Stump diameter and age affect coppicing of downy birch (Betula pubescens Ehrh.)

Vol.:(0123456789) 1 3 Eu opean Jou nal o Fo es Resea ch h ps://doi.o g/10.1007/s10342-019-01175-5 ORIGINAL PAPER S ump diame e andage a ec coppicing o downy bi ch (Be ula pubescens Eh h.) Jy kiHy önen1 Recei ed: 9 Ap il 2018 / Re ised: 28 Janua y 2019 / Accep ed: 31 Janua y 2019 © The Au ho (s) 2019 Abs ac Downy bi ch is a p ima y successional ee species colonizing open a eas and h i ing on pea lands. Sho - o a ion coppice managemen in na u al, dense, downy bi ch s ands could be one managemen op ion. The e ec o s ump diame e , s ump heigh and s and age on he sp ou ing o downy bi ch was s udied by clea -cu ing six s ands om h ee age classes (A: 10–12yea s, B: 15–16yea s, C: 22–24yea s) loca ed in no he n Finland and measu ing he sp ou s in he ollowing au umn. The pe cen age o non-sp ou ing s umps inc eased wi h he s and age (A: 9%, B: 14%, C: 27%). The smalles (< 1cm) and bigges (> 9cm) s umps showed highe mo ali y han medium-sized s umps. Sp ou s o igina ed close o he g ound le el: o e 50% we e loca ed below 2cm om he g ound le el. An inc ease in he diame e o s umps led o highe numbe s o sp ou s p oduced pe s ump, and highe mean, dominan and cumula i e heigh o sp ou s pe s ump and highe biomass o sp ou s pe s ump. The e ec o he diame e on he g ow h o sp ou s depended on he s and age. In he same diame e class, he mean heigh , dominan heigh and biomass pe s ump we e highe he younge he s and was. The biomass pe s ump co ela ed bes wi h he o al heigh o he sp ou s on a s ump. The esul s ha e implica ions o s a egies in con olling sp ou ing in coni e ous s ands and o s and managemen p ac ices when he aim is o g ow downy bi ch coppices. Keywo ds Coppicing· S ump diame e · Damage· Downy bi ch· Biomass p oduc ion In oduc ion Bi ches a e he single mos impo an deciduous ee species in mos o he No dic coun ies. The p opo ion o bi ch (sil e bi ch Be ula pendula Ro h, downy bi ch Be ula pube- scens Eh h.) ou o he o al olume is high in Finland (16%), o he No dic (11–16%) and he Bal ic (17–28%) coun ies (Hynynen e al. 2010). Downy bi ch ep esen s abou 12% o he o al olume o he g owing s ock in Finland (Niemis ö and Ko honen 2008). Acco ding o he Finnish Na ional Fo es In en o y, 90% and 98% o he o al bi ch olume consis o downy bi ch on pea lands in Sou he n and No h- e n Finland, espec i ely (Ko honen e al. 2007). Downy bi ch is a biologically igo ous, ea ly successional, pionee ee species h i ing on pea lands and in mine al soils wi h poo d ainage. Downy bi ch is used mainly o pulpwood and ene gy wood. Sp ou ing in deciduous ee species is an induced esponse o inju y o d ama ic change in su ounding en i- onmen al condi ions (Del T edici 2001). Bi ch is gene ally conside ed a poo ly sp ou ing species. When cu , bi ches p oduce s ump sp ou s om do man basal buds which ac i a e soon a e he cu ing o he ee, and in a ou able condi ions will bu s o h om 2weeks o 1mon h (Kauppi e al. 1987, 1988a, b, 1991a). Mos o he buds (70–95%) a e loca ed unde g ound (Kauppi e al. 1987, 1988b; Johansson 1992a). The o igin, s uc u e, de elopmen , spa ial dis ibu- ion, numbe and bu s ing dynamics a e impo an aspec s which all a ec coppicing (Senne by-Fo sse e al. 1992). The educed le el o phenolic subs ances caused by elling he ee is also a p econdi ion o sp ou ing (Kauppi e al. 1991b). Many ex e nal ac o s and managemen measu es ha e been shown o ha e only a mino e ec on he num- be o sp ou s pe s ump, o he numbe o li ing s umps in downy bi ch. Fo example he cu ing season, he size and age o he ees, he s ump heigh and si e quali y can signi i- can ly a ec he ea ly heigh g ow h o bi ch sp ou s (Mikola Communica ed by Mi en del Rio. * Jy ki Hy önen jy ki.h[email p o ec ed] 1 Na u al Resou ces Ins i u e Finland, Na u al Resou ces, Teknologiaka u 7, 67100Kokkola, Finland Eu opean Jou nal o Fo es Resea ch 1 3 1942; Ande sson 1966; E holén 1974; Fe m and Issakainen 1981; Fe m 1990; Johansson 1987, 1992b, c; Hy önen 1994; Hy önen and Issakainen 2001). Gene ally cu ing du ing he ac i e g owing pe iod will inc ease mo ali y and educe g ow h, compa ed o do man season cu ing (Blake 1981; Blake and Rai anen 1981; Hy önen 1994). Resul s on he e ec o s ump heigh on coppicing o bi ch ha e been a i- able (Mikola 1942; K aalen 1989; Johansson 1987, 1992c, Jobidon 1997). The e a e only ew s udies compa ing he sp ou ing o downy bi ch and sil e bi ch. Acco ding o Mikola (1942), downy bi ch sp ou s a e conside ably be - e han sil e bi ch. Johansson (2008) also epo ed downy bi ch o p oduce mo e sp ou s pe s ump han sil e bi ch. In con en ional sil icul u e, igo ously sp ou ing downy bi ch is o en conside ed in a nega i e ligh , especially when egene a ing and in e mixed wi h so woods. The compe i- ion o e ed by as -g owing, deciduous ees o sp ou o i- gin o en impai s he ou come o o es egene a ion. The coni e seedlings un he isk o su e ing om shading and mechanical inju y in lic ed by bi ch o such an ex en ha he sapling s and may ul ima ely be los and deciduous ees may ake o e he si e. Since con olling o sp ou s accoun s o a conside able amoun o he cos s o young s and managemen , i s op imiza ion is an impo an pa o o es egene a ion. Thus, mos s udies dealing wi h he sp ou ing o bi ch ha e been done o s udy means o educ- ing he sp ou ing (e.g. E holén 1974; Johansson 1992a, b, c, 2008). Many s udies on he coppicing o bi ch ha e been done wi h young 1- o 5-yea -old seedlings wi h s ump diam- e e s anging om 1 o 5cm (Johansson 1987, 1992b, 2008; Kauppi e al. 1990, 1991a). Such small bi ches a e common in young ha dwood plan a ions and hey a e emo ed in ea ly cleaning. An al e na i e managemen op ion o exis ing hicke s o bi ch, especially on pea lands, could a e clea -cu ing be g owing o sp ou -o igina ed ees applying he p inciples o sho - o a ion managemen ins ead o soil p epa a ion, plan ing, weed con ol and young s and ea men . Es ab- lishmen o dense downy bi ch s ands on ma ginal si es, such as cu away pea lands, has been success ul wi h ash e iliza ion and na u al egene a ion o sowing (e.g. Huo- a i e al. 2008; Hy önen e al. 2016). Ene gy wood p oduc- ion by g owing dense downy bi ch s ands wi h o a ions o 23–26yea s, assuming ha second bi ch o a ion can be achie ed h ough sp ou ing, has been calcula ed o be eco- nomically easible on cu away pea lands (Jylhä e al. 2015). Addi ionally, o dense downy bi ch s ands on pea lands, he mos p o i able managemen op ion is o g ow hem o ene gy wi hou hinnings un il whole- ee inal cu ing a he s and age o 40–45yea s (Niemis ö e al. 2017). I sp ou - ing is success ul, a second o a ion bi ch s and could be es ablished wi hou cos s, p o ided he de elopmen o he sp ou s is a ou able. Howe e , a he momen in p ac ical o es y coppice egene a ion o downy bi ch is no used. Re-sp ou ing a e ha es and main aining p oduc i i y o e mul iple cu ing cycles is undamen al o sho - o a ion cop- pice o es y, which u ilizes he excep ional g ow h a es o s ump sp ou s o oo sucke s. Since he economic o a ion leng h o sho - o a ion bi ch exceeds 20yea s (Jylhä e al. 2015), esul s on coppicing o e y young ees may no be applicable. Olde and bigge bi ches could sp ou be e han small and young ees due o inc easing numbe o buds wi h inc easing s ump diame e , o hei sp ou ing could be poo e due o inc eased ba k hickness o o ma ion o bud clus e s (Kauppi e al. 1987, 1988a, b). Thus age and diam- e e could ha e independen e ec o on sp ou ing. The main objec i e o he p esen s udy was o in es iga e he e ec o s ump diame e and ee age and hei in e ac- ion on he coppicing o downy bi ch. Sp ou ing success was assessed in se e al ways including: he numbe o dead s umps, he numbe o sp ou s pe s ump, he mean heigh o he sp ou s, he heigh o he alles sp ou on a s ump, he o al cumula i e heigh o he sp ou s on a s ump and he biomass o sp ou s on s ump. Addi ionally, he loca ion o he sp ou s in he s ump and he e ec o damage o s ump we e s udied. Ma e ials andme hods Two na u ally egene a ed dense un hinned downy bi ch s ands om each o he h ee age classes (A: 10–12yea s; B: 15–16yea s, C: 22–24yea s) we e selec ed om he same cu away pea land a ea loca ed in no he n Finland a Liminka, (Hi ine a, 64°48′N, 25°24′E). The dep h o he esidual pea laye a ied om 18 o 60cm. The es i- ma es o he s and ages we e based on he mean biological age o dominan ees on each sampled s and. Thei ages we e de e mined om inc emen co es aken om he base and by adding 2yea s o he numbe o annual ings. The age a ia ion wi hin he dominan ees was small, mos ly 2–3yea s, indica ing ha he s ands we e e en-aged and had been es ablished in a sho pe iod o ime. The mean age o he dominan ees in he six s ands a ied om 10 o 24yea s, and hei mean heigh om 2.8 o 9.0m (Table1). Each o he s ands was clea -cu (size 520–1800m2) in he sp ing (6 h o May 2011). The ees we e do man a he ime o cu ing. Daily mean empe a u es in Ap il we e 3.6°C and in May be o e cu - ing 3.2°C. All he s ands we e cu manually using a mo o saw, excep o he wo oldes s ands, which we e cu by a ha es e . A e cu ing he ees we e emo ed om he s udy a eas. The summe ollowing he clea -cu ing was wa me han he 10-yea a e age (d.d. 1382 s. 1210 d.d. in 2006–2016). Addi ionally, he p ecipi a ion in June–Augus Eu opean Jou nal o Fo es Resea ch 1 3 was highe han he a e age (239mm s. 209mm in 2006–2016). The sp ou ing was measu ed in No embe , a e he i s g owing season. Ci cula sample plo s (1–4 in each s and, size 30–150m2 depending on densi y o s ands) we e es ab- lished on each o he s udy s ands. Since he aim was o measu e simila numbe o s umps om each s and, la ge sized sample plo s we e es ablished in he cen e o he clea -cu olde s ands. In he younge and dense s ands, 3–4 smalle plo s dis ibu ed uni o mly o e he clea -cu a eas we e es ablished. All s umps wi hin he sample plo s we e measu ed o hei diame e and heigh . Mo ali y o s umps was isually assessed by de e mining he p esence o absence o li ing sp ou s. S umps wi hou sp ou s we e classi ied as dead. To al numbe o measu ed s umps was 1258 (Table1). Du ing ha es ing, some s umps we e dam- aged and he damage class o all s umps was assessed (1 = no damage, 2 = sligh damage, 3 = la ge damage). The numbe and heigh o all sp ou s in he s umps we e measu ed. To al numbe o measu ed sp ou s was 6874. Since some s umps may ha e many sho sp ou s and some s umps ha e only ew longe sp ou s, mean heigh o sp ou s is no always a good indica o o sp ou ing success. Thus also he heigh o he alles sp ou on each s ump (dominan sp ou ) and he o al cumula i e heigh o all sp ou s in each s ump we e cal- cula ed. F om 111, 146 and 35 bi ch sp ou s in age classes A, B and C, espec i ely, he loca ion o sp ou s in he s ump was measu ed as dis ance om g ound le el. One sp ou pe s ump was selec ed using sys ema ic sampling. Sp ou s loca ing unde g ound we e ma ked as o igina ing om 0cm om he g ound. Al oge he 30 bi ch sample sp ou s co e ing he heigh a ia ion we e aken o modelling he biomass p oduc ion. The base diame e o he sample sp ou s a ied om 0.2 o 1.6cm and hei heigh om 27 o 187cm. The lea less sp ou s we e anspo ed o labo a o y, and hei d y mass was de e mined a e d ying a 105°C o cons an weigh . The biomass o he sp ou s was es ima ed wi h allome ic model based on he sample ee da a Y=0.0001432 ∗X2.496. In he model, Y = d y mass (g) and X = heigh o sp ou s (cm). The model had an R2 alue o 89.2% and was co ec ed a e loga i hmic ans o ma ion linea izing he allome ic equa ion wi h s2/s. The biomass o he sp ou s in each s ump was calcula ed wi h he model based on sp ou heigh . Fo analysing mo ali y o he s umps, hey we e classi- ied in o diame e classes and mo ali y pe cen age in each diame e class was calcula ed. Subsequen ly he e ec o age class and diame e class and hei in e ac ion was analysed by analysis o a iance. A one-way analysis o a iance was used o es he di e ences in s ump heigh and he loca ion o he sp ou s be ween he s ands. The analysis o s ump damage on sp ou ing was con ined o he wo oldes s ands since s umps in age classes A and B did no ha e any se e e damages and only 4.4% o he s umps had sligh damage. In all o he calcula ions, damaged s umps we e excluded and esul s a e p esen ed o undamaged s umps. The e ec o age and s ump diame e and hei in e ac ion on he meas- u ed sp ou ing cha ac e is ics was s udied by analysis o a iance using gene al linea model. In he model, s and age was ixed ac o and s ump diame e was used as co a ia e. Co ela ion coe icien s be ween he biomass o sp ou s pe s ump and o he sp ou ing cha ac e is ic we e calcula ed. When es ing igu es in pe cen age o m, a iance s abilizing ans o ma ion o squa e oo a csine was used. To compa e he means o he esul s, a signi icance le el o p ≤ 0.05 was used. All s a is ical analyses we e ca ied ou using IBM SPSS S a is ics 22 so wa e. Resul s Mo ali y o s umps No all he bi ch s umps sp ou ed. The mean mo ali y o he s umps was 9.3%, 14.5% and 27.1% in age classes A, B and C, espec i ely. The s ump diame e class had a signi ican e ec on he mo ali y o he s umps (p = 0.002), bu he e ec o age class was no signi ican (p = 0.315). Signi ican in e ac ion be ween diame e class and age class (p = 0.039) Table 1 S and densi y, mean heigh and lea less abo e-g ound biomass o he s ands be o e cu ing and numbe o measu ed s umps, hei mean diame e , numbe o measu ed downy bi ch sp ou s and numbe o sample plo s Age Age class No. s ems (ha−1) Mean heigh (m) Biomass (Mgha−1) No. meas- u ed s umps Mean diame e (SD and ange) o he measu ed s umps (cm) No. meas- u ed sp ou s No. sample plo s (size, m2) 10 A 129,100 2.8 26.8 262 1.0 (1.0; 0.2–5.2) 978 4 (30) 12 A 57,800 3.6 29.3 183 2.4 (1.6; 0.2–8.3) 1255 3 (40) 15 B 30,200 5.2 55.9 193 2.7 (1.6; 0.2–7.5) 1229 1 (50) 16 B 45,400 4.8 33.6 423 2.6 (2.3; 0.4–18,8) 2058 2 (100) 22 C 10,600 9.0 66.9 92 5.5 (3.5; 1.1–16.3) 688 3 (150) 24 C 12,200 9.0 76.2 105 8.2 (4.2; 3.0–20.0) 666 1 (100) Eu opean Jou nal o Fo es Resea ch 1 3 indica ed ha he e ec o diame e on mo ali y depended on age. When he diame e o s umps inc eased, he mo al- i y o olde s umps inc eased mo e han mo ali y o younge s umps (Fig.1a). Ve y small s umps (< 1cm in diame e ) and la ge s umps (> 9cm in diame e ) sp ou ed poo e han s umps in be ween. Heigh o  heo igin o sp ou s The mean heigh o he o igin o he sp ou s in he s umps a ied om 2 o 4cm om g ound le el. The s and age class (p = 0.488) o s ump diame e class (p = 0.992) did no a ec he o igin o he sp ou s. Mos o he sp ou s o igina ed qui e close o he g ound le el o e en below i : 22% we e o igina ed om g ound le el o below g ound and o e 50% o he sp ou s o igina ed less han 2cm om g ound le el (Fig.2). The sha e o he sp ou s loca ing abo e 10cm om g ound le el was 3%. The mean heigh o he s umps in he s udy s ands a ied om 9 o 18cm. S ump heigh did no co ela e wi h he heigh o he o igin o sp ou s (p = 0.853). No did he heigh o o igin o he sp ou s co ela e wi h he heigh o sp ou s ( = 0.145). Fig. 1 The e ec o s and age and s ump diame e on he sha e o s umps wi hou sp ou s (a), numbe o sp ou s pe s ump (b), mean heigh o sp ou s pe s ump (c), mean heigh o alles sp ou s pe s ump (d), cumula i e heigh o all sp ou s pe s ump (e) and biomass o all sp ou s pe s ump ( ). In he analysis o sha e o s umps wi hou sp ou s, all s umps we e included. All o he analysis included only s umps wi h sp ou s Eu opean Jou nal o Fo es Resea ch 1 3 S ump damage The s ands cu manually by mo o saw (age classes A and B) had only a small numbe o damaged s umps. How- e e , i was possible o analyse he e ec o damage on he sp ou ing in he wo oldes s ands (age class C) cu wi h a ha es e causing damage when d i ing on he s umps. In hese s ands, 27.5% and 23.9% o he s umps we e eco ded wi h ligh and se e e damage, espec i ely. The mo ali y o s umps was equally dis ibu ed in he di e en dam- age classes (no damage, sligh damage, se e e damage) (χ2 = 2.600, p = 0.273) indica ing ha damaging o s umps did no inc ease mo ali y. Damaging o he s umps did no educe he numbe o sp ou s pe s ump (Table2). Howe e , he e ec o damage on mean and dominan heigh o he sp ou s was signi i- can , bu no on cumula i e heigh o sp ou s pe s ump. The mean heigh o sp ou s pe s ump eco ded o ha e sligh damage was he sho es . E en hough he e ec o s ump damage on biomass pe s ump was also signi ican (Table2), Tukey’s mul iple ange es did no ind signi ican di e - ences be ween he mean alues. Numbe o sp ou s pe s ump Age class (p < 0.001), s ump diame e (p < 0.001) and hei in e ac ion (p < 0.001) had signi ican e ec o he numbe o sp ou s pe li ing s ump. The mean numbe o sp ou s pe s ump inc eased wi h he inc ease in s and age (A: 5.9, B: 6.9, C: 10.3). The numbe o sp ou s pe li ing s ump inc eased wi h inc easing diame e in all age classes up o 5cm (Fig.1b). Fu he inc ease in s ump diame e om 5 o 9cm did no inc ease he numbe o sp ou s pe s ump in he wo oldes age classes. Heigh o sp ou s The mean heigh o sp ou s was 20–30cm sho e han he heigh o he alles sp ou s on s ump (A: 60.2 s. 79.4cm, B: 60.8 s. 91.8cm, C: 73.0 s. 98.5cm). The heigh o all sp ou s on a s ump was 7–9 imes highe han he mean heigh o sp ou s (A: 403cm, B: 427cm, C: 625cm). The age class had a signi ican e ec on he heigh o he alles sp ou s on s ump (p = 0.003) and heigh o all sp ou s pe s ump (p < 0.001), bu no on he mean heigh o sp ou s (p = 0.450). S ump diame e and in e ac ion be ween s ump diame e and s and age class had a signi ican e ec on mean heigh o sp ou s (p < 0.001), alles sp ou s on s ump (p < 0.001) and heigh o all sp ou s pe s ump (p < 0.001). The heigh o sp ou s inc eased wi h he inc ease in diam- e e , he younges age class p oduced he alles sp ou s and he oldes sho es (Fig.1c–e). The o al cumula i e heigh o all sp ou s pe s ump inc eased wi h an inc easing s ump diame e up o 3–5cm and s ayed a he same le el in he wo olde age classes (Fig.2e). Howe e , signi ican diam- e e s and age in e ac ion showed ha he e ec o diame e depended on age. Fig. 2 Heigh o loca ion o he sp ou s om g ound le el in diame e classes Table 2 The e ec o he s ump damage class on he numbe o sp ou s pe s ump, mean heigh o sp ou s pe s ump, heigh o all sp ou s on a s ump and he biomass o all sp ou s on a s ump Only li ing s umps om s and age class C (22–24yea s) included in he analysis. The s anda d e o is shown inside b acke s. The means ma ked wi h he same le e s do no di e om each o he a he 0.05 signi icance le el Va iable Damage class F p No Sligh Se e e No. sp ou s pe s ump 10.4 (0.8)a 9.7 (1.0)a 8.9 (1.1) a 0.581 0.561 Mean heigh o sp ou s pe s ump (cm) 65.2 (2.3)a 51.4 (2.7)b 59.9 (4.0)a 6.794 0.002 Heigh o dominan sp ou s pe s ump (cm) 98.9 (3.8)a 77.7 (4.9)b 85.1 (5.4)ab 6.330 0.002 To al heigh o all sp ou s pe s ump 675 (56)a 547 (74)a 504 (64)a 2.160 0.119 Biomass o sp ou s pe s ump (g) 58.8 (6.8)a 37.3 (7.5)a 37.1 (7.1)a 3.231 0.043 Eu opean Jou nal o Fo es Resea ch 1 3 Biomass The o al biomass o all he sp ou s pe s ump inc eased wi h he inc ease in s and age (p ≤ 0.001) (A: 31.4g, B: 44.6g, C: 58.5g) and diame e (p > 0.001). Also he in e - ac ion be ween diame e and s and age class was signi ican (p < 0.001). The s umps o equal diame e p oduced mo e biomass in he younges age class (A: 10–12yea s) han in he wo olde age classes and di e ence be ween age classes inc eased wi h inc easing diame e . The amoun o biomass pe li ing s ump co ela ed bes wi h he o al heigh o all he sp ou s pe s ump (Table3). Mean dominan heigh (heigh o he alles sp ou pe s ump) co ela ed be e wi h biomass on he s umps han he mean heigh o he sp ou s. The o al biomass in he s udy a eas a e one g ow- ing season was highes in he younges age class (A: 2.8Mgha−1) and dec eased wi h an inc ease in he age class (B: 1.1Mgha−1; C: 0.3Mgha−1). The biomass on an a ea basis was ela ed o he numbe o s ems in he s ands (Table1). Discussion The bi ch s ands we e cu a he beginning o May when he ees we e s ill lea less and he g owing season had no ye begun. Gene ally, he beginning o he g owing season is conside ed a ime when cu ing bi ches leads o poo e g ow h o he sp ou s han cu ing done in o he seasons (Fe m and Issakainen 1981; Hy önen 1994; E holén 1974; Johansson 1992b, c). Fo sus ainable sho - o a ion coppice o es y, a high numbe o sp ou ing s umps is a p e equisi e and he amoun o d y mass p oduced by he sp ou s in he s umps is a good indica o o sp ou ing success. Howe e , in con en ional o es y, on he o he hand, a low numbe o sp ou ing s umps is desi ed and he dominan heigh o he sp ou s and hei numbe is mo e impo an han he biomass. Sp ou ing success was assessed in se e al ways in his s udy including: he numbe o dead s umps, he numbe o sp ou s pe s ump, he mean heigh o he sp ou s, he heigh o dominan sp ou s, he o al cumula i e heigh o he sp ou s on a s ump and he biomass o sp ou s on s ump. The s udy e ealed ha sp ou ing o downy bi ch is a ec ed bo h by age o ees and s ump diame e . The numbe o non-sp ou ing s umps in his s udy was a ec ed by s ump diame e , bu he e ec o s ump diame e depended on he age class. The highe he s ump diame e and he olde he s and he highe was he mo ali y. The high mo ali y o hinnes s umps (< 1cm) is p obably asso- cia ed wi h low numbe o buds in hin s umps. Mo ali y o hickes s umps (> 9cm) especially in he oldes s and was high. Thus when sho - o a ion managemen p inciples a e applied in bi ch s ands, g owing he bi ch o o e 10–15cm in diame e could al eady inc ease he mo ali y (Mikola 1942; Fe m e al. 1985) o such an ex en ha he biomass p oduc ion dec eases. Repea ed coppicing and sho o a- ions can also inc ease he s ump mo ali y. The mo ali y o bi ch s umps has been obse ed o inc ease mo e wi h each successi e coppice cu ing he sho e he o a ion is (Hy önen and Issakainen 2001). The mo ali y was in line wi h ea lie s udies epo ing he numbe o non-sp ou ing bi ch s umps o be gene - ally wi hin he ange o 10–40% (Moilanen and Oika inen 1980; Fe m and Issakainen 1981; Hy önen 1994; Kauppi e al. 1988b; Johansson 1987, 1992c, 2008; Hy önen and Issakainen 2001). K aalen (1989); howe e , epo ed only 1–2% ini ial mo ali y o sil e bi ches a e cu ing. The weakening o bi ch coppicing abili y in olde ees has been associa ed wi h an inc ease in ba k hickness, which is supposed o educe he numbe o buds and p e- en hem pene a ing he su ace (Mikola 1942). Howe e , acco ding o Kauppi e al. (1988b) bi ch ba k does no g ow in such hickness ha i would p e en bud g ow h. When he ees g ow, he p ima y buds b anch and o m clus e s o seconda y buds loca ed in he axis o hei scales. Al hough b anching inc eases he bud numbe in he s ump, he o ma- ion o bud clus e s is no a ou able o coppicing (Fe m and Kauppi 1990) and i is conside ed o be he majo cause o weakened sp ou ing abili y in olde ees (Kauppi e al. 1988b). Gene ally, he me hod o cu ing he bi ch (axe, billhook, manual saw, chain saw) o a i icial damaging o he s ump ollowing cu ing has no a ec ed he numbe o sp ou ing s umps o he g ow h o he bi ch sp ou s (Mikola 1942; Fe m and Issakainen 1981). This was mos ly ue also in his s udy whe e damage o he s umps did no a ec he numbe o sp ou s pe s ump. Howe e , damaging o he s umps dec eased he mean heigh o sp ou s pe s ump and hei biomass. This could be due o damage caused o he oo sys ems by ha es ing machine d i ing o e he s umps. Acco ding o his s udy, he e ec o s ump heigh on sp ou ing is small, since 53% o he sp ou s o igina ed Table 3 Co ela ion coe icien s be ween he biomass o he sp ou s pe s ump and he numbe o he sp ou s, he mean heigh o he sp ou s, heigh o dominan sp ou s and heigh o all he sp ou s on a s ump S a s indica e s a is ical signi icance: ***p < 0.001, **p < 0.01, *p < 0.05 S and age class Numbe o sp ou s pe s ump Mean heigh o sp ou s Heigh o dominan sp ou s Heigh o all sp ou s on a s ump A 0.762*** 0.612*** 0.755*** 0.920*** B 0.629*** 0.596*** 0.741*** 0.891*** C 0.610*** 0.642*** 0.762*** 0.865*** Eu opean Jou nal o Fo es Resea ch 1 3 2cm o lowe om he g ound le el and only 3% o igi- na ed abo e 10cm om he g ound. Thus lea ing 10cm s umps would no p ac ically a ec spou ing a all, and e en e y low s umps would no conside ably educe he numbe o sp ou s. Low s umps could e en be bene icial o la e de elopmen o he sp ou s since shoo s loca ed close o he g ound a e mo e likely o be connec ed o indi idual oo s han o he oo sys em as a whole (Fe m and Kauppi 1990) and his is belie ed o gi e some ad an age in e ms o a ailabili y o wa e and me aboli es. E en hough he majo pa o he buds (70–95%) a e loca ed below he soil su ace (Kauppi e al. 1987, 1988b; Johansson 1992a), s ill 44% o he sp ou s in his s udy o igina ed om buds loca ed o e 2 bu below 11cm om g ound le el. E en hough buds loca ed below g ound le el p oduce abundan ly sp ou s, he numbe eaching he soil su ace is much smalle (Kauppi e al. 1987, 1988b) and e en one hi d o bi ch sp ou s can o igina e om buds loca ing abo e-g ound (Fe m and Kauppi 1990). Thus, cu ing he ee e y close o g ound le el (0cm s ump) could educe he numbe o sp ou s pe s ump o he numbe o ees p oducing sp ou s bu cu ing ees lea ing such low s umps would be qui e di icul in p ac ical o es y ope a ions. Howe e , he e ec o s ump heigh on sp ou ing has been qui e a iable on o he s udies (Mikola 1942; Johansson 1987, 1992c) and he ini ial e ec o s ump heigh on sp ou ing may also change o e subse- quen yea s (K aalen 1989; Jobidon 1997). In his s udy, he ee- o- ee a ia ion in sp ou ing was qui e high. S umps wi h same diame e p oduced a iable numbe o sp ou s. The main eason o his is ha he num- be o buds a ies ma kedly om one ee o ano he so ha i can ange om 0 o se e al hund ed in 15–40-yea -old downy bi ch ees (Kauppi e al. 1987, 1988b). The numbe o sp ou s pe s ump inc eased wi h he inc easing diam- e e and age o he s umps. P obably bud clus e o ma ion, associa ed wi h decline in sp ou ing abili y in olde bi ches (Kauppi e al. 1988a, b) had no ad anced conside ably e en in he oldes age class. In line wi h his s udy, Johansson (1987, 2008) ound inc easing numbe o sp ou s pe s ump wi h he inc eases in he s ump diame e om 1 o 5cm. The e ec o diame e is explained by he inc ease in he numbe o buds wi h he inc easing diame e o he s umps (Johansson 1992a). Howe e , when s ump diame e in he wo oldes age classes exceeded 5cm he numbe o sp ou s pe li ing s ump did no inc ease any mo e. Wi h he inc ease in s ump diame e , he heigh o sp ou s (mean heigh , dominan heigh , o al heigh o all sp ou s) inc eased. A simila s ump diame e , younge ees p o- duced alle sp ou s han olde ees. In young s and cleaning in con en ional sil icul u e cu ing ees when hey a e s ill hin would dec ease heigh g ow h and dec ease compe i ion in lic ed by bi ch sp ou s on coni e seedlings. The heigh o dominan sp ou is mo e impo an han he mean heigh o sp ou s, since he alles sp ou s ha e he highes isk o causing shading o mechanical inju y. When managing coppiced s ands o p oduc ion o ligno- cellulosic biomass g ow h is impo an sp ou ing cha ac e - is ic. The d y weigh o sp ou s on a s ump inc eased wi h inc eases in s ump diame e om 1 o 2cm in acco dance wi h Johansson (1987). This s udy showed ha inc ease con- inues a leas up o 9cm and depends on s and age. Younge s umps o he same size p oduced mo e biomass han olde s umps. Thus as -g owing young s ands p oducing s umps sized 9cm would be ideal o sho - o a ion managemen o bi ch. The o al biomass o he sp ou s on an a ea basis in he s udy s ands was ela ed o he numbe o ees in he s ands. Since he young s ands had mo e s umps pe hec a e han he olde s ands, hey had highe biomass on a ea basis. Wi h he inc ease in diame e , he numbe o sp ou s and hei heigh and biomass inc eased in all s and age classes. The e ec o age was in his s udy seen o emos in he inc ease in mo ali y o s umps in he oldes age class. Also when compa ing s umps o equal size, he heigh o sp ou s and hei biomass was he highe he younge he s and was. When sho - o a ion managemen o bi ch is conside ed, he oldes s ands (22–24yea s old) had he highes numbe s o non-sp ou ing s umps, which is ques ionable o he sus ain- abili y o he coppice sys em. Wi h simila s ump diame e olde ees also p oduced less biomass han younge ees. This a ou s coppicing o young ees. Howe e , since he e ec o diame e on he numbe o sp ou s and hei g ow h is high, he oldes s ands, ha ing highe a e age s ump diam- e e han young s ands, p oduced simila o e en sligh ly highe numbe o sp ou s pe s ump, had he simila mean heigh and biomass o sp ou s pe s ump han younge s ands. Thus, age in he ange o 10–25yea s does no limi coppice managemen p o ided ha he diame e o s umps emains unde 10–15cm. Acknowledgemen s Open access unding p o ided by Na u al Resou ces Ins i u e Finland (LUKE). Jo ma Issakainen, Heikki Vesala and Kauko Kylmänen a e acknowledged o es ablishing he expe i- men s and Seppo Vihan a and Ee o Saa i o measu ing hem. In addi- ion, Seppo Vihan a helped wi h he da a handling. Open Access This a icle is dis ibu ed unde he e ms o he C ea- i e Commons A ibu ion 4.0 In e na ional License (h p://c ea i eco mmons .o g/licen ses/by/4.0/), which pe mi s un es ic ed use, dis ibu- ion, and ep oduc ion in any medium, p o ided you gi e app op ia e c edi o he o iginal au ho (s) and he sou ce, p o ide a link o he C ea i e Commons license, and indica e i changes we e made. Re e ences Ande sson O (1966) Some hing on sp ou ing o bi ch. S e iges Skogs- å ds ö enings Tidsk i 441–450 (in Swedish) Eu opean Jou nal o Fo es Resea ch 1 3 Blake TT (1981) G ow h- ela ed p oblems o aging and senescence in as g owing ees g own on sho o a ions. IEA Repo . Na ional Swedish Boa d o Ene gy Sou ce De elopmen . NE 21 Blake TJ, Rai anen WE (1981) A summa y o ac o s a ec ing cop- picing. IEA Repo . Na ional Swedish Boa d o Ene gy Sou ce De elopmen . 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