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1
Chap e
In luence o Sil icul u al
Ope a ions on he G ow h and
Wood Densi y P ope ies o
Medi e anean Pines
DanielMo eno-Fe nández, And eaHe ia, Icia Albe di
and IsabelCañellas
Abs ac
Sil icul u al ope a ions a e widely used o o es egene a ion and p omo ion
o ee g ow h by educing compe i ion. The main aim o p uning, on he o he
hand, is o dis up e ical uel con inui y and enhance wood quali y, al hough he
impac o sil icul u e on wood p ope ies has sca cely been s udied in he case o
Medi e anean coni e o es s. Ou main goal is o syn hesize he p ima y indings
ega ding he impac o hinning and p uning on ee g ow h and wood densi y o
Medi e anean coni e s. Fo his pu pose, we used da a om h ee hinning and
p uning ials in Cen al Spain, speci ically in o es s o Pinus syl es is and wo
subspecies o Pinus nig a. Ou esul s indica e ha hinning enhanced ee g ow h o
he h ee species bu did no signi ican ly a ec wood densi y. In con as , no signi i-
can e ec s o p uning we e obse ed, ei he on ee g ow h o on wood densi y. We
concluded ha hinning in combina ion wi h p uning is a sui able way o p omo e
ee g ow h wi hou comp omising wood quali y.
Keywo ds: kno - ee imbe , mic odensi ome y, Medi e anean o es y, sus ainable
o es managemen , ime quali y
1. In oduc ion
High-quali y wood, such as sawn wood and enee , ypically necessi a es high-g ade
logs, la ge in diame e , con aining mos ly clea wood, wi h s aigh s ems and a sig-
ni ican amoun o hea wood [1]. Fo his, i is desi able ha any kno s a e limi ed o a
na ow cen al co e in o de o ob ain he so-called clea wood [2], ee o kno s, o mo e
aluable wood [3]. Howe e , clea wood no only inc eases he quali y o he highes -
alue by-p oduc s by emo ing isual de ec s bu also educes he in luence o kno s on
he magni ude o pi h eccen ici y, s em cu a u e, and bending [1, 4, 5].
Besides he abo emen ioned wood p ope ies ha a e desi able o high-quali y
uses, o he cha ac e is ics such as wood densi y a e a majo physical c i e ion o
wood quali y [6] since hey a e ela ed o many o he aspec s o quali y such as
Coni e s - F om Seed o Sus ainable S ands
2
wood s eng h and sh inkage, ibe p ope ies, and lexibili y o s i ness, among
o he s [7, 8]. Fu he mo e, i has been demons a ed ha wood densi y a ec s
ca bon s o age [9–11].
The a iabili y o wood densi y is no only dependen on he unc ional g oup
o species [12, 13] bu has also been obse ed o a y among p o enances [14] and
clima e [15], a high le el o a iabili y being a ibu able o his ac o . O he ac o s,
such as si e condi ions o gene ics, also a ec wood densi y [16]. In addi ion, wood
densi y does no emain cons an ac oss he unk bu a ies bo h in adial ( om
pi h o ba k) and axial di ec ions, o ming ju enile and adul wood (also known as
co ewood and ou e wood, espec i ely) [17, 18]. Fu he mo e, a ia ions in wood
densi y also occu a he in a- ing le el because o he di e en ia ion be ween
ea ly and la ewood. Ea lywood usually p esen s lowe densi y alues han la ewood,
al hough i s sec ion is no mally la ge [19]. In con as o ea lywood, he densi y and
sec ion o la ewood inc ease wi h cambial age [20, 21]. In his ega d, he p opo ion
o la ewood eme ged as a key a iable in he cha ac e iza ion o wood densi y.
Sil icul u al ea men s, such as hinning, ha e commonly been employed o
educe s and densi y and inc ease he diame e g ow h a es o he emaining ees
[22, 23] ha ing a majo in luence on wood quali y [8]. P uning ope a ions, mean-
while, in ol e he emo al o b anches, which con ibu es o limi ing kno s and o he
b anch- ela ed de ec s o a cen al “kno y co e” [13] esul ing in mo e aluable wood
(clea wood) [3]. Addi ionally, bo h ope a ions can play a key ole in he c own i e
haza d [24] since hinning can educe uel loading and connec i i y and p uning dis-
up s he e ical con inui y o uel, educing he se e i y o o es i es [25]. On he
o he hand, p uning usually has a nega i e impac on ee diame e g ow h [3, 26, 27]
al hough he magni ude o his e ec depends on he p opo ion o c own emo ed
by p uning [4, 28]. As ega ds he impac o sil icul u al ope a ions on wood densi y,
mos s udies s a e ha hinning has a limi ed impac on wood densi y [9, 20, 29, 30].
As o p uning, while [16] and [31] epo ed an inc emen in wood densi y a e
p uning, o he au ho s such as [32] ound no signi ican in luence o p uning on
wood densi y p ope ies.
The way in which sil icul u e a ec s wood densi y is an impo an issue as highe
g ow h a es coupled wi h lowe wood densi y as a esul o hinning and/o p uning
ope a ions could lead o bias in he es ima ion o o es biomass and he e o e ca bon
accoun ing [33, 34].
The join impac o hinning and p uning on ee g ow h and wood densi y has
been poo ly e alua ed in Medi e anean coni e o es s. In his s udy, ou objec i e
is o syn hesize and e alua e he p ima y indings p esen ed by [2, 35] ega ding
he impac o hese sil icul u al p ac ices on ee g ow h and wood densi y. Fo
his pu pose, we used da a om h ee hinning and p uning ials in Cen al Spain,
speci ically in o es s o Pinus syl es is L. and wo subspecies o Pinus nig a A nold.
These species a e impo an no only o he o es y sec o in Spain bu also om an
ecological pe spec i e.
2. Ma e ial and me hods
2.1 Ma e ial
We used da a om h ee hinning and p uning ials loca ed in Cen al Spain. These
expe imen al ials we e es ablished in monospeci ic e o es a ions o P. syl es is, Pinus
3
In luence o Sil icul u al Ope a ions on he G ow h and Wood Densi y P ope ies…
DOI: h p://dx.doi.o g/10.5772/in echopen.1003005
nig a subsp. nig a A nold, and Pinus nig a subsp. salzmannii (Dunal) F anco. The ials
we e ini ia ed a he beginning o he 1990s when he P. syl es is s and was 37yea s old,
he P. nig a nig a 26yea s old, and he P. nig a salzmannii 31. While bo h he P. ni g a
ials a e adjacen and sha e simila ecological cha ac e is ics, he P. syl es is s and is
loca ed a a highe al i ude wi h colde and we e condi ions (see Table 1).
The P. syl es is ial was ini ia ed in 1991 when he i s hinning was unde aken.
Since hen, i e in en o ies ha e been conduc ed, in 1991, 1996, 2001, 2006, and
2011, including diame e a b eas heigh measu emen s. The expe imen consis ed o
nine pe manen plo s, each co e ing 0.1 hec a es, wi h a 10m bu e a ea o elimina e
he edge e ec (Table 2). Th ee ea men s we e applied (i.e., h ee plo s pe ea -
men ): con ol ea men in which only dead ees we e elled (C), hinning om
below wi hou p uning (T), and hinning om below combined wi h p uning (TP).
Thinning in ensi y was a ound 30% in e ms o basal a ea. In he TP ea men , ees
we e p uned o a heigh o 6 me e s, and 40 dominan and codominan ees pe plo
we e selec ed o p uning. This esul ed in a s and densi y o 400 ees pe hec a e,
ensu ing an adequa e numbe o p uned ees o achie e he desi ed s and densi y
du ing he egene a ion phase (200–300 ees pe hec a e).
In 2001, he second hinning ope a ion (ca. 15% in basal a ea) was ca ied ou in
he s udy plo s. Howe e , i is impo an o no e ha one plo pe ea men had o be
excluded om he analysis due o a se e e s o m in Janua y 1996, which esul ed in
signi ican snow- h ows.
The Pinus nig a nig a expe imen wi h six plo s was es ablished in 1993. Dasome ic
in en o ies we e conduc ed in 1993, 1998, 2002, 2006, and 2011 (Table 1). Figu e 1
illus a es he appea ance o a hinned plo in May 2023.
In he case o Pinus nig a salzmannii, he es ablishmen , in en o ies, and hinnings
ollowed he same schedule as he Pinus nig a nig a ial. The same h ee ea men s
(C, T, and TP), wi h wo eplica es in six plo s (0.1ha), we e e alua ed in he P. nig a
salzmannii ial and in six plo s o Pinus nig a nig a. Thinning in ensi y, howe e , was
g ea e o P. nig a nig a (40% in e ms o basal a ea) han o Pinus nig a salzmannii
(25–30%) In 2006, he second hinning wi h an in ensi y o 16% o he basal a ea was
pe o med in hese wo ials.
To in es iga e he impac o sil icul u al ope a ions on wood densi y, six co es we e
aken a a heigh o 1.3m abo e g ound le el (b eas heigh ) om six ees pe ea -
men and axa in Janua y 2013. The e o e, he ull da ase included 18 co es o axa,
i.e., a o al o 54 co es. These ees we e selec ed om he second and hi d qua iles
o he diame ic dis ibu ion, ep esen ing he codominan ees wi hin he s and. I
is wo h no ing ha bo h dominan and codominan ees we e p esen in he s and
Fea u e P. syl es is P. nig a
Coo dina es 40°520N, 3°510W 41°020N, 3°040W
Al i ude (m asl) 1650 1050
Aspec No h acing None
Slope (%) 10–40 0–3
A e age annual ain all (mm) 1062 620
A e age annual empe a u e (°C) 710.5
Table 1.
Ecological cha ac e is ics o he hinning ials.
Coni e s - F om Seed o Sus ainable S ands
4
T ea men Fi s hinning Second hinning
Age NDg BA %BA Age NDg BA %BA
Pinus syl es is
C37 2332 14.5 38.5 0.7*47 1997 17.2 46.4 9.9*
T37 2037 14.6 34.1 28.2 47 928 20.7 31.2 18.6
TP 37 2082 14.4 33.9 34.8 47 821 21.2 29.0 14.4
Pinus nig a nig a
C26 1392 18.2 36.2 0.0 39 1250 21.2 44.1 0.0
T26 1447 17.8 36.0 41.9 39 725 23.6 31.7 17.6
TP 26 1455 17.7 35.8 40.2 39 756 23.3 32.2 16.5
Pinus nig a salzmannii
C31 1597 15.7 30.9 0.0 44 1446 18.1 37.2 0.0
T31 1574 15.6 30.1 24.8 44 1064 19.6 32.1 16.9
TP 31 1498 16.6 32.4 30.4 44 907 20.9 31.1 16.9
C = con ol ea men . T = hinning wi hou p uning. TP = hinning wi h p uning he bes ees. Adap ed om [35].*Na u al mo ali y.
Table 2.
Mean alues o quad a ic mean diame e (dg; cm) be o e hinning, basal a ea (BA; m2 ha−1) be o e hinning and pe cen age o basal a ea emo ed (%BA) pe ea men and hinning
in ensi y.

5
In luence o Sil icul u al Ope a ions on he G ow h and Wood Densi y P ope ies…
DOI: h p://dx.doi.o g/10.5772/in echopen.1003005
un il he s a o he egene a ion pe iod. To ob ain he wood co es, a 5mm diame e
inc emen bo e was used. In he TP ea men , inc emen co es we e exclusi ely aken
om he p uned ees, as hese we e he ocus o his pa icula ea men .
2.2 X- ay mic odensi ome y measu emen s
In he labo a o y, each inc emen co e ob ained was moun ed on a wooden
holde . The co es we e hen cu in o longi udinal adial s ips, app oxima ely 1mm
hick, using a win-blade saw. To emo e esins, he samples we e e luxed in 96%
e hanol using a Soxhle appa a us. The e luxing p ocess las ed 24hou s o P.
syl es is and 48hou s o P. n i g a . The esul ing hin s ips we e hen s o ed unde
cons an empe a u e and humidi y condi ions be o e being subjec ed o X- ay
analysis. X- ay imaging was pe o med using an I ax Mul iscanne (Cox Analy ical
Sys ems,Mölndal, Sweden) a he CETEMAS labo a o y in As u ias, Spain. The
Mul iscanne , equipped wi h a Cu- ube ope a ing a 30 KV, 50mA, 25ms wi h 20μm
s eps, p oduced adiog aphic images ha we e la e analyzed using WinDend o
so wa e (Regen Ins umen s, Québec, QC, Canada). F om he adiog aphic images,
a e age wood densi y alues o ee ings (RD, in g cm−3) and he p opo ion o
la ewood densi y ela i e o he en i e ing wid h (LWP, in %) we e ex ac ed. This
ex ac ion in ol ed calib a ing he g eyscale in ensi ies o wood densi ies using a ligh
calib a ion cu e de i ed om a calib a ion wedge [36]. C oss-da ing accu acy was
assessed using s a is ical pa ame e s p o ided by he dend och onological so wa e
COFECHA (Uni e si y o A izona, Tucson, AZ, USA) [37].
2.3 S a is ical analyses
To e alua e he e ec o he sil icul u al ope a ions on he s and a iables and ee
wood densi y o each axon, we used linea mixed models. The assump ion is made
Figu e 1.
Pho og aph o a P. nig a nig a hinned plo in May 2023 (au ho D. Mo eno-Fe nández).
Coni e s - F om Seed o Sus ainable S ands
6
ha measu emen s ob ained om he same ee o plo exhibi a s onge co ela ion
han hose om di e en ees o plo s. Addi ionally, measu emen s aken in close
p oximi y in ime on he same ee o plo a e expec ed o ha e a highe deg ee o co -
ela ion han hose aken u he apa in ime [38, 39]. Consequen ly, he adi ional
assump ions o independen and homogeneous e o a iance a e no longe appli-
cable due o he inhe en co ela ion pa e n among obse a ions. To sol e his, we
en e ed an au oco ela i e s uc u e o e o s and andom e ec s in he wood densi y
models [39, 40]. As esponse a iables, we conside ed he id, ee diame e inc emen
(mmyea −1) calcula ed as he a io o he di e ence be ween wo consecu i e o es
in en o ies and he empo al lapse be ween in en o ies, RD, ing densi y (gcm−3),
and LWP, pe cen age o la ewood (%). Thus, he linea mixed model included an
in e cep , ea men , Time (pe iods be ween in en o ies o id and yea o RD and
LWP), as well as hei in e ac ion, as ixed e ec s. The model also included andom
in e cep e ec s o he ee and plo o accoun o he abo emen ioned co ela ions.
Bo h andom e ec s ollow a no mal dis ibu ion wi h mean ze o and a iance σb2
and σs2. We included he diame e eco ded in he p e ious in en o y and he a io o
he basal a ea o la ge ees o he plo basal a ea (BAL/B) in he id model o con ol
he e ec s a ibu able o ee size and compe i ion [41, 42]. In he da ase o P.
syl e is, he e we e 1533 id obse a ions o C, 696 o T and 630 o TP. Meanwhile,
he da ase o P. n i g a con ained 1025 id obse a ions o C, 549 o T and 576 o TP,
while he da ase o P. nig a salzmannii included 1188 id obse a ions o C, 818 o T
and 693 o TP.
To accoun o he ini ial di e ences in wood densi y p ope ies, a co a ia e
(AM5) was used. This co a ia e was calcula ed as he a i hme ic mean o he speci ic
wood p ope y wi hin he annual ings o med 5 yea s p io o he commencemen
o he ials [29, 43, 44]. Finally, he models included a ε andom e o e m. All he
s a is ical analyses we e un in R using he “lme” unc ion o he “nlme” package [45]
and he es ic ed maximum likelihood op ion. Model s uc u es we e compa ed
using Akaike’s In o ma ion C i e ion. We used Tukey’s pos hoc es o conduc pai -
wise compa isons be ween g oup means o iden i y which g oups di e signi ican ly
om each o he using he “emmeans” package.
3. Resul s
3.1 Impac o sil icul u al ope a ions on diame e inc emen
The species displaying he la ges ee diame e inc emen , ega dless o he
hinning ea men applied, we e P. ni g a and P. syl es is (mean g ow h o bo h
species was 2.8mmyea −1 wi h s anda d de ia ion o 1.6mmyea −1), while P. nig a
salzmannii exhibi ed sligh ly lowe g ow h a es (2.1 ± 1.3mmyea −1).
We ound a signi ican e ec (p≤0.05) o he T ea men and Time on ee g ow h
o he h ee axa, while he in e ac ion be ween hem was ound o be signi ican
in he P. nig a nig a ial (Table 3). Tukey’s pos hoc es e ealed ha he ees in C
plo s exhibi ed signi ican ly lowe g ow h han hose in hinned plo s (Figu e 2). As
ega ds he hinning ea men s, we only ound signi ican di e ences be ween T and
TP o he P. n i g a ial, wi h TP p esen ing la ge diame e inc emen han T.
The diame e a he beginning o he pe iod and he compe i ion index BAL/B
we e ound o ha e a signi ican e ec on ee g ow h (Table 3) in bo h he P. syl es-
is and he P. ni g a ials. The diame e a he beginning o he pe iod displayed a
7
In luence o Sil icul u al Ope a ions on he G ow h and Wood Densi y P ope ies…
DOI: h p://dx.doi.o g/10.5772/in echopen.1003005
nega i e ela ionship wi h diame e inc emen , indica ing ha hinne ees exhibi ed
mo e g ow h han la ge ees. The BAL/B was nega i ely co ela ed wi h diame e
g ow h in P. syl es is and bo h P. ni g a subpsecies. A nega i e es ima ion coe icien
o BAL/B implies ha ees wi h la ge BAL/B ( hinne diame e s and mo e compe i-
ion) exhibi ed less g ow h compa ed o la ge ees. This di e gence be ween he
e ec o he diame e a he beginning o he pe iod and BAL/B can be explained by
he s ong, nega i e co ela ion be ween he wo a iables (α = 99.9%).
3.2 Impac o he sil icul u al ope a ions on wood p ope ies
The mean alue o P. nig a salzmannii wood densi y was 0.66kgcm−3 wi h a
s anda d de ia ion o 0.10kgcm−3. P. nig a nig a a had a wood densi y mean alue o
0.62 ± 0.11kgcm−3, whe eas P. syl es is exhibi ed a mean alue o 0.54 ± 0.08kgcm−3.
As ega ds la ewood pe cen age, his a iable eached a alue o 37.5 ± 14.4% o P. ni g a
salzmannii, 31.9 ± 10.7% o P. nig a nig a, and 28.0 ± 11.2% o P. syl es is. All o hese
alues we e calcula ed using he empo al se ies s a ing om expe imen ini ia ion
(1991 o P. syl es is and 1993 o P. ni g a ) up un il he da e he co es we e ex ac ed.
Species T ea men Time T ea men *Time dbeg BAL/B
P. syl es is <0.0001 <0.0001 n.s. <0.0001
(−)
<0.0001
(−)
Pinus nig a nig a <0.0001 <0.05 <0.001 <0.001 (−)<0.0001
(−)
P. nig a salzmannii <0.05 <0.0001 n.s. <0.0001 (−)<0.0001 (−)
Adap ed om [2]. dbeg: diame e a he beginning o each pe iod, espec i ely, and BAL/B: he a io be ween he basal
a ea o he la ges ees and he s and basal a ea. n.s. = non-signi ican (p > 0.05).
Table 3.
Mixed model esul s o he diame e inc emen models o Pinus syl es is (2859 obse a ions), Pinus nig a nig a
(2510 obse a ions), and Pinus nig a salzmannii (2699 obse a ions).
Figu e 2.
Boxplo o ee diame e inc emen o he h ee s udied species and ea men s.
Coni e s - F om Seed o Sus ainable S ands
8
Despi e he isual di e ences obse ed among ea men s as shown in Figu e 3,
he e was no s a is ically signi ican e ec o he ea men ac o on he wo wood
densi y a iables s udied (RD and LWP) o any o he h ee species. Addi ionally, he
co a ia e AM5 appea ed o be signi ican in all models excep o LWP in bo h P. nig a
nig a and P. nig a salzmannii (Table 4), sugges ing ha he abo emen ioned di e -
ences be ween ea men s may be pa ially associa ed wi h RD and LWP empo al
ends p io o ini ia ing he ials.
4. Discussion
In his chap e , we ha e e alua ed he impac s o common sil icul u al ea men s
on ee g ow h and wood p ope ies (wood densi y and LWP) o wo dominan pine
species ound in he Spanish moun ains.
Va iable AM5 Time T ea men T ea men x Time
Pinus syl es is
RD <0.0001 n.s. n.s. n.s.
LWP <0.05 n.s. n.s. n.s.
Pinus nig a nig a
RD <0.0001 n.s. n.s. n.s.
LWP n.s. n.s. n.s. n.s.
Pinus nig a salzmannii
RD <0.0001 n.s. n.s. n.s.
LWP n.s. n.s. n.s. n.s.
Adap ed om [35]. n.s. = non-signi ican (p≥0.05).
Table 4.
P- alue o AM5 (5-yea a i hme ic mean p io o he ini ia ion o he ials), ime, ea men , and in e ac ion o
ea men × ime in he RD ( ing densi y) and LWP (pe cen age o la ewood) models.
Figu e 3.
Boxplo o (A) ee ing densi y alues and (B) la ewood pe cen age o he h ee s udied species and ea men s.
The da a used anged om expe imen ini ia ion o co e collec ion da e.