligible, whe eas VPD dec eased slowly a aining i s minimum in he mo ning a 8:00 h. On a sunny day in he d y season (Figu e 31 B), sap low s a ed al eady a 9:00 h and con inued, inally a a low a e, un il midnigh . High alues abo e 35 ml min -1 we e eco ded a noon be ween 11:30 and 15:00 h whe eas VPD s ill inc eased and eached i s maximum o 14.6 hPa la e in he a e noon a 16:00 h. Like in he ainy season, VPD dec eased slowly du ing he nigh , he lowes alues we e eco ded again a 8:00 h. Compa ed o he cloudy day, alues o VPD in a d y-season-day we e wo old highe du ing day ime and up o i e imes highe in he cou se o he nigh . Sap low was mo e han doubled, eaching a es o up o 41 ml min -1 . To al sap low on hese wo days was 4.6 l d -1 and 10.7 l d -1 , espec i ely (Figu e 34). 3 Resul s 59 Sap low Sap low VPD [hPa] 0 5 10 15 20 VPD B Sap low [ml min -1 ] 0 15 30 45 60 Sap low VPD [hPa] 0 5 10 15 20 VPD A Sap low [ml min -1 ] 0 15 30 45 60 Sap low Sap low 0 4 8 12 16 20 0 ime o he day [h] cloudy day 0 4 8 12 16 20 0 ime o he day [h] sunny day Figu e 31: Rela ion be ween sap low and VPD in he na u al o es . Diu nal cou ses o sap low o a small Podoca pus alca us ee (dbh 8.7 cm) and o VPD. A: cloudy day (June 1, 2006) and B: d y season’s day (Janua y 22, 2007). The diu nal cou ses o sap low o he Podoca pus alca us sapling in he Pinus plan a ion on wo selec ed days a e shown in Figu e 32. On he ainy day sap low (Figu e 32 A) s a ed a 10:00 h and ceased a 20:00 h. Sap low, again in e up ed by a midday dep ession, was peaking a a a e o app oxima ely 18 ml min -1 a 16:00 h. The co esponding alue o VPD was 9.3 hPa. In p inciple a simila ela ion be ween sap low a es and VPD as shown abo e o he Podoca pus ee in he na u al o es was eco ded unde he canopy o Pinus: On he ainy day sap low a es pa alleled VPD whe eas he co ela ion be ween bo h diu nal cou ses was less close on a d y season’s day (Figu e 32 B) when he peak o sap low (30 ml min -1 a 11:30 h) p eceded ha o VPD (13.5 hPa) by 6 h. Sap low was eco ded on a ainy day o e 10 h while i ook place o e 18 h du ing he d y season’s day. I las ed un il 22:00 h in he e ening while anspi a ion had inished abou 3 h ea lie . VPD emained ela i ely high du ing he whole nigh eaching i s minimum o abou 1.5 hPa sho ly a e sun ise. To al sap low on he p esen ed days was 2.9 l d -1 on he cloudy day in Ap il and 6.9 l d -1 on he sunny day in Decembe (Figu e 34). I should be kep in mind ha he sapling unde he Pinus canopy was conside ably smalle han ha in he na u al o es . 3 Resul s 60 Figu e 32: Rela ion be ween sap low and VPD in he Pinus plan a ion. Diu nal cou ses o sap low o a Podoca pus alca us sapling (dbh 5.2 cm) and o VPD. A: cloudy day (Ap il 9, 2006) and B: sunny day (Decembe 15, 2006). The same ype o co ela ion be ween sap low and VPD, as desc ibed o Podoca pus saplings in he na u al o es and he Pinus plan a ion was also eco ded wi h he sapling unde he Eucalyp us canopy. On he ainy season’s day, sap low was ela i ely high wi h ega d o VPD, especially in he mo ning hou s and he midday dep essions o bo h a iables we e mo e p onounced (Figu e 33 A). The peak a e o sap low (20 ml min -1 ) was a ained a 17:00 h when also VPD peaked (5.6 hPa). Bo h a iables declined slowly un il midnigh . In he d y season (Figu e 33 B), sap low peaked sho ly be o e noon (41.1 ml min -1 ) and declined g adually un il 22:00 h when i became ze o. VPD a ained maximum om 15:00 o 19:00 h (15.3 hPa), a e which i dec eased wi h a high a e un il 22:00 h and hen mo e slowly un il 8:30 h in he mo ning. In con as o he si ua ion in he Pinus plan a ion sap low s a ed concomi an ly wi h he inc ease o VPD in he mo ning. To al sap low on he p esen ed cloudy day was 4.5 l d -1 . On he d y season’s day i was wice as much (10.4 l d -1 ) Sap low VPD [hPa] 0 5 10 15 20 VPD A Sap low [ml min -1 ] 0 15 30 45 60 Sap low VPD [hPa] 0 5 10 15 20 VPD B Sap low [ml min -1 ] 0 15 30 45 60 0 4 8 12 16 20 0 ime o he day [h] cloudy day 0 4 8 12 16 20 0 ime o he day [h] sunny day 3 Resul s 61 Figu e 33: Rela ion be ween sap low and VPD in he Eucalyp us plan a ion. Diu nal cou ses o sap low o a Podoca pus alca us sapling (dbh 8.7 cm) and o VPD. A: cloudy day (Ap il 11, 2006) and B: sunny day (Feb ua y 11, 2006). 3.6.2 Daily sums o sap low o he Podoca pus alca us saplings in he di e en si es on example days in he ainy and d y season As men ioned abo e and shown in Figu e 34, he daily sums o sap low o he Podoca pus saplings di e ed wi h ee size and season. In bo h seasons, he wo Podoca pus sapling in he na u al o es and in he Eucalyp us plan a ion had almos iden ical daily sums o 4.6 and 4.5 l d -1 , espec i ely on he ainy day, and 10.7 and 10.4 l d -1 , espec i ely on he d y day. Bo h saplings we e o compa able size wi h a dbh o 8.7 cm and a heigh o 7.6 m o he bigge sapling in he na u al o es and a dbh o 8.7 cm and heigh o 6.3 m o he sapling in he Eucalyp us si e. The smalle Podoca pus sapling in he Pinus si e wi h a dbh o 5.2 cm and a heigh o 4.8 m had clea ly lowe daily sums o sap low o 2.9 l d -1 on he ainy and 6.9 l d -1 on he d y day. ASap low VPD [hPa] 0 5 10 15 20 VPD B Sap low [ml min -1 ] 0 15 30 45 60 Sap low VPD [hPa] 0 5 10 15 20 VPD Sap low [ml min -1 ] 0 15 30 45 60 0 4 8 12 16 20 0 ime o he day [h] sunny day 0 4 8 12 16 20 0 ime o he day [h] cloudy day 3 Resul s 68 Table 9: Daily sums o sap low o all in es iga ed ees on cloudy and sunny days (mean sums, and numbe o examined days). PF: Podoca pus alca us, PP: Pinus pa ula, ES: Eucalyp us saligna; NF: na u al o es , PP: Pinus plan a ion, ES: Eucalyp us plan a ion T ee (dbh) Sap low [l d - 1 ] cloudy days Sap low [l d - 1 ] sunny days Saplings PF NF (8.7 cm) 5.9 (29 days) 3.6 (11 days) 9.6 ( 3 days) 10.0 (60 days) 8.3 (11 days) 14.0 (4 days) PF PP (5.1 cm) PF ES (8.7 cm) Shel e - ee s PF 1 (21.7 cm) 7.8 (29 days) 7.2 (29 days) 8.8 (29 days) 21.8 (64 days) 15.9 (64 days) 19.7 (64 days) PF 2 (10.9 cm) PF 3 (22.4 cm) PP 1 (28.8 cm) 11.6 (11 days) 13.0 (11 days) 20.4 (11 days) 19.3 (11 days) 25.9 (11 days) 33.3 (11 days) PP 2 (35.4 cm) PP 3 (41.2 cm) ES 1 (17.0 cm), coppiced 3.5 (3 days) 1.2 (3 days) 21.3 (3 days) 5.6 (3 days) 3.8 (3 days) 5.4 (4 days) 3.9 (4 days) 27.6 (4 days) 11.0 (4 days) 6.3 (4 days) ES 2 (18.5 cm), coppiced ES 3 (37.5 cm), non - coppiced ES 4 (17.2 cm), non - coppiced ES 5 (11.2 cm), coppiced 3.6.5 T anspi a ion e sus sap low T anspi a ion and sap low, al hough ep esen ing physiologically connec ed pa ame e s, a e exp essed in di e en nominal dimensions and hus can only be co ela ed in e ms o he daily dynamics. Sap low p o ides a measu e o he o al anspi ed wa e , whe eas anspi a ion is ela ed o a no malized anspi ing a ea. T anspi a ion ollows mo e closely he daily cou se o VPD whe eas he a e o sap low is empo ally bu e ed by he amoun o wa e s o ed in he conduc ing issue o he axes. Daily cou ses o VPD, anspi a ion, s oma al conduc ance and sap low o a Podoca pus alca us sapling in he Pinus o es a e shown in Figu e 41 A and B and o a Pinus pa ula shel e - ee in Figu e 42 A and B o a ainy and a d y-season day. While he daily cou se o anspi a ion ollows in gene al ha o VPD on bo h he sunny and he ainy day (in he mo ning hou s mo e closely han in he a e noon) and o bo h ees, he kine ics o sap low di e ed in h ee espec s: i) The ela ion o he size o he peaks 3 Resul s 69 di e ed conside ably om he ela ion o he peaks in anspi a ion, ii) he dynamics o peaks and minima was delayed by abou 1 h wi h espec o ha o anspi a ion, and iii) sap low con inued in o he nigh whe eas anspi a ion ceased sho ly a e sunse . While on he ainy day anspi a ion and sap low s a ed simul aneously in he mo ning, on he sunny day onse o sap low was delayed by one hou indica ing some xylem sap ese es in he s em which supplied he ini ial anspi a ion. Replenishmen o ha s o e ook place du ing he nigh hou s when anspi a ion was mo e o less ze o. The inc ease in sap low in he mo ning o he ainy day was much as e han unde d y season condi ions and he anspi a ion a es we e also sligh ly highe han on he sunny day, indica ing some s oma al limi a ion al eady in he mo ning. Again a s ong midday dep ession o sap low and anspi a ion was eco ded on he ainy day as a esul o he dec ease o VPD and ligh in ensi y (da a no shown) due o hea y clouds coming up in he cou se o he mo ning. As a esul o upcoming ain in he e ening (s a ing a 16:45 h), s oma a we e closing and anspi a ion s opped. Figu e 41: Diu nal cou ses o sap low (black), anspi a ion (blue) and s oma al conduc ance (g s , g ey) o a Podoca pus alca us sapling, and VPD (da k ed) in he Pinus plan a ion. A: ainy season day (Ap il 9, 2006) and B: sunny day (Decembe 13, 2006). Dbh o he sapling (PP PF 1): 5.2 cm. Conce ning he kine ics, he daily cou se o he Pinus shel e - ee we e quie simila o hose o he Podoca pus sapling. S a ing poin o sap low was, like in he sapling, a he same ime as anspi a ion on he cloudy day and s a ed wi h one hou delay on he day wi h sunny wea he condi ions. The inc ease o sap low was also as e on he ainy day, bu anspi a ion a es we e highe on he sunny day o he Pinus shel e - ee. In con as o he Podoca pus sapling, a midday dep ession in sap low could no be obse ed. 8 10 12 14 16 18 ime o he day [h] sunny day 8 10 12 14 16 18 ime o he day [h] cloudy day Sap low [ml min -1 ] VPD [hPa] g s [mmol m -2 s -1 ] 0 10 20 30 SF VPD g s T anspi a ion [mmol m -2 s -1 ] 0.0 0.5 1.0 1.5 T anspi a ion Sap low [ml min -1 ] VPD [hPa] g s [mmol m -2 s -1 ] 0 10 20 30 SF VPD g s T anspi a ion [mmol -2 s -1 ] 0.0 0.5 1.0 1.5 T anspi a ion AB Rain 3 Resul s 70 Figu e 42: Diu nal cou ses o sap low (black), s oma al conduc ance (g ey) and anspi a ion (blue) o a Pinus pa ula shel e - ee, and VPD (da k ed) in he Pinus plan a ion. A: cloudy day (Ap il 10, 2006) and B: sunny day (Decembe 14, 2006). Dbh o he ee PP 1: 28.8 cm. 3.7 Ca bon iso opes (δ 13 C) o he lea es o he Podoca pus alca us saplings and nu se- ees δ 13 C alues o lea issue a e commonly used o cha ac e ize he long e m wa e ela ions o a plan , aking in conside a ion he gene al di e ence be ween he sligh ly disc imina ing C4- ype and s ongly disc imina ing C3- ype pho osyn hesis. All ee species in es iga ed in his s udy pe o m C3- ype pho osyn hesis cha ac e ized by an a e age iso ope a io o 30‰. Sligh ly highe disc imina ion indica es long- e m high s oma al conduc i i y and ice e sa (Scheidegge e al. 2000). Podoca pus p oduces i s lea es du ing he ainy season (Yig emachew Lemma, pe sonal communica ion) when he wa e ela ions o he ees a e elaxed. The e o e in addi ion o he usually examined ma u e lea es he δ 13 C alues o young lea es we e analysed o assess he s a emen o he 13 C disc imina ion alues. δ 13 C alues o young and ma u e lea es o he same ee we e i ually iden ical and close o 30‰ excep he ma u e lea es om saplings in he Pinus plan a ion which we e sligh ly lowe (Table 10). Al hough he di e ence o he o he alues was s a is ically no signi ican , i migh indica e some wa e sho age du ing he d y season. Signi ican ly di e ing (p < 0.001) δ 13 C alues we e ound be ween Pinus pa ula shel e - ees and all o he ees (n = 18, p < 0.001) excep Eucalyp us (n = 18, p = 0.08); and be ween he Podoca pus alca us shel e - ees and he saplings unde he na u al (n = 18, p = 0.03) and he Eucalyp us canopy (n = 18, p = 0.01), espec i ely. O all ees 8 10 12 14 16 18 ime o he day [h] cloudy day SF VPD g s Sap low [ml min -1 ] VPD [hPa] g s [mmol m -2 s -1 ] 0 20 40 60 80 100 120 A Sap low [ml min -1 ] VPD [hPa] g s [mmol m -2 s -1 ] 0 20 40 60 80 100 120 8 10 12 14 16 18 ime o he day [h] sunny day T anspi a ion [mmol m -2 s -1 ] 0 1 2 3 T anspi a ion B T anspi a ion [mmol m -2 s -1 ] 0 1 2 3 T anspi a ion SF VPD g s 3 Resul s 71 Podoca pus alca us shel e - ees showed he highes (-28.8 ‰) and Pinus pa ula he lowes (-31.0 ‰) alues indica ing pe manen ly elaxed wa e ela ions o he Pinus shel e - ee and a leas empo a y wa e s ess on he Podoca pus shel e - ee. Table 10: δ 13 C iso ope a ios o lea es o Podoca pus saplings and adul shel e - ees. Numbe s ep esen means o h ee ees wi h a sample size o h ee bulk samples o young and ma u e lea es and s anda d e o . Di e en le e s indica e signi ican di e ences be ween he lea es. T ees δ 13 C alues o young lea es (n = 9) [‰ ] δ 13 C alues o ma u e lea es (n = 9) [‰ ] Podoca pus saplings (na u al o es ) -29.5 ± 0.2 a -29.4 ± 0.3 a Podoca pus saplings (Pinus plan a ion) -29.4 ± 0.3 ab -28.6 ± 0.4 ab Podoca pus saplings (Eucalyp us plan a ion) -29.3 ± 0.3 a -29.6 ± 0.4 a Podoca pus shel e - ee -28.8 ± 0.1 b -28.7 ± 1.3 b Pinus pa ula shel e - ee -31.0 ± 0.2 c -31.1 ± 1.2 c Eucalyp us saligna shel e - ee -29.3 ± 0.6 abc -30.1 ± 3.0 abc 4 Discussion 72 4 Discussion This wo k ocuses on g ow h o young Podoca pus alca us ees, in he con ex o he na u al eju ena ion o Podoca pus alca us in h ee di e en o es ypes o he Munessa-Shashamene Fo es (S obl e al. in p ess)(c . S obl e al. in p ess). Conside ing only na u al egene a ion, he s udy had o use young ees which we e no uni o m in size and age and g ew a a ious densi ies in he h ee o es s (Feye a e al. 2002). Howe e , e ec s o densi ies, i.e. dis ance o he indi idual saplings we e no in he ocus o his s udy. This s udy a he concen a es on he g ow h o he Podoca pus saplings unde he h ee di e en canopies o he shel e - ees which acco ding o se e al o he au ho s (Pa o a 1992; Fimbel and Fimbel 1996; Pa o a 1997; Fe ene and Feleke 2001; Feye a e al. 2002; Lue ge e al. 2003; Fe ene and Beck 2004) should be be e unde Eucalyp us and Pinus han unde he canopy o he na u al Podoca pus mixed o es . To analyse his unexpec ed obse a ion wi h saplings o di e en age and size a de ailed s udy o he sub-canopy mic oclima es was pe o med, in o de o comp ehend di e ences in he mic oen i onmen o he young ees which could explain di e en g ow h a es. As esponse o he espec i e mic oclima es, pho osyn hesis and wa e ela ions o he saplings we e s udied. 4.1 Ve i ica ion o he shel e - ee e ec on he g ow h o Podoca pus saplings Fi s o all, he epo ed g ow h-s imula ing nu se- o shel e - ee e ec s had o be e i ied, using he na u al Podoca pus o es as con ol si ua ion. G ow h was measu ed as ela i e g ow h a es o he s em diame e , al hough his measu e is subjec o u he modi ica ions: Fi s , especially wi h espec o he di e en size o he saplings , i is s ongly depending on he age o he young ees, as epo ed by se e al au ho s (B ienen and Zuidema 2006; Ma ínez-Vilal a e al. 2007). Secondly i depends on he size o he c owns o he saplings. Since LAI is no a use ul measu e o he c own unde he canopy o shel e - ees ano he p oxy was in oduced o ep esen he c own size: The c own p ojec ion a ea (Figu e 8). Highes ela i e g ow h a es wi h and wi hou he co ec ion by he c own size we e ound o he Podoca pus saplings unde he shel e o Pinus pa ula. Unco ec ed RGR was only sligh ly highe unde Eucalyp us han unde he na u al canopy, howe e , when co ec ed by he p oxy o he c own size (Table 11), 4 Discussion 73 i was less han hal o i . As a esul , o he obse a ion pe iod o 2 yea s, he posi i e shel e - ee e ec could only be con i med o he Pinus plan a ion. Table 11: Rela i e diame e (a b eas heigh ) g ow h a es (RGR), c own p ojec ion a eas (CPA) and a io o RGR and CPA o he Podoca pus saplings in he h ee di e en o es si es. Numbe s gi en o RGR and CPA a e means wi h s anda d e o s (na u al o es : n = 5, Pinus plan a ion: n = 9, Eucalyp us plan a ion: n = 7). Lowe case le e s indica e signi ican di e ences be ween he si es. Na u al o es Pinus plan a ion Eucalyp us plan a ion RGR [mm cm -1 mon h -1 ] 0.08 ± 0.02 a 0.30 ± 0.06 b 0.09 ± 0.02 a CPA [m 2 ] 2.6 ± 1.1 3.7 ± 0.4 7.9 ± 2.1 No malized RGR/CPA [mm cm -1 mon h -1 ] [m -2 ] 0.03 0.08 0.01 A e he epo s o a posi i e “nu se- ee e ec ” o Eucalyp us on he g ow h o Podoca pus saplings (Senbe a e al. 2002; Yi daw and Luukkanen 2003; Selwyn and Ganesan 2009; Teshome 2009) w ong? Fo a ai assessmen o he si ua ion, i is necessa y o conside he managemen p ac ices o he na u al o es and he exo ic plan a ions by he owne s o he o es (Fo es En e p ise, A si Negele, E hiopia). Theo e ically, he na u al o es is a p o ec ed a ea whe e i is no allowed o ell ees, bu due o he high demand o i ewood (Pohjonen and Pukkala 1990) and he selec i e logging by local people and ca le g azing (K epkowski e al. 2011), he o es is highly dis u bed. Al hough Podoca pus is no a ec ed by he bi o es (Tes aye e al. 2002), he gene al lowe numbe o saplings and ees in he na u al o es can be a ibu ed mainly o human dis u bances such as cu ing o ees o di e en uses (Teke ay 1997b; Teke ay 1997a; Senbe a and Teke ay 2001). The plan a ions a e p o ec ed by gua ds agains illegal logging, and g azing is es ic ed a leas in younge plan a ions. Pinus plan a ions a e usually clea -cu a e 25 o 30 yea s, wi h pe iodic hinning once in a while, whe eas Eucalyp us plan a ions a e usually coppiced in in e als o 5 - 7 yea s (Feye a e al. 2002; Tadele 2004). This sho o a ion sys em esul s in a la gely changing ligh clima e o he unde g ow h (Feye a e al. 2002). In ela ed s udies, a highe densi y and a be e egene a ion o na i e woody plan s was ound in coppiced s ands o Eucalyp us saligna compa ed o he na u al o es and coni e plan a ions (Michelsen e al. 1996; Senbe a e al. 2002), whe e a be e ligh clima e o he saplings is p o ided by he Eucalyp us canopy due o i s be e ligh egime caused by a less dense c own. The densi y o he c owns in he Eucalyp us plan a ion changes 4 Discussion 74 conside ably wi h he ime a e he las coppicing. The Eucalyp us plan a ion o he s udy si e in he Munessa o es was coppiced a leas once, bu mo e likely wo o h ee imes as es ima ed om he age (31 yea s) and heigh o o e opping indi iduals (35 – 40 m). The heigh o he young Eucalyp us ees (12.6 and 26.0 m) which had sp ou ed om he oo s ocks a e coppicing indica e a leas a ime span o 7 yea s o he smalle and 15 o he bigge coppice, conside ing he epo ed g ow h a es o Eucalyp us saligna (Whi esell e al. 1987), a he egion. Due o coppicing he canopy o he in es iga ed Eucalyp us si e was a leas wo- ie ed wi h a pa chy uppe laye o he c owns o he uncoppiced and a lowe laye o med by he c owns o he e-sp ou ed ees. Coppicing changes he ligh egime o he unde g ow h undamen ally om shade in o a high-ligh si ua ion and pho osyn he ic CO 2 ne up ake om ligh limi a ion o ligh sa u a ion. This in u n s imula es g ow h as long as he Podoca pus saplings a e no o e opped by he as e g owing new Eucalyp us shoo s. As ou in es iga ions ook place some yea s a e he las coppicing, he saplings in he Eucalyp us si e we e conside ably shadowed and hus in he s a e o educed g ow h which will u n in o maximum g ow h a es a e he nex coppicing. Whe eas he Podoca pus saplings in he na u al o es and unde he shel e o Pinus g ow mo e o less con inuously, hose in he Eucalyp us plan a ion show in e mi en g ow h ollowing he changes in he ligh clima e. The e o e, a longe obse a ion pe iod unde he canopy o Eucalyp us is equi ed, ha encompasses he eac ion o he Podoca pus saplings o he common p ac ice o coppicing o he shel e - ees. In e es ingly, g ow h a es o he saplings did no di e signi ican ly du ing he we and he d y seasons. Al hough daily wa e consump ion as measu ed by o al sap low was conside ably highe on days o he d y season han on ainy days (Table 9), s onge limi a ion o anspi a ion by d ough -induced s oma al closu e (Lloyd and Fa quha 2008) could no be de ec ed du ing he d y season. On he con a y, educed sap low could be a ibu ed o a low VPD a he han o a sho age o wa e supply o he young as well as o he shel e - ees (Ve beeck e al. 2007). 4.2 In luence o clima e ac o s on he pe o mance and wa e ela ions o he Podoca pus saplings Ligh and VPD we e he mos e ec i e abio ic a iables con olling pho osyn he ic ne CO 2 up ake by he Podoca pus saplings (c . 3.4.1 In es iga ion o ac o s in luencing 4 Discussion 75 CO 2 ne up ake). Since g ow h models based on daily sums o adia ion and s oma al conduc ance a e no a ailable o Podoca pus, pho osyn he ic CO 2 assimila ion was used as a p oxy o biomass p oduc ion and g ow h. I is esponding o he in ensi y o PAR, bu limi ed by empe a u e and s oma al conduc ance. Co ela ion analysis indica ed ha 71% o he daily ca bon gain esul ed om esponse o PAR while only 4% could be a ibu ed o VPD- and empe a u e e ec s. The emaining 25% which could no be aced o speci ic en i onmen al ac o s may ha e esul ed om limi a ion h ough s oma al conduc ance and om combina ions o he a iables. 4.2.1 Tempe a u es and VPD In he annual cou se o he mic oclima e, mon hly means o he clima e ac o s empe a u e and VPD showed ha in bo h plan a ions, bu especially in he Pinus si e, condi ions we e d ie compa ed o he na u al o es which could be de imen al o he ec ui men o seedlings (K epkowski e al. 2011). Ai empe a u e was up o 1.8 °C highe in bo h plan a ions, bu highe VPD could only be obse ed in he Pinus plan a ion in he d y season. In he daily cou ses, ai empe a u es, anging be ween a minimum o 4 °C usually a o sho ly a e sun ise and a maximum o 26 °C in he a e noon could a ec pho osyn he ic ne ca bon gain; bu du ing he daily hou s, when pho osyn hesis is possible, he ai empe a u es we e in a ange whe e small di e ences as eco ded be ween he 3 si es a e o less impo ance; supe -op imal empe a u es occu ed only du ing a sho ime pe iod (1 - 2 hou s) a noon. Ra he ai empe a u es a ec pho osyn he ic CO 2 up ake ia VPD (Coms ock 2002) which in he a e noon esul ed in a pa ial closu e o he s oma a (Figu e 28). The daily cou ses o VPD also indica ed a d ie clima e in he plan a ions compa ed o he na u al o es . D y season alues o VPD whe e highe in he Pinus plan a ion du ing he whole day, whe eas in he Eucalyp us si e VPD exceeded ha in he na u al o es only in he a e noon. Highes hou ly means in he plan a ions du ing he d y season we e al eady in a ange which could a ec he pho osyn he ic CO 2 up ake o he saplings by s oma al closu e (Diaz- Espejo e al. 2007). 4.2.2 Th ough all Mon hly h ough all was simila in all si es, bu du ing single hea y ain e en s, a highe maximal h ough all was measu ed in he na u al o es . Th ough all depends on many ac o s, such as he s uc u e and densi y o he canopy, in ensi y and dis ibu ion o he 4 Discussion 76 ain all e en s, wind speed, VPD o he ai and he p opo ion o su ace s em low (C ock o d and Richa dson 2000). In e cep ion anges be ween 8.9 and 39% and s em low be ween 0.1 and 13% in opical and sub opical o es s (C ock o d and Richa dson 1990). Canopy co e in he h ee si es was calcula ed as pe cen age o he p ojec ed c own a ea in ela ion o he g ound a ea (Roehle 1986). C own a ea p ojec ion o he plan a ions was simila wi h 68% o Pinus and 72% o Eucalyp us, whe eas in he na u al o es , he canopy was closed (99% co e age) wi h la gely o e lapping c owns. In he plan a ions, h ough all was no homogenous because o he pa chy canopy wi h bigge gaps. Fo gap a eas, 70% o g oss p ecipi a ion could be added (Asdak e al. 1998) o he amoun s o h ough all. Conside ing his, h ough all in he plan a ions ma ches he amoun o h ough all in he na u al o es , and consequen ly wa e supply is simila in all si es. The e o e, d ie condi ions, especially in he Pinus plan a ion, a e no caused by lowe h ough all, bu a he by highe empe a u es and VPD. 4.2.3 Sub-canopy ligh ela ions (PAR) The expe imen al simula ion o he mic oclima e (Figu e 24) showed ha he mos c ucial ac o o ca bon up ake and he e o e also o he g ow h o he saplings is he ligh egime unde he h ee di e en canopies. The mon hly a e age o daily accumula ed PAR ou side he o es anged om 17 mol m -2 d -1 in he ainy o 41 mol m - 2 d -1 in he d y season, bu losses in i adiance upon passage h ough he canopy we e ex emely high as only 0.8% (na u al o es ), 2.6% (Pinus plan a ion) and 3.4% (Eucalyp us plan a ion) o he ou side PAR eached he saplings le el. Those alues a e in good ag eemen wi h alues epo ed o a opical lowland ain o es o Cos a Rica (Chazdon and Fe che 1984), o Cali o nian edwood o es s (Pea cy and P i sch 1994), and a mixed coni e ous-deciduous o es in New England (Canham e al. 1994). Values o PAR measu ed by he mic oclima e s a ions in he h ee si es we e 3 o 4 imes highe in he plan a ions compa ed o he na u al o es (Table 3), bu PAR measu ed on selec ed days wi h he quan um senso o he po ome e in he Eucalyp us plan a ion showed lowe PAR in ensi y compa ed o he o he wo si es (Table 7). This disc epancy be ween he measu emen s migh be mainly a ibu ed o he ac ha he senso s o each mic oclima e s a ion we e ixed on a place in he plo ep esen ing a ypical shel e - ee si ua ion wi h he espec i e ligh egime o each si e. In he Eucalyp us plan a ion, PAR alues o he senso s o he mic oclima e s a ion and o he po ome e we e in good ag eemen , whe eas in he o he wo si es, alues measu ed 4 Discussion 77 wi h he po ome e we e signi ican ly highe han hose eco ded by he mic oclima e s a ions. The majo eason o he di e ence was he acciden al dis ibu ion o he Podoca pus saplings in he plo s (Figu e 8) in ela ion o he selec ed posi ion o he mic oclima e s a ions. Al hough he c own co e in he na u al o es was 99%, ligh in ensi ies could di e be ween 1 o 77% o he ou side ligh wi hin he si e (Feye a e al. 2002) e en on a small scale. Acco dingly he measu emen s o he PAR senso o he po ome e showed no an e en dis ibu ion o he adia ion o e he plo as could ha e been p esumed om he mic oclima e s a ions da a. The same could be obse ed o he Pinus plan a ion whe e he pa chiness o he canopy leads o an une en dis ibu ion o he ligh in ensi ies wi hin he plo , and al hough Podoca pus is a shade ole an species (Teke ay 2011), eju ena ion ec ui men o he saplings is less success ul in he deep shade. 4.2.4 S oma al esponses o mic oclima e ac o s and e ec s on CO 2 up ake The pho osyn he ic esponse is usually mo e o less cons ained by s oma al conduc ance (Dengel and G ace 2010). S oma al mo emen s espond o signals om he oo s, om ligh and om he a mosphe ic wa e apou de ici (Coms ock 2002). Since s oma al conduc ance is calcula ed om anspi a ion and VPD, he ela ion be ween s oma al conduc ance and VPD is au o-co ela ed and he e o e no independen . Measu emen s o he oo signal was beyond he possibili ies o he p esen wo k; he e o e only he co ela ion be ween changes in s oma al conduc ance and changes in he ligh in ensi ies could be examined (Table 8). In gene al, only weak co ela ions we e ound, he s eng h o which di e ed be ween he h ee o es ypes: In he na u al o es and Eucalyp us plan a ion, ligh in ensi ies had almos no in luence on s oma al conduc ance o he lea es o he Podoca pus saplings ( ² = 0.19; n = 17 and ² = 0.13; n = 18, espec i ely), while in he Pinus plan a ion some e ec was indica ed by he co ela ion ac o o ² = 0.28 (n = 22). Conside ing ha ligh in ensi ies a e gene ally highe in he Pinus plan a ion compa ed o he o he wo si es, i is no su p ising ha he in luence o PAR on s oma al conduc ance is mo e ob ious in his ype o o es . The daily cou se o ca bon up ake and he co esponding clima e ac o s, measu ed wi h a Podoca pus sapling in he Pinus plan a ion (Figu e 28 c and d), shows a ypical example o limi a ion o pho osyn hesis by o he ambien ac o s, mos p obably s oma al esis ance, han ligh . High adia ion and concomi an ly high VPD could cause s oma al closu e (G ace e al. 1975; U ban e al. 2007), wha is indica ed a all h ee si es by a 4 Discussion 84 he ainy season he ma ic wa e po en ial o he soil is be ween 0 and -15 kPa, i dec eases down o -60 kPa a he end o he d y season (F i zsche e al. 2006). Expec edly he e is a delay by up o 3 mon hs o he seasonal changes in ma ic po en ial a dep hs deepe han 1 m, bu he po en ials as such appea mo e o less independen o he soil dep h (down o 2 m) (Mohan e al. 1993) and he ange o he seasonal changes a e compa a i ely small. Un o una ely he ho izon al and e ical ex ensions o he oo sys ems, in pa icula o he li ing ine oo s, a e no su icien ly known. Da a om he Kuke si e a e a ailable o Podoca pus and Eucalyp us (F i zsche e al. 2006), bu no o Pinus pa ula. In gene al, ep esen a i es o he genus Pinus a e known as ap oo plan s (Cou s e al. 1998), bu he highes ine oo s densi ies a e always ound in he uppe soil ho izons, mos ly in he li e laye (Dames e al. 2002). This may be due o he highe nu ien con en o he li e laye which is exploi ed by he ec o ophic myco hiza. Howe e , compa ed o o he opical ees, ine- oo biomass o Pinus pa ula in he uppe soil laye is small (Val e de-Ba an es e al. 2009). I espec i e o ha , Pinus pa ula is capable o wa e up ake om bo h he uppe o ganic soil laye s and om e y deep mine al soil ho izons. Podoca pus alca us is also a ap oo plan , howe e wi h ap oo s a ely ex ending deepe han 1.5 – 2 m. High densi ies o ine oo s ha e been de e mined along he en i e ap oo (F i zsche e al. 2006), bu especially so in he uppe 10 cm whe e peaks o ine oo g ow h ha e been eco ded pa icula ly du ing he d y season. The oo sys em o Eucalyp us saligna is mainly shallow (Rob 2004), ex ending ho izon ally om he bole while only a ew s ong oo s ancho he ee deepe in he soil. Acco ding o p elimina y δ 18 O iso ope s udies du ing he d y season in 2002 Eucalyp us ook up soil wa e p e e en ially om soil laye s below 20 cm while Podoca pus appea ed o ap he opsoil (F i zsche e al. 2006). Un o una ely hese s udies ha e no ye been epea ed. Conside ing he gene ally small ma ic po en ial o less han -1 ba o he soil laye s ha bou ing he majo pa s o he oo sys ems and he di e en dis ibu ions o he ine oo s in he soil, compe i ion o soil wa e be ween he Podoca pus saplings and he shel e - ee species may no be e y p onounced. Ne e heless i should be men ioned ha sap low in he saplings (and he smalles o he Podoca pus shel e - ees as well) and s oma al conduc ance s a ed ea lie o dec ease in he cou se o he day han ha in he shel e - ees. A signi ican di e ence be ween he si ua ions in he h ee o es s was no isible. 4 Discussion 85 4.3 Conclusion The so called “nu se- ee e ec ” o wo exo ic species and o he indigenous ees in he na u al o es on he g ow h o Podoca pus alca us saplings could be aced down o a con e sion o he high global adia ion in o a bene icial ligh clima e while o he a iables o he clima e we e less a ec ed. The p esen ed esul s do no suppo he opinion o a de imen al e ec o Pinus on he es ablishmen and g ow h o Podoca pus alca us. Howe e , such conclusions could be d awn om he pe o mance o Podoca pus alca us unde he shel e o Eucalyp us saligna. In ha case, he wo- ie ed canopy o he shel e - ees abso bed signi ican ly mo e PAR han he o he wo canopies and hus pe se ga e ise o a lowe pho osyn he ic p oduc ion. Howe e , no only pho osyn hesis was educed unde he shel e o Eucalyp us, bu also g ow h, compa ed o he Pinus plan a ion. In con as o he si ua ion in he Pinus si e, whe e he ees a e usually elled a e 30 o 40 yea s o g ow h, he Eucalyp us ees a e egula ly coppiced in 7 yea s in e als. When his happens he Podoca pus saplings shoo up (Feye a e al. 2002), making use o he imp o ed adia ion. Al hough da a a e no ye a ailable, he je ky g ow h modus o Podoca pus saplings in he Eucalyp us plan a ion may be, on he whole, no less e ec i e han he mo e e en g ow h unde Pinus o in he na u al o es . Nu se- ees a e usually seen o p o ide nu ien s h ough li e and sedimen accumula ion, highe mine aliza ion a e, ni ogen ans e and inc ease o ma ion o ec omyco hiza (Padilla and Pugnai e 2006) o p o ide wa e h ough hyd aulic li (P ie o e al. in p ess). In ela ed s udies in he Munessa-Shashamene Fo es sha ing o myco hiza be ween Podoca pus and he exo ic ee species could be excluded (Wube e al. 2009), as well as a be e nu ien supply om he soils in he plan a ion (F i zsche e al. 2006; F eie e al. 2010). In he case o ou s udy, i u ned ou ha he posi i e e ec o he plan a ion ees was due o he mo e bene icial ligh clima e, caused by he canopies o he ees. F om a scien i ic iewpoin o use he e m “shel e - ee e ec ” would be mo e app op ia e han “nu se- ee e ec ”. 5 Summa y 86 5 Summa y E hiopian o es s disappea wi h a a e o 1.1% pe yea due o he high demand o i ewood and imbe . To p o ec he emaining pa s o he o es s and o mee he equi emen s o he popula ion, as g owing exo ic ee plan a ions we e es ablished 60 yea s ago. Bu he e a e conside able conce ns ega ding exo ic plan a ions: hey a e ulne able o pes calami ies and ha e he epu a ion o cause damage o he ecosys ems due o high demand o wa e and nu ien s, and he elease o allelopa hic subs ances. Conside ing he en i onmen al de e io a ion caused by mono onous plan a ions o exo ic ee species, he chance o indigenous woody plan s o eju ena e na u ally in hose plan a ions appea s o be e y small. Bu he e a e obse a ions o indigenous ee species egene a ing unde he shel e o exo ic ee plan a ion o pine and eucalyp s. This enhanced g ow h o indigenous saplings unde he canopy o exo ics has been e med “nu se- ee e ec ”. In he Munessa-Shashamene Fo es , a opical mon ane o es in E hiopia consis ing o plan a ions o exo ic ee species and emnan s o dis u bed na u al o es , egene a ion and an enhanced g ow h o na i e Podoca pus alca us saplings unde he shel e o exo ic ee plan a ions (Pinus and Eucalyp us) was obse ed. The ocus o his wo k was o examine he di e en g ow h pa e ns o he saplings in he si es, he e ec s o he mic oclima e ( adia ion, empe a u e, ela i e humidi y, apou p essu e de ici (VPD) and h ough all) on he pho osyn he ic pe o mance, and o compa e he wa e ela ions o he Podoca pus saplings and hose o he shel e - ees. Plo s we e es ablished in he wo plan a ions and in he na u al o es o in es iga e he nu se- ee si ua ion in he h ee si es, o which he na u al o es was conside ed as a con ol. A he beginning o he s udy he Podoca pus alca us saplings in he h ee si es had a diame e a b eas heigh (dbh) be ween 1.0 and 8.7 cm and a heigh be ween 0.8 and 9.7 m. The esul s o he s udy a e summa ized as ollows: 1. Obse a ions o e wo yea s showed ha he ela i e g ow h a es o he saplings we e mo e han h ee imes highe in he Pinus plan a ion, whe eas in he na u al o es and he Eucalyp us si e ela i e g ow h a es we e s a is ically no di e en . Thus, a leas o he Pinus plan a ion, a signi ican shel e - ee e ec could be e i ied 3 .2Rela i e g ow h a es du ing he d y and he ainy season we e mo e o less iden ical. 32 Fo commen on he „nu se- ee e ec “ o Eucalyp us see 8. 5 Summa y 87 2. In es iga ion o he sub-canopy mic oclima e p o ed PAR and VPD as majo componen s wi h impac on he pho osyn he ic pe o mance o he saplings. 71% o he a ia ions in pho osyn he ic ca bon up ake could be explained by PAR and 4% by VPD. Ai empe a u e and ela i e humidi y did no di e g ea ly be ween he o es ypes. The Pinus plan a ion was sligh ly wa me and d ie compa ed o he o he wo si es, which is also indica ed by he sligh ly highe δ 13 C a io o he Podoca pus lea es om he saplings in he Pinus plan a ion. Due o he a ying densi ies o he canopies eaching 99% in he na u al o es , 68 and 72 % in he Pinus and Eucalyp us plan a ions 4 ,3 espec i ely, i adiance unde he canopies was di e en . 3. Sub-canopy adia ion is composed o di use ligh and o di ec adia ion by sun lecks. Fo an assessmen o he pho osyn he ic e iciency o he ligh clima e, ligh esponse cu es o pho osyn he ic ne CO 2 up ake we e p oduced and he e icacy o he indi idual sha es o he i adia ion we e de e mined om hese cu es. The ime spans and dis ibu ion o hese sha es o he daily accumula ed adia ion we e eco ded om he daily cou ses. The pho osyn he ic e icacy o he di use adia ion was compa ed wi h ha o he sun lecks. I u ned ou ha pho osyn he ic ac i e adia ion (PAR), p o ided only as di use adia ion o low in ensi y, would inc ease he pho osyn he ic ca bon gain by abou 30%. Lowe quan um e iciency o he sun lecks esul ed om hei high in ensi y which exceeded he linea sec ion o he ligh esponse cu e. Daily accumula ed CO 2 up ake was compa ed wi h a heo e ical op imum unde he indi idual canopies o de e mine he espec i e quan um e iciencies. Gene ally, quan um e iciencies we e highe unde ainy season condi ions when he in ensi ies o he sun lecks we e lowe . 4. Highes PAR alues o all si es we e eco ded in he Pinus plan a ion. Howe e he e iciency o he adia ion was ela i ely low (70%), because o he high in ensi y o he sun lecks, especially du ing he d y season. On cloudy days (which domina ed du ing he e y mois yea 2006), he e iciency was nea ly 100% and esul ed in an op imum pho osyn he ic pe o mance o he saplings in he Pinus plan a ion. In bo h seasons, he pe cen age o daily accumula ed PAR esul ing om sun lecks was high (72%). 43 The in es iga ed Eucalyp us plo had pa ially a wo- i ed canopy om he o iginal ees and he ees which had eg own a e coppicing. 5 Summa y 88 In he Eucalyp us plan a ion, PAR alues we e he lowes o he h ee si es. The wo- i ed canopy o coppiced and uncoppiced Eucalyp us ees esul ed in a highe p opo ion o di use adia ion and less daily accumula ed PAR om sun lecks (46%). Also he e iciency o he ac ual adia ion was he lowes o all si es on cloudy (72%) and sunny (53%) days. Daily accumula ed PAR unde he canopy o he na u al o es was in be ween he o he o es ypes. Such mid-posi ion was also ue o he sha e o he sun lecks and he CO 2 up ake. E icacy o he adia ion was 80% on sunny and 86% on cloudy days. The o al ca bon gain by he Podoca pus saplings was abou he same on d y season and we season days. 5. Wa e ela ions can subs an ially a ec he pho osyn he ic pe o mance o plan s. Especially in he a e noons o he d y season a dec ease o pho osyn he ic CO 2 up ake by he Podoca pus saplings became appa en . Whole- ee wa e consump ion was de e mined by measu ing sap low wi h he G anie sys em. To ha end he sys em had o be calib a ed o Podoca pus. In p inciple sap low (and anspi a ion) ollowed VPD. Howe e , due o wa e s o ed in he axial issue o Podoca pus and Pinus sap low was empo ally shi ed, beginning la e in he mo ning han anspi a ion and las ing longe in he e ening. A 5 - 7 m high Podoca pus sapling consumed 6 - 7 l wa e on a ainy and up o 14 l on a sunny day, whe eas a 17 m high Podoca pus shel e - ee anspi ed 8 o 22 l pe day, depending on he season. The co esponding amoun s o wa e consump ion we e 20 and 35 l, espec i ely, o a 35 m high Pinus pa ula, and 21 and 28 l o a compa able Eucalyp us ee. 6. Compa ison o he daily cou ses o anspi a ion and s oma al conduc ance and sap low showed an ea lie dec ease o anspi a ion by he lea es o he saplings han by he shel e - ees, sugges ing sligh wa e sho age especially du ing he d y season. This in e p e a ion is co obo a ed by he highe 13 C alues in he lea issue o he saplings om he Pinus plan a ion. Ne e heless se e e d ough s ess did no occu du ing he wo yea s o in es iga ion and compe i ion be ween he Podoca pus saplings and he shel e - ees o soil wa e appea s o play a mino ole. 7. The li e a u e on he „nu se- ee e ec “ men ions in pa icula Eucalyp us as shel e - ee, a inding which is no in ag eemen wi h he da a o his s udy: Nei he pho osyn hesis no g ow h was enhanced compa ed wi h he con ol saplings in he na u al o es . The disc epancy be ween his wo k and he li e a u e can be sol ed when he managemen o he Eucalyp us plan a ion is 5 Summa y 89 conside ed. As long as he Podoca pus saplings g ow unde he wo- i ed canopy o he coppiced ees, g ow h is as slow as in he na u al o es . Howe e , a e coppicing he ligh clima e o he saplings amelio a es conside ably and g ow h a es inc ease. Al hough he in es iga ed Eucalyp us plan a ion was no coppiced du ing he ime o he p esen s udy, he posi i e e ec on he g ow h o he Podoca pus saplings could be obse ed in ano he pa o he Munessa-Shashamene Fo es . Thus, a shel e - ee e ec could also be obse ed unde Eucalyp us, bu i s dynamics is s epwise a he han con inuous. 8. The shel e - ee e ec o Pinus pa ula and Eucalyp us saligna (and p esumably also o he species) in Podoca pus alca us could be used o an imp o ed o es managemen in oducing a o a ion be ween he exo ic shel e - ees and he indigenous Podoca pus. Fas e ec ui men and g ow h o Podoca pus unde he shel e would p o ide an al eady es ablished young Podoca pus o es upon clea - elling o he exo ic ees. Such o a ion, in addi ion o he p oduc ion o Podoca pus as a plan a ion ee, would also coun e ac he aliena ion o he o iginal ecosys em. 6 Zusammen assung 90 6 Zusammen assung Die Res bes ände de Na u wälde Ä hiopiens sch ump en du ch die mi dem Be ölke ungswachs um s eigende Nach age nach Feue - und Bauholz mi eine Ra e on 1,1 % p o Jah . Um die e bleibenden Wälde zu schü zen und zugleich den Ansp üchen de Be ölke ung ge ech zu we den, wu den o 60 Jah en Plan agen mi schnell wachsenden exo ischen Bauma en wie Zyp esse, Kie e ode Eukalyp us angeleg . Alle dings gib es besonde s in den T open schwe wiegende ökologische Bedenken gegen Monokul u en exo ische Bauma en: sie sind an ällig gegen Schädlingsbe all und de a ige Kalami ä en sind in den ( opischen) En wicklungslände n besonde s schwe wiegend. Auße dem s ehen besonde s die exo ischen Eukalyp usplan agen in dem Ru , Ökosys eme au g und des hohen Wasse - und Näh s o e b auchs einsei ig zu belas en und du ch die Abgabe allelopa hische Subs anzen das Au kommen na ü liche Vege a ion zu e hinde n. Dies gil insbesonde e ü indigene Bauma en, die an die Bedingungen in den na ü lichen Ökosys emen angepass sind. Dennoch gib es Be ich e, dass einheimische Bauma en un e dem K onendach on Monokul u en exo ische Bauma en Fuß assen können und dann soga schnelle he anwachsen als im Na u wald. Dieses une wa e e Phänomen is in die Li e a u als „Nu se- ee e ec “ (Ammenbaum- ode K onendache ek ) eingegangen. Im Munessa-Shashamene Wald, einem opischen Be gwald im zen alen Ä hiopien, wi d ein D i el des u sp ünglichen Waldgebie s mi le weile on Plan agen eingenommen. De e bliebene Na u wald is du ch menschliche Nu zung an e schiedenen S ellen s a k ges ö . In Höhenlagen um 2000 m dominie im Na u wald die S eineibe (Podoca pus alca us). Au ge o s e wi d ausschließlich mi exo ischen schnellwüchsigen Bauma en: Cup essus lusi anica, Pinus pa ula und Eucalyp us saligna. Wäh end de seh dich gep lanz e Zyp essen o s kaum Un e wuchs ha , zeig sich im Kie e n- und Eukalyp us o s be äch liche Na u e jüngung on Podoca pus. Ziel de o liegenden A bei wa es, das un e schiedliche Wachs ums e hal en des Podoca pus-Jungwuchses un e den K onendäche n eine Kie e - und eine Eukalyp usplan age zu e assen und mi dem Wachs um on Jungbäumen im Na u wald zu e gleichen. Des wei e en soll e zu Ve i izie ung des K onendache ek s ü diesen eine ökophysiologische E klä ung ge unden we den. Zu diesem Zweck wu de de E ek des jeweiligen Mik oklimas (S ahlung, Tempe a u , ela i e Lu euch e, Wasse damp - 6 Zusammen assung 91 Sä igungsde izi de Lu und Bes andesniede schlag) au die Pho osyn heseleis ung de jungen Bäume un e den e schiedenen K onendäche n un e such und mi de Leis ung de „Ammenbäume“ e glichen. Ebenso wu de de Wasse haushal des Podoca pus-Jungwuchses und de Ammenbäume un e such . Da ü wu den in den zwei Plan agen und im Na u wald Un e suchungs lächen mi meh e en jungen S eineiben und K onenbäumen einge ich e . Die Un e suchungs läche im Na u wald dien e als Kon olle ü den K onendache ek . Da es sich um Na u e jüngung handel , wa en die jungen Podoca pus-Bäume un egelmäßig im Plo e eil und auch un e schiedlich al und g oß. Zu Beginn de S udie ha e de Podoca pus-Jungwuchs in den d ei Bes änden einen B us höhendu chmesse zwischen 1,0 und 8,7 cm und eine Höhe zwischen 0,8 und 9,7 m. Im olgenden sind die E gebnisse de A bei da ges ell : 1. Im zweijäh igen Un e suchungszei aum zeig e sich, dass die ela i en Wachs ums a en de jungen S eineiben in de Kie e nplan age d eimal höhe wa en als die im Na u wald und in de Eukalyp usplan age. Dami wa de K onendache ek zumindes ü die Pinus-Plan age 54 bes ä ig . Un e schiede im Wachs um in de Regen- und T ockenzei a en nich au . 2. Es wu de es ges ell , dass die ü die Pho osyn hese wich igs en Komponen en des Mik oklimas die S ahlung (PAR) und das Sä igungsde izi de Lu sind, du ch welche jeweils 71% und 4% de Un e schiede bei de Kohlendioxidau nahme e klä we den können. De Ve gleich des Mik oklimas an den d ei S ando en zeig e, dass die Kie e nplan age im Gegensa z zu den ande en beiden S ando en e was wä me und ockene wa . Diese Tendenz bes ä ig e sich auch du ch die e was höhe e Iso open e häl nis de Blä e des Podoca pus-Jungwuchses in de Kie e nplan age (δ 13 C: -28.6‰ gegenübe -29.4‰ on Podoca pus-Blä e n aus dem Na u wald). Un e schiedlich wa en alle dings die S ahlungs e lus e beim Lich du ch i du ch die 3 K onendäche . Das zu 99% geschlossene K onendach des Na u waldes ließ 0,8% de Gesam s ahlung passie en, wäh end die Du chlässigkei de ehe lückigen K onendäche de Pinus- und de Eukalyp usplan age mi 2,6% und 3,4% de Gesam s ahlung höhe wa . Alle dings gab es in de Eukalyp usplan age ein zwei es ie e gelegenes K onendach on denjenigen Eukalyp us-Bäumen, die nach dem „Au -S ock- 54 Übe den K onendache ek un e Eucalyp us s. 7. 6 Zusammen assung 92 se zen“ wiede ausge ieben ha en. Dadu ch wa de Lich gewinn bei einigen Podoca pus Jungbäumen noch ge inge als de im Na u wald. 3. Die im Ve gleich zu Gesam s ahlung ge ing ügige S ahlung un e den Baumk onen se z sich aus de di usen Himmelss ahlung und de di ek en S ahlung in den das K onendach du chd ingenden Lich s ahlen, den sog. Lich lecken, zusammen. Zu Beu eilung de pho osyn he ischen Wi ksamkei des Lich klimas wu den Lich sä igungsku en de Ne o-CO 2 -Au nahme bei gleichbleibenden äuße en Bedingungen au genommen und die Wi ksamkei de di usen S ahlung und de Lich lecken anhand de Lich sä igungsku en be echne . Dazu wu den die S ahlungsmengen in An eile bes imm e In ensi ä en ze leg , de en Be eiche sich aus den Sä igungsku en e gaben. Die Daue und Ve eilung übe den Tag diese S ahlungspake e wu den aus gemessenen Tagesgängen de Lich in ensi ä en e mi el . In einem Simula ionsexpe imen wu de die pho osyn he ische Wi ksamkei on Lich lecken mi de jenigen de di usen S ahlung e glichen. Wü de man die in einem Tag akkumulie e PAR-Menge nu als gleichbleibende di use S ahlung anbie en, so wü de sich de ägliche Pho osyn hesegewinn um ca. 30% e höhen, so e n keine Limi a ion du ch die S oma a ein i . Die ge inge e Quan enwi ksamkei de Lich lecken läss sich dadu ch e klä en, dass ih e S ahlungsin ensi ä en g ößen eils obe halb des linea en Teils de Lich sä igungsku en liegen. Die wi ksams en Lich lecken lagen im Be eich zwischen 70 und 100 µmol m -2 s -1 . Die Ausbeu e e besse e sich un e dem bewölk en Himmel in de Regenzei . 4. Die sich aus den Tagesgängen e gebende Tagesleis ung de Pho osyn hese wu de mi eine aus de Lich e eilung e echne en op imalen Nu zung de Lich menge e glichen, um die a sächliche pho osyn he ische Lich ausnu zung un e den e schiedenen K onendäche n zu e mi eln. Die höchs en S ahlungswe e (PAR) wu den in de Kie e nplan age gemessen. Wegen de hohen In ensi ä de Lich lecken, o allem in de T ockenzei , wa die pho osy he ische E izienz de S ahlung alle dings e häl nismäßig ge ing (70%), denn de An eil de Lich lecken an de gesam en S ahlungssumme eines Tages wa un e dem K onendach de Kie e n seh hoch (72%). Un e bewölk em Himmel, d.h. un e Regenzei -We e bedingungen (die au g und de langen Regenpe iode on Mä z bis Ok obe im Jah 2006 o he sch en), wa die E izienz jedoch as 100%. 6 Zusammen assung 93 In de Eukalyp usplan age wa en die S ahlungssummen im Ve gleich zu den ande en S ando en am nied igs en. Alle dings üh e das doppel e K onendach, dass du ch das „Au -S ock-Se zen“ de Eukalyp usbäume zus ande komm , zu einem höhe en An eil on di use S ahlung und einem nied ige en An eil aus Lich lecken (46%). Ebenso wa die Ausnu zung de gemessenen S ahlung mi 72% an bewölk en und 53% an sonnigen Tagen e häl nismäßig schlech . Die äglichen S ahlungsmengen un e dem K onendach des Na u walds lagen zwischen denen in de Kie e n- und de Eukalyp usplan age. Die Mi els ellung gal auch ü den S ahlungsan eil de Lich lecken am Lich klima und die CO 2 - Au nahme. Die pho osyn he ische S ahlungswi ksamkei lag zwischen 80 % (an Sonnen agen) und 86 % (bei Bewölkung). Ande s als in den Plan agen wa die Kohlens o au nahme des Jungwuchses wäh end bewölk e und sonnige We e bedingungen gleich. 5. Auße dem Lich klima kann auch de Wasse haushal de Bäume den pho osyn he ischen Kohlens o gewinn e heblich beein lussen. Die Tagesgänge de s oma ä en Lei ähigkei de Blä e und de T anspi a ion wu den im Zuge de Po ome e messungen mi e olg . De gesam e ägliche Wasse e b auch de Jungp lanzen und K onenbäume wu de du ch Sa lussmessungen nach de G anie me hode e mi el . Fü Podoca pus gib es dazu keine Li e a u da en, weshalb eine eigene Eichung de Me hode ü diese A du chge üh wu de. E wa ungsgemäß wa de ägliche Wasse b auch on de Bauma , de G öße de Bäume und on den We e bedingungen abhängig. Im Allgemeinen ko elie e de Sa luss mi dem Sä igungsde izi de Lu , solange die S oma a geö ne blieben. Dies wa meis am Vo mi ag de Fall, wäh end nachmi ags ö e s eine Ve inge ung de s oma ä en Lei ähigkei den Wasse e b auch (und die Pho osyn hese) einsch änk e. Aus dem Ve gleich des Tagesgangs de T anspi a ion und des Sa lusses kann auch au Wasse speiche im S amm und Geäs de Bäume geschlossen we den. Ein solche Speiche zeig e sich bei den Podoca pus- und Pinus K onenbäumen, nich abe bei Eucalyp us. De ägliche Wasse e b auch lag bei 5 – 7 m hohen jungen Podoca pus- Bäumen zwischen 6 – 7 l an einem egne ischen und 14 l an einem Sonnen ag. Ein Podoca pus-K onenbaum mi 17 m Höhe e b auch e en sp echend 8 bzw. 22 l. Die en sp echenden Tagesmengen eine 35 m hohen Pinus pa ula lagen bei 20 bzw. 35 l und die eines e gleichba en Eucalyp us bei 21 und 28 l. 6. Im Ve gleich de T anspi a ion mi den Sa luss a en und de s oma ä en Lei ähigkei zeig e sich eine Ve inge ung sowohl de T anspi a ions a en als 7 Li e a u e 100 Lemenih M (2006) Expedi ing ecological es o a ion wi h he help o os e ee plan a ions in E hiopia. Jounal o he D ylands 1:72-84 Lemenih M, Gidyelew T, Teke ay D (2004) E ec s o canopy co e and unde s o y en i onmen o ee plan a ions on ichness, densi y and size o colonizing woody species in sou he n E hiopia. Fo es Ecology and Managemen 194:1-10 Lemenih M, Teke ay D (2005) E ec o p io land use on he ecoloniza ion o na i e woody species unde plan a ion o es s in he highlands o E hiopia. Fo es Ecology and Managemen 218:60-73 Lisanewo k N, Michelsen A (1993) Allelopa hy in ag o o es y sys ems: he e ec s o lea ex ac s o Cup essus lusi anica and h ee Eucalyp us spp. on ou E hiopian c ops. Ag o o es y Sys ems:63-74 Li le C, La a A, McPhee J, U u ia R (2009) Re ealing he impac o o es exo ic plan a ions on wa e yield in la ge scale wa e sheds in Sou h-Cen al Chile. Jou nal o Hyd ology 374:162-170 Lloyd J, Fa quha GD (2008) E ec s o ising empe a u es and [CO2] on he physiology o opical o es ees Phil. T ans. R. Soc. B 363:1811-1181 Lue ge U, Be g A, Fe ene M, Nauke P, Pe e D, Beck E (2003) Compa a i e cha ac e iza ion o pho osyn he ic pe o mance and wa e ela ions o na i e ees and exo ic plan a ion ees in an E hiopian o es . T ees-S uc u e and Func ion 17:40-50 Lundg en BaL (1969) The Munessa o es : A plan ecological s udy. CADU Publica ions, Addis Ababa Mamo N, S e ba H (2006) Si e index unc ions o Cup essus lusi anica a Munesa Shashemene, E hiopia. Fo es Ecology and Managemen 237:429-435 Ma ínez-Vilal a J, Vande klein D, Mencuccini M (2007) T ee heigh and age- ela ed decline in g ow h in Sco s pine (Pinus syl es is). Oecologia 150:529-544 Michelsen A, Lisanewo k N, I F, Hols N (1996) Compa isons o unde s o ey ege a ion and soil e ili y in plan a ions and adjacen na u al o es s in he E hiopian highlands. Jou nal o Applied Ecology 33:627-642 Michelsen AL, N; F ies, Ib and Hols s, N (1993) Impac s o ee plan a ions in he E hiopian highland on soil e ili y, shoo and oo g ow h, nu ien u iliza ion and myco hizal coloniza ion. Fo es Ecology and Managemen 61:299-324 Mohan V, Na a ajan K, Ingleby K (1993) Ana omical s udies on ec omyco hizas. Myco hiza 3:43-49 Mon agnini F (2001) S a egies o he eco e y o deg aded ecosys ems: Expe iences om La in Ame ica. In e ciencia 26:498-503 Mo ze T (2003) Bes andesklima, Ene giehaushal und E apo anspi a ion eines opischen Be g egenwaldes (Süd-Ecuado ). PhD Thesis. In: Depa men o Geog aphy. Uni e si y o Mannheim, Mannheim 7 Li e a u e 101 Muelle -Hohens ein K, Aba e A (2004) Rain o es ma gins and hei dynamics in sou h- eas E hiopia. En i onmen al Science, Sp inge , Be lin Nino K (2009) Isola ion and iden i ica ion o ungi associa ed wi h needle bligh and dea h o Pinus pa ula ees in o es plan a ions o A si Fo es En e p ise, E hiopia. Mas e Thesis, Wondo Gene College o Fo es y and Na u al Resou ces, Wondo Gene , E hiopia. Nyoka BI (2003) Biosecu i y in o es y: a case s udy on he s a us o in asi e o es ees species in Sou he n A ica. Fo es Biosecu i y Wo king Pape FBS/1E. Fo es y Depa men . FAO, Rome (unpublished). Obe hause U (1997) Seconda y o es egene a ion benea h pine (Pinus kesiya) plan a ions in he no he n Thai highlands: a ch onosequence s udy. Fo es Ecology and Managemen 99:171-183 O wa C, Mu ua A, Kind R, Jamnadass R, Simons A (2009) Ag o o es ee Da abase:a ee e e ence and selec ion guide e sion 4.0. O samo R (1998) E ec o nu se ee species on ea ly g ow h o Anisop e a ma gina a Ko h. (Dip e oca paceae) on an Impe a a cylind ica (L.) Beau . g assland si e in sou h Kaliman an, Indonesia. Fo es Ecology and Managemen 105:303-311 Padilla FM, Pugnai e FI (2006) The ole o nu se plan s in he es o a ion o deg aded en i onmen s. F on ie s in Ecology and he En i onmen 4:196-202 Pa o a JA (1992) The ole o plan a ion o es s in ehabili a ing deg aded opical ecosys ems. Ag icul u e, Ecosys ems and En i onmen :115-133 Pa o a JA (1995) In luence o o e s o y composi ion on unde s o y coloniza ion by na i e species in plan a ions on a deg aded opical si e. Jou nal o Vege a ion Science 6:627-636 Pa o a JT, JW and Jones, N (1997) Ca alyzing na i e o es egene a ion on deg aded opical lands. Fo es Ecology and Managemen 99:1-7 Pea cy RW (1988) Pho osyn he ic u iliza ion o ligh lecks by unde s o y plan s. Aus alian Jou nal o Plan Physiology 15:223-238 Pea cy RW (1990) Sun lecks and pho osyn hesis in plan canopies. Annual Re iew o Plan Physiology and Plan Molecula Biology 41:421-453 Pea cy RW, P i sch WA (1994) Consequences o sun lecks o pho osyn hesis and g ow h o o es unde s o y plan s. In: Schulze ED, Caldwell MM (eds) Ecophysiology o pho osyn hesis. Sp inge , Be lin, pp 343-359 P i sch WA, Pea cy RW (1992) G ow h and ep oduc i e alloca ion o Adenocaulon bicolo ollowing expe imen al emo al o sun lecks. Ecology 73:2109-2117 Pohjonen V, Pukkala T (1990) Eucalyp us globulus in E hiopian o es y. Fo es Ecology and Managemen 36:19-31 Poo e MaF, C (1985) The ecological e ec s o Eucalyp us. In: FAO (ed), Rome, p 87 7 Li e a u e 102 P ie o I, Padilla FM, A mas C, Pugnai e FI (in p ess) The ole o hyd aulic li on seedling es ablishmen unde a nu se plan species in a semi-a id en i onmen . Pe spec i es in Plan Ecology, E olu ion and Sys ema ics In P ess, Co ec ed P oo Rao CRN (1984) Pho osyn he ically ac i e componen s o global sola adia ion - measu emen s and model compu a ions. A chi es o Me eo ology Geophysics and Bioclima ology Se ies B-Theo e ical and Applied Clima ology 34:353-364 Rob C (2004) Sydney blue gum (Eucalyp us saligna) o sawlogs in he 450-650 mm ain all zone. Fa mno es, Depa emen o Ag icul u e. Go e nmen o Wes e n Aus alia. Roehle H (1986) Ve gleichende Un e suchungen zu E mi lung de Genauigkei bei de Ablo ung on K onen adien. Fo s a chi 2:67-71 Russ GW (1945) Repo s on E hiopian o es s. Compiled by Woldemichael Kelecha, 1979. Addis Ababa, p 215. San iago-Ga cia RJ, Colon SM, Sollins P, Van Bloem SJ (2008) The ole o nu se ees in mi iga ing i e e ec s on opical d y o es es o a ion: A case s udy. Ambio 37:604-608 Scheidegge Y, Sau e M, Bahn M, Siegwol R (2000) Linking s able oxygen and ca bon iso opes wi h s oma al conduc ance and pho osyn he ic capaci y: a concep ual model. Oecologia 125:350-357 Selwyn MA, Ganesan R (2009) E alua ing he po en ial ole o Eucalyp us plan a ions in he egene a ion o na i e ees in sou he n Wes e n Gha s, India. T opical Ecology 50:173-189 Senbe a DA, Shamseldin AY, O'Conno KM (1999) Modi ica ion o he p obabili y- dis ibu ed in e ac ing s o age capaci y model. Jou nal o Hyd ology 224:149-168 Senbe a F, Teke ay D (2001) Regene a ion o indigenous woody species unde he canopies o ee plan a ions in Cen al E hiopia. T opical Ecology 42:175-185 Senbe a F, Teke ay D, Naslund BA (2002) Na i e woody species egene a ion in exo ic ee plan a ions a Munessa-Shashemene Fo es , sou he n E hiopia. New Fo es s 24:131-145 Sil ano a (1996) En e p ise o ma ion o he Munessa-Shashemene s a e o es y p ojec , . O omia Bu eau o ag icul u e de elopmen , Addis Ababa, E hiopia, 78 p S obl S, Fe ene M, Beck E (in p ess) Analysis o he “shel e ee-e ec ” o na u al and exo ic o es canopies on he g ow h o young Podoca pus alca us ees in sou he n E hiopia. T ees - S uc u e and Func ion: in p ess Tadele D (2004) G ow h and es ablishmen o indigenous plan s inside exo ic ee plan a ions. Mas e Thesis. In: Depa emen o Biology, Bahi Da Uni e si y, E hiopia 7 Li e a u e 103 Teke ay D (1997a) The impac o clea ing and con e sion o d y A omon ane o es s in o a able land on he composi ion and densi y o soil seed banks. Ac a Oecologica-In e na ional Jou nal o Ecology 18:557-573 Teke ay D (1997b) Seedling popula ions and egene a ion o woody species in d y a omon ane o es s o E hiopia. Fo es Ecology and Managemen 98:149-165 Teke ay D (2011) Na u al Regene a ion and Managemen o Podoca pus alca us (Thunb.) Mi b. in he A omon ane Fo es s o E hiopia. In: S imm B, Gün e S, Webe M, Mosandl R (eds) Sil icul u e in he T opics, ol 8. Sp inge Be lin Heidelbe g, pp 325-337 Tes aye G (2008) Ecology o egne a ion and phenology o se en indigenous ee species in a d y a omon ane o es o Eh iopia. PhD Thesis. Addis Ababa Uni e si y, Addis Ababa. In: Tes aye G, Teke ay D, Fe ene M (2002) Regene a ion o ou een ee species in Ha enna o es , sou heas e n E hiopia. Flo a 197:461-474 Tes aye G, Teke ay D, Fe ene M, Beck E (2010) Regene a ion o se en indigenous ee species in a d y a omon ane o es , sou he n E hiopia. Flo a 205:135-143 Teshome T (2009) Is Eucalyp us Ecologically Haza dous T ee Species? E hiopian eJou nal o Reseach and Inno a ion Fo esigh 1:128-134 U ban O e al. (2007) Ecophysiological con ols o e he ne ecosys em exchange o moun ain sp uce s and. Compa ison o he esponse in di ec s. di use sola adia ion. Global Change Biology 13:157-168 Vallada es F, Allen MT, Pea cy RW (1997) Pho osyn he ic esponses o dynamic ligh unde ield condi ions in six opical ain o es sh ubs occu ing along a ligh g adien . Oecologia 111:505-514 Val e de-Ba an es O, Raich J, Russell A (2009) Fine- oo mass, g ow h and ni ogen con en o six opical ee species. Plan and Soil 320:333-334 Ve beeck H e al. (2007) Model analysis o he e ec s o a mosphe ic d i e s on s o age wa e use in Sco s pine. Biogeosciences 4:657 - 671 on B ei enbach F (1961) Fo es s and woodlands o E hiopia. E hiopian Fo es y Re iew 1:19-39 on B ei enbach F (1962) Na ional o es y de elopmen planning: A easibili y and p io i y s udy on he example o E hiopia. E hiopian Fo es y Re iew 3:41-68 Wa son GW, Voeg lin DJ, Mu phy ST, Foo i RG (1999) Biogeog aphy o he Cina a cup essi complex (Hemip e a: Aphididae) on Cup essaceae, wi h desc ip ion o a pes species in oduced in o A ica. Bulle in o En omological Resea ch 89:271- 283 Webe JA, Ju ik TW, Tenhunen JD, Ga es DM (1985) Analysis o gas-exchange in seedlings o Ace saccha um - In eg a ion o ield and labo a o y s udies. Oecologia 65:338-347 7 Li e a u e 104 Whi esell CD, DeBell DS, Schube TH (1987) Six-yea g ow h o Eucalyp us saligna plan ings as a ec ed by ni ogen and phospho us e ilize . USDA Fo es Se ice Resea ch Pape PSW-188. 5 pp. WRB IWG (2007) Wo ld Re e ence Base o Soil Resou ces 2006, i s upda e 2007. Wo ld Soil Resou ces Repo s No. 103. FAO, Rome. Wube T, Ko ke I, Teke ay D, Obe winkle F (2003) Myco hizal s a us o indigenous ees in d y a omon ane o es s o E hiopia. Fo es Ecology and Managemen 179:387-399 Wube T, Ko ke I, Teke ay D, Obe winkle F (2009) A buscula myco hizal ungal communi y s uc u es di e be ween co-occu ing ee species o d y A omon ane opical o es , and hei seedlings exhibi po en ial o ap isola es sui ed o e o es a ion. Mycological P og ess 8:317-328 Yi daw E (2001) Di e si y o na u ally- egene a ed na i e woody species in o es plan a ions in he E hiopian highlands. New Fo es s 22:159-177 Yi daw E, Luukkanen O (2003) Indigenous woody species di e si y in Eucalyp us globulus Labill. ssp globulus plan a ions in he E hiopian highlands. Biodi e si y and Conse a ion 12:567-582 Yi daw E, Luukkanen O (2004) Pho osyn he ically ac i e adia ion ansmi ance o o es plan a ion canopies in he E hiopian highlands. Fo es Ecology and Managemen 188:17-24 Zeleke G, Hu ni H (2001) Implica ions o land use and land co e dynamics o moun ain esou ce deg ada ion in he No hwes e n E hiopian highlands. Moun ain Resea ch and De elopmen 21:184-191 8 Acknowledgemen 105 8 Acknowledgemen This hesis is based on esea ch conduc ed om 2005 o 2011 a he Depa men o Plan Physiology, Uni e si y o Bay eu h, a he Depa men o Biology, Addis Ababa Uni e si y, E hiopia, and a he Resea ch S a ion a he Munessa- Shashamene Fo es , E hiopia. Fi s o all I would like o hank my supe iso P o . E win Beck, who in ellec ually and pe sonally suppo ed me h ough all my ime a he Depa men o Plan Physiology. He ga e me he oppo uni y o wo k in an in e es ing and challenging egion o E hiopia and le me he eedom o de elop my own scien i ic ideas. The many discussions wi h him shaped my unde s anding o plan ecophysiology and in pa icula o he impo ance o a plan ’s en i onmen . I would also like o hank P o . Mas esha Fe ene who in oduced me o he li e in E hiopia no only in a scien i ic way bu also o he imp essing landscapes and he di e se cul u e o his coun y. He ga e me a lo o scien i ic and pe sonal suppo du ing my s ays in E hiopia. Many o he people suppo ed my esea ch du ing he las yea s in E hiopia wi h ui ul and mo i a ing discussions, wi h close collabo a ion in he esea ch p ojec , and wi h iendship. I would like o hank As e achew Aba e o acili a ing so many hings in Addis Ababa and in Kuke wi h his diploma ic skills and his good spi i . I am e y g a e ul o my co-wo ke And eas Nenninge o assis ing me wi h his chainsaw du ing he sap low calib a ion expe imen and o sha ing his ime wi h me in Kuke. Many hanks o Yig emachew Seyoum o he good imes in he ield and he aluable scien i ic exchange also in he o ice. I am g a e ul o Awol Ase a o his help in ins alling s em low echnique in a lo o ees. Many hanks also o Heike Hubel, Wol gang Zech, Julia K epkowski, Olga Shibis o a, Ma ianne Benesch, Achim B äuning, Yonas Yohannes, As e Geb eki s os, Geo g Guggenbe ge , Hany El Ka eb, G ima Abebe, Ge achew Tes aye and Flo ian F i zsche o c ea ing an enabling en i onmen du ing ou s ay in he ield. I also like o hank ou d i e s Sisay and Ge u o doing an excellen job and also o hei help in he ield. Thanks also o ou gua ds Daksiso, Ge u, Tadele, 8 Acknowledgemen 106 Shon a, Gemedu, E aim and Mus a a o minimizing incon eniences and hei aluable help in he ield. This wo k would ha e been much mo e di icul wi hou he en husiasm and help o all my colleagues and iends in Ge many. I like o hank he people o my wo k g oup om he Depa men o Plan Physiology: K is in Roos, U sula Fe e a, Osca Valdes, Ma c Böheim, Ch is iane Reinbo he, Claudia Rossig and Daniel Souza o sha ing he o ice, co ee and good spi i s. Many hanks o Heiko Rödel o his pa ience and help wi h he s a is ical analyses. Many hanks o my iends, la ma es and amily in S u ga , Bay eu h and Munich o sha ing his ime, gi ing me suppo and keeping my mo i a ion high! I would also like o hank he DFG o unding ou p ojec s in E hiopia, gi ing me he oppo uni y o s udy u he in he subjec o plan ecophysiology in his exci ing and challenging en i onmen . 9 Decla a ion 107 Decla a ion Hie mi e klä e ich, dass ich die A bei selbs ändig e ass und keine ande en als die on mi angegebenen Quellen und Hil smi el e wende habe. Des wei e en e siche e ich, dass ich wede diese noch eine ande e gleicha ige Dok o p ü ung an eine ande en Hochschule endgül ig nich bes anden habe. Simone S obl Bay eu h, den 19. Mä z 2012