ISSN 1897-1695 (online), 1733-8387 (p in )
© 2013 Silesian Uni e si y o Technology, Gliwice, Poland.
All igh s ese ed.
GEOCHRONOMETRIA 41(1) 2013: 92–103
DOI 10.2478/s13386-013-0137-2
A ailable online a
www.sp inge link.com
OAK DECLINE IN A SOUTHERN FINNISH FOREST AS AFFECTED
BY A DROUGHT SEQUENCE
KRISTINA SOHAR1, SAMULI HELAMA2, ALAR LÄÄNELAID1,
JUHA RAISIO3 and HEIKKI TUOMENVIRTA4
1Depa men o Geog aphy, Ins i u e o Ecology and Ea h Sciences, Uni e si y o Ta u, Vanemuise 46, 51014 Ta u, Es onia
2Finnish Fo es Resea ch Ins i u e, No he n Uni , P.O. Box 16, 96301 Ro aniemi, Finland
3The Ci y o Helsinki, The Public Wo ks Depa men , S ee and Pa k Di ision, P.O. Box 1515, 00099 Helsinki, Finland
4Finnish Me eo ological Ins i u e, P.O. Box 503, 00101 Helsinki, Finland
Recei ed 28 Ma ch 2013 Accep ed 21 Augus 2013
Abs ac : We in es iga ed he decline o a peduncula e oak (Que cus obu L.) o es g owing on
shallow soil a he no he n dis ibu ional limi o he species in sou he n Finland, using he dend o-
clima ic app oach. Abou 200-yea -old ees in h ee igou classes – heal hy, declining and dead –
we e sampled in 2008. Annual ee- ing, ea lywood and la ewood wid hs we e measu ed and ch o-
nologies we e es ablished. The ee- ing da a we e co ela ed wi h mon hly and seasonal clima e da a.
Radial inc emen o oaks was posi i ely ela ed o he June and July p ecipi a ions. This was ex-
p essed especially in o al ing wid h and la ewood wid h, whe eas he ea lywood was mo e in lu-
enced by he wa me win e and sp ing. Fu he mo e, he co ela ion be ween he cu en yea ea -
lywood wid h and he p eceding yea la ewood wid h was highe han be ween he ea lywood and
la ewood o he same yea . The analyses showed ha he dead oaks and pa o he declining oaks had
ceased g owing du ing 2005-2007 a e a decade-long summe d ough se ies. This indica es a ime
lag in he oak dieback. The adial g ow h o he declining and he dead oaks had d opped al eady
since he 1990s, while he heal hy oaks had be e long- e m g ow h and highe adap i e capaci y o
clima e a ia ion.
Keywo ds: dend oclima ology, mo ali y, ee ings, ea lywood, la ewood, Que cus obu L.
1. INTRODUCTION
Fo es mo ali y has been epo ed wo ldwide ecen ly
and has been a ibu ed o clima e change- ela ed d ough
and hea s ess (Allen e al., 2010). Besides, se e al s ud-
ies ha e shown a la ge-scale decline o Que cus species
h oughou Eu ope (e.g. Füh e , 1998; Siwecki and U -
nalski, 1998; Sonesson, 1999; Peñuelas e al., 2001;
Landmann and D eye , 2006; D obyshe e al., 2007a,
2007b) as well as in No h Ame ica (e.g. S a kley and
Oak, 1989; S a kley e al., 1989; Fabe -Langendoen and
Tes e , 1993; S a kley e al., 2004, Ca on e al., 2007).
As his ex ensi e mo ali y causes conce n o o es e s,
ec ea ion manage s as well as o he wide communi y,
he e is an in e es and demand o sea ch o he easons.
Acco ding o McC acken (1985) h ee concep s o oak
dieback can be dis inguished: (1) single causal ac o s
(like an ex eme wea he e en o a pa hogen), (2) coho
senescence (combina ion o age and en i onmen al
s ess), and (3) decline synd ome complex. The la e
in ol es long- e m p edisposing ac o s like ee age,
clima e and soil condi ions, and long- e m con ibu ing
Co esponding au ho : K. Soha
e
-mail: k is ina.soha[email p o ec ed]
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM
K. Soha e al.
93
ac o s such as pa hogens, as well as sho - e m inci ing
ac o s like a single ex eme wea he o ai -pollu ion
e en (Manion, 1981). Thus, he easons a e ela ed wi h
se e al bio ic and abio ic ac o s, and a e equen ly a
combina ion o di e en se e e de e minan s (e.g. Wa go,
1996; Gibbs and G eig, 1997; Thomas e al., 2002), pa -
ly wi h si e-speci ic causes (Jung e al., 2000; Jönsson e
al., 2005).
Al hough oaks ha e bo h mo phological and physiolog-
ical adap a ions o ole a e d ough (e.g. deep oo ing, con-
ol o s oma al conduc ance, non-s oma al con ol o ca -
bon ixa ion) (Dickson and Tomlinson, 1996), hese eac-
ions lose impo ance wi h inc easing d ough s ess mak-
ing ees mo e suscep ible o o he s ess ac o s (Thomas
e al., 2002). I has been shown ha expe imen ally applied
d ough educes s em and shoo g ow h, and whole- ee
lea a ea (A end e al., 2011) while mode a e clima e
change does no a ec nei he lea ni ogen no non-
s uc u al ca bohyd a es (Li e al., 2013). All ha consid-
e ed, d ough has been assumed o be one o he main
ac o s causing oak decline h ough educ ion o wa e
up ake (e.g. Siwecki and U nalski, 1998; D obyshe e al.,
2007b) o weakening he ees agains o he s ess de e mi-
nan s like pa hogenic ungi (e.g. mildew) and insec pes s
(e.g. lea olle ). All his esul s in de olia ion which leads
o he educ ion o pho osyn hesis and o dea h (e.g. Si-
wecki and U nalski, 1998; Thomas e al., 2002).
I is well known ha ees p o ide in o ma ion on he
pas g owing condi ions in hei annual ings, and di e -
en pa ame e s o he la e can be easily measu ed as a
con inuous sequence o yea s and di ec ly calib a ed
agains any p edisposing en i onmen al ime se ies, o
example clima ic eco ds (F i s, 1976). Dend och ono-
logical echniques allow us o ex ac ex e nal o in e nal
g ow h signals om he o e all g ow h a iabili y (Cook,
1987) and o de e mine he ela i e impo ance o an
en i onmen al ac o (e.g. a wea he a iable) o ee
igou . A ee- ing wid h a chi e can be used in explain-
ing mo ali y e ospec i ely, o example, iden i ying he
p esence and spa io empo al pa e ns o p e-mo em
g ow h dep essions and da ing he exac ime o dea h
(D obyshe e al., 2007b). The dend och onological da a
can be used o p edic ing he ime o ee dea h as well
(Pede sen, 1998; Che ubini e al., 2002; Bigle and Bug-
mann, 2004; Dobbe in, 2005).
A decline in peduncula e oaks (Que cus obu L.) as
well as o he ee species has been obse ed in he Hel-
sinki me opoli an a ea in Finland du ing he ecen yea s,
especially 2003 (Ympä is ö apo oinnin asian un i-
ja yö yhmä, 2004; Holopainen e al., 2006). Finnish oaks
g ow a he species’ no he nmos na u al egene a ion
bo de (e.g. Axel od, 1983; Dahl, 1998). Cold ha diness
du ing he au umn is conside ed as a main ac o limi ing
oak seedling o sp ead u he no h (Repo e al., 2008),
combined wi h he des uc ion by humans and he compe-
i ion wi h sp uce (Rainio, 1977). On he o he hand,
dend oclima ological analyses ha e e ealed ha adial
g ow h is con olled especially by summe ain all, and
mo ali y has been associa ed wi h d ough s, likewise
wi h shallow soil dep h, which inc ease en i onmen al
ee s ess (Helama e al., 2009).
Ou wo k is a pa o a wide esea ch on oak mo ali-
y in Finland, and he e o e i ollows simila s udy de-
sign and he me hods used be o e (Helama e al., 2009).
The goal was o de e mine he empo al mo ali y pa e n
and o examine he decline o peduncula e oaks in he
Tammis o o es using long- e m ee- ing se ies (ea -
lywood, la ewood and o al annual ing wid h) in connec-
ion wi h clima ic and soil da a.
2. MATERIAL AND METHODS
T ee- ing da a
The Tammis o Pa k is a 15.5 ha na u e ese e o na -
u al o es loca ed in Van aa, Helsinki me opoli an a ea
(60°16’35”N, 24°57’49”E; Fig. 1). A spo adically ex-
posed bed ock idge makes up he cen e o he a ea, up
o 38 m abo e sea le el, and is co e ed by Pinus syl-
es is. The no he n slope is domina ed by Picea abies
while he sou he n side is co e ed by b oadlea o es . In
addi ion o Que cus obu , Tilia co da a and Ace pla -
anoides a e ound while he unde s o y is occupied by
Co ylus a ellana. Sp uce o e g ow h is s opped by he
p o ec ion ac i i ies (Honkanen, 2009).
We had a pe mission o co e no mo e han 30 pedun-
cula e oaks o his s udy in July 2008. Following he
c i e ia used ea lie (Helama e al., 2009), en heal hy
ees de ined as li ing ees wi h g een oliage, en declin-
ing ees as diagnosed by educed c own condi ion, mod-
Fig. 1.
Loca ion o he s udy si e. Dis ibu ion o oak in g ey
(EUFORGEN, 2009).
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM
OAK DECLINE IN A SOUTHERN FINNISH FOREST AS AFFECTED BY A DROUGHT SEQUENCE
94
es oliage degene a ion and/o some b anch dea h, and
en dead ees diagnosed by de olia ion and o e all
b anch dea h we e andomly chosen. We ook ee- ing
samples wi h an inc emen bo e om b eas heigh o-
wa ds he pi h om he no he n side o he unk and
su eyed he soil dep h by d i ing a soil p obe in o he
g ound un il e usal (Tes a e al., 2009) a loca ions se-
lec ed om ou di ec ions a a dis ance o wo me e s
om he s em. The a i hme ic mean o he ou obse a-
ions, and he shallowes obse a ion as minimum soil
dep h, we e used in he da a analysis.
Wi hin he ee ings we measu ed he ea ly- and
la ewood wid hs sepa a ely o he nea es 1/100 mm using
a Lin ab™ measu ing able (Heidelbe g, Ge many)
equipped wi h a ligh mic oscope. We dis inguished he
bounda y be ween he ea lywood and la ewood acco ding
o a quali a i e aspec : he ea lywood con ains he la ge
essel zone, while he la ewood comp ises he small po e
zone (e.g. Schweing ube , 2007). The sum o he ea ly-
and la ewood measu emen s was adop ed as he o al
annual ee- ing wid h. The TSAP-Win so wa e (Rinn,
2003) was used o eco d he measu ed alues and plo
he g aphs. The quali y con ol o he se ies was pe -
o med isually om he g aphs and wi h he Co echa
so wa e om he Dend och onology P og am Lib a y
(Holmes, 1983). As he da e o co ing was known, he
las annual ing o heal hy oaks could be coupled wi h he
calenda yea 2008. The es o he samples we e c oss-
da ed agains he mean ch onology o heal hy oaks using
he dend och onological p og am CATRAS (Aniol,
1983) and he da ing esul s we e checked isually om
he g aphs. This c oss-da ing esul ed wi h he calenda
yea s o all ea lywood, la ewood, and annual ing
wid hs.
Dend och onological analysis
A e age se ies o ea lywood, la ewood, and annual
ing wid hs we e c ea ed om each igou class acco d-
ing o he cambial age (e.g. B i a e al., 1992) whe e he
ings we e aligned by hei age s a ing om he pi h
ins ead o he calenda yea s a b eas heigh . Al hough
he e we e only wo co es con aining he pi h, he majo i-
y o he co es s ill had nea -pi h ee ings acco ding o
he cu ed inne mos ing shape (on a e age, six inne -
mos missing ings pe co e acco ding o a pi h indica o
empla e). Only one ee had a oo la ge diame e o
ca ching he pi h and one ee was o en inside. The
ela i e g ow h a e (RGR) (B i a and Mel in, 2011;
Helama e al., 2012) o each ee was calcula ed as
∑∑
==
=
n
n
xxRGR
11
(2.1)
whe e
x
is he ee- ing wid h in yea ,
x
is he mean
wid h o all ings in yea , and n is he numbe o ings in
he se ies. Thus, i is a a io o he ee adius a i s inal
yea o he a e age o e all-sample adius a ha yea . The
RGR alues we e a e aged ac oss each igou class.
As ollows, we adop ed a s anda diza ion p ocedu e
(F i s, 1976) and con e ed he measu emen se ies in o
dimensionless indices. To emo e he ee-age- ela ed
g ow h end and o educe non-clima ic noise (i.e. low-
equency noise), he measu emen se ies we e de ended
using a s i spline unc ion, which p ese es 50% o he
a iance con ained in wo- hi ds o he indi idual se ies
leng h (Cook and Pe e s, 1981). The spline cu e was
i ed and he indices de i ed om he cu e as a ios
using he A s an p og am (Cook, 1985).
In o de o compa e he ee g ow h a iabili y wi h
he soil da a, he s anda d de ia ion, he mean sensi i i y
(MS), and he i s -o de au oco ela ion o each index
se ies we e compu ed by he A s an p og am. While he
s anda d de ia ion desc ibes he o al a ia ion in he
se ies, he mean sensi i i y indica es he yea - o-yea
a iabili y be ween he adjacen ing wid hs and can be
de e mined as
∑
−=
=+
+
+
−
−
=
1
11
1)(2
1
1n
xx
xx
n
MS
(2.2)
whe e x is he ee- ing wid h in yea , and n is he num-
be o yea s/ ee- ings in he se ies (F i s, 1976). Also,
we compa ed he RGR o each ee wi h he minimum
soil dep h da a. As all hese a iables we e no mally
dis ibu ed, we used he Pea son co ela ion coe icien
( ) o desc ibe hei ela ionships.
Dend oclima ologial analysis
Fo he dend oclima ological analysis, he index se ies
we e p e-whi ened in he A s an o emo e he pe sis-
ence due o au oco ela ion. The index se ies we e a e -
aged using a bi-weigh obus mean es ima ion o educe
ou lie e ec s (Cook, 1985). As a esul , we ecei ed nine
esidual ch onologies acco ding o he h ee wood ypes
and he h ee igou classes. These ch onologies we e
used o calcula ing he c oss-co ela ions and o he
dend oclima ological analysis. In addi ion, we co ela ed
he ea lywood wid h ch onology wi h he la ewood wid h
ch onology o he p eceding yea . The common pe iod
1894-2004 was used o all ch onologies. This ime ange
con ained a leas i e ees in each igou class
(Läänelaid, 2000).
We compa ed ou s anda dised ee- ing da a wi h
mon hly mean empe a u es and p ecipi a ion sums om
he Helsinki Kaisaniemi wea he s a ion (60°10’48”N,
24°56’24”E, 4 m a.s.l.), loca ed ca. 11 km om Tammis-
o. We used homogenised and de ended mon hly eco ds
(Tuomen i a, 2004) and he Dend oClim2002 p og am
(Biondi and Waikul, 2004) o examine he ela ionships
be ween he ee- ing da a and he me eo ological a ia-
bles. This p ocess uses boo s apped con idence in e als
o es ima e he signi icance (p < 0.05) o he esponse
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM
K. Soha e al.
95
unc ion coe icien s, which a e mul i a ia e es ima es
om a p incipal componen eg ession model (B i a and
Cook, 1990). He e we used he 12-mon h window om
he p e ious yea ’s Oc obe o he cu en yea ’s Sep em-
be . Th ee-mon hly seasonal a e age empe a u es and
p ecipi a ion sums om he p e ious Sep embe o he
concu en Augus we e calcula ed and co ela ed wi h
he ee- ing ch onologies.
3. RESULTS
Age and dea h da es o ees
Al oge he , we measu ed and da ed 30 oak ees
equally dis ibu ed be ween he h ee igou classes. The
dend och onological s a is ics o he aw da a as well as
o he s anda dized ch onologies by igou class a e
summa ised in Table 1. The sample size is shown in Fig.
2. Compa ing he igou classes, he declining oaks co -
e ed he longes ime pe iod (1799-2008) while he dead
and he heal hy oaks co e ed 1812-2006 and 1836-2008,
espec i ely. Howe e , acco ding o he - es , mean ee
age did no di e signi ican ly be ween he igou classes
(p > 0.05), as well as mean annual ing wid h, s anda d
de ia ion, mean sensi i i y and au oco ela ion. Thus,
acco ding o he s a is ics he e is no ele an di e ence
be ween igou classes. The oaks diagnosed as heal hy
we e ound o ming he ing in he sampling yea 2008.
Among he declining oaks, i e ees we e ound s ill
g owing in he summe o 2008 ( wo o hem ha ing only
ea lywood). The ou e mos pa s o wo ees we e dam-
aged (da ed as 1950 and 1988), and wo ees had o med
hei las ing in yea 2006 and one in 2007, a leas in he
no he n pa o he s em. Among he dead ees, ou
oaks had s opped g owing in he yea 2006 and one in he
yea 2005 ( h ee o hem ha ing only ea lywood), he
o he i e had damaged ou e mos ings and hese we e
da ed as 1976, 1989, 1991, 1992 and 1993.
T ee- ing g ow h
The a e age ee- ing se ies o he declining and he
dead ees e ealed clea p e-mo em g ow h educ ion
du ing he las decades in all ing wid h pa ame e s (Fig.
2). Fo example, he mean annual ing wid hs di e ed
signi ican ly be ween he wo pe iods ( - es , p < 0.05)
being 1.3 and 1.2 mm o he declining and he dead
ees, espec i ely, du ing he pe iod 1973-1990, and 0.8
and 0.7 mm, espec i ely, du ing he pe iod 1991-2008.
A he same ime he heal hy oaks had also a signi ican
bu s ill lowe g ow h educ ion (a di e ence 0.3 mm
be ween wo pe iods). The lowe inc emen a he heal hy
oaks’ ea ly li e ime was caused by he excep ionally
small sample eplica ion (only one ee). The la ewood
and he annual ing wid h cambial g ow h pa e n (Fig. 3)
showed ha he heal hy and he dead ees had simila
Table 1. S a is ics on he ee- ing measu emen s and on he indexed ch onology.
Vi
gou
class
T ee- ing measu emen s
Residual ch onology
Mean numbe
o yea s
Mean ing
wid h (mm)
S d. de ia ion
(mm)
Mean
sensi i i y
1s o de au o-
co ela ion
S d. de ia ion
Mean
sensi i i y
1s o de au o-
co ela ion
Heal hy
118
1.77
0.77
0.21
0.73
0.16
0.18
0.02
Declining
126
1.60
0.73
0.23
0.69
0.23
0.24
-0.07
Dead
129
1.52
0.73
0.22
0.74
0.22
0.21
-0.03
Fig. 2. Annual sample eplica io
n and a e age ea lywood, la ewood,
and o al annual ing wid h se ies by igou class.
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM
OAK DECLINE IN A SOUTHERN FINNISH FOREST AS AFFECTED BY A DROUGHT SEQUENCE
96
g ow h s a egies o e hei li espan; howe e he dead
oaks had a lowe ela i e g ow h a e (Eq. 2.1). The de-
clining oaks appea ed o ha e a sligh g ow h ecession
du ing he middle o hei li e ime. The cambial g ow h
pa e ns o ea lywood se ies seemed o ha e a mo e he -
e ogeneous wi hin he igou classes wi h a dec ease in
he second hal o he dead ees’ inc emen becoming
dis inguishable. The heal hy ees’ g ow h decline a hei
age 30-40 was caused by he simila age o mos ees
whe e o e he e ec o ad e se calenda yea s was no
smoo hed ou om he ime se ies. O e all, acco ding o
he - es , he di e ences in he ela i e g ow h a es be-
ween he nine subse s we e no s a is ically signi ican
(p > 0.05).
The co ela ions be ween he p e-whi ened ch onolo-
gies (da a om he same yea ) we e posi i e and s a is i-
cally signi ican (p < 0.05; Table 2). Howe e , he co e-
la ions wi hin he ea lywood ch onologies we e lowe
han wi hin he la ewood and he o al ing wid h subse s.
In addi ion, he simila i y be ween he ea lywood wid h
o he cu en yea and he la ewood wid h o he p eced-
ing yea was highe han be ween he la ewood and ea -
lywood wid hs o he same yea in each igou class,
especially wi hin he heal hy ees. The co ela ions be-
ween he ea lywood wid h and he o al ing wid h ch o-
nologies we e ema kably lowe han be ween he la e-
wood wid h and he o al ing wid h ch onologies. Thus,
la ewood wid h was mo e ele an in de e mining he
annual ing wid h han ea lywood wid h, which a ied
less be ween he yea s (Fig. 2).
T ee- ing wid h and soil ela ionships
Mean soil dep h anged be ween 29-66 cm, 28-66 cm,
and 29-86 cm a ound he heal hy, he declining, and he
dead ees, espec i ely. The shallowes soil obse a ions
anged be ween 8-44 cm a ound bo h he heal hy and he
declining oaks, and 14-76 cm a ound he dead oaks. No
s a is ically signi ican di e ences in soil measu emen s
be ween he igou classes we e iden i ied ( - es ,
p > 0.05). Mo eo e , none o he co ela ions be ween he
g ow h a iabili ies o annual ing wid h indices, he ela-
i e g ow h a e and minimum soil hickness a ound each
Fig.
3. Ea lywood, la ewood, and
o al annual ing wid h a iabili y by
igou class du ing he 1
-
115 yea s cambial age being he common
pe iod ha con ains a leas i e se ies in each igou class. A e age
ela i e g ow h a es (RGR) a e calcula ed om indi idual ee cha ac-
e is ics ac oss hei en i e li espan.
Table 2. Pea son co ela ion coe icien s be ween he esidual ch onologies du ing 1894-2004: ea lywood wid h (EW), la ewood wid h (LW), p eced-
ing yea ’s la ewood wid
h (pLW), o al annual ing wid h (ARW) o heal hy (HE), declining (DE), and dead (DD) oaks. S a is ically signi ican ela io
n-
ships (p
< 0.05) a e in bold.
EWHE
EWDE
EWDD
LWHE
LWDE
LWDD
pLWHE
pLWDE
pLWDD
ARWHE
ARWDE
ARWDD
EWHE
-
EWDE
0.69
-
EWDD
0.71
0.74
-
LWHE
0.25
0.36
0.36
-
LWDE
0.25
0.41
0.39
0.82
-
LWDD
0.27
0.43
0.39
0.85
0.82
-
pLWHE
0.62
0.42
0.46
0.01
0.06
0.09
-
pLWDE
0.54
0.48
0.47
-0.01
0.01
0.02
0.82
-
pLWDD
0.57
0.44
0.50
0.03
0.11
0.11
0.85
0.83
-
ARWHE
0.39
0.41
0.44
0.94
0.79
0.80
0.03
-0.02
0.05
-
ARWDE
0.37
0.60
0.50
0.79
0.95
0.83
0.07
0.03
0.11
0.79
-
ARWDD
0.45
0.60
0.65
0.79
0.81
0.92
0.16
0.09
0.16
0.79
0.88
-
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM

K. Soha e al.
97
ee we e signi ican (p > 0.05; Fig. 4). The esul s we e
alike wi h he ea lywood and he la ewood wid h cha ac e -
is ics (no shown). Acco dingly, soil dep h was ound o
ha e no signi ican e ec on g ow h a ia ion in his si e.
T ee- ing wid h and clima ic ela ionships
The esponse alues be ween he ee- ing da a and
he mon hly clima e a iables e ealed ha oak g ow h
was especially limi ed by June and July ain all in all
igou classes based on he da a om 1894-2004
(p < 0.05; Fig. 5). This associa ion was posi i e and
common o la ewood and annual ing wid h in all igou
classes. Response o declining oak di e ed om o he
igou classes in ha May empe a u e had a posi i e
e ec on la ewood o ma ion and simila ly on annual ing
wid h. Ea lywood wid h was less e iden ly con olled by
he clima e, only he declining oaks showing an excep-
ionally posi i e esponse o Ma ch p ecipi a ion. On he
o he hand, he majo i y o win e and sp ing mon h em-
pe a u es had posi i ely a ec ed ea lywood o ma ion,
bu he ela ionships we e insigni ican on mon hly scale.
On seasonal scale, we ound ha wa me win e and
sp ing bene i ed he ea lywood dimension signi ican ly,
while he la ewood was sensi i e o summe ain all
(p < 0.05; Table 3).
4. DISCUSSION
Speci ics o oak decline in Tammis o
The c oss-da ing esul s showed ha Tammis o oaks
ha e died mos ly du ing 2005-2007 o e en be o e ha
ime, as he las ings we e uniden i iable in some sam-
ples. The causes canno be associa ed wi h hese yea s
igo ously because dieback can be a decade-long p ocess
and dea h migh be lagging behind he iming o he de-
cline-inducing ac o s (Che ubini e al., 2002; D obyshe
e al., 2007b; Ande sson e al., 2011). The p e-mo em
g ow h educ ion o he declining and dead ees was
illus a ed o ha e occu ed al eady om he mid-1990s
(Fig. 2). A simila deg ada ion pa e n has been iden i ied
ea lie in he F amnäs oak si e in sou h-wes e n Finland
(Helama e al., in p ep.) and in he Annala Pa k in Hel-
sinki whe e an ab up oak g ow h educ ion appea ed
Fig.
4.
Rela ionships be ween g ow h a iabili y o annual ing wid h
indices (s anda d de ia ion, mean sensi i i y, au oco ela ion), ela i e
g ow h a e o each ee and minimum soil hickness a ound each ee,
as desc ibed by Pea son co ela ion coe icien s ( ).
Table 3. Pea son co ela ion coe icien s be ween he esidual ch o-
nologies (ea lywood wid h (EW), la ewood wid h (LW), o al annual ing
wid h (ARW) o heal hy (HE), declining (DE) dead (DD) oaks) and
wea he cha ac e is ic
s o ou seasons om he p e ious yea (small
le e s) un il he cu en yea (capi al le e s) du ing he pe iod 1894
-
2004. S a is ically signi ican ela ionships (p < 0.05) a e in bold.
Tempe a u e
P ecipi a ion
son
dJF
MAM
JJA
son
dJF
MAM
JJA
EWHE
0.06
0.33
0.34
0.08
0.19
0.01
0.00
0.11
EWDE
0.00
0.18
0.21
-0.07
0.07
-0.02
0.18
0.22
EWDD
0.01
0.20
0.20
-0.08
0.15
0.00
-0.03
0.15
LWHE
-0.02
0.07
0.20
-0.10
0.03
0.08
0.01
0.46
LWDE
-0.07
0.09
0.17
-0.15
0.03
0.09
0.01
0.55
LWDD
-0.03
0.06
0.18
-0.14
0.03
0.05
0.07
0.47
ARWHE
0.01
0.09
0.26
-0.09
0.05
0.08
-0.01
0.42
ARWDE
-0.06
0.12
0.21
-0.13
0.06
0.05
0.06
0.53
ARWDD
-0.02
0.15
0.25
-0.13
0.08
0.06
0.00
0.44
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM
OAK DECLINE IN A SOUTHERN FINNISH FOREST AS AFFECTED BY A DROUGHT SEQUENCE
98
some yea s la e , om 2002 o 2003 (Helama e al.,
2009). Thus, i seems o be a common ea u e o he oaks
g owing a he no he n dis ibu ional limi in Finland.
La ewood wid h was mo e ele an in de e mining
annual ing wid h han ea lywood wid h (Table 2), like i
has been demons a ed be o e as well (Doležal e al.,
2010; Ma isons and B ūmelis, 2012). Compa ing ou
la ewood and annual ing wid h ch onologies and he
co esponding cambial age g ow h pa e ns, he heal hy
oaks showed be e long- e m g ow h han he declining
and he dead ees (Figs. 2 and 3). I was u he shown
ha he ela i e g ow h a e was no ela ed o soil hick-
ness (Fig. 4). The be e long- e m g ow h may hus be
ela ed o some long- e m s esses, such as in e - ee
compe i ion (Dobbe in, 2005; Rozas and Ga cía Gonzá-
lez, 2012) as he heal hy oaks ha e eco e ed om he
g ow h descen supposedly due o hei a ou ed s a us in
he s and hie a chy. Be e adial g ow h in he heal hy
igou class o e he en i e li espan has been obse ed
p e iously in o he Finnish oak si es as well (Helama e
al., 2009; Helama e al., in p ep.).
Fu he mo e, he a o emen ioned s udy conduc ed in
an u ban pa k in Helsinki has shown ha a shallow soil
laye can cause addi ional en i onmen al s ess on ee
Fig.
5. Response alues be ween he nine ch onologies a
nd he mon hly me eo ological a iables om he p e ious (small le e s) and cu en yea s
(capi al le e s) du ing he pe iod 1894-2004. S a is ically signi ican ela ionships (p<0.05) a e indica ed as illed ba s.
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM
K. Soha e al.
99
g ow h. Con e sely, we ound ha soil dep h has no
signi ican e ec on g ow h a ia ion in he conce ned
si e (Fig. 4). Supposedly, soil condi ions a e equally poo
on his spo adically exposed bed ock and he ees ha e
ceased o esis o he wa e s ess du ing he d ough s.
Insec pes s and pa hogenic ungi can con ibu e o
dieback as well (Ha mann e al., 1989; Füh e , 1998;
Siwecki and U nalski, 1998; Jung e al., 2000; Thomas e
al., 2002). Fo example, de olia ion by insec s leads o
ex ensi e losses o pho osyn ha es and deple ion o ca -
bohyd a e ese es, oo pa hogens o Phy oph ho a spp.
can des uc he ine oo sys em and, in a combined e -
ec wi h se e e d ough , h ea en he heal h o ees.
Mo eo e , oo pa hogens can dec ease he abili y o hos
ees o cope wi h d ough and s op cambial ac i i y like
i has shown on sp uces in he Eas e n Alps (Go i e al.,
2013). A ou si e we did no examine he bio ic ac o s a
all, hus hei con ibu ion in he analysed dieback canno
be disca ded. On he o he hand, no single pa hogen o
insec can cause oak decline on a la ge scale (Siwecki and
U nalski, 1998), bu oak o es decline has epo ed wide-
ly all o e sou he n Finland ecen ly (Ympä is ö apo -
oinnin asian un ija yö yhmä, 2004; Holopainen e al.,
2006; Helama e al., 2009). Thus, some disease could
ha e con ibu ed o he decline in Tammis o bu mos
p obably he weakening and dieback we e igge ed by a
common la ge-scale ac o (e.g. clima e).
Summe p ecipi a ion signal
As g ow h was mos ly con olled by summe p ecipi-
a ion (Fig. 5; Table 3) in all igou classes, he na ow
ee ings can be coupled wi h d y g owing seasons and
poo plan -wa e ela ions o e all (Thomas and Ha -
mann, 1998). Summe d ough s ha e been sugges ed as a
con ibu ing decline ac o o oak in Poland (Siwecki and
U nalski, 1998), in combina ion wi h excep ional win e
os s in G ea B i ain (Gibbs and G eig, 1997) and Ge -
many (Ha mann e al., 1989). The geog aphically closes
s udy o Finland de i es om sou he n Sweden, whe e
D obyshe e al. (2007b) ha e sugges ed ha he peak in
oak mo ali y a ound he yea 2000 was igge ed by he
sp ing and summe d ough ha occu ed al eady in 1992.
Ano he s udy om sou h-eas e n Sweden has shown
p onounced peaks in oak mo ali y in 2004 and 2006 wi h
educed g ow h a e a se e e d ough in 1992, oo (An-
de sson e al., 2011). June and July 1992 we e excep ion-
ally d y in Helsinki as well, in addi ion o se e al o he
summe s om he 1990s like: 1991, 1994, 1995, 1997
and 1999 (Fig. 6). In o he wo ds, i was he pe iod when
a p e-mo em g ow h educ ion o he declining and dead
ees was obse ed in ou s udy si e. The yea 2003, wi h
an excep ionally d y g owing season h oughou Eu ope
(Fink e al., 2004) as well as in Finland (Silande and
Jä inen, 2004), showed a nega i e peak in ou ee- ing
se ies o each igou class (Fig. 2). The same happened
in 2006, which he Finnish Me eo ological Ins i u e
(2012) desc ibed as he ho es and d ies g owing season
in he Helsinki-Van aa s a ion du ing he 1961-2006
pe iod. Thus, hese sequen ial d ough s migh ha e led o
he dieback du ing 2005-2007. In addi ion o he 1990s, a
mo e se e e d ough pe iod was expe ienced in Finland
du ing he pe iod 1939-1942 (Hyd og a inen oimis o,
1944, 1948; Kuusis o, 2003, 2004). An inc emen d op in
he 1940 and 1941 in he ee- ing ch onologies was ob-
se able in e e y igou class bu he g ow h educ ion
did no con inue (Fig. 2). This can be ela ed o he phys-
iologically younge ee age eco e ing he o me s a us
easie . In addi ion, he young oak ap- oo is known as
well-de ined (Jones, 1959) and may be e each he low-
e ed g oundwa e le el.
Ou dend oclima ic indings (Fig. 5) a e suppo ed by
he ea lie s udies which ha e e ealed a posi i e e-
sponse o oak g ow h o summe p ecipi a ion in Finland
(Helama e al., 2009; Hilas uo i and Be ninge , 2010) as
well as in Sweden (D obyshe e al., 2008). This kind o
ela ionship has been known o long (S ewa , 1913) and
has been desc ibed o peduncula e oak widely a ound
Eu ope ecen ly. Fo example in he Bal ic coun ies,
June ain all has he s onges posi i e in luence on ee
g ow h in Es onia (Läänelaid e al., 2008), Augus ain all
in La ia (Ma isons e al., 2012), and mois summe s in
he well-d ained si es in Li huania (Ruseckas, 2006).
Also, a he eas in he middle Volga egion in Russia, a
posi i e g ow h in luence o sp ing-summe p ecipi a ion
has been obse ed (Askeye e al., 2005). Acco ding o
Ced o (2007) as well as B onisz e al. (2012) oak g ow h
in Poland is domina ed by summe p ecipi a ion while
high empe a u e has nega i e in luence. Poo oak inc e-
men is mainly asc ibed o he wa e de ici du ing he
ea ly summe in he Czech Republic (Doležal e al.,
2010) and in Ge many (F ied ichs e al., 2009; Scha n-
Fig. 6. Reco ds o June and July
p ecipi a ion sums om he Helsinki
Kaisaniemi wea he s a ion.
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM
OAK DECLINE IN A SOUTHERN FINNISH FOREST AS AFFECTED BY A DROUGHT SEQUENCE
100
webe e al., 2011; Zang e al., 2012). Oak s udies in he
B i ish Isles ha e shown ha high ain all du ing he
g owing season and high empe a u e du ing he ea ly
summe p omo e g ow h (Pilche and G ay, 1982; B idge
e al., 1996). An enhancing e ec o p ecipi a ion is
widely obse ed in he Medi e anean en i onmen s
(San ini e al., 1994; Tessie e al., 1994; Ču a e al.,
2008) and he A lan ic Spain (Rozas, 2001, 2005), whe e
high p ecipi a ion c ea es a ou able and high empe a-
u e un a ou able g ow h condi ions du ing he summe
pe iod. On he o he hand, wa e excess can be limi ing
o g ow h and is igge ing o es dieback in ainy em-
pe a e deciduous o es (Rozas and Ga cía González,
2012). Anyway, he impo ance o summe p ecipi a ion
o oak ee- ing wid h is e iden ac oss Eu ope.
Rela ionships o win e and sp ing condi ions
On he seasonal scale, ee- ings and especially ea -
lywood wid hs we e posi i ely co ela ed wi h sp ing
(Ma ch-May) empe a u e in e e y igou class (Table
3). On a mon hly scale, only he declining oaks showed a
posi i e esponse o May empe a u e (Fig. 5). Ea lywood
wid h was con olled by win e (Decembe –Feb ua y)
a e age empe a u e as well (Table 3), which means ha
mild a he han cool win e s a e mo e a ou able o
ea lywood o ma ion. As his pa o he ee- ing in-
ol es wa e -conduc ing essels o ees, he iming o
g ound mel ing and g ound wa e accessibili y is ele an .
Doležal e al. (2010) ha e associa ed ea lywood g ow h
wi h p e ious au umn and win e empe a u es in he
Whi e Ca pa hians in he Czech Republic. Vessel lumen
a ea, ano he ea lywood cha ac e is ic, shows also he
highes posi i e co ela ions wi h empe a u es om
win e and sp ing mon hs in La ia (Ma isons and
B ūmelis, 2012).
E en i oak ea lywood essels enla ge in a sho ime
in sp ing, be ween he bud b eak and he lea expansion
(Sass-Klaassen e al., 2011), he p ocess can depend on
he p e ious yea ’s la ewood (Nola, 1996). Mo eo e ,
acco ding o Ki in e al. (1999) in ing-po ous ha dwood
ea lywood essel elemen s mos p obably o igina e om
he o e win e ed cambial de i a i es. Nola (1996),
Ga cía González and Ecks ein (2003) ha e demons a ed
a highe co ela ion be ween he cu en yea ’s ea lywood
and he p eceding yea ’s la ewood wid h han he same
yea ’s co esponding po ions. Based on ou s udy we can
admi a simila ela ionship: he co ela ion coe icien
be ween ea lywood wid h o he cu en yea and he
la ewood wid h o he p e ious yea we e 0.62, 0.48, and
0.50 in he heal hy, declining and dead oaks, espec i ely.
The simila i y cha ac e is ics be ween he la ewood and
ea lywood wid hs o he same yea we e 0.25, 0.41 and
0.39, espec i ely (Table 2). Thus, he heal hy ees
showed he s onges ela ionship, which may e e o
s onge biological dependence ins ead o en i onmen al
s ess. The easons behind ha phenomenon we e beyond
he aim o his s udy and should be analysed in mo e
de ail in he u u e.
A he same ime, he annual ing wid h showed no
signi ican ela ionships o empe a u e du ing he deep
do mancy pe iod (Fig. 5; Table 3). Thus, os damages,
which can gene a e ba k nec osis and ini ia e decline,
seem no o be associa ed wi h mo ali y a ou si e, as i
has been ound in sou he n Sweden (Ba klund and Wahl-
s öm, 1998). Mo eo e , p e ious s udy om Finland has
shown signi ican nega i e co ela ion be ween ee- ing
g ow h and win e empe a u es, which is explained
h ough pe manen snow-co e appea ance du ing below
ze o empe a u es and hus be e oo insula ion (Helama
e al., 2009). Alike ela ionships we e no ound in ou
s udy si e. Excep ionally, he declining oak ea lywood
showed a posi i e esponse o Ma ch p ecipi a ion. Mos
p obably his is andom coinciden al and no ela ed o
oo insula ion by he snowpack because he snow co e
o ms o e se e al mon hs and o he do mancy mon hs
did no show a signi ican co ela ion be ween p ecipi a-
ion and he inc emen .
5. CONCLUSIONS
The esul s suppo he p e ious oak decline s udy
om Finland (Helama e al., 2009) which showed
d ough inci ed oak decline on he shallow soil. The com-
pa ison o oak igou classes ( he li ing, he declining,
and he dead) in he Tammis o o es e ealed no signi i-
can di e ences in age, mean ing wid h, mean sensi i i-
y, ela i e g ow h a e, no soil dep h a ound he ee,
e en hough di e ences in he oliage and i al capaci y
we e isible. We can assume he soil condi ions a e
equally poo on he spo adically exposed bed ock. The
dend oclima ic analysis showed a simila ly posi i e
‘summe esponse’ meaning he summe d ough s had an
inhibi ing e ec on he oaks. Wa e s ess is equal o oaks
in all igou classes, ob iously due o he shallow soil.
Appa en ly, he sequen ial d ough s du ing he p eceding
decade inci ed he dieback o he declining and he dead
ees du ing 2005-2007. Thus, he e appea s o be a ime
lag be ween he mo ali y-inducing ac o s and ac ual
dea h. Ou esul s di e om he p e ious s udy in a lack
o clea nega i e clima e ‘win e esponse’. On he sea-
sonal scale, we can admi a a ou able sp ing wa m h
e ec on bo h ea lywood and o al annual ing g ow h
and a posi i e e ec o mild win e on ea lywood o -
ma ion.
ACKNOWLEDGEMENTS
The ield wo k was ca ied ou unde he license om
he Ci y o Van aa (Dno YM 2930/2008/516). The e-
sea ch was suppo ed by he Eu opean Social Fund’s
Doc o al S udies and In e na ionalisa ion P og amme
DoRa, which is ca ied ou by Founda ion A chimedes,
by he Es onian S a e Ta ge Founda ion
B ough o you by | Me la Finnish Fo es Resea ch Ins i u e
Au hen ica ed
Download Da e | 12/20/16 11:16 AM