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Under predicted climate change, native silver fir (Abies alba) and European beech (Fagus sylvatica) are the most likely replacement species for the Norway spruce (Picea abies) monocultures planted across large parts of continental Europe. Our current understanding of the adaptation potential of fir-beech mixed forests to climate change is limited because long-term responses of the two species to environmental changes have not yet been comprehensively quantified. We compiled and analysed tree-ring width (TRW) series from 2855 dominant, co-dominant, sub-dominant and suppressed fir and beech trees sampled in 17 managed and unmanaged mixed beech-fir forest sites across Continental Europe, including Bosnia and Herzegovina, Germany, Italy, Romania and Slovakia. Dendroecological techniques that combine various detrending methods were used to investigate variation in radial growth of co-occurring fir and beech trees. Coincidental with peak SO2 emissions, the growth of silver fir declined between 1950 and 1980 at most sites, whereas beech growth increased during this period. Correspondent to a significant warming trend from 1990–2010, average beech growth declined, but silver fir growth increased. Long-term growth patterns and growth-climate sensitivity of fir and beech trees did not significantly differ between managed and unmanaged forests. Multi-decadal changes in the growth rate of all vertical tree classes were similar. In contrast to previous indications of limited drought susceptibility of beech mixed stands, this study suggests that the mixture of tree species in forest stands does not necessarily prevent growth depressions induced by long-term environmental change. Our results further imply that forest management does not necessarily alter their sensitivity to environmental changes.
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Contrasting effects of environmental change on the radial growth of
co-occurring beech and r trees across Europe
Michal Bosela
a,b,
,MartinLukac
b,c
, Daniele Castagneri
d
, Róbert Sedmák
a,b
, Peter Biber
e
, Marco Carrer
d
,
Bohdan Konôpka
f,b
, Paola Nola
g
,ThomasA.Nagel
h,b
, Ionel Popa
i,j
, Catalin Constantin Roibu
k
,
Miroslav Svoboda
b
, Volodymyr Trotsiuk
b
, Ulf Büntgen
l,m,n,o
a
Faculty of Forestry, Technical University in Zvolen, Zvolen, Slovakia
b
Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Czech Republic
c
School of Agriculture, Policy and Development, University of Reading, Reading RG6 6AR, UK
d
Department TeSAF, Università degli Studi di Padova, Padua, Italy
e
Forest Growth and Yield Science, Technical University of Munich (TUM), Freising, Germany
f
National Forest Centre, Forest Research Institute, Zvolen, Slovakia
g
Department of Earth and Environmental Sciences, Università degli Studi di Pavia, Pavia, Italy
h
Biotechnical Faculty, Universityof Ljubljana, Slovenia
i
National Research and Development Institute for Silviculture, Forest Research Station for Norway Spruce Silviculture, Campulung Moldovenesc, Romania
j
INCE - Mountain Economy Center CE-MONT Vatra Dornei, Romania
k
Forest Biometrics Laboratory, Stefan cel MareUniversity of Suceava, Romania
l
Department of Geography, University of Cambridge, CB2 3EN, UK
m
Swiss Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland
n
CzechGlobe, Global Change Research Institute CAS, Brno, Czech Republic
o
Masaryk University, Kotřská 2, 61137 Brno, Czech Republic
HIGHLIGHTS
European r and beech growth acceler-
ated during the last century.
Beech growth declined in northern
Europe since 2000.
Fir growth rates increased over most of
Europe since 1980.
Growth-climate responses were similar
for most tree social classes.
Climate sensitivity of both species was
not affected by forest management.
GRAPHICAL ABSTRACT
abstractarticle info
Article history:
Received 11 August 2017
Received in revised form 9 September 2017
Accepted 10 September 2017
Available online 19 October 2017
Editor: Elena Paoletti
Under predicted climate change, native silver r(Abies alba)andEuropeanbeech(Fagus sylvatica) are the most
likely replacement species for the Norway spruce (Picea abies) monocultures planted across large parts of conti-
nental Europe. Our current understanding of the adaptation potential of r-beech mixed forests to climate
change is limited because long-term responses of the two species to environmental changes have not yet been
comprehensively quantied. We compiled and analysed tree-ring width (TRW) series from 2855 dominant,
co-dominant, sub-dominant and suppressed r and beech trees sampled in 17 managed and unmanaged
mixed beech-r forest sites across Continental Europe, including Bosnia and Herzegovina, Germany, Italy,
Science of the Total Environment 615 (2018) 14601469
Corresponding author at: T.G. Masaryka 24, 960 53 Zvolen, Slovakia.
E-mail address: michal.bosela@tuzvo.sk (M. Bosela).
https://doi.org/10.1016/j.scitotenv.2017.09.092
0048-9697/© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Contents lists available at ScienceDirect
Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv
Romania and Slovakia. Dendroecological techniques that combine various detrending methods were used to in-
vestigate variation in radial growth of co-occurring r and beechtrees. Coincidental with peak SO
2
emissions, the
growth of silver r declined between 1950 and 1980 at most sites, whereas beech growth increased during this
period.Correspondent to a signicant warming trend from 19902010, average beech growth declined, but silver
r growthincreased. Long-term growth patterns andgrowth-climate sensitivityof r and beech trees did not sig-
nicantly differ between managed and unmanaged forests. Multi-decadal changes in the growth rate of all ver-
tical tree classes were similar. In contrast to previous indications of limited drought susceptibility of beech mixed
stands, this study suggests that the mixture of tree species in forest stands does not necessarily prevent growth
depressions inducedby long-term environmental change. Our results further imply thatforest managementdoes
not necessarily alter their sensitivity to environmental changes.
© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords:
Dendroecology
Climate change
Growth sensitivity
Mixed forests
Plantclimate interactions
Tree rings
1. Introduction
Beech (Fagus sylvatica L.) is Europe's most abundant forest species
(Ellenberg, 1996). Naturally distributed across most of continental
Europe, it either grows in pure broad leaved forests or in mixtures
with conifer species. Beech has been increasingly used to convert coni-
fer monocultures to mixed stands, reecting the current transition of
forest management strategies to accommodate non-productive forest
functions and adapt to climate change (Knoke et al., 2008; Tarp et al.,
2000). Silver r(Abies alba Mill.) is a coniferous species native to
Europe, with a geographical distribution similar to that of beech, but
largely limited to the Alpine and the Carpathian arcs. There are indica-
tions that silver r might be more suitable to future European climate
as it grew well under warmer-than-present conditions during the
mid-Holocene (Tinner et al., 2013; Ruosch et al., 2016). Today, mixed
r-beech forests represent an important forest ecosystem forming an
essential part of central and south-eastern European landscapes (EEA,
2006).
Since the mid-19th century or even earlier, a large proportion of
European beech-r forests was converted to conifer monocultures of
Norway spruce (Picea abies L. Karst.) (Spiecker et al., 2004). However,
considerable areas of Norway spruce forests in central Europe suffered
from acid deposition during the second half of the 20th century
(Ulrich, 1995). Today, in many locations it is clear that Norway spruce
is becoming increasingly susceptible to the more frequent summer
droughts induced by climate change (Lévesque et al., 2013; Zang et al.,
2014), as well as the devastating effects of severe windstorms and sub-
sequent bark beetle outbreaks (Hlásny and Turčáni, 2013; Jönsson et al.,
2009). Therefore, the introduction of appropriate replacement species,
such as beech and r, has become a key task (IPCC, 2014).
Despite recent publications describing the growth of silver r and
European beech (Bosela et al., 2016b; Büntgen et al., 2014; Cavin and
Jump, 2016; Dittmar et al., 2003; Gazol et al., 2015; Pretzsch et al.,
2014), relatively little is known about how these species react to envi-
ronmental changes when growing in mixed stands (Vitali et al., 2017).
Recent evidence shows that beech (Bosela et al., 2015), but also rto
some extent (Toïgo et al., 2015), may reach higher stem growth produc-
tivity in mixed stands. There are suggestions that growth sensitivity of
silver r and European beech to summer droughts decreases when
growing in mixed stands (Lebourgeois et al., 2013; Metz et al., 2016;
Vitali et al., 2017), but this has neither been tested nor conrmed
under varying natural conditions across different parts of Europe. A
higher diversity of tree species has been shown to potentially stimulate
radial stem growth by better niche utilisation, but also via improved re-
sistance and resilience at a forest ecosystem level (Gazol et al., 2016;
Jucker et al., 2014; Metz et al., 2016; Paquette and Messier, 2011;
Ruiz-Benito et al., 2014; Vitali et al., 2017). Nevertheless, we still lack
unequivocal evidence supporting the notion that growing in mixed
stands mitigates some of the negative long-term effects of rising tem-
peratures, often associated with increased frequency and/or severity
of droughts. A detailed understanding of the relationship between
diversity and ecosystem productivity and stability is indeed crucial for
advising the policy-forming processes at national and international
levels.
To further complicate the picture, most dendroecological data that
describe growth-climate relationships in European forests originate
from western Europe and tend to consider only dominant and co-
dominant trees (Büntgen et al., 2014; Cavin and Jump, 2016;
Nehrbass-Ahles et al., 2014; Pretzsch et al., 2014). Yet, it is possible
that populations of the same species inhabiting the eastern part of
their distributional range possess different sensitivity levels to environ-
mental factors due to genetic variation (Bosela et al., 2016a).
A Europe-wide investigation of species-specicgrowthdynamicsin
mixed forest stands affected by contrasting environmental factors is so
far lacking. To ll this gap, we compiled a database of tree-ring width
(TRW) samples from managed and unmanaged European mixed
beech-r forests covering most of the regions where these two species
co-occur. Our aim was to test the following hypotheses: (H1) do radial
growth patterns of beech and r in mixed forests vary geographically,
(H2) does tree status within the canopy or (H3) forest management in-
terventions affect long-term variation in annual growth, and nally
(H4) was the growth behaviour of co-occurring beech and rsimilarly
affected by the 19701990 period of heavy pollution and the warming
during recent decades?
2. Material and methods
2.1. Tree-ring sampling
A network of 17 beech-r mixed forest stands located in ve
European countries was used to compile 2855 core samples (Fig. 1).
Taking in Slovakia, Romania, Bosnia & Herzegovina, Italy and
Germany, the network covers a large part of Europe's natural distribu-
tion range of mixed beech-r forests. The sites were allocated to 8 re-
gional groups, reecting differences in post-glacial recolonization from
different forest refugia, but also current climatic conditions (Tables 1
and S1). The followingselection criteria were followed atall sites to en-
sure reasonable comparability of observations: 1) growing conditions
were characterised by mesic soils and mean annual precipitation in ex-
cess of 800 mm year
1
, 2) no forest management interventions were
carried out for at least 30 years prior to sampling, 3) specimens of
both species were present in all four social classes, as described by
Oliver & Larson (1996; dominant, co-dominant, sub-dominant and sup-
pressed), 4) all trees above a registration threshold within a xed-area
plot were marked and then either all or a randomly selected subset
were cored. A single location in Slovakia where managed beech-r
stands are found in close vicinity to unmanaged stands was used to
investigate the impact of forest management on growth-climate
sensitivity.
1461M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
2.2. Tree-ring standardisation
Four standardisation techniques were applied toremove age-related
trends from raw TRW measurements, all aim to preserve the effects of
environmental signals at inter-annual to multi-decadal timescales. The
following detrending methods were used and compared in this study;
a) Modied Exponential Function (MEF, Fritts, 2001). The MEF method
was rst applied to individual tree TRW series, followed by the cal-
culation of ring-width indices (RWI) dened as the ratio between
raw measurements and corresponding MEF function values. Mean
RWI chronologies for each site were calculated as bi-weight robust
means of all individual tree series (Cook and Kairiukstis, 2013)
b) cubic Smoothing Spline with 50% frequency response cut-off at
100 years (SS; Cook, 1985). This setting was used to preserve the
inter-annual to multi-decadal growth uctuations (Büntgen et al.,
2008). The SS standardisation was applied in the same manner as
the MEF approach, the only variation was the use of a different
function.
c) Regional Curve Standardisation (RCS; Briffa and Melvin, 2011). RCS
detrending was applied to individual tree data, but only after the ex-
clusion of all partial-length TRW series where it was not possible to
estimate the number of rings from the beginning of the core to the
pith (Table 1). For example, this includes data series where the be-
ginning of the core was too far from the pith and no ring arc was vis-
ible (Briffa and Melvin, 2011). Raw TRW series were aligned by
cambial age (ring number from bark to pith), followed by mean
TRW calculation for each series. A smoothing spline with a 50% fre-
quency response cut-off at 10% maximum cambial age curve wave-
length (i.e. the Regional Curve (RC)) was then tted to mean TRW
series. RWIs were calculated as ratios between individual series
and the smoothed RC. Individual RWI series were re-aligned by
calendar dates. The nal site chronology was then developed by
using bi-weight robust means.
d) Korf growth function (Korf; Korf, 1939). Multi-decadal growth
changes may be underestimated by common detrending methods
in even-aged forests (Briffa and Melvin, 2011). To counter this ten-
dency we applied a growth function developed by Korf (1939).
Raw TRW series were aligned by age andthe mean curve was calcu-
lated. Then, in contrast to the RCS method, regression parameters of
the Korf function were estimated from the rst 50 years of the mean
curve only. An extrapolation to the full length of the curve was then
carried out, assuming that the rst 50 years indicate both growth
culmination and decline. RWI series at each site were then calculat-
ed as the ratio between raw TRW and estimated Korf's function.
Bi-weight robust mean was used to develop a mean site chronology
as in previous methods, and Korf standardisation was used only on
sites where growth culmination was clearly visible.
Most dendrochronological studies report site chronologies devel-
oped from data describing the dominant trees only (Nehrbass-Ahles
et al., 2014), an approach which may not capture the growth history
of the whole stand. To shed light on this issue, at each site we developed
a mean site chronology for both species from a sample of the 15 largest
trees only (hereafter dominant trees) and compared it to that cover-
ing all measured individuals.
2.3. Growth variability and sensitivity assessments
Growth trends describing several predened periods were
compared to identify effects of known environmental factors. The
predened periods, such as the decades characterised by heavy air
Fig. 1. a) Sampling sites used in the study, with corre sponding Climate Research Unit (CRU) climate data points; b) current distribution of Abies alba and c) current distribution of Fagus sylvatica.
(Source: EUFORGEN).
1462 M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
pollution in Europe (19501990) and the unprecedented climate
warming (19802000, resp. 19902010), were selected on the basis of
published descriptions of major environmental issues and trends
(Bosela et al., 2016a, 2016b; Büntgen et al., 2014; Gazol et al., 2015;
Jump et al., 2006; Linares and Camarero, 2012). Simple linear regression
was used to describe growth trends within selected periods; regression
coefcients denoting the slope were then used to compare tree growth
between the periods and between regional groups of sites. In this com-
parison,we applied generalized additive models using gammfunction
in mgcvR package (Wood, 2011)tolter out inter-annual high
frequency variation and preserve multi-decadal growth trends. The
gammfunction used Generalized Cross Validation (GCV) to estimate
the smoothing parameter. Populations of regression parameters de-
scribing individual site RWI series were assessed for differences be-
tween species, regional groups, time periods and detrending methods
by ANOVA. All populations were tested for normality of distribution
and equality of variance; no conversion of data was necessary.
Bonferroni correction was used in pair-wise comparisons, and differ-
ences were considered signicant at p b0.05.
Monthly temperature means, precipitation totals and drought indi-
ces (scPDSI self-calibrated Palmer Drought Severity Index) were ob-
tained from gridded CRU TS 3.10 database (http://www.cru.uea.ac.uk/
data/) via Climate Explorer (http://climexp.knmi.nl/)(Dai, 2011;
Harris et al., 2014; Mitchell and Jones, 2005). Data from half-degree
lat/lon grid points nearest to each study site were used to analyse the re-
lationship betweengrowth of both species and climate variation at each
site (Fig. 1). Radial growth responses to climate (standardised mean
chronologies) were quantied by Pearson's correlation coefcients
computed over 31-yr moving window segments to investigate tempo-
ral changes in the climate-growth relationships (Büntgen et al., 2010;
Wilson and Elling, 2004). Bootstrapping was applied to calculate 95%
condence intervals of the correlation coefcients using the bootRes
R package (Zang and Biondi, 2013). The signicance of the correlation
was then tested using 95% percentile range method (Dixon, 2002).
Correlation coefcients describing the relationship between site
chronologies and climate variables were analysed by principal compo-
nent analysis (PCA). PCA was performed with the hclustfunction in
the R Stats package (R Development Core Team, 2008). The distance
matrix was computed using the Euclidian measure. The dendextent
package (Galili, 2015) was used to visualise PCA results. Ward Hierar-
chical Clustering was used to interpret growth trend responses to cli-
mate. Findings from the Ward clustering were then compared with
PCA grouping in a 2-dimmensional space.
3. Results
Regional growth trends identied by the four detrending methods
applied in this study show a wide variation of growth between sites,
species and time periods across Europe (Fig. 2), yet a certain amount
of generalisation is possible (Table 2). Beech growth accelerated be-
tween the 1950s and 1980s in the more northernforests, loosely de-
ned as those above 47°N parallel. Growth acceleration in the north
was followed by a slow decline in annual ring width, with the exception
of the Bavarian forest where beech growth accelerated continuously
since about the 1940s (Fig. 2,Table 2).
At the southernsites, mid-century acceleration has slowed down or
even decreased. At the Cansiglio site in northern Italy, we observed the
earliest onset of this decline starting in the 1950s. While forming the
same forest stands in a mixture with beech, r has shown very different
growth patterns during the last century (H1). A decline of r growth
rate was observed between the1950s and 1980s in most locations
apart from the populations in the southern Carpathians, which
Table 1
Brief description of site location, total number of tree-ring width series used per site (N1) and the number of tree-ring width series that intercepted the pith or were sufciently close to
estimatethe number of ringsto the ptith (N2). Timespan is the minimumand maximum calendaryear of the site chronology. B&Hdenotes Bosnia andHerzegovina, Altdenotes altitudein
m a.s.l.
Country Species Locality (abr.) N1 N2 Time span Mountain range Long Lat Alt
B & H Abies Lom 158 158 15832005 Western Dinaric Mts 16.47 44.45 1350
B & H Fagus (bh_lom) 440 440 16252005
B & H Abies Perucica b1 44 43 17862006 Eastern Dinaric Mts 18.71 43.3 1200
B & H Fagus (bh_perb1) 81 75 15952006
B & H Abies Perucica b2 76 69 16632007
B & H Fagus (bh_perb2) 70 63 15092007
B & H Abies Perucica f1 118 109 16862006
B & H Fagus (bh_perf1) 35 27 16142006
B & H Abies Perucica f2 82 71 17022007
B & H Fagus (bh_perf2) 64 60 17032007
Germany Abies Bodenmais 28 18201995 Bavarian Forest 13.1 49.09 800
Germany Fagus (de) 21 18211995
Italy Abies Cansiglio 140 140 19312012 Southern Alps 12.42 46.1 1100
Italy Fagus (it) 205 184 18562012
Romania Abies Botiza 54 25 17742013 Eastern Carpathians 24.09 47.61 1050
Romania Fagus (ro_bo) 67 23 16142013
Romania Abies Sinca 281 184 16652013 Southern Carpathians 25.17 45.67 1140
Romania Fagus (ro_si) 163 101 15562013
Slovakia Abies Polana 22 22 18602010 Western Carpathians 19.57 48.62 760
Slovakia Fagus (sk_p) 58 58 18672010
Slovakia Abies Spis S1 20 20 18962010 20.73 48.77 760
Slovakia Fagus (sk_s1) 19 19 18812010
Slovakia Abies Spis S2 36 36 17942010 20.73 48.77 760
Slovakia Fagus (sk_s2) 33 33 18112010
Slovakia Abies Spis S3 59 59 18202011 20.67 48.79 760
Slovakia Fagus (sk_s3) 14 14 18212011
Slovakia Abies Spis S4 24 24 18482010 20.72 48.76 830
Slovakia Fagus (sk_s4) 26 26 18982010
Slovakia Abies OBR 25 21 18052013 Western Carpathians 19.47 48.88 887
Slovakia Fagus (sk_obr) 146 120 17402014
Slovakia Abies SRA 57 57 17832013 19.11 49.19 1048
Slovakia Fagus (sk_sra) 133 133 17172013
Slovakia Abies SUT 29 28 18142013 19.09 49.18 1029
Slovakia Fagus (sk_sut) 27 24 17612013
1463M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
exhibited a slight acceleration of growth during this period (Fig. 2). This
period of r decline was followed by a rapid acceleration of growth in
the north, and a steep decline in the south, again with the exception
of the southern Carpathians.
A comparison of growth trends created from dominant trees only or
all trees above a DBH threshold (H2) did not show any effect of canopy
position (Fig. S5). Regression parameters denoting the slope of the t
were not affected by tree social status in any of the time periods
under consideration, nor for beech (p = 0.128 to 0.516) or r(p=
0.336 to 0.990). Similarly, we did not nd any difference in annual
growth between managed stands and old-growth unmanaged forests
in the western Carpathians when comparing mean RWI growth trends
within each of the time periods under consideration (H3, p = 0.063 to
0.441), indicating that factors other than forest management affect
long-term growth trends in beech and r. We made use of the pre-
dened periods of environmental stress to explore whether beech and
r respond differentially to acid deposition (19501980) and accelerat-
ing climate change (19902010). We found a strong interaction be-
tween species and time period (H4; p b0.001) when comparing mean
growth rates in these two periods. Considering all sites used in this
study (Fig. 3a), rRWIy
1
was smaller than thatof beech in the period
19501980 but the growth trends of these two species reversed by
19902010. An interesting observation emerged when considering the
more northern and southern sites separately; the relationship between
Fig. 2. Mean ring-width index (RWI) chronologies of silver r and European beech after modied exponential (exp) and Regional Curve Standardisation (RCS) techniques for aggregate
sites (west_carp_man: managed stands in western Carpathians, west_carp_unm unmanaged forests in western Carpathians, east_carp: eastern Carpathians, south_carp: southern
Carpathians, east_dinaric:eastern Dinaric,west_dinaric,south_alps: southernAlps, BavarianForest). Generalized Additive Model (GAM)was applied to lter outthe inter-annual variation
and preserve multi-decadal changes. The shaded bands denote 95% condence intervals.
Table 2
A comparison of detrending methodsapplied to tree-ringwidth data describing radialgrowth of Europeanbeech (Fagus sylvatica) and Silverr(Abies alba)intwotime
periods characterisedby different environmental conditions. Linear regressionwas tted to data detrended by Modied exponential function(MEF), smoothing spline
(SS), regional curvestandardisation (RCS) andKorf growth function(Korf). Colouredcell backgrounds denotea negative regression trend.Stars denote signicance level
of regression tat:***-b0.001, ** - b0.01, * - b0.05. Empty cells represent a non-signicant t, and a dash is used in cases where regression was not possible to t.
European beech Silver fir
MEF SS RCS Korf MEF SS RCS Korf
Locality
1950-80
1990-10
1950-80
1990-10
1950-80
1990-10
1950-80
1990-10
1950-80
1990-10
1950-80
1990-10
1950-80
1990-10
1950-80
1990-10
de *** - - - - - - *-*** - - - - -
sk_p *** ** *** *** *** *** ** * *** ***
sk_s1 ** ** * **** *** *** *** ** *** ***
sk_s2 *** *** *** *** *** *** *** *** *** *** *** *** *** ** ***
sk_s3 *** *** * *** *** * *** *** *** *** *** ***
sk_s4 *** ** ** ** *** *** *** *** *** *** ***
sk_obr *** ** ** *** ** *** *** ***
sk_sra *** * *** - - ** *** *** *** ** *** ** ***
sk_sut * ***** - - *** *** *** *** ** *** *** ***
ro_bo * ** - - *** *** *** *** ***
ro_si * ** * * *** ****** ** ** **
1464 M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
environmental factors and the rate of radial growth was not affected by
species in thesouth (p = 0.359; Fig. 3c), but there was a strong effect in
the north (p b0.001, Fig. 3b). There was no difference between
the trends identied by the four standardisation methods in 195080
(p = 0.249) and only the Korf standardisation method differed from
the other three in 19902010 (p = 0.004).
Differential response of r and beech growth to environmental
change was conrmed by a PCA testing as well as by a cluster analysis
for the strength of relationship between previous- and current-year
temperature, precipitation and PDSI and tree growth (Fig. 4). Fir growth
at the southern sites was mainly inuenced by drought (scPDSI),
whereas temperature was the most dominant driver of tree ring
width at the northern sites. There was considerable variation between
individual sites in observed effects of climate on r and beech growth,
however a very similar grouping of tree populations and sites was
achieved by cluster analysis (Fig. 5).
In a further attempt to contrast the growth behaviour of the
two species within the sampled range of sites, we calculated correlation
coefcients between RWI and current-year summer temperature and
drought over the century-long time period (Fig. 6). Fig. S6 shows a
large temporal variation of correlation coefcients over the past centu-
ry. On average, a negative correlation between RWI and drought domi-
nates in the south, while a positive correlation with temperature is
present in the north.
4. Discussion
4.1. European beech
Published literature describing the dendroecology of European
beech at European and regional scales does not paint a clear picture;
there is evidence of (i) either increased or decreased growth rates of
beech in the last two decades in Central Europe (Dittmar et al., 2003;
Pretzsch et al., 2014), and (ii) either increased or decreased radial
growth of beech at the southern edge of distribution (Jump et al.,
2006; Tegel et al., 2014). Our study conrms that beech growth rates
have increased during the period between 1950 and 1980 across
Europe, an observation which is in line with published measurements
(Bosela et al., 2016b; Hlásny et al., 2011; Pretzsch et al., 2014)and
model simulations (Hlásny et al., 2011). However, our results contradict
those of Dittmar et al. (2003), who in a Europe-wide study found no de-
tectable increase of beech growth in Europe, but documented a decline
of the rate of growth at high altitudes in central Europe. Interestingly,
the authors found that high summer temperatures favoured radial
growth at the expense of vertical growth. Existing studies and observa-
tions presented in this paper suggest a positive effect of increasing sum-
mer temperature at higher latitudes or altitudes on beechgrowth. Thus,
given the summer period warming observed in the last century
(Büntgen et al., 2011; Luterbacher, 2004) and predicted warming across
Europe (IPCC), it seems reasonable to expect further acceleration of
beech growth at the northern edge of its distribution. A recent
Europe-wide study documents an increased basal area increment in
the last decades in beech forests in temperate and continental core re-
gions of the species distribution range (Cavin and Jump, 2016). Our
study adds evidence suggesting that the growth decline in the southern
localities started in mid-20th century and continues until today. How-
ever, a recent increase in beech radial increments in some Mediterra-
nean beech-rforests(
Tegel et al., 2014) suggests strong regional
differences, probably related to regional climate or site productivity
(Aertsenet al., 2014; Bosela et al., 2016b), which limit any broad extrap-
olation of our results.
Hacket-Pain et al. (2016) found no clear spatial pattern in the
drought sensitivity of European beech, indicating that the populations
from the southern and northern range edges respond to summer
drought equally. In contrast, we found a strong spatial pattern in the
growth responses to summer temperature and to drought. While radial
growth of the species generally did not respond to summer drought in
central Europe (Germany, Slovakia and Romania), it became highly re-
sponsive in the Balkan Peninsula (Bosnia & Herzegovina, except for
the Lom site). Our study thus supports existing observations showing
that some southern European beech populations are increasingly suffer-
ing from summer drought (Linares and Camarero, 2012; Piovesan et al.,
2008). Not only can we conrm the same trends, but we are also able to
pinpoint the onset and the severity of the decline allowing for investiga-
tion of site-specic reasons for growth modication. For example,
unlike beech trees in Perucica, which were sensitive to drought, the
population in the Lom site in the same climatic zone was non-
responsive to sc-PDSI. Trees at the Lom site were substantially younger
than those at Perucica (Fig. S1), growth plasticity of a younger popula-
tion of beech might thus explain the difference as outlined by the
age-related climate response hypothesis (Carrer and Urbinati, 2004;
Primicia et al., 2015).
4.2. Silver r
Silver r experienced a severe growth decline in Europe during
19701990, driven by sulphur dioxide emissions (Büntgen et al.,
2014), an event often referred to as Europe-wide r dieback (Cramer,
1984; Larsen, 1986; Meyer, 1957). Our study provides tree-ring width
evidence of this event; however, it is not possible to exclude the possi-
bility that lower summer temperatures during this period might have
contributed to the growth depression (Fig.S2). In contrast to other stud-
ies, our investigation shows that the growth of silver r did not decline
in the eastern part of its distribution range during this period (southern
Carpathians and partly eastern Dinaric Mts.). It has been suggested that
the greater genetic diversity of the Balkan populations helps the species
mitigate effects of changing environmental conditions (Bosela et al.,
2016a), and this study supports that suggestion. Increased genetic di-
versity, but also a greater functional diversity of forest stands where it
occurs, have been shown to increase the capacity of silver r to tolerate
drought (Gazol et al., 2016). The latter relationship is indicative of the
need to understand the implications of ecosystem diversity for species
performance and production stability.
Fig. 3. Linear regression trends of silver r and European beech ring-width indices (RWI)
in two distincttime periods of acid deposition (19501980) and climate warming (1990
2010). Dots indicate average RWI change per annum representing the whole range of
stands considered in this study (A) or in two sub-sets according to geographical location
(B and C). Error bars denote standard deviation.
1465M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
Followingthe period of growth decline, silver r experienced a rapid
recovery reaching unprecedented levels across most of its distributional
range, coincidental with successful pan-European effort to limit acid de-
position. Even at the Cansiglio site (Italy) characterised by warm and
dry conditions, the growth pattern almost exactly followed that seen
in Slovakia until around 19952000, when at Cansiglio it turned to an-
other decline. This nding brings a new angle to a recent Europe-wide
study of silver r growth throughout the Holocene. Büntgen et al.
(2014) showed an increasing radial increment of r trees growing in
Italian Alps and Apennines until 2000, but did not indicate growth
trends after that year. Our observations from the Cansiglio site indicate
that r populations in the southern parts of the Alps may have recently
experienced a drought-stress related growth decline (Fig. 6a).
4.3. Long-term patterns of radial growth
For the rst time, to our knowledge, this study compares growth
pattern response to climate between managed and unmanaged forests.
We were able to make this comparison only for a series of sites in the
western Carpathians, however a pattern typical for many other sites
where these two species co-exist emerges. There was no discernible dif-
ference between tree growth in managed and unmanaged forests, but
beech RWIs were positive during 19501980 while those of r were
negative. By 19902010, the pattern reversed; RWIs describing r
growth were positive as the species recovered both in managed and un-
managed forests, but those depicting beech growth declined to negative
values. Again, this observation underlines the effect of long-term
Fig. 4. Principal componentanalysis (PCA) of growth-climate responses of silverr and European beech across Europe: a) dissimilarities between the study localities and species and in-
dication of northern and southern sites in the ordination space; b) ordination of contributing climate variables. The matrix of the correlation coefcients between site chronologies (pro-
duced by smoothing spline with 70% cut-off at 10-year segments) and climate variables (temperature, precipitation and sc-Palmer Drought Index) was used as an input to the PCA.
Abbreviations in labels: bh Bosnia & Herzegovina, it Italy, ro Romania, sk Slovakia, per Perucica; a silver randbEuropean beech; temp monthly temperature, ptemp
monthly temperature in the previous year, prec monthly precipitation, pprec monthly precipitation in the previous year, pdsi sc-Palmer drought index, ppdsi monthly sc-Palmer
drought index in the previous year.
Fig. 5. Dissimilaritiesin climate responses of silver r and European beech across Europeansites using hierarchical clustering. The analysis showsa differentiation between northern (red
and dashed-line rectangle) andsouthern (blueand solid-line rectangle) populationsof r and beech. The southernsites that were clusteredwithin the northerncluster are highlighted by a
blue rectangle around the labels. Abbreviations in the x-axislabel: bh Bosnia & Herzegovina, it Italy, ro Romania, sk Slovakia, per Perucica; a silver randbEuropean beech.
1466 M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
environmental conditions on tree-ring width, which seems to override
even the effect of forest management designed to stimulate bole wood
productivity.
While our observations of European beech show a wide variation of
growth patterns driven by severalfactors, the resultsfor European silver
r are quite consistent. A number of recent studies provides evidence
that diversity, whether species or functional, has a positive effect on
tree growth (Toïgo et al., 2015; Zhang et al., 2012). Higher diversity is
also believed to mitigate the negative impacts of extreme climate events
through higher growth resistance and resilience (e.g. Jucker et al., 2014;
Gazol et al., 2016; Metz et al., 2016). Although our study cannot directly
estimate the benets of growing ina diverse stand, theresults clearly in-
dicate that growing in a mixture does not shield the two species from
impacts of long-term changes in environmental conditions. For exam-
ple, we show that beech growth has been declining over the last two de-
cades in both managed and unmanaged forests and across a range of
conditions in Europe, regardless of the species composition and forest
structure. The same holds true for r's unusual radial increment pat-
terns, whereby long-term changes of environmental conditions seem
to prevailover local ecology.In this context, anycalculation of resistance
and resilience indices based on RWI must take into account multi-
decadal trends as these form the backgroundagainst which tree
growth must be considered.
5. Conclusions
Our study shows that state-of-the-art dendroecologicial techniques
can unravel complex environmental factors that inuence species-
specic tree growth trends. Although growing under the same condi-
tions, European beech and silver r exhibited remarkably different
growth patterns over the last half a century. While r responded posi-
tively to the recent warming, beech growth has declined across our
range of sites, suggesting that r is less susceptible to warmer and
drier conditions than beech. A comparison of growth patterns between
managed and unmanaged mixed beech-r forests revealed that the
long-term growth patterns were the same, suggesting only a limited
scope for tree growth stimulation by active forest management. There
is some support for the use of mixed forests as an adaptation strategy
to climate change. We show that a higher tree species diversity might
help mitigate the effects of short-term climatic events such as drought
and acidication, but may not prevent mixed forests from the long-
term consequences of climate change. Thus, any effort to convert
Norway spruce monocultures to preserve long-term growth at the for-
est ecosystem level should consider a purposeful decision to utilise
both beech and r as replacement species. Further scienticeffort
should be directed towards investigating effects of various management
interventions designed to aid the adaptation of beech-r ecosystems to
future climate change.
Acknowledgements
The work was fully supported by the Slovak Research and Develop-
ment Agency (SRDA) under the contract no. APVV-15-0265. BK was also
supported by the SRDA under the contract no. APVV-14-0086. MS and
VT were supported by the projects CIGA no. 20154316 and COST CZ
LD14074 (The Ministry of Education, Youth and Sports of the Czech
Republic). UB received funding from the Ministry of Education, Youth
and Sports of Czech Republic within the National Sustainability Program
I (NPU I; grant number LO1415).
Authors' contributions
MB conceived the ideasand MB, ML, DC and RS designed methodol-
ogy. MB andML analysed data. MB, ML and UB wrote the manuscript. All
Fig. 6. Correlation between the sitering-width index(RWI) chronologies and meantemperature (a)and sc-Palmer Drought Index(PDSI) (b) duringthe period of Juneto August in silverr
(green dashed lines) and European beech (red solid lines) in different localities across Europe (west_carp_man: managed stands in western Carpathians, west_carp_unm unmanaged
forests in western Carpathians, east_carp: easternCarpathians, south_carp: southern Carpathians, east_dinaric: eastern Dinaric,west_dinaric, south_alps: southern Alps, Bavarian Forest).
RWI were obtained after detrending by modied negative exponential function; bootstrapped correlation was computed over the whole period of about 110 years; values shown repre-
sent mean and 95% condence intervals.
1467M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
authors collected data, contributed critically to the drafts and gave nal
approval for publication.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.scitotenv.2017.09.092.
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1469M. Bosela et al. / Science of the Total Environment 615 (2018) 14601469
... At lower altitudinal belts, conifers coexist with beech. Beech and conifer mixed forests are more successful than pure beech stands [25,26], but Norway spruce grows more and remains relatively unaffected compared to F. sylvatica during drought [106][107][108]. A. alba is also less susceptible to warmer and drier conditions than F. sylvatica [25]. ...
... Beech and conifer mixed forests are more successful than pure beech stands [25,26], but Norway spruce grows more and remains relatively unaffected compared to F. sylvatica during drought [106][107][108]. A. alba is also less susceptible to warmer and drier conditions than F. sylvatica [25]. Thus, at the stand level, the association between F. sylvatica and A. alba is not only advantageous for enduring drought [25,26,106,107] but also for sunlight use [104,109]. ...
... A. alba is also less susceptible to warmer and drier conditions than F. sylvatica [25]. Thus, at the stand level, the association between F. sylvatica and A. alba is not only advantageous for enduring drought [25,26,106,107] but also for sunlight use [104,109]. Our results for the Southern Carpathians suggest that climate change will contribute to A. alba encroachment in F. sylvatica pure forest stands. ...
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The structure and functioning of temperate forests are shifting due to changes in climate. Foreseeing the trajectory of such changes is critical to implementing adequate management practices and defining long-term strategies. This study investigated future shifts in temperate forest species composition and abundance expected to occur due to climate change. It also identified the ecological mechanisms underpinning such changes. Using an altitudinal gradient in the Romanian Carpathian temperate forests encompassing several vegetation types, we explored forest change using the Landis-II landscape model coupled with the PnET ecophysiological process model. We specifically assessed the change in biomass, forest production, species composition and natural disturbance impacts under three climate change scenarios, namely, RCP 2.6, 4.5 and 8.5. The results show that, over the short term (15 years), biomass across all forest types in the altitudinal gradient will increase, and species composition will remain unaltered. In contrast, over the medium and long terms (after 2040), changes in species composition will accelerate, with some species spreading (e.g., Abies alba Mill.) and others declining (e.g., Fagus sylvatica L.), particularly under the most extreme climate change scenario. Some forest types (e.g., Picea abies (L.) karst forests) in the Southern Carpathians will notably increase their standing biomass due to climate change, compared to other types, such as Quercus forests. Our findings suggest that climate change will alter the forest composition and species abundance, with some forests being particularly vulnerable to climate change, e.g., F. sylvatica forests. As far as productivity and forest composition changes are concerned, management practices should accommodate the new conditions in order to mitigate climate change impacts.
... The climate sensitivity analysis demonstrates that all five species studied in the south-east European beech-oak ecotone are primarily limited by climatic aridity and high temperatures in the summer months, while water availability and temperature in spring are of lower importance (question 1). These results comply with findings for temperate beech and oak forests of Central, Southern and Eastern Europe (Berki et al., 2009;Bose et al., 2021;Bosela et al., 2018;Dittmar et al., 2003;Grace et al., 2002;Jump et al., 2006;Mäkinen et al., 2002;Petritan et al., 2021;Scharnweber et al., 2011;Takahashi et al., 2001) All species showed a long-term BAI increase from the 1950s to the late 1970s, which presumably reflects a release phase in the stand development cycle, when the young trees left the pole-wood phase with intense competition prior to 1960 and approached maturity. According Table 3 (a) Mean (SD) basal area increment (BAI in cm 2 yr − 1 ) of the five species (and two site types of beech) in the time intervals 1960-1979, 1980-1999 and 2000-2017 averaged over all three transects. ...
... Indeed, inter-annual MSP fluctuation, together with SWB variation, was in all species the most influential climatic factor driving the BAI variation, even in the absence of precipitation trends and also when controlling for age in the models. In agreement with our findings, various dendrochronological studies in southern and south-eastern Europe, but also in Central Europe, have demonstrated long-term growth declines in beech in recent time, which coincide with the warming trend and often an increased drought frequency in summer (Jump et al., 2006, Scharnweber et al., 2011, Knutzen et al., 2017, Bosela et al., 2018. ...
... In southern and south-eastern Europe, where beech occurs close to its drought and heat limit, negative growth trends prevailed in beech stands at lower elevation at the mountain foot (Bosela et al., 2018;Jump et al., 2006;Peñuelas et al., 2008;Piovesan et al., 2008;Serra-Maluquer et al., 2019), while stable or positive growth trends have been found at higher elevation (Hacket-Pain and Friend, 2017;Tegel et al., 2014). Our coring across the beech-oak ecotone and in isolated rear-edge beech populations at the mountain foot in western Romania close to the species' distribution limit demonstrates that mean BAI is lower and negative growth trends are more pronounced in the by ~1.5 • C warmer lowelevation xeric F. sylvatica stands as compared to the higher and somewhat cooler mesic beech stands (question 2). ...
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Global warming and increasing drought severity are exposing temperate forests to increasing stress, challenging silvicultural decision making. Growth analyses in marginal tree populations at drought-induced range limits may provide valuable information on tree species’ adaptive potentials and species-specific climate turning points. We studied the climate sensitivity and resilience to drought of radial growth, and long-term growth trends of mesic and rear-edge populations of Fagus sylvatica in comparison to three oak species (Quercus petraea, Q. frainetto, Q. cerris) and Tilia tomentosa in natural ecotones from mesic beech to xeric oak forests along three elevation transects in western Romania. Radial growth of all species was positively influenced by summer precipitation and low drought intensity, and negatively by high summer temperatures. The basal area increment (BAI) of F. sylvatica and T. tomentosa has declined in the last 10–20 years with warming and a deterioration of the summer water balance, while the three Quercus species maintained stable growth rates, though at lower BAI levels, suggesting a negative relationship between mean BAI and drought resistance among the five species. Growth reductions during three severe drought events (2000, 2003, 2012) were stronger, and growth resilience lower, in F. sylvatica and T. tomentosa than in the Quercus species, pointing at a thermal limit of beech at June–August temperatures of 20–21 °C. As the climate of the studied ecotones is similar to the predicted climate at colline/submontane elevation in Central Europe in about 50 years, a decline in beech growth and vitality is likely also in drought-affected regions in the distribution centre with future warming. Our results demonstrate that choosing stress-tolerant Q. petraea (as well as Q. frainetto and Q. cerris) instead of more productive timber species is a relatively safe option for Central European forestry in a warmer climate.
... For the assessment of the forest ecosystems state, most researchers use dendrochronological and dendroclimatic methods based on the study of the radial increment of individual trees and forest stands (Schweingruber 1996, Hughes 2002, Matveev 2003, Speer 2009, Sheppard 2010. Radial increment is the most universal and comprehensive measure of forest growth throughout its life span, and therefore provides an opportunity to identify their reactions to the impact of external factors (Mölder and Leuschner 2014, Augustaitis et al. 2015, Remeš et al. 2015, Bosela et al. 2018, Šimůnek et al. 2019. The studying of radial increment dynamics of the mountain beech forests which grow in climate change conditions (Mazepa and Shyshkanynets 2013) is important to assess condition and productivity of stands and develop their predictive models. ...
... Annual growth of beech is most significantly influenced by the climate and atmospheric air pollution. Correspondent to a significant warming trend from 1990-2010, average beech growth declined in the mixed beech-fir forest sites across Continental Europe, including Bosnia and Herzegovina, Germany, Italy, Romania and Slovakia (Bosela et al. 2018). The studies of Augustaitis et al. (2015) showed that frost in winter months and heat in June, along with drought in the vegetation period, limited beech tree growth outside its natural distribution range in northeast Europe (Poland, Lithuania and Latvia). ...
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The objects of the study were pure and mixed middle-aged beech stands that grow on humid fertile hornbeam-beech forest type conditions on the southern and northern slopes at the altitude of 550–600 m a.s.l. We found a correlative relationship between beech radial increment and climate indices. Average radial increment of beech varies within the limits of 1.71 to 2.41 mm depending on tree composition with the maximum in the mixed stands. The share of early wood and late wood of the annual ring of beech fluctuates within the limits of 83–88 % and 12–17 %, respectively. In the mixed stands that grow on the northern slopes, annual radial increment of beech is maximal. In the mixed and pure forest stands average radial increment of beech on the northern side of the slope compared to the southern side is higher. It has been found that radial increment of the south-facing side of beech trees growing on the southern mountain slope and the north-facing side of them growing on the northern mountain slope is higher in comparison to the opposite side of the trees. Radial increment extremes in many cases are identical with climate in�dices extremes. In the years of the most intensive solar activity beech radial increment is minimal. Relationship between beech increment and climate indices is stronger in the pure beech stands than it is in the mixed stands. Relationship between beech increment and air temperature as well as precipitation becomes weak in the mixed stands and it is moderate in the pure stands. Beech increment correlates greatly with humidity deficiency, air temperature and precipitation, which is especially marked during the period from 2003 to 2013. Beech wood radial increment correlates closely with air humidity and humidity deficiency both in the pure and in the mixed stands
... Dendroecological studies highlighting an increase in the average annual ring width of silver fir during the warming period from 1990 to 2010 confirmed the adaptation of the species to higher temperatures (Büntgen et al. 2014;Bošeľa et al. 2018), suggesting a higher than expected drought tolerance (e.g., Vitali et al. 2017). Other studies, in contrast, suggested sensitivity to Mediterranean summer droughts (Gazol et al. 2015). ...
... A generalized increase in summer drought frequency and intensity as revealed by the SPEI values of the last 20 years in Varramista caused a TRW reduction starting at the beginning of the present century. This is in line with what is reported at the European scale (Bošeľa et al. 2018;EEA 2017;Gazol et al. 2016). In this context, Lebourgeois et al. (2010) emphasized the importance of soil water holding capacity for buffering the negative consequences of increasing summer drought intensities and frequencies for silver fir stands at low elevation. ...
Article
The potential ecological envelope of silver fir (Abies alba Mill.) based on its present distribution suggests a high suitability for moist rather than warm and dry environments. This contrasts with paleoecological evidence reporting its former presence at low elevations under meso-Mediterranean conditions. In this study, we evaluated the growth performance of silver fir at low elevation (20-60 m a.s.l.) under meso-Mediterranean climatic conditions in Tuscany (central Italy). We conducted a dendroecological analysis on Abies alba trees along a geomorphological gradient (from depression to upper slope conditions). Climate-growth relationships were assessed by means of correlations, response functions, pointer years, and superposed epoch analysis. Silver fir was found to grow and regenerate well in these stands mixed with evergreen (e.g., Quercus ilex L.) and thermophilous deciduous Mediterranean tree species (e.g., Q. cerris L.). Summer drought was the most growth-influencing factor, with immediate (i.e., current season) negative impacts on tree-ring widths (TRW). No significant impacts were observed in the four years following extreme summer droughts, but the TRW series (which started between the 1930s and 1950s) showed a growth decline since the mid-1990s that is likely drought-related. Our results show that, provided there is a sufficiently large soil water holding capacity, silver fir provenances exist which are able to withstand Mediterranean summer droughts, can naturally and regularly regenerate in these systems, and may even dominate over typical meso-Mediterranean species. As long as annual precipitation is not too low (i.e., >850 mm) and summer drought conditions not too extreme (i.e., less than three months), silver fir has thus the potential to thrive under warm Mediterranean conditions.
... Specifically, the current warming trend may accelerate the cambial growth of beech at its latitudinal and elevational limits. High summer temperatures promote the radial growth of beech, suggesting a positive effect of increasing mean summer temperature at higher latitudes or elevations on the cambial activity of beech (Bosela et al., 2018). Conversely, southern European beech populations are increasingly suffering from summer drought (Piovesan et al., 2008;Linares and Camarero, 2012), which may trigger episodes of increased tree mortality (Bolte et al., 2016;Cocozza et al., 2016). ...
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European beech (Fagus sylvatica L.) is a widespread and economically important temperate tree species in Europe. The warmer temperatures and severe drought events expected in the future, especially in Mediterranean areas, could affect the vitality and productivity of beech stands that have been intensively used in these areas in the past. Here, we aim to assess the wood anatomical responses of beech to environmental variability and silvicultural practices by investigating three beech stands along an elevational gradient (1,200 to 1,950 m a.s.l.) in the Apennines (Italy). Therefore, we quantified several anatomical traits of the xylem vessels related to tree hydraulics from five trees per stand and investigated variability between and within tree rings. Our results suggest generally limited trait plasticity, with higher plasticity of mean vessel lumen area and theoretical hydraulic conductivity, while maximum vessel size and mean hydraulic diameter were less plastic, likely because of the stronger determination by tree height. High-elevation trees were hydraulically more limited than trees at a mid and lower elevation as indicated by the more conservative anatomical configuration, i.e., comparatively smaller vessels and a 50% tighter trait coordination. Cessation of coppicing resulted in a hydraulically safer anatomy with comparatively smaller vessels at the most intensively used site (1,200 m), triggered by increased water demand due to an increase in canopy density, and thus, an increase in stand transpiration. Furthermore, maximum vessel size at the beginning showed different climate sensitivity compared to the rest of the tree ring, while intra-ring anatomical profiles showed little difference between normal and the 5 years with the highest and lowest mean temperature and precipitation. Overall, this study highlights the challenges to separate the externally induced medium-to longer-term responses from ontogenetically determined patterns.
... The finding that the growth of silver fir dropped less and recovered faster than the growth of Norway spruce in drought years means that the vitality changed in favour of silver fir in the last decades. Consequently, in the very widespread mixed-species stands of Norway spruce, silver fir and European beech in European mountain regions, silver fir gained in competitive strength and productivity compared to the other species (Pretzsch et al. 2015;Bosela et al. 2018;Hilmers et al. 2019). ...
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In this chapter, we review the current long-term growth trends and short-term growth reaction to single or repeated stress events on tree and stand level in Europe. Based on growth trend analyses, the chapter reveals the strong human footprint on forest ecosystems. First, we use long-term experiments and increment cores to show change in growth trends within the last centuries. Growth reactions are caused by deposition and climate change rather than by silvicultural measures. Second, we look closer on regional-specific deviations from the general trend. Climate change, drought events, acid rain and O 3 are causing regional-specific growth reaction patterns. Third, we assess stress events and the resilience and resistance of monospecific and mixed stands against biotic and abiotic stress in view of the ongoing growth trends. The revealed tree and stand growth behaviours are highly relevant, as any changes of forest growth and structure have strong impacts on the provision of goods and ecosystem services. The results underline the importance of biomonitoring and suggest counteracting measures by forest planning, adaptation of silvicultural guidelines for existing forest and innovative design of future forests stands.
... On a European scale, the increased growth of forest ecosystems has been evident since the 1970s, often attributed to rising temperatures combined with increased nitrogen deposition and increasing CO2 in the atmosphere [22,108]. On the other hand, other researchers have shown a decrease in growth [109,110]. From our results, the increase in growth was evident in Norway spruce (46.1%) and European beech (20.6%) in the last 20 years, but was not demonstrated in mountain elm (0.1%), sycamore maple (−12.5%), and European ash (−14.9%), which grow prevailingly in the most extreme conditions of shallow grounded rubble (with the largest skeletality and the shallowest soil profile). ...
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Scree forests with large numbers of protected plants and wildlife are seriously threatened by climate change due to more frequent drought episodes, which cause challenges for very stony, shallow soils. The effect of environmental factors on the radial growth of five tree species—European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst.), sycamore maple (Acer pseudoplatanus L.), European ash (Fraxinus excelsior L.), and mountain elm (Ulmus glabra Huds.)—was studied in the mixed stands (105–157 years) in the western Krkonoše Mountains (Czech Republic) concerning climate change. These are communities of maple to fir beechwoods (association Aceri-Fagetum sylvaticae and Luzulo-Abietetum albae) on ranker soils at the altitude 590–700 m a.s.l. Production, structure, and biodiversity were evaluated in seven permanent research plots and the relationships of the radial growth (150 cores) to climatic parameters (precipitation, temperature, and extreme conditions) and air pollution (SO2, NOX, ozone exposure). The stand volume reached 557–814 m3 ha–1 with high production potential of spruce and ash. The radial growth of beech and spruce growing in relatively favorable habitat conditions (deeper soil profile and less skeletal soils) has increased by 16.6%–46.1% in the last 20 years. By contrast, for sycamore and ash growing in more extreme soil conditions, the radial growth decreased by 12.5%–14.6%. However, growth variability increased (12.7%–29.5%) for all tree species, as did the occurrence of negative pointer years (extremely low radial growth) in the last two decades. The most sensitive tree species to climate and air pollution were spruce and beech compared to the resilience of sycamore and ash. Spectral analysis recorded the largest cyclical fluctuations (especially the 12-year solar cycle) in spruce, while ash did not show any significant cycle processes. The limiting factors of growth were droughts with high temperatures in the vegetation period for spruce and late frosts for beech. According to the degree of extreme habitat conditions, individual tree species thus respond appropriately to advancing climate change, especially to an increase in the mean temperature (by 2.1 °C), unevenness in precipitation, and occurrence of extreme climate events in the last 60 years.
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Drought-induced dieback has been extensively studied in various forests habitats. We used a retrospective tree ring width (TRW), basal area increment (BAI), oxygen isotope ratios in tree ring cellulose (δ18OTR) and carbon isotope ratios in tree ring cellulose (δ13CTR) to assess causes in declining Pinus sylvestris L. and Pinus nigra J.F. Arnold. The climate data analysis indicates a significant increased trend occurred after 1980 in minimum, mean and maximum temperature and a reduced amount of precipitation compared to the 1920–1980-time scale. According to the Palmer Drought Severity Index, we found two extreme drought years (1946 and 2000) and three years with severe drought (1990, 2003 and 2012). One-way ANOVA indicated no significant difference between P. nigra and P sylvestris tree ring width, basal area increment, but a considerable difference between δ13CTR and δ18OTR. Basal area increment evaluated the climate-growth relationship most accurately, comparing to δ18OTR and δ13CTR, which explained the influences of environmental factors in tree rings formation. The δ13CTR was mainly negatively correlated with high temperatures from April-August current growing seasons. The negative correlation between δ13CTR and NDVI indices (June, August) shows a decreased carbon uptake induced by drought from summer to early autumn. The low δ18OTR signal was associated with a complex of factors, including the strong influence of heavy precipitation occurring in the growing season and a weak reaction of declined trees to resources. Species-specific responses to drought in 1990, 2003 and 2012 indicated P. sylvestris as more sensitive to drought whit higher demand for water supply in the optimal compared with P. nigra. Weak and unstable correlations in time with increasing/decreasing values in drought periods were obtained more accurately using δ18OTR compared to δ13CTR. The species-specific resilience response to drought years showed a weak resilience and resistance in P. sylvestris occurred more evident after the 2012 event compared to less sensitive P. nigra trees. Decision-makers can use presented results to reinforce specific management plans capable of protecting and changing local compositions where is the case with species more resistant to drouth.
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Purpose of Review This paper aims to retrace the most significant management strategies adopted across European beech forests over the last 25 years, highlighting those that are most efficient and promising. We investigate five main topics including forest management, forest models, species mixture, genetic, and regeneration. Recent Findings European beech is one of the most widespread and important tree species for the European forest sector. In the light of the ongoing climate crisis, understanding the growth dynamics and the response of beech forests to climate change is crucial to identify advantageous management strategies. Ecology, growth, management, distribution, interaction with other species, genetic, and regeneration aspects of European beech were investigated in different geographical areas of Europe. Despite recent researches focusing on climate change issues, how adaptation and mitigation measures can be integrated into silvicultural guidelines to improve the resilience of European beech forests remains unclear. Summary To answer this question, we collected and reviewed articles about the management of European beech facing climate change, which were published in peer-reviewed journals over the last 25 years. Articles were grouped into five geographic European areas, according to the classification used by the State of Europe’s forests. Obtained articles were further clustered into five main topics: management, mixed forest, modelling, genetic, and regeneration. The review highlighted the importance of using long-term monitoring plots to understand the effect of climate change on the stability of European beech forests, suggesting climate-smart measures that would help these forests adapt to climate change.
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Mountains are highly sensitive to the effects of climate change, including extreme short- and long-term weather phenomena. Therefore, in spite of relatively high annual precipitation totals, mountains might become endangered by droughts. The paper presents drought trends in the Polish Carpathians located in Central Europe. Data from the period 1991–2020 from 12 meteorological stations located in various vertical climate zones of the mountains were used to define drought conditions using the following indices: Standardized Precipitation (SPI), Standardized Precipitation Evapotranspiration (SPEI), Relative Precipitation (RPI) and Sielianinov. Additionally, four forest drought indices were used in order to estimate the impact of drought on beech as a typical Carpathian tree species, i.e., the Ellenberg (EQ), Forestry Aridity (FAI), Mayr Tetratherm (MT) and De Martonne Aridity (AI) indices. Statistically significant but weak trends were obtained for the 6-month SPI for four stations (indicating an increase in seasonal to mid-term precipitation), for the 1-month SPEI for three stations, for the 3-month SPEI for four stations, and for MT for all stations (indicating an increase in drought intensity). The analysis of dry month frequency according to particular indices shows that at most of the stations during the last decade of the study period, the frequency of dry months was much higher than in previous decades, especially in the cold half-year. Two zones of the Polish Carpathians are the most prone to drought occurrence: the peak zone due to the shift in climatic vertical zones triggered by the air temperature increase, and the forelands and foothills, together with basins located about 200–400 m a.s.l., where the mean annual air temperature is the highest in all the vertical profile, the annual sums of precipitation are very diversified, and the conditions for beech are already unfavorable.
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Improving our understanding of the potential of forest adaptation is an urgent task in the light of predicted climate change. Long-term alternatives for susceptible yet economically important tree species such as Norway spruce (Picea abies) are required if the frequency and intensity of summer droughts will continue to increase. Although Silver fir (Abies alba) and Douglas fir (Pseudotsuga menziesii) have both been described as drought-tolerant species, our understanding of their growth responses to drought extremes is still limited. Here, we use a dendroecological approach to assess the resistance, resilience, and recovery of these important central Europe to conifer species the exceptional droughts in 1976 and 2003. A total of 270 trees per species were sampled in 18 managed mixed-species stands along an altitudinal gradient (400-1200 m a.s.l.) at the western slopes of the southern and central Black Forest in southwest Germany. While radial growth in all species responded similarly to the 1976 drought, Norway spruce was least resistant and resilient to the 2003 summer drought. Silver fir showed the overall highest resistance to drought, similarly to Douglas fir, which exhibited the widest growth rings. Silver fir trees from lower elevations were more drought-prone than trees at higher elevations. Douglas fir and Norway spruce, however, revealed lower drought resilience at higher altitudes. Although the 1976 and 2003 drought extremes were quite different, Douglas fir maintained consistently the highest radial growth. Although our study did not examine population level responses, it clearly indicates that Silver fir and Douglas fir are generally more resistant and resilient to previous drought extremes and are therefore suitable alternatives to Norway spruce; Silver fir more so at higher altitudes. Cultivating these species instead of Norway spruce will contribute to maintaining a high level of productivity across many Central European mountain forests under future climate change.
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The aim of our study was to determine variation in the response of radial growth in Fagus sylvatica L (European Beech) to climate across the species full geographical distribution and climatic tolerance. We combined new and existing data to build a database of 140 tree-ring chronologies to investigate patterns in growth–climate relationships. Our novel meta-analysis approach has allowed the first investigation of the effect of climate on tree growth across the entire geographical distribution of the species. We identified key climate signals in tree-ring chronologies and then investigated how these varied geographically and according to mean local climate, and by tree age and size. We found that the most important climate variables significantly correlated with growth did not show strong geographical patterns. Growth of trees in the core and at the southern edge of the distribution was reduced by high temperature and low precipitation during the growing season, and by high temperatures in the previous summer. However, growth of trees growing in warmer and drier locations was more frequently significantly correlated with summer precipitation than other populations. Additionally, the growth of older and larger trees was more frequently significantly correlated with previous summer temperature than younger and smaller trees. Trees growing at the south of the species geographical distributions are often considered most at risk from climate change, but our results indicate that radial growth of populations in other areas of the distribution is equally likely to be significantly correlated with summer climate and may also be vulnerable. Additionally, tree-rings from older trees contain particular growth–climate relationships that are rarely found in younger trees. These results have important implications for predicting forest carbon balance, resource use and likely future changes to forest composition across the continent.
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Biogeographical and ecological theory suggests that species distributions should be driven to higher altitudes and latitudes as global temperatures rise. Such changes occur as growth improves at the poleward edge of a species distribution and declines at the range edge in the opposite or equatorial direction, mirrored by changes in the establishment of new individuals. A substantial body of evidence demonstrates that such processes are underway for a wide variety of species. Case studies from populations at the equatorial range edge of a variety of woody species have led us to understand that widespread growth decline and distributional shifts are underway. However, in apparent contrast, other studies report high productivity and reproduction in some range edge populations. We sought to assess temporal trends in the growth of the widespread European beech tree (Fagus sylvatica) across its latitudinal range. We explored the stability of populations to major drought events and the implications for predicted widespread growth decline at its equatorial range edge. In contrast to expectations, we found greatest sensitivity and low resistance to drought in the core of the species range, whilst dry range edge populations showed particularly high resistance to drought and little evidence of drought-linked growth decline. We hypothesize that this high range edge resistance to drought is driven primarily by local environmental factors that allow relict populations to persist despite regionally unfavourable climate. The persistence of such populations demonstrates that range-edge decline is not ubiquitous and is likely to be driven by declining population density at the landscape scale rather than sudden and widespread range retraction.
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It is expected that extreme climate events such as droughts will increase in both severity and intensity as a consequence of forecasted climate change. Complementarity among tree species in resource acquisition strategy may reduce interspecific competition and increase the occurrence of facilitative interactions, resulting in an improved tree growth and resilience to extreme climatic events. However, the response of individual trees growing in more functionally diverse stands to extreme events is still under debate.
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Growth rates of European silver fir (Abies alba Mill.) rapidly increased in the last century. At the same time, ring widths declined at the species southern distribution limits in the Mediterranean. Such diverse growth trends and responses have largely been attributed to regional climate conditions, but this was prior to considering the species’ postglacial phylogeny. 2.A dendrochronological network composed of 1,961 tree-ring width series (TRW) from 78 silver fir sites between 365 and 1,400 m a.s.l. along the Carpathian Arc was compiled. Spatial differences in the species’ genetic diversity were investigated from genetic data of 69 silver fir populations in the region. Differences in growth variability and climate sensitivity were then related to postglacial phylogeny and genetic diversity. 3.Significant differences in inter-annual and longer-term growth trends and climate responses across the Carpathian Arc were found to coincide with the geographical north-south separation of two postglacial populations from effective refugia originating from the Apennine and Balkan peninsulas. Summer temperature was the main driver of growth in the western (Apennine) lineage, whereas ring widths in the Balkan population from the east were predominantly controlled by summer drought. Fir specimens that originated from the Balkan lineage exhibited higher genetic diversity, more regular growth dynamics, and also appeared to be less sensitive to air pollution during the 1970s. 4.Synthesis. Although the phylogeny of forest trees has largely been neglected in most dendroecological studies, results here indicate the importance of different postglacial histories for the growth sensitivity and adaptability to varying environmental factors. Decision making under future climate warming scenarios (for building resilience through forest management) should therefore consider different phylogenetic origins. This article is protected by copyright. All rights reserved.
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Summary. Recent work by Reiss and Ogden provides a theoretical basis for sometimes preferring restricted maximum likelihood (REML) to generalized cross-validation (GCV) for smoothing parameter selection in semiparametric regression. However, existing REML or marginal likelihood (ML) based methods for semiparametric generalized linear models (GLMs) use iterative REML or ML estimation of the smoothing parameters of working linear approximations to the GLM. Such indirect schemes need not converge and fail to do so in a non-negligible proportion of practical analyses. By contrast, very reliable prediction error criteria smoothing parameter selection methods are available, based on direct optimization of GCV, or related criteria, for the GLM itself. Since such methods directly optimize properly defined functions of the smoothing parameters, they have much more reliable convergence properties. The paper develops the first such method for REML or ML estimation of smoothing parameters. A Laplace approximation is used to obtain an approximate REML or ML for any GLM, which is suitable for efficient direct optimization. This REML or ML criterion requires that Newton–Raphson iteration, rather than Fisher scoring, be used for GLM fitting, and a computationally stable approach to this is proposed. The REML or ML criterion itself is optimized by a Newton method, with the derivatives required obtained by a mixture of implicit differentiation and direct methods. The method will cope with numerical rank deficiency in the fitted model and in fact provides a slight improvement in numerical robustness on the earlier method of Wood for prediction error criteria based smoothness selection. Simulation results suggest that the new REML and ML methods offer some improvement in mean-square error performance relative to GCV or Akaike's information criterion in most cases, without the small number of severe undersmoothing failures to which Akaike's information criterion and GCV are prone. This is achieved at the same computational cost as GCV or Akaike's information criterion. The new approach also eliminates the convergence failures of previous REML- or ML-based approaches for penalized GLMs and usually has lower computational cost than these alternatives. Example applications are presented in adaptive smoothing, scalar on function regression and generalized additive model selection.