Complementarity effects on tree growth are contingent on tree size and climatic conditions across Europe

1 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 www.na u e.com/scien i ic epo s Complemen a i y e ec s on ee g ow h a e con ingen on ee size and clima ic condi ions ac oss Eu ope Jaime Mad igal-González1, Paloma Ruiz-Beni o1,2, Sophia Ra cli e3, Joaquín Cala ayud1,4, Ge ald Kändle 5, Aleksi Leh onen6, Jonas Dahlg en7, Ch is ian Wi h3,8 & Miguel A. Za ala1 Neglec ing ee size and s and s uc u e dynamics migh bias he in e p e a ion o he di e si y- p oduc i i y ela ionship in o es s. He e we show e idence ha complemen a i y is con ingen on ee size ac oss la ge-scale clima ic g adien s in Eu ope. We compiled g ow h da a o he 14 mos dominan ee species in 32,628 pe manen plo s co e ing bo eal, empe a e and Medi e anean o es biomes. Niche complemen a i y is expec ed o esul in signi ican g ow h inc emen s o ees su ounded by a la ge p opo ion o unc ionally dissimila neighbou s. Func ional dissimila i y a he ee le el was assessed using ou unc ional ypes: i.e. b oad-lea ed deciduous, b oad-lea ed e e g een, needle-lea ed deciduous and needle-lea ed e e g een. Using Linea Mixed Models we show ha , complemen a i y e ec s depend on ee size along an ene gy a ailabili y g adien ac oss Eu ope. Speci ically: (i) complemen a i y e ec s a low and in e media e posi ions o he g adien (coldes - empe a e a eas) we e s onge o small han o la ge ees; (ii) in con as , a he uppe end o he g adien (wa me egions), complemen a i y is mo e widesp ead in la ge han smalle ees, which in u n showed nega i e g ow h esponses o inc eased unc ional dissimila i y. Ou indings sugges ha he ou come o species mixing on s and p oduc i i y migh c i ically depend on indi idual size dis ibu ion s uc u e along g adien s o en i onmen al a ia ion. G owing e idence suppo ing a causal ela ionship be ween inc eased ee unc ional di e si y and abo e-g ound wood p oduc ion1–4 e lec s a majo ole o biodi e si y on ecosys em unc ioning in o es s5–8. Fo es s co e almos one hi d o he eme ged lands and ep esen s a egic esou ces o human socie ies so cu en species loss a es aise majo challenges o human well being on Ea h9. Consequences o species loss on o es p oduc- i i y a e howe e unce ain since di e si y e ec s and he in e ac ions wi h associa ed abio ic and bio ic de e - minan s a e s ill poo ly unde s ood10. In pa icula , he ole o popula ion and indi idual ee le el ea u es such as size o age on he di e si y-p oduc i i y ela ionship emain unclea 11. Classical expe imen s, mos ly conduc ed on sho -li ed communi ies (i.e. g asslands, a h opod communi- ies and mic obial mic ocosms), poin o niche complemen a i y, and he g ea e po en ial o species packing, as a chie mechanism by which he p oduc i i y o species mix u es is enhanced compa ed o he espec i e monocul u es12 (i.e. o e yielding). In o es s, empi ical e idence o a mo e in ense exploi a ion o abo e-13 and below-g ound esou ces14 in species mix u es also sugges s a majo ole o niche complemen a i y. Howe e , ecen s udies based on he use o di e en di e si y me ics2,7,15 and modelling expe imen s16 a e inconclusi e as o whe e and when niche complemen a i y is a ele an mechanism d i ing di e si y-p oduc i i y ela ions17. 1Fo es Ecology and Res o a ion G oup, Depa amen o de Ciencias de la Vida, Facul ad de Ciencias, Uni e sidad de Alcalá, Campus Uni e si a io, 28871, Alcalá de Hena es (Mad id), Spain. 2Biological and En i onmen al Sciences, School o Na u al Sciences.Uni e si y o S i ling, FK9 4LA, S i ling, Uni ed Kingdom. 3Depa men o Sys ema ic Bo any and Func ional Biodi e si y, Ins i u e o Biology, Uni e si y Leipzig (ULE, Ge many). 4Depa men o Biogeog aphy and Global Change, Museo Nacional de Ciencias Na u ales (MNCN-CSIC), C/José Gu ié ez Abascal 2, 28006 Mad id Spain. 5Fo s liche Ve suchs- und Fo schungsans al Baden-Wü embe g (FVA, Ge many). 6Na u al Resou ce Ins i u e Finland (LUKE, Finland). 7Swedish Uni e si y o Ag icul u al Sciences (SLU, Sweden). 8Ge man Cen e o In eg a i e Biodi e si y Resea ch (iDi , Ge many). Co espondence and eques s o ma e ials should be add essed o J.M.-G. (email: [email p o ec ed]) Recei ed: 25 Feb ua y 2016 accep ed: 01 Augus 2016 Published: 30 Augus 2016 OPEN www.na u e.com/scien i ic epo s/ 2 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 To unde s and he unc ioning o long-li ed communi ies an app ecia ion o hei size s uc u e dynamics is essen ial18. T ees ha e a con inuous size de elopmen , which modula es hei g ow h19, s and p oduc i i y20 and wi hin-communi y in e ac ions21. A di e en size implies niche di e en ia ion (bo h be ween conspeci - ics o he e ospeci ics22) o esou ce up ake abo e- and belowg ound and so i could de e mine idiosync a ic g ow h esponses along clima ic and s uc u al g adien s23,24 hus d i ing popula ion and communi y dynamics ia ee- ee in e ac ions25. Expe imen al e idence om opical o es plan a ions has demons a ed ha i biodi- e si y e ec s can be educed o a neighbou hood e ec , esponses o biodi e si y will esul om he agg ega ed e ec s o local neighbou hoods wi hin plo s26. Acco dingly, a ee-le el app oach may allow us o p ope ly e alu- a e complemen a i y by accoun ing o indi idual ee a ibu es ha can be c i ical in hei esponse o he local en i onmen 27. In si ua ions whe e s ong in e speci ic compe i ion is mos ly es ablished abo eg ound, size s a - i ica ion combined wi h dispa a e ligh use s a egies can lead o imp o ed ligh -use e iciency and hus inc eased biomass packing and p oduc i i y13. In suppo o his idea, ecen li e a u e shows how ee size inequali y in mixed communi ies enhances ligh - esou ce-use e iciency hus p omo ing posi i e di e si y-p oduc i i y ela- ionships h ough inc eased abo e-g ound biomass packing28,29. In con as , ee size inequali y in monospeci ic o es s has been shown o exe ne nega i e e ec s on s and p oduc i i y due o s ong in aspeci ic asymme ic compe i ion30. Thus, size-s uc u e dynamics and shi ing ee- ee in e ac ions du ing seconda y succession a e expec ed o al e he biodi e si y-ecosys em unc ioning ela ionship31–33. Un o una ely, classical expe imen s a e unsui able o add essing long- e m p ocesses ela ed wi h communi y size-s uc u e dynamics a b oad spa- ial scales34,35, and o es expe imen s a e s ill a an ea ly s age o p o ide solid e idence o mechanisms unde pin- ning long- e m di e si y e ec s36. He e, we in es iga ed whe he complemen a i y e ec s a e con ingen on ee size ac oss he main clima ic g adien o Eu ope om sou he n Spain o no he n Scandina ian o es s. Niche complemen a i y a he ee le el would imply imp o ed indi idual ee g ow h a es when g owing in neighbou hoods su ounded by a la ge p opo ion o unc ionally dissimila neighbou s. Al hough ee g ow h does no necessa ily co ela e in a one- o-one ela ionship wi h s and p oduc i i y, o es ecosys em p oduc ion can, as a i s app oxima ion, be e alua ed as he collec i e sum o indi idual ee p oduc i i y as indi idual ee g ow h plays a pi o al ole in ecosys em unc ioning19. Speci ically, we assessed o each ocal ee he s and ela i e abundance (es ima ed as he p opo ion o he s and basal a ea) o unc ionally dissimila ee species (POFT) (i.e. b oad-lea ed decidu- ous, b oad-lea ed e e g een, needle-lea ed deciduous, needle-lea ed-e e g een). The ea e , we eg essed ocal ees g ow h agains in e ac i e e ec s o abundance o unc ionally dissimila neighbou s (POFT), ocal ee size (SIZE), s and basal a ea (SBA) and po en ial e apo anspi a ion (PET). We e alua ed whe he posi i e g ow h esponses o inc eased neighbou hood dissimila i y a e modula ed by ee size ac oss s and s uc u e (i.e. SBA as a p oxy o he in ensi y o in e ac ions) and clima ic g adien s (e.g. PET as a p oxy o a ailable ene gy). We expec ha , in absence o s ong belowg ound limi a ions, size asymme ic compe i ion would a ou complemen a i y e ec s acco ding o size s a i ica ion o ea ly- and la e-successional species du ing seconda y succession13,32. La ge ees, in u n, may o may no expe ience signi ican posi i e e ec s om species mixing depending on whe he belowg ound in e ac ions esul in acili a ion37 o compe i ion38. Recen indings in empe a e o es s sugges , in acco dance wi h p edic ions o he S ess G adien Hypo hesis, ha inc easing equency o posi i e plan -plan in e ac ions due o enhanced s essed condi ions migh play a key ole in d i ing in e speci ic in e - ac ions and hus highe biodi e si y migh lead o inc eased p oduc i i y37,39. None heless, posi i e in e ac ions ep esen only a ac ion o complemen a i y e ec s and so posi i e plan -plan in e ac ions migh be obscu ed by pe asi e in e speci ic compe i ion e en in less p oduc i e en i onmen s40. Resul s The backwa d selec ion o p edic o a iables in he Linea Mixed Model sugges ed ha one ou o he ou pos- sible h ee- a iable in e ac ions (i.e. SIZE × POFT × PET) and wo pai wise in e ac ions (e.g. SIZE × SBA and SBA × PET) should be included in he ixed e ec s model (Table1, see also pa ame e es ima es in Appendix A Table A1). A andom e m wi h wo componen s was included in he bes suppo ed model: species was included o a ec he in e cep and he slopes associa ed wi h POFT and SIZE; and plo s nes ed in coun ies was included o a ec he in e cep pa ame e and he main e ec s o POFT (see andom e m selec ion based on in o ma ion c i e ion in Table B1, Appendix B). In e es ingly, he e ec s o SBA we e no a ec ed by he andom s uc u e ‘plo s nes ed in coun ies’. The analysis o esiduals indica es ha he main assump ions o linea models we e me (see Fig. A1a,b,c in Appendix A), and he pseudo-R2 poin ed o a high goodness o i , wi h mo e han 70% o a iance explained by he inal model (see Table1). Fi s ly, a iable selec ion poin ed o signi ican in e ac i e e ec s o PET × SBA and SIZE × SBA. Nega i e e ec s o SBA we e pe asi e along he en i e PET g adien (Fig.1) al hough hey we e no ably s onge in smalle ees. In e es ingly, he e ec s o POFT on ee g ow h we e independen o SBA as shown by he esul s o he backwa d selec ion ound#2, whe e he in e ac ion SBA × POFT was inally disca ded ollowing he Bayesian in o ma ion c i e ion (see Table1). Secondly, we ound ha POFT e ec s on ee g ow h depend on ee size and he in ensi y and sign o his dependency change along he PET g adien . In pa icula , in a eas o low PET (≈ 400–500 mm, bo eal and alpine biomes), ou esul s indica e complemen a i y e ec s on ee g ow h o small and la ge ees (Fig.2a3,b3). Speci ically, small ocal ees (e.g. 10 cm DBH) su ounded by neighbo hoods composed o 50% o o he unc- ional ypes can g ow 44.4% mo e han simila ocal ees om monospeci ic s ands. A simila POFT scena io in la ge ees (e.g. 66 cm DBH) p edic ed ee g ow h a es o be only 0.68% highe in mix u es han monospeci ic s ands. Unde mode a e PET alues (i.e. 700–800 mm) he pa e n is o e all simila o ha o bo eal a eas: i.e. complemen a i y ended o dec ease no ably owa ds sized ees which only g ow 3.7% mo e when su ounded by neighbo hoods composed o 50% o o he unc ional ypes (see Fig.2a2,b2). In simila condi ions, smalle ees g ew up o 37% mo e in mix u es han monospeci ic s ands. Finally, g ow h esponses o a g ea e POFT in www.na u e.com/scien i ic epo s/ 3 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 Medi e anean la i udes shi ed om ne nega i e o posi i e as ee size inc eased (see Fig.2a1,b1). Thus, a neigh- bo hood composed o 50% o o he unc ional ypes de e mines g ow h a es inc emen s up o 21% compa ed o monospeci ic s ands in la ge ees and g ow h educ ions o 24% in small ees. Discussion T ee size and complemen a i y e ec s. We ound ee size o be a c i ical ac o d i ing complemen- a i y e ec s in o es s ac oss Eu ope. This ag ees wi h ou expec a ions associa ed limi ing esou ces along he la ge-scale PET g adien . Hence, complemen a i y e ec s can eme ge om niche sepa a ion along spa ial/ em- po al g adien s o esou ce a ailabili y and hus ee size plays a pi o al ole in de e mining esou ce use pa - i ioning. In space, he combina ion o di e en ligh in e cep ing s a egies and size s a i ica ion ha e been epo ed o signi ican ly enhance esou ce yielding and biomass packing in mixed o es s ands41,42. Pa i ioning o soil nu ien up ake h ough di e en deg ees o ine oo de elopmen can also igge o e yielding among dissimila ee indi iduals al hough his poses majo me hodological challenges and unce ain ies o iden i y43. E idence om g assland s udies sugges s ha in e speci ic di e ences in lea phenology migh de e mine em- po al seg ega ion o ligh cap u e and hus species coexis ence44. Decoupled ligh use pa e ns associa ed wi h a di e en du a ion o he g owing pe iods be ween young and old ees45–47 migh explain size-dependen o e - yielding in species mix u es. This is he case o young e e g een ees in bo eal- empe a e o es s whe e a seasonal decoupling o pho osyn he ic ac i i y wi h adul b oad-lea ed ees migh lead o complemen a y usage o ligh and hus coexis ence48. Thus, di e ences in Speci ic Lea A ea, c own a chi ec u e and lea phenology, and he subsequen ligh use s a egies play a pi o al ole in o es dynamics and ee de elopmen 49–51. P ojec ed on o a seconda y succession scena io in empe a e la i udes, species mixing is common in ansi ional s ages when adul indi iduals o ea ly succesional ee species coincide wi h ju enile indi iduals o la e-succesional species and hus size s a i ica ion allows o biomass packing and o e yielding. T ee size e ec s on complemen a i y ac oss he ene gy a ailabili y g adien . In bo eo-alpine o es s (400–500 mm) ou esul s indica ed ha s ong complemen a i y e ec s on small indi iduals no a- bly weakens wi h size de elopmen . Complemen a i y in ni ogen up ake43 and bidi ec ional ans e ences o soil ca bohyd a es ia myco hiza52 ha e been epo ed as impo an mechanisms unde pinning he posi- i e di e si y-p oduc i i y ela ionship in bo eal o es s. In e es ingly, Ca a d and cols53 showed how posi- i e di e si y-g ow h ela ionships in species mix u es disappea as ee communi ies ma u e. Soil nu ien dilapida ion du ing pos - i e seconda y succession was in oked a plausible explana ion o his educ ion o complemen a i y e ec s in ime. Recen indings in Eu ope sugges a compa a i ely mino ole o unc ional dispe sion on s and g ow h owa ds no he n la i udes15 which is consis en wi h his successional scheme i we assume ha la ge ees ha e an exponen ially highe con ibu ion wi h s and p oduc i i y han smalle ones and hus unc ional esponses o ee communi ies mos ly esemble la ge- ee esponses. O he wise, a posi i e di e si y-p oduc i i y ela ionship has been ex ensi ely epo ed in Eu opean and No h Ame ican bo eal o es s in suppo o he idea ha complemen a i y e ec s, al hough compa a i ely less impo an han o he d i e s o ee g ow h in hese la i udes, a e impo an de e minan s o o es p oduc i i y as well. In empe a e o es s, complemen a i y e ec s depic a simila pa e n o he one obse ed in bo eal o es s: e.g. s ong complemen a i y e ec s dec ease wi h ee de elopmen . Young b oad-lea ed deciduous ees a e known o bene i om highe ligh a ailabili y when pa o he o es o e s o ey is occupied by ea ly successional coni e s32. A ecen e iew, howe e , highligh ed he g ea numbe o po en ial ac o s ha migh al e he ela- i e ole o niche complemen a i y d i ing ee g ow h in empe a e o es s54. Mo eo e , esul s ob ained om pe manen plo s in cen al Eu ope sugges ha he lack o o e yielding in empe a e o es s migh be a ibu ed Fixed e ec s selec ion d BIC Del a BIC R2-m R2-c Full-model ( ound #1) 33 610912.3 0 SIZE × SBA × POFT ( emo ed) 32 610889.8 − 12.5 SIZE × POFT × PET ( emo ed) 31 610937.1 24.8 POFT × SBA × PET ( emo ed) 31 610900.8 − 11.5 SIZE × SBA × PET ( emo ed) 31 610914.1 1.8 Full-model ( ound #2)* 28 610891.0 0 SIZE × SBA ( emo ed) 27 614430.1 3539.1 POFT × SBA ( emo ed) 27 610885.3 − 5.7 PET × SBA ( emo ed) 26 611043.7 152.7 Bes -suppo ed model** 23 610885.3 0 0.367 0.705 null model (in e cep only) 6 719146.1 108260.8 Table 1. Fixed e ec s selec ion using he Bayesian In o ma ion C i e ion (BIC). We used a hie a chical backwa d selec ion o ixed e ms s a ing wi h a ull model ha included all he possible h ee- a iable in e ac ions be ween he p opo ion o o he unc ional ypes (POFT), ee basal a ea (SIZE, m2), s and basal a ea (SBA, m2 ha−1), and po en ial e apo anspi a ion (PET, mm). We es ed he con ibu ion o each in e ac ion by emo ing hem one a a ime. R2-m is he ma ginal pseudo R2 ( ixed e ec s only) and R2-c is he condi ional pseudo R2 (including bo h ixed and condi ional e ec s). *The ound#2 o he backwa d selec ion s a ed wi h he bes suppo ed model ob ained in he i s ound. **Bes suppo ed model: SIZE × POFT × PET+ SIZE × SBA + PET × SBA. www.na u e.com/scien i ic epo s/ 4 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 o me hodological ac o s associa ed wi h speci ic esponse a iables and me hods o compa e pu e and mixed s ands27. In pa icula , accoun ing o c own biomass changes has been ound o be decisi e in de ec ing o e- yielding in empe a e o es s. Thus, o es in en o y da a may be limi ed o disce n such ine-scale di e si y e ec s. In Medi e anean o es s, ou esul s poin o s ong complemen a i y e ec s in la ge ees, and con a y, nega i e e ec s o unc ional dissimila i y in small ees. Assuming ha la ge ees ha e a compa a i ely highe con ibu ion o o al s and biomass and s and basal a ea change, his inding is consis en wi h he exis ing li e a- u e posing signi ican posi i e di e si y-p oduc i i y ela ionships in Medi e anean o es s3,7. Complemen a i y e ec s in la ge ees ha e been associa ed wi h dispa a e ligh -use s a egies and inc eased ligh -use e iciency3 and inc eased soil e ili y55 due o enhanced li e quali y. A posi i e di e si y-p oduc i i y ela ionship in wa e -limi ed ecosys ems has been also discussed in he heo e ical amewo k o he S ess G adien Hypo hesis: e.g. inc eased abio ic s ess condi ions lead o inc easing equency and in ensi y o posi i e in e speci ic in e - ac ions37. Al e na i ely, insigh s om adial g ow h inc emen s in mixed and monospeci ic pine-oak s ands in Cen al Spain a e consis en wi h he idea ha s essed condi ions due o soil wa e sca ci y du ing in ense d ough s lea e less oom o complemen a i y e ec s in he Medi e anean38. Ye ou esul s do no allow us o disce n which mechanisms unde lie he obse ed e e sal, lacking complemen a i y e ec s in small ees could be a ibu ed o ine i able ade-o s associa ed wi h adap a ions o cope simul aneously wi h shade and d ough 56. Figu e 1. P edic ed ee g ow h as unc ion o po en ial e apo anspi a ion and s and basal a ea keeping size and he p opo ion o o he unc ional ypes cons an in mean alues. Red a ows indica e he main ends o ee g ow h a low, in e media e and high PET alues. www.na u e.com/scien i ic epo s/ 5 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 Ecological s udies on plan -plan acili a ion in a id lands du ing he las wo decades sugges ha shade imposes an in es men in abo eg ound pa s (e.g. lea es) o inc ease ligh in e cep ion in he unde s o y a he cos o exace ba ed wa e losses due o highe shoo o oo a io57. Hence, size s a i ica ion is no an e icien way o op imize ligh in e cep ion, as in o he biomes, because high e apo anspi a ion egimes expose unde s o y ee indi iduals o wa e s ess. I is impo an o no e ha in wa me Medi e anean a eas, he dominan unc ional ypes a e b oad-lea ed e e g een ee species and needle-lea ed e e g een ee species. This implies ha seasonal decoupling o lea phenology is no longe a plausible complemen a i y mechanism in ime so young/small coni e ees mus o e come s ong compe i ion o ligh wi h adul e e g een b oad-lea ed ees. On he o he hand, many species a e esp ou e s and many o he smalle indi iduals a e ame s which ha e be e de eloped oo sys ems and ca bohyd a e s o ages ela i e o supp essed saplings in pine s ands. Complemen a i y among adul ees, in con as , is less dependen on unc ional ade-o s associa ed wi h ligh and soil wa e limi a ions and dispa a e wa e -use s a egies o oo a chi ec u e may amelio a e in aspeci ic compe i ion o soil wa e . Concluding ema ks and u u e lines. Neglec ing ee size and s and s uc u e and assessing s and g ow h as an agg ega ed ee g ow h measu emen migh bias he in e p e a ion o he di e si y-p oduc i i y ela- ionship in o es s29 because g ow h esponses o la ge ees o e ide hose o smalle ees gi en he exponen ial ela ionship be ween g ow h and size19. Posi i e e ec s o ee di e si y on s and g ow h in he Medi e anean3 and almos neu al-posi i e e ec s in empe a e and bo eal o es s14,15 would mask he ac ual con ibu ion o each indi idual ee. Thus, i is c i ical o conside ee size o p ope ly e alua e di e si y e ec s on ee g ow h h oughou he cou se o ee de elopmen in di e en o es ypes ac oss clima ic g adien s29,54,58. Fu u e esea ch e o s a e needed o unde s and ecophysiological p ocesses unde pinning la ge-scale e e sals in complemen- a i y due o ee size. I is c i ical o unde s and how indi idual ee ea u es such as size de e mine ee- ee in e ac ions and how hey in luence seconda y succession dynamics and ecosys em unc ion. This would allow us o be e unde s and he ole o posi i e and nega i e in e ac ions on size-s uc u ed communi y dynamics, and Figu e 2. P edic ed ee g ow h as unc ion o po en ial e apo anspi a ion and he p opo ion o o he unc ional ypes o small (a) and la ge ees (b) (basal a ea 0.008 m2 and 0.35 m2 espec i ely) keeping s and basal a ea in he mean alue (25 m2 ha−1). Plo s on he igh ep esen p edic ed g ow h ela i e o g ow h in monocul u e (%) o small (c) and la ge ees (d) keeping s and basal a ea in he mean alue (25 m2 ha−1). Red a ows a e indica i e o he main ends o ee g ow h along low, in e media e and high PET alues. www.na u e.com/scien i ic epo s/ 6 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 o es ablish mo e e icien conse a ion and managemen s a egies based on communi y s uc u e and species in e ac ions a he han on indi idual species. Ou b oad scale app oach, howe e , lacks in o ma ion on po en ial d i e s o p oduc i i y such as soil nu i- en s, he bi o y, dis u bances and sligh de ia ions om long- e m clima ic condi ions a each sampling pe iod migh a ec ou indings since all hese unce ain ies migh al e he di e si y-p oduc i i y ela ionship. Gi en he impossibili y o long- e m expe imen s o explo ing biodi e si y-ecosys em unc ioning ela ionships in o es s (a leas o some yea s o come), we ely on imp o ed la ge-scale da a analyses and modelling. The e o e, u he e o s a e needed o imp o e o es in en o y p o ocols and la ge-scale da a ha moniza ion o accoun o po en ial con ounding d i e s o p oduc i i y such as soil in o ma ion, managemen , seconda y succession and he bi o y in o es ecosys ems. Me hods Na ional o es in en o y da a: plo selec ion and ocal species. We used da a compiled om he Na ional Fo es In en o ies (NFIs) o i e Eu opean coun ies (Finland, Ge many, Spain, Sweden and Belgium - egion o Wallonia, see a de ailed desc ip ion o each NFI in Ra cli e and cols15). Pe manen plo s wi h wo consecu i e su eys and no e idence o ee ha es ing be o e and wi hin consecu i e su eys we e selec ed. F om hose plo s, only ees > = 10 cm diame e a b eas heigh (DBH) we e included in he da ase o s anda dise ee selec ion be ween he di e en in en o ies. The 14 mos ep esen a i e ee species in e ms o abundance and dis ibu ion we e selec ed as ocal ees: Abies alba (needle-lea ed e e g een, empe a e moun ains), Ace pseu- dopla anus (b oad-lea ed deciduous, empe a e), Be ula pendula (b oad-lea ed deciduous, bo eal- empe a e), Be ula pubescens (b oad-lea ed deciduous, bo eal- empe a e), Ca pinus be ulus (b oad-lea ed deciduous, empe a e), Cas anea sa i a (b oad-lea ed deciduous, empe a e), Fagus syl a i a (b oad-lea ed deciduous, empe a e), Junipe us hu i e a (needle-lea ed e e g een, Medi e anean moun ains), Picea abies (needle-lea ed e e g een, bo eal-alpine), Pinus halepensis (needle-lea ed e e g een, Medi e anean), Pinus syl es is (needle-lea ed e e g een, bo eal-alpine- empe a e), Que cus py enaica (b oad-lea ed deciduous, Medi e anean- empe a e ansi ion), Que cus obu (b oad-lea ed deciduous, empe a e), and Que cus ilex (b oad-lea ed e e - g een, Medi e anean). These species ep esen mo e han one hi d o he o al s and basal a ea measu ed in he Figu e 3. (a) Loca ion o o es in en o y plo s ac oss he s udy a ea (Eu ope) and (b) po en ial e apo anspi a ion (uni s) h oughou he s udy a ea. Own p epa a ion based on (a) plo coo dina es included in he Na ional Fo es In en o ies conside ed, and (b) Po en ial E apo anspi a ion da a a ailable in CGIAR-CSI GeoPo al60 using so wa e A cGIS 13.0 by Es i (license Uni e si y o Alcalá). www.na u e.com/scien i ic epo s/ 7 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 whole da ase and a e he dominan ee species in a leas one o he h ee p incipal o es biomes o Eu ope (i.e. Medi e anean, empe a e and bo eal). The inal numbe o plo s was 32,628 and he numbe o su i ing ees 275,558 a e emo ing dead ees o su i ing ees wi h nega i e g ow h a es (7209 ees, 2.6%). Table2 de ails he numbe o plo s in he analysis and impo an plo -le el s a is ics. Figu e3a illus a es he dis ibu ion o plo s ac oss he con inen . T ee g ow h and complemen a i y. We assessed indi idual ee g ow h as he basal a ea inc emen (BAI) ela i e o he ini ial ee basal a ea and he numbe o yea s be ween consecu i e su eys (i.e. annual basal a ea inc emen ). T ee basal a ea in each in en o y was calcula ed using dbh measu emen s as: π =BA xdbh 4(1) 2 whe e dbh is he diame e a b eas heigh (i.e. 1.3 me e s abo e g ound su ace) in me es. Complemen a i y e ec s (CE) a he ee le el imply ha any gi en ee will g ow as e when, keeping bio ic and abio ic sou ces o a iabili y cons an , i s neighbo hood is composed o a la ge p opo ion o unc ionally dissimila ees. Wi h his in mind we assessed he p opo ion o he s and basal a ea (SBA m2 ha−1) occupied by unc ional ypes o he han he ocal ee (POFT) as ollows: =′ POFT SBA SBA (2) FT TOT whe e SBAFT′ is he s and basal a ea o unc ional ypes di e en om he ocal ee and SBATOT is he o al s and basal a ea. Posi i e e ec s o his index on ee g ow h will be in e p e ed as complemen a i y e ec s while neg- a i e e ec s will be assumed p e ailing in e speci ic compe i ion. Ye his is o cou se an elemen a y app oach o he complex wo ld o niche complemen a i y me ics, i s quan i a i e na u e mee s he a ionale o he a o e- men ioned de ini ion o complemen a i y om he iewpoin o indi idual ees. We conside ed he ou mos gene al and di e gen unc ional ypes ega ding lea phenology and mo phology (i.e. b oad-lea ed deciduous, b oad –lea ed e e g een, needle-lea ed deciduous, needle-lea ed e e g een). Speci ic lea a ea has been iden i- ied as a c i ical ai linked o species compe i i e abili y (i.e. b oad-lea ed species end o be mo e ole an o compe i ion and exhibi s onge compe i i e e ec s ela i e o needle-lea ed species49). This classi ica ion is also cohe en wi h unc ional di e en ia ion based on wood densi y as needle-lea ed ees end o ha e lowe wood densi y han b oad-lea ed ees and weake compe i i e e ec s49. In gene al, di e ences in c own a chi ec u e, lea phenology, pho osyn he ic ac i i y, and oo a chi ec u e be ween hese gene al unc ional ypes ha e been shown o p o ide o e yielding in bo eal and empe a e o es s14,41,42. Abio ic and bio ic d i e s o ee g ow h. Fo each indi idual ee we no ed he species iden i y and calcula ed he basal a ea o he ee (SIZE, mm) and he plo basal a ea (SBA, m2 ha−1) in which he ee esided. Mean clima e (i.e. annual mean empe a u e (MAT, C), annual p ecipi a ion (AP, mm) and mean po en ial e apo anspi a ion (PET, mm)) o each plo we e ex ac ed om he Wo ldClim da abase59 and CGIAR-CSI GeoPo al60. Using PET and AP we assessed a wa e a ailabili y index (WAI) as: =−WAIAPPET (3) whe e nega i e alues o his index deno e wa e de ici because a mosphe ic wa e demand exceeds clima ic inpu s in ain all. Because o he high co ela ion be ween PET and MAT ( = 0.93) and be ween PET and WAI ( = − 0.71), we selec ed PET as an in eg a i e a iable ha summa izes he wo main clima ic s ess g adien s in con inen al Eu ope, i.e. wa e de ici owa ds sou he n la i udes and low empe a u e owa ds no he n la i udes and alpine a eas (Fig.3b). Da a analysis. We i ed Linea Mixed Models (LMM) o model ee g ow h as unc ion o SIZE, SBA, PET and POFT. Plo nes ed in coun y and species we e included as wo independen andom e ms in he model. Spain Wallonia Ge many Sweden Finland To al No. plo s 18 083 90 7 649 4 621 1 619 32 628 No. ees 146 799 668 38 620 48 902 15 888 275 558 No. species 11 4 9 5 6 14 PET (± SD) 1018.9 ± 163.2 715.8 ± 42.1 732.9 ± 49.1 508.8 ± 57.9 505.6 ± 42.5 812.2 ± 241.7 SBA (± SD) 9.4 ± 9.5 23.3 ± 12.5 25.6 ± 14.8 12.6 ± 10.7 10.3 ± 8.5 20.131 ± 13.0 MTBA (± SD) 0.06 ± 0.08 0.15 ± 0.18 0.09 ± 0.09 0.03 ± 0.03 0.03 ± 0.02 0.06 ± 0.08 Table 2. Desc ip i e s a is ics o plo -le el in o ma ion o each Na ional Fo es In en o y (NFI) o he andomly selec ed popula ions o ees ac oss Eu ope. Species ID (alphabe ical o de ): Abies alba (1), Ace pseudopla anus (2), Be ula pendula (3), Be ula pubescens (4), Ca pinus be ulus (5), Cas anea sa i a (6), Fagus syl a i a (7), Junipe us hu i e a (8), Picea abies (9), Pinus halepensis (10), Pinus syl es is (11), Que cus ilex (12), Que cus py enaica (13), Que cus obu (14). PET–Po en ial E apo anspi a ion (mm); SBA–S and Basal A ea (m2 ha−1); MTBA– Mean T ee Basal A ea (m2). www.na u e.com/scien i ic epo s/ 8 Scien i ic RepoR s | 6:32233 | DOI: 10.1038/s ep32233 Species was conside ed o a ec he in e cep pa ame e and he slopes associa ed wi h main e ec s o bo h POFT and SIZE unde he assump ion ha (i) g ow h esponses o an inc easing p opo ion o o he unc ional ypes migh a y among he species conside ed in his s udy, and (ii) ha g ow h pa e ns h oughou he on ogeny migh di e among species. Plo nes ed in coun y was conside ed o a ec he in e cep pa ame e and he e ec s o POFT on ee g ow h assuming ha di e ences in plo size and sampling me hodologies migh a ec he POFT assessmen and hus he sensi i i y o ee g ow h o his index. The model equa ion akes he o m: ∑α=+∈+∈ = TG X (4) i p ii an es 1 whe e TG is ee g ow h, αi is he se o p pa ame e s associa ed wi h he main and in e ac i e e ec s o Xi en i- onmen al a iables, ∈ an is he a iance componen associa ed wi h he andom e ms, and ∈ es is he esidual no mally-dis ibu ed e o . We conside ed a ixed-e ec e m in he maximal model ha included all he po en- ial pai -wise in e ac ions as well as he h ee a iables in e ac ions (i.e. SIZE × SBA × PET, SIZE × SBA × DIV, SIZE × PET × DIV, SBA × PET × DIV). SIZE was included in a log- ans o med o m and PET as a second o de polynomial. T ee g ow h was log- ans o med o mee no mali y and homogenei y o a iance. Model selec ion was conduc ed using a backwa d p ocedu e o p edic o a iables s a ing wi h he maximal model61. We used he Bayesian In o ma ion C i e ion (BIC) ollowing he ule ha ne inc emen s lowe han 2 uni s o BIC associa ed wi h he elimina ion o any pa ame e in he maximal model de e mined he exclu- sion o he pa ame e om he inal model61. We s a ed wi h he selec ion o he h ee- a iable in e ac ions ( ound#1) and hen es ed he pai wise in e ac ions ( ound#2) and so downwa ds he main e ec s o each p e- dic o ( ound#3). A pseudo-R2 was assessed ollowing Nakagawa and Schielze h62. This index can be spli in o ma ginal and condi ional e ec s, being he ma ginal R2 he goodness o i o he ixed e ec e m only and he condi ional R2 he goodness o i o he whole model including he andom e m. Re e ences 1. Ruiz-Jaen, M. C. & Po in, C. T ee di e si y explains a ia ion in ecosys em unc ion in a neo opical o es in Panama. Bio opica 42, 638–646 (2010). 2. Paque e, A. & Messie , C. The e ec o biodi e si y on ee p oduc i i y: om empe a e o bo eal o es s. Glob. Ecol. Biogeog . 20, 170–180 (2011). 3. Vilà, M. e al. 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A gene al and simple me hod o ob aining R2 om gene alized linea mixed-e ec s models. Me hod. Ecol. E ol. 4, 133–142 (2013). Acknowledgemen s This manusc ip was unded by he Eu opean Union Se en h F amewo k P og am (FP7/2007–2013) unde g an ag eemen no. 265171, p ojec FUNDIV-Eu ope, and om p ojec FUNDIVER (MINECO, Spain; CGL2015- 69186-C2-2-R). We hank he MAGRAMA o g an ing access o he Spanish Fo es In en o y, he Johann Hein ich on Thünen-Ins i u o access o he i s and second Ge man Na ional Fo es In en o ies, Na u al Resou ce Ins i u e Finland (LUKE) o making pe manen sample plo da a om 1985-86 and 1995 a ailable, he Swedish Uni e si y o Ag icul u al Sciences o making he Swedish NFI da a a ailable, and Hugues Lecom e, om he Walloon Fo es In en o y, o access o he Walloon NFI da a. J.C. holds a Spanish FPU PhD G an (FPU12/00575). PR-B was g an ed by he Eu opean Union Se en h F amewo k P og amme (FP7/2007-2013) unde g an ag eemen No. 265171 (p ojec FunDi EUROPE) and No. PCOFUND-GA-2010-267243 (Plan Fellows). Au ho Con ibu ions J.M.-G. and M.A.Z. concei ed he idea. P.R.-B., S.R., G.K., J.D., C.W. and A.L. p o ided da a and ha monized he o es da abase. J.M.-G., P.R.-B. and J.C. conduc ed he s a is ical analyses. J.M.-G., M.A.Z. and S.R. w o e he main manusc ip and all he coau ho s e iewed he manusc ip .