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Questions: How have the historical frequency and severity of natural disturbances in primary Picea abies forests varied at the forest stand and landscape level during recent centuries? Is there a relationship between physiographic attributes and historical patterns of disturbance severity in this system? Location: Primary P. abies forests of the Eastern Carpathian Mountains, Romania; a region thought to hold the largest concentration of primary P. abies forests in Europe’s temperate zone. Methods: We used dendrochronological methods applied to many plots over a large area (132 plots representing six stands in two landscapes), thereby providing information at both stand and landscape levels. Evidence of past canopy disturbance was derived from two patterns of radial growth: (1) abrupt, sustained increases in growth (releases) and (2) rapid early growth rates (gap recruitment). Thesemethods were augmented with non-metricmultidimensional scaling to facilitate the interpretation of factors influencing past disturbance. Results: Of the two growth pattern criteria used to assess past disturbance, gap recruitment was the most common, representing 80% of disturbance evidence overall. Disturbance severities varied over the landscape, including stand-replacing events, as well as low- and intermediate-severity disturbances. More than half of the study plots experienced extreme-severity disturbances at the plot level, although they were not always synchronized across stands and landscapes. Plots indicating high-severity disturbances were often spatially clustered (indicating disturbances up to 20 ha), while this tendency was less clear for lowand moderate-severity disturbances. Physiographic attributes such as altitude and land form were only weakly correlated with disturbance severity. Historical documents suggest windstorms as the primary disturbance agent, while the role of bark beetles (Ips typographus) remains unclear. Conclusions: The historical disturbance regime revealed in this multi-scale study is characterized by considerable spatial and temporal heterogeneity,which could be seen among plots within stands, among stands within landscapes and between the two landscapes. When the disturbance regime was evaluated at these larger scales, the entire range of disturbance severity was revealed within this landscape.
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Journal of Vegetation Science 25 (2014) 386–401
Landscape-level variability in historical disturbance in
primary Picea abies mountain forests of the Eastern
Carpathians, Romania
Miroslav Svoboda, Pavel Janda, Radek Ba
ce, Shawn Fraver, Thomas A. Nagel, Jan Rejzek,
Martin Mikol
a
s, Jan Douda, Karel Boubl
ık, Pavel
Samonil, Vojt
ech
Cada, Volodymyr Trotsiuk,
Marius Teodosiu, Olivier Bouriaud, Adrian I. Biris
ß,Ond
rej S
ykora, Petr Uzel, Ji
r
ıZelenka,V
ıt
Sedl
ak & Ji
r
ıLehej
cek
Keywords
bark beetle outbreak; blowdown;
dendroecology; disturbance regime; forest
dynamics; multidimensional scaling; natural
disturbance; Norwayspruce; old-growth
forest; spatiotemporal variability; temperate
forest
Nomenclature
Kub
at et al. (2002)
Received 18 March 2013
Accepted 29 June 2013
Co-ordinating Editor: John Morgan
Svoboda, M. (corresponding author,
svobodam@fld.czu.cz),
Janda, P. (jandap@fld.czu .cz),
Ba
ce, R. (bace@fld.czu.cz),
Rejzek, J. (rejzek@fld.czu.cz),
Mikol
a
s, M. (mikolasm@fld.czu.cz),
Cada, V. (cada@fld.czu.cz),
Trotsiuk, V. (vtrotsiuk@gmail.com),
S
ykora, O. (ondrejsykora@atlas.cz),
Uzel, P. (petauzel@seznam.cz),
Zelenka, J. (zeli.iceman@seznam.cz),
Sedl
ak, V. (sedlakvit@gmail.com) &
Lehej
cek, J. (lehejcek@fld.czu.cz): Faculty of
Forestry and Wood Sciences, Czech University
of Life Sciences Prague, Kam
yck
a129,Praha6
Suchdol, Prague, 16521, Czech Republic
Fraver, S. (srfraver@umn.edu): Department of
Forest Resources, University of Minnesota, St.
Paul, Minnesota, 55108, USA
Nagel, T.A. (tom.nagel@bf.uni-lj.si):
Biotechnical Faculty, Department of Forestry
and Renewable Forest Resources, University of
Ljubljana, Vecna Pot 83, Ljubljana, 1000,
Slovenia
Douda, J. (douda@fzp.czu.cz) & Boubl
ık, K.
(boublik@fzp.czu.cz): Faculty of Environment,
Czech University of Life Sciences Prague,
Kam
yck
a129,Praha6Suchdol, Prague,
16521, Czech Republic
Abstract
Questions: How have the historical frequency and severity of natural distur-
bances in primary Picea abies forests varied at the forest stand and landscape level
during recent centuries? Is therea relationship between physiographic attributes
and historical patterns of disturbance severity in this system?
Location: Primary P. abies forests of the Eastern Carpathian Mountains, Roma-
nia; a region thought to hold the largest concentration of primary P. abies forests
in Europe’s temperate zone.
Methods: We used dendrochronological methods applied to many plots over a
large area (132 plots representing six stands in two landscapes), thereby provid-
ing information at both stand and landscape levels. Evidence of past canopy dis-
turbance was derived from two patterns of radial growth: (1) abrupt, sustained
increases in growth (releases) and (2) rapid early growth rates (gap recruit-
ment). These methods were augmented with non-metric multidimensional scal-
ing to facilitate the interpretation of factors influencing past disturbance.
Results: Of the two growth pattern criteria used to assess past disturbance, gap
recruitment was the most common, representing 80% of disturbance evidence
overall. Disturbance severities varied over the landscape, including stand-replac-
ing events, as well as low- and intermediate-severity disturbances. More than
half of the study plots experienced extreme-severity disturbances at the plot
level, although they were not always synchronized across stands and land-
scapes. Plots indicating high-severity disturbances were often spatially clustered
(indicating disturbances up to 20 ha), while this tendency was less clear for low-
and moderate-severity disturbances. Physiographic attributes such as altitude
and land form were only weakly correlated with disturbance severity. Historical
documents suggest windstorms as the primary disturbance agent, while the role
of bark beetles (Ips typographus) remains unclear.
Conclusions: The historical disturbance regime revealed in this multi-scale
study is characterized by considerable spatial and temporal heterogeneity, which
could be seen among plots within stands, among stands within landscapes and
between the two landscapes. When the disturbance regime was evaluated at
these larger scales, the entire range of disturbance severity was revealed within
this landscape.
Journal of Vegetation Science
386 Doi:10.1111/jvs.12109 ©2013 International Association for Vegetation Science
Introduction
Natural disturbances strongly influence the dynamics of
forest ecosystems (Pickett & White 1985; Turner 2010).
Variation in disturbance size, frequency and severity plays
an important role in shaping forest structural and composi-
tional heterogeneity at landscape scales (Turner 1987;
Fraver et al. 2009; Donato et al. 2012). This heterogeneity,
in turn, influences a variety of ecosystem properties and
processes, such as nutrient cycling (Turner 1989), carbon
pools (Coomes et al. 2012; Seidl et al. 2012), species diver-
sity (Angelstam 1998; Bengtsson et al. 2000; Kuuluvainen
2002; Dittrich et al. 2012) and susceptibility to future dis-
turbances (Bigler et al. 2005). Characterizing the historical
range of variability of natural disturbance often requires
retrospective studies in primary forests, i.e. forests rela-
tively uninfluenced by human activities.
Knowledge of historical natural disturbances also pro-
vides the context for gauging the apparent recent increases
in disturbance activity (Westerling et al. 2006; Allen et al.
2010; Mitton & Ferrenberg 2012). This issue is especially
relevant in temperate Europe’s Picea abies forests, where
recent wind and bark beetle disturbances have caused
widespread damage (Hais et al. 2009; Jonasova et al. 2010;
Lausch et al. 2011; Seidl et al. 2011), raising concerns that
human land use and climate change may have altered the
disturbance regime in this region. Most previous studies of
disturbance regimes in temperate forests have been con-
ducted at the stand level (but see Frelich & Lorimer 1991;
D’Amato & Orwig 2008; Fraver et al. 2009). However,
understanding the interaction of disturbances, such as
severe windstorms and bark beetle outbreaks, requires a
landscape-level approach to fully capture the spatial vari-
ability inherent in these disturbances. Limitations of previ-
ous stand-level studies are in part due to the scarcity of large
tracts of primary forest that would permit a landscape-level
analysis. In Europe’s temperate zone, for example, many of
the remaining primary forests exist as isolated fragments,
the result of long-term human land use in this region. How-
ever, studying historical disturbances in a number of pri-
mary fragments situated within the same landscape or
region may reveal a representative characterization of dis-
turbance severity and synchronization over quite large
areas (D’Amato & Orwig 2008). Understanding this land-
scape-level variability is not only important for advancing
theories of forest dynamics, but also for ecological forest
management, which intends to emulate the historic range
of forest structure, composition and processes that result
from natural disturbances (Seymour & Hunter 1999; Cyr
et al. 2009; Kuuluvainen 2009; Mori 2011).
The general objective of this study was to evaluate land-
scape-level disturbance patterns, using P. abies as our study
system. The large number of reported primary P. abies
stands in Romania’s Eastern Carpathians (Veen et al.
2010) present an ideal opportunity to study landscape-
level disturbance patterns, using verified dendrochrono-
logical methods. This region may hold the largest
concentration of primary P. abies forests in Europe’s tem-
perate zone, yet has been little studied with respect to his-
torical disturbance. To this end, we applied
dendrochronological methods to a large number of plots
over the landscape, thereby providing information about
historical disturbances at both stand and landscape levels.
Previous stand-level studies for this forest system report a
wide range of disturbance regimes throughout central Eur-
ope, from small-scale gap dynamics (Szewczyk et al. 2011)
to moderate- and high-severity events caused by wind-
storms and bark beetle outbreaks (Zielonka et al. 2010;
Panayotov et al. 2011; Svoboda et al. 2012). We assumed
that the synchronization of disturbance evidence from
many plots across the landscape suggests large-scale distur-
bances, while temporally independent disturbance evi-
dence seen only on individual plots suggests localized
small-scale events. Further, we suspected that physio-
graphic attributes, such as altitude or slope position, would
influence disturbance frequency and severity.
Our specific objectives were to: (i) quantify the temporal
and spatial pattern of the disturbances, including the range
of variability, at the forest stand and landscape level; and
(ii) examine the relationship between physiographic attri-
butes and patterns of disturbance severity. Our results will
shed much light on the dominant disturbance agents, as
well as the variability of the disturbance regime for P. abies
forests, and provide important background information for
forest management and conservation efforts in the temper-
ate zone of Europe.
Methods
Study area
We conducted this study in the C
alimani and Giumal
au
Mountains, in the Eastern Carpathian Mountains of
Samonil, P. (samonil@vukoz.cz): Department of
Forest Ecology, Silva Tarouca Research Institute
for Landscapeand Ornamental Gardening, Brno,
65720, Czech Republic
Teodosiu, M. (marius.teodosiu@gmail.com) &
Bouriaud, O. (obouriaud@gmail.com): Forest
Research and Management Institute, Station
C^
ampulung Moldovenesc, Calea Bucovinei 73b,
C^
ampulung Moldovenesc Suceava, 725100,
Romania
Biris
ß,A.I.(iovu.biris@gmail.co m): Forest
Research and Management Institute, Bd. Eroilor
128, Voluntari Ilfov, 077190, Romania
Journal of Vegetation Science
Doi: 10.1111/jvs.12109©2013 International Association for Vegetation Science 387
M. Svoboda et al. Landscape-level disturbance in Picea forests
Romania. The Carpathians are thought to contain the larg-
est tracts of primary forests in Central and Eastern Europe
(Veen et al. 2010; Knorn et al. 2012b), including the larg-
est remnants of primary Picea abies forest in temperate Eur-
ope, making this region ideal for investigating natural
disturbance processes over large spatial scales. We refer to
our study areas as ‘primary forest’, in that stands developed
under a regime of natural disturbances and show little to
no evidence of past human impact, but are not necessarily
in an old-growth stage of development.
C
alimani National Park (hereafter Calimani,
24 000 ha) was officially operative in 2003 (Knorn et al.
2012a,b). It is part of the C
alimani Mountains, and the
core zone (i.e. strictly protected areas) covers an area of
about 16 800 ha. The Nature Reserve Giumal
au (hereaf-
ter Giumalau) has been protected since 1941, with a size
of ca. 310 ha (Lamedica et al. 2011; Teodosiu & Bour-
iaud 2012). It is part of the smaller mountain range of
Giumal
au. Primary closed-canopy P. abies mountain for-
ests, the focus of our study, occur on slopes between
about 1200 and 1700 ma.s.l. (Popa & Kern 2009; Cen-
us
ß
a 2010). Picea abies is the dominant tree species, with
a lesser admixture of Sorbus aucuparia, and rarely Pinus
cembra, Larix decidua, Acer pseudoplatanus and Betula pen-
dula. These forests have a dense understorey dominated
by Vaccinium myrtillus,Calamagrostis villosa,Luzula sylvati-
ca and Avenella flexuosa. Plant nomenclature follows
Kub
at et al. (2002).
Average annual temperature in the study region varies
from 2.4 to ca. 4.0 °C; precipitation varies between 1100
and 1650 mm annually, and increases with altitude (Food
and Agriculture Organization (FAO) Local Climate Estima-
tor New_LocCLim v. 1). Snow is present 139208 days per
year, and contributes up to 500 mm of the total annual
precipitation. Bedrock in Calimani is volcanic (andesites)
(Seghedi et al. 2005) and crystalinic (phyllite, gneiss) in
Giumalau (Balintoni 1996). Soils in the study area are very
diverse, including mainly podzols, while cambisols occur
very rarely at lower altitudes, leptosols at stony and
exposed sites and stagnosols at wet sites (M. Valtera,
P.
Samonil & K. Boubl
ık unpubl. data).
Study site selection
Potential study sites were first selected using a previous
inventory of primary forest remnants in Romania (Veen
et al. 2010). Using a GIS, potential P. abies stands were
selected. These stands were then located in the field and
surveyed for indicators of naturalness (e.g. coarse woody
debris in various stages of decay, pit-and-mound topogra-
phy) and signs of human impact; stands with evidence of
past logging and grazing were avoided, as were stands in
close proximity to formerly grazed areas. Additionally, we
searched all the available archival information regarding
the history of land use in these areas. Historical data indi-
cate the areas selected for study escaped logging in the
18th and 19th centuries and have been protected since this
time.
Based on our initial field survey and historical informa-
tion, we selected five stands in the C
alimani Mountains, all
within C
alimani National Park (Fig. 1). These include a
stand of ca. 40 ha (C1) and four stands (C2C5), each ca.
812 ha. In the Gium
alau Mountains, we selected a 101-
ha stand within the Gium
alau Nature Reserve (G1); the
large size of this stand required that we sample at two
intensities (see below). The Calimani and Giumalau land-
scapes, which are separated by ca. 50 km, each include a
broad range of geographic variability regarding elevation,
slope and aspect; thus, to some degree, they represent the
landscape-scale heterogeneity found in the study region.
However, a statistical stratification of stands across the var-
ious geographic positions was not possible because of the
limited distribution of primary forest fragments.
Field and laboratory procedures
Sample plots were established in each stand using a strati-
fied random design. Using a GIS, a 100 9100-m or
141.4 9141.4-m grid was overlain on each stand. Within
Fig. 1. Study area showing the two landscapes (Calimani, Giumalau) and
stands (alpha-numeric codes). The Coordinate Reference System WGS84
was used.
Journal of Vegetation Science
388 Doi:10.1111/jvs.12109 ©2013 International Association for Vegetation Science
Landscape-level disturbance in Picea forests M. Svoboda et al.
each grid cell, a circular sample plot (1000 m
2
) was estab-
lished at a restricted random position (generated in a GIS)
using GPS. Plot centres were restricted to the inner 0.25
and 0.49 ha core in each 1-ha or 2-ha cell, respectively. In
Calimani, the 40-ha stand (C1) was sampled using a 1-ha
grid cell size (40 plots), whereas stands C2C5 were sam-
pled with a 2-ha grid cell size (total of 21 plots). Sampling
in Giumalau covered 101 ha, with a 1-ha grid cell size in
the core 41-ha zone and a 2-ha grid cell size in the remain-
ing area (total of 71 plots). In total, 132 plots were estab-
lished in the six stands (Table 1).
In each 1000-m
2
sample plot, we labeled all living trees
10 cm diameter at breast height (DBH) and recorded their
DBH. Using a random number generator, we selected 25
canopy P. abies trees per plot for increment core extraction.
Trees with a significant part of the crown projection receiv-
ing direct sunlight from above were classified as canopy
trees (Lorimer & Frelich 1989). Suppressed trees were
avoided because their growth patterns may lack informa-
tion important for disturbance history reconstruction
(Frelich & Lorimer 1991; Splechtna et al. 2005; Svoboda
et al. 2012). One core per tree was extracted 1.0 m above
the ground level for radial growth analysis and age deter-
mination. We also measured the crown dimension of five
randomly selected canopy trees per plot. For each tree
crown, two orthogonal axes were measured for the
purpose of predicting crown area from DBH. Finally, phys-
iographic attributes were recorded for each plot, including
slope, aspect and elevation. The topographic location of
each plot was classified based on its slope position, further
reported as ‘land form’ (upper slope value 1, middle slope
value 2, and lower slope value 3).
On plots (58% of the total number of plots) with a high
tree density (>500 stemsha
1
) and homogenous struc-
ture, the plot size was reduced to 500 m
2
. For these plots,
where most trees appeared to be of the same age cohort
(based on tree size and stand structure), we also decreased
the number of increment core samples to up to 15 per plot
to decrease the work load. For plots in stand C1, where the
stand structure was homogenous (based on tree size and
structure), we extracted cores from an additional one to
five trees of advanced age, indicated by their bark, branch-
ing and crown characteristics, to supplement the distur-
bance history reconstruction. The location of such trees
was restricted to within 50 m of plot borders.
Increment cores were dried, secured on wooden mounts
and shaved with a razor blade. For cores that missed the
pith, the number of missing rings was estimated using
Duncan’s (1989) method. The pith was reached in 72.3%
of samples, while the remaining 22.3% and 4.7% were
Table 1. Physiographic parameters, number of the plots and basic stand structural characteristics.
Stands Giumalau G1 Calimani C1 Calimani C2 Calimani C3 Calimani C4 Calimani C5
Mean elevation
(ma.s.l.)
1434 1556 1626 1484 1557 1558
Range of elevation
(ma.s.l.)
12491606 14681657 15991653 14151549 15051601 15121598
Mean slope (°)272138222820
Geographic position
(E°,N°in WGS84)
25.4679,
47.4421
25.2587, 47.1136 25.2837, 47.1450 25.1928, 47.0663 25.2037, 47.0650 25.2255, 47.0687
Size of sample area
(ha)
101 40 8 12 12 10
Numberofplots71404665
Mean tree density
(Nha
1
)
470 597 368 837 412 432
Mean DBH (cm) 32.3 32.2 36.5 24.3 38.2 39.7
Mean height (m) 23.1 23.8 19.7 20.8 24 23.7
Mean basal area
(m²ha
1
)
43.9 51.3 46.4 44.6 53.2 61
% suppressed trees
(SE)
24.0 (13.1) 29.9 (14.4) 3.6 (2.3) 31.0 (8.9) 4.2 (4.6) 8.8 (4.3)
%suppressed
projection(SE)
15.0 (10.0) 21.3 (11.3) 2.1 (1.6) 22.5 (7.3) 2.5 (2.7) 4.6 (2.5)
% trees showing
gap recruitment
79.6 77.3 79.6 96.7 85.8 85.0
% trees showing
release
14.9 19.0 17.5 2.7 11.0 12.6
%ofshowing
multiple
release
5.5 3.7 2.9 0.6 3.2 2.4
Journal of Vegetation Science
Doi: 10.1111/jvs.12109©2013 International Association for Vegetation Science 389
M. Svoboda et al. Landscape-level disturbance in Picea forests
<0.5 and 1.0 cm from the pith, respectively. All ages in this
study are expressed as recruitment ages at 1 m, the height
at which trees were cored. No attempt was made to esti-
mate actual tree age because P. abies seedlings can establish
and persist for decades under shade, such that germination
ages may poorly coincide with the timing of past distur-
bances (Niklasson 2002). Annual ring widths were mea-
sured to the nearest 0.01 mm using a stereomicroscope
and Lintab
TM
sliding-stage measuring device in conjunction
with TSAP-Win
TM
software (www.rinntech.de). Cores
were first visually cross-dated using the marker year
approach (Yamaguchi 1991), verified with PAST4 software
(www.sciem.com), and then confirmed with COFECHA
software (Holmes 1983). Considering that trees were
growing in relatively mesic, closed-canopy stands the ser-
ies intercorrelation (0.480 for Calimani, 0.494 for Giuma-
lau) was rather high.
Dendrochronological analysis
Disturbance history was reconstructed from two patterns
of radial growth: (1) abrupt, sustained increases in radial
growth (releases) indicating mortality of a former canopy
tree, and (2) rapid early growth rates (gap recruitment)
indicating recruitment in a former canopy gap (Frelich &
Lorimer 1991). While growth of suppressed trees typically
increases immediately after mortality of an overtopping
canopy tree, establishment of new trees following gap-cre-
ating disturbances can last from years to decades (Kula-
kowski & Veblen 2003; Rammig et al. 2006). Picea abies is
considered a shade-tolerant species (Schmidt-Vogt 1977);
its tolerance to shade is highest during the juvenile stage
and decreases with age (Tjoelker et al. 2007). In P. abies
forests, for example, the absence of advance regeneration
in closed-canopy stands, coupled with the slow establish-
ment and growth of seedlings, can result in episodes of gap
recruitment (at 1.3 m) lasting up to 40 yrs after a large
disturbance event (Holeksa et al. 2007; Panayotov et al.
2011; Szewczyk et al. 2011; Svoboda et al. 2012).
Therefore, disturbance histories reconstructed mainly from
gap-recruited trees, as is the case in this study, need to be
carefully interpreted because peaks in gap recruitment
lasting several decades are likely to indicate a former high-
severity disturbance rather than successive lower-severity
events.
To identify gap-recruited trees, we determined the
growth rate threshold that best separates open-grown trees
from those under closed canopies (Fraver & White 2005a;
Svoboda et al. 2012). This calculation was based on a com-
parison of juvenile growth rates of saplings growing under
closed canopy and in different-sized gaps in this same
study area. Average growth rates were calculated from
5-yr growth periods beginning when the tree reached
4 cm DBH. The growth rate of suppressed saplings
(N=46) was compared with those of saplings growing in
all gaps (N=175), gaps over 500 m
2
(N=87) and gaps
over 1000 m
2
(N=63). Growth rate thresholds were
calculated using logistic regression, as per Svoboda et al.
(2012). Trees were thus considered to be gap-recruited if
the average growth rate was 1.7 mmyr
1
(likelihood
ratio v
2
=142.3, P<0.0001) and 1.9 mmyr
1
(likelihood
ratio v
2
=144.1, P<0.0001), which correspond to gap
recruitment in openings larger than 500 and 1000 m
2
,
respectively.
Growth releases were identified with boundary line cri-
teria (Black & Abrams 2003) applied to consecutive 10-yr
running means. This method scales the release criteria to
account for varying pre-disturbance growth rates, thereby
reducing the number of falsely identified releases typical of
the traditional percentage increase method (Black &
Abrams 2003; Fraver & White 2005b). The maximum per-
centage growth change in each release pulse was used to
date the disturbance. To reduce the detection of growth
release caused by climate anomalies, we only used poten-
tial releases with percentage growth change above 50%
(Splechtna et al. 2005; Firm et al. 2009). Site-specific
boundary lines were constructed separately for Giumalau
and Calimani, based on the approach proposed in Black &
Abrams (2003) and Aakala et al. (2011). Following Black
& Abrams (2003), a moderate release was defined as any
growth change value between 20% and 50% of the
boundary line, and major releases were those >50% of the
boundary line. To be considered a valid release, the ele-
vated growth rate also had to be sustained for at least 7 yrs
(Fraver et al. 2009); shorter-term recoveries to prior
growth rates were not considered releases. Finally, we dis-
counted apparent releases shown on trees determined to
have been in the canopy at the time of the disturbance, as
such growth increases would suggest the loss of a neigh-
bouring, not overtopping tree, the focus of our work (see
Lorimer & Frelich 1989). Trees were assumed to have been
in the canopy if their diameter at the time of the event
exceeded 25 cm, which was determined by logistic regres-
sion (as above applied to gap recruitment criteria) of can-
opy and suppressed tree diameters.
For a small number of cores, radial growth patterns did
not meet the gap recruitment or release criteria described
above. The inferred disturbance dates on these samples
were categorized as either gap-recruited or released based
on their overall radial growth pattern (Lorimer & Frelich
1989). Samples with a declining, flat or parabolic pattern
were included into the gap-recruited group and samples
with an ambiguous or irregular pattern were categorized
as released trees, following Lorimer & Frelich (1989).
Finally, because P. abies is shade-tolerant, especially during
the juvenile life stage, more than one disturbance may be
Journal of Vegetation Science
390 Doi:10.1111/jvs.12109 ©2013 International Association for Vegetation Science
Landscape-level disturbance in Picea forests M. Svoboda et al.
needed to attain canopy status (Lorimer & Frelich 1989).
Thus, multiple major releases from the same tree were
allowed in the disturbance chronologies. However, from
the total number of trees, only 3% showed more than one
major release. Moderate releases were included in the
chronologies only when no other releases were present on
acore.
Construction of the disturbance chronologies
The number of growth releases and gap recruitment events
were converted to total canopy area disturbed in each dec-
ade following the approach and rationale of Lorimer & Fre-
lich (1989), thereby producing a disturbance chronology
for each plot. This conversion scales the evidence of distur-
bance according to the tree’s current crown area; it is
required because the magnitude of disturbance inferred
from small-crowned trees differs from that inferred from
large-crowned trees. Current crown areas were predicted
from current DBHs using a regression equation developed
from these same data.
We calculated a composite disturbance chronology,
based on all disturbance evidence, for Calimani and
Giumalau separately. However, because the composite is
based on a large number of plots, each with a unique dis-
turbance history, it represents only the most general his-
tory of disturbance. We therefore constructed additional
disturbance chronologies, one for each stand, based on
plots within stands (as opposed to trees within plots). As
such, these chronologies express the proportion of plots
(within stands) showing light (to 20% canopy disturbed),
moderate (20.140%), heavy (40.160%) or extreme
(>60%) disturbance severities within each decade (catego-
ries based on Frelich & Lorimer (1991), except for the
highest category, added here (see example of plot level dis-
turbance chronology in Appendix S1). The composite
chronologies were truncated when the total number of
trees dropped below 20%, while the plot level disturbance
chronologies were truncated when the number of trees in
a decade dropped below 20% of the total number of trees
per plot. The last decade in the analyses was 19801990
because of the length of time needed for trees to respond to
disturbance events.
Finally, because we ultimately found that (1) gap
recruitment was the most common form of disturbance
response and (2) recruitment periods were quite pro-
tracted, spanning decades following disturbance, we
sought a means of presenting the disturbance evidence
that better captures these long periods of gap recruit-
ment. To this end, we summed plot-level disturbance
evidence over three consecutive decades (assuming pro-
tracted recruitment as the explanation for these lengthy
periods). Thus, for each plot, the three-decade running
sum was used to refine our inferences about past dis-
turbance. Periods with sums >60% or 80% canopy dis-
turbance were selected. We take the first decade in
each of these selected periods to represent the timing of
the disturbance. Plots with a proportion over 60 and
80% were tallied. When a plot reached 80%, it was
not included in the 60% class. The periods with the
highest number of plots meeting the 60 and 80% crite-
ria are then shown for each stand in Table 2. Longer
periods of tree establishment for disturbance severity
assessment have similarly been used in sub-alpine for-
ests of other regions. For example, Veblen et al. (1994);
Kulakowski & Veblen (2006) and DeRose & Long
(2012) used a 40-yr period of tree establishment to
identify stand-replacing fires in the Rocky Mountains,
USA.
Landscape-scale ordination analysis of the disturbance
chronologies
To facilitate interpretation of the disturbance history at the
landscape level, we performed non-metric multidimen-
sional scaling (NMDS), which is a nonparametric, uncon-
strained ordination technique. NMDS is more suitable for
analysing disturbance chronologies than is principal com-
ponents analysis, because decadal disturbance rates are
typically non-normally distributed and discontinuous in
scale (D’Amato & Orwig 2008). The NMDS was based on a
plot-by-decade matrix (132 plots, 22 decades), with the
proportion of canopy area disturbed occupying matrix
cells. Ordinations were performed in R 2.12.0 (R Founda-
tion for Statistical Computing, Vienna, AT) with the
Table 2. Proportion of plots with extreme disturbance rates over 60 and
80% in three consecutive decades in individual stands. For each plot, a run-
ning window summing the disturbance rates over three consecutive dec-
ades was calculated, and plots summing over 60 and 80% were selected
(see Methods). The periods with highest number of plots meeting the 60
and 80% criteria are shown for each site. Number of plots with heavy and
extreme disturbance rate was 70 from a total of 132 plots.
Disturbance
severity
6080% Over 80%
Percentage
of plots
Important
decades
Percentage
of plots
Important
decades
Giumalau G1 25 18001830
19001930
19501980
11 18001830
19001930
19501980
Calimani C1 30 18401870
19001930
50 18401870
19001930
Calimani C2 0 0
Calimani C3 0 100 19301960
Calimani C4 50 18001830
19001930
0
Calimani C5 60 18201850 0
Journal of Vegetation Science
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M. Svoboda et al. Landscape-level disturbance in Picea forests
‘vegan’ library and ‘mgcv’, using the ‘metaMDS’ function,
along with the BrayCurtis similarity metric and two
dimensions. Physiographic attributes (land form, slope
steepness, slope aspect, altitude) were then passively pro-
jected onto the ordination space to examine their relation-
ship with disturbance patterns, using the ‘envfit’ function.
This method produces vectors that represent the most rap-
idly changing direction for a given variable and have
lengths proportional to the strength of the correlation
between it and the ordination. Significance was calculated
using 9999 permutations. Aspect values were transformed
using the following formula: aspect =cosine (45-azimuth
degrees) +1 (see D’Amato & Orwig 2008). This formula
transforms values so as to be maximal on northeastern
slopes and minimal on southwestern slopes. To quantify
the severity of the disturbance regime per plot we created a
disturbance index (DI), based on the Shannon index as
follows,
DI ¼X
N
i¼1
pilogpið1Þ
where p
i
is the proportion of canopy area disturbed
belonging to the ith decade and Nis the number of dec-
ades. The maximum theoretical value of DI reaches 0 (for
100% canopy area disturbed in a given decade, i.e. high-
severity disturbance regime), while the minimum theoret-
ical value for 20 decades reaches ca. 3 (indicative of a
low-severity disturbance regime with similar canopy area
disturbed in all decades). The DI was likewise included into
the ordination using a function that creates a DI surface,
shown with contour lines in ordination space.
Spatial aspects of disturbance
Spatial aspects of disturbance, synchronization of past dis-
turbances and DI values among plots were analysed using
matrix correlation via Mantel’s test. The test evaluates the
correlation between two plot-by-plot matrices (132 plots,
22 decades), one containing the geographic distance
between all pairs of plots, another containing a measure of
similarity between plots based on disturbance metrics.
Matrix correlation allowed us to assess the importance of
plot location, specifically if plots close to each other share
similar disturbance histories and metrics. If we found that
both synchronization of past disturbances and DI values
were clustered in space, we tested if similarity in DI was
confounded by similarities in the synchronization of past
disturbances using a partial Mantel test. The Mantel test
was conducted in R 2.12.0 under library ‘vegan’ and
‘ade4’. The BrayCurtis distance was used as a similarity
measure among plots based on 9999 replicates in a Monte
Carlo test. Tests were performed only for stands with
adequate numbers of plots, i.e. Giumalau and Calimani
stand C1.
Results
Forest structure
Picea abies dominated the forest canopy on all plots, repre-
senting ca. 99% of plot basal area overall. Datapooled from
all plots revealed a living tree basal area of 47.3 m
2
ha
1
,
and density of 518 treesha
1
(the two landscapes did not
differ appreciably). Less than 1% (22 of ca. 3500) of trees
exceeded 300 yrs in age, with the maximum at 380 yrs.
Structure and general conditions for each stand are shown
in Table 1.
Disturbance histories
Composite disturbance chronologies for the Giumalau
(N=71 plots) and Calimani (N=61 plots) are shown in
Fig. 2. Of the two growth rate criteria used to assess past
disturbance (growth releases and gap recruitments), gap
recruitment was by far the most common for all stands
(Table 1), representing 80% of disturbance evidence over-
all. Even during disturbance peaks gap recruitment events
remained prevalent, typically being more numerous than
releases (Fig. 2). Particularly noteworthy is a disturbance
peak beginning in ca. 1810 at Giumalau that consists
almost exclusively of gap recruitment events (Fig. 2).
The composite disturbance chronology in Fig. 2, which
combines a large number of plots, necessarily masks plot-
to-plot variability. Therefore we created a set of chronolo-
gies in which the proportion of plots, per stand, experienc-
ing various disturbance severities is expressed for each
decade (Fig. 3). These chronologies better capture the tem-
poral variability in disturbance severity and thus support
the result of the ordination analysis. Both Calimani C1 and
C3 showed extreme severity disturbance (>60% of trees
showing disturbance evidence) on a portion of plots,
although in different decades for each stand (Fig. 3). High-
severity disturbances in Calimani C1 were also confirmed
with evidence of disturbance among the trees of advance
age sampled outside plots (Appendix S2). These trees
showed peaks in disturbance that clearly matched those in
the C1 disturbance chronology. In contrast, Calimani
stands C2, C4 and C5 had lower disturbance rates, with
most plots recording light disturbance (<20% of trees
showing evidence). Giumalau also showed relatively low
disturbance evidence, with only a small number of plots
showing heavy or extreme severities, respectively, in any
decade.
The results of summing disturbance evidence over three
consecutive decades (to account for the protracted periods
of gap recruitment following disturbance) revealed several
Journal of Vegetation Science
392 Doi:10.1111/jvs.12109 ©2013 International Association for Vegetation Science
Landscape-level disturbance in Picea forests M. Svoboda et al.
periods of extreme disturbance in all stands (Table 2).
Assuming protracted recruitment as the explanation for
these lengthy periods (see Discussion), we take the first
decade in each period to represent the timing of the distur-
bance. Using this approach, Calimani stands C1 and C3
showed 80 and 100% of plots with extreme disturbance
over three consecutive decades (Table 2). On the other
hand, in Calimani C2, C4 and C5 many plots showed light
disturbance (Table 2). In Giumalau, 36% of plots showed
extreme disturbance, whereas many plots showed light
disturbance (Table 2). The periods of extreme disturbances
varied from stand to stand, but several periods (1800
1830, 18201850, 18401870, 19001930 and 1950
1980) were common between the stands (Table 2).
However, disturbance synchronicity among stands and
landscapes was not strong, with peak periods in distur-
bance in one stand only partially matched in another
stand. For example, in stand C1, about 20 plots (20 ha)
showed extreme disturbance in 19001930, while only a
small number of plots in Giumalau and other stands in Cal-
imani had evidence of high-severity disturbances during
this period (Table 2). The period 18001830 showed syn-
chronicity between Giumalau and Calimani C4, when a
relatively large number of plots showed extreme distur-
bance in both landscapes. Together, these findings suggest
considerable stand-to-stand spatial heterogeneity in distur-
bance patterns.
Spatial aspects of disturbance and ordination analysis
A visual assessment of within-stand spatial patterning for
the Calimani and Giumalau landscapes shows clustering
of heavily disturbed plots within given time periods
(Fig. 4). In Calimani stand C1, matrix correlation revealed
that geographically close plots shared similar disturbance
histories (Mantel test P<0.001, r=0.43), as well as simi-
lar DI indices (P=0.019, r=0.13), although this latter
correlation was weaker. However, close plots with non-
synchronous disturbance history did not have similar DI
values (Partial Mantel test P=0.348, r=0.022), indicat-
ing that geographic distance is confounded by similarities
in disturbance history when testing DI clustering.
In Giumalau, matrix correlation revealed only weak corre-
lation between geographic proximity and similarity in dis-
turbance histories (P=0.002, r=0.13), and no
significant correlation existed between geographic prox-
imity and similarity in DI indices (P=0.12, r=0.06).
At Calimani, a cluster of plots representing roughly 20 ha
(half of the stand) registered extreme disturbance between
1900 and 1930. Further, between 1935 and 1945 on
0
0.1
0.2
0.3
(a)
(b)
1805
1815
1825
1835
1845
1855
1865
1875
1885
1895
1905
1915
1925
1935
1945
1955
1965
1975
1985
Decade
Proportion of canopy area
disturbed
0
500
1000
1500
Number of trees
Giumalau - 71 plots
0
0.1
0.2
0.3
1805
1815
1825
1835
1845
1855
1865
1875
1885
1895
1905
1915
1925
1935
1945
1955
1965
1975
1985
Decade
Proportion of canopy area
disturbed
0
500
1000
1500
Number of trees
Gap recruitment
Releases
Recruitment to 1.0 m
Sample depth
Gap recruitment
Releases
Recruitment to 1.0 m
Sample depth
Calimani - 61 plots
Fig. 2. Canopy area disturbed for each of the study landscapes Giumalau (a) and Calimani (b; stands pooled for Calimani), summed per decade (as
midpoints). In this figure, only disturbance events that allowed suppressed trees in the understorey or newly established trees to enter the canopy were
included. The chronologies were truncated when the number of trees fell below 20% of the total. Sample depth represents the cumulative number of trees
contributing to the chronology.
Journal of Vegetation Science
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M. Svoboda et al. Landscape-level disturbance in Picea forests
Calimani stand C3, all plots experienced moderate to
extreme disturbance, which we interpret as a stand-
replacing event, with the disturbance patch at least as
large as the stand (12 ha; data not shown). Similarly, an
apparent cluster of plots registering moderate to extreme
disturbance between 1800 and 1830 can be seen at
Giumalau; however, the lack of data from many plots dur-
ing that time limits a complete interpretation of the pat-
tern. In contrast, the spatial pattern during periods of light
to moderate disturbances was less pronounced. For exam-
ple, in Calimani stand C1, the period 18401870 showed a
variable spatial pattern of disturbance over a 14-ha area
(i.e. 14 plots), and at Giumalau the spatial pattern was
similarly variable during the two moderate peaks in dis-
turbance activity (19001930, 19501980; Fig. 4 but see
also Fig. 5 and Appendix S3).
The ordination analysis (Fig. 5, Appendices S3S6) of
the disturbance chronologies confirmed marked variability
of the disturbance histories. At Calimani, the ordination
explained 98% (non-metric fit) of the variance in the raw
data (ordination stress =0.15). The ordination analysis
showed somewhat distinct clusters of plots in ordination
0
0.2
0.4
0.6
0.8
1Giumalau G1 - 71 plots
0
0.2
0.4
0.6
0.8
1Calimani C1 - 40 plots
0
0.2
0.4
0.6
0.8
1Calimani C2 - 4 plots
0
0.2
0.4
0.6
0.8
1
extreme
heavy
moderate
light
Disturbance rates
0
0.2
0.4
0.6
0.8
1Calimani C4 - 6 plots
0
0.2
0.4
0.6
0.8
1
1765
1775
1785
1795
1805
1815
1825
1835
1845
1855
1865
1875
1885
1895
1905
1915
1925
1935
1945
1955
1965
1975
1985
Calimani C5 - 5 plots
Proportion of plots
Decade
Fig. 3. Disturbance chronologies showing the proportion of plots (per stand) experiencing various disturbance severities, per decade. Thesechronologies
are based on the same data as in Fig. 2, but with results shown at the stand level, with four disturbance severity classes 0.120% (light), 20.140%
(moderate), 40.160% (heavy), >60% (extreme). For each stand, the chronologies were truncated on the plot when the number of trees fell below 20% of the
total. The vertical lines show the periods with extreme disturbance rates from Table 2.
Journal of Vegetation Science
394 Doi:10.1111/jvs.12109 ©2013 International Association for Vegetation Science
Landscape-level disturbance in Picea forests M. Svoboda et al.
space, the result of similar histories of high-severity
disturbance, particularly evident for sites C3 and C1
(Fig. 5). However, there was no clear evidence for syn-
chronization in disturbance histories among individual
sites in Calimani. The clusters of plots in C3 and partly C1
were located in ordination space with high values of the
DI. When projected onto ordination space, the DI
increased in all directions from low values in the centre of
ordination space (minimum possible value 3 for low dis-
turbance severity), such that plots with higher DIs were
located away from this central space (maximum possible
value 0 for high disturbance severity). DIs for Calimani
showed significant correlation with ordination axes
(P<0.001, r
2
=0.42). A large proportion of plots belonged
to the zone with DI values >1.5, indicating a history of
relatively high disturbance severity. At Giumalau, plots
form a broad distribution in ordination space, without
distinct groups reflecting similar disturbance histories
(Appendix S3). This ordination explained 96% (non-met-
ric fit) of the variance in the raw data (ordination
stress =0.21).
Ordination analysis revealed only partial effects of phys-
iographic attributes on plot disturbance histories. In Cali-
mani, both plot altitude (r
2
=0.37, P<0.001) and land
form (r
2
=0.35, P<0.001) were correlated with ordina-
tion axes. Altitude was negatively and land form positively
correlated with disturbance severity (Fig. 5), suggesting
that plots with higher altitude showed a lower DI, and con-
versely, plots on lower slope positions showed a higher DI.
In Giumalau, only altitude (r
2
=0.29, P<0.001) was cor-
related with ordination axes, with no clear relationship
with DI (Appendix S3). No other physiographic attributes
were significantly (P>0.05) correlated with ordination
axes in either Giumalau or Calimani.
Discussion
The historical disturbance regime revealed in this compre-
hensive study (ca. 3500 increment cores collected from
132 plots) is characterized by considerable spatial variabil-
ity, which could be seen among plots within stands, among
stands within landscapes and between the two landscapes.
A wide range of disturbance severities was also docu-
mented, ranging from periods of light disturbances (pre-
sumably tree-fall gaps) to periods of heavy to extreme
disturbance (including stand replacement), the latter
showing clustering up to 20 ha. In the discussion that fol-
lows, we first consider in detail our interpretation of the
historical disturbance regime in this region and then we
address methodological challenges encountered in studies
such as this.
Landscape-level disturbance history interpretation
The spatial and temporal variation in disturbance severity
documented in this study yields new insight into land-
scape-scale disturbance processes in mountain P. abies for-
ests of Europe’s temperate zone. Analysis of disturbance
severity complemented by NMDS ordination revealed a
gradient of disturbance severity across the landscape. In
part, our results challenge the traditional model of P. abies
forest dynamics in Europe’s temperate zone, which places
emphasis on small-scale, canopy gap processes (Korpel’
1995). More than half of the 132 plots showed evidence of
past extreme severity disturbance based onthe analysis that
summed disturbance evidence over three consecutive dec-
ades (see Table 2). By comparison, if we base our interpre-
tation on the decadal disturbance chronology, 12% of the
plots had evidence of extreme severity disturbance. The
Fig. 4. Maps of disturbance rates for Giumalau (G1) and Calimani (C1) for periods with the most severe disturbances. To capture prolonged recruitment
periods, disturbance rates were summed in three consecutive decades for selected periods. The size of the circle represents disturbance class: 0%, 0.1
20%, 20.140%, 40.160%, >60% canopy area disturbed per plot. Crosses represent plots without information due to younger tree ages.
Journal of Vegetation Science
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M. Svoboda et al. Landscape-level disturbance in Picea forests
occurrence of past high-severity disturbance was especially
evident in the Calimani landscape, where evidence of
stand-replacing events was found over areas as large as
20 ha. Similarly, recent work in other primary P. abies for-
ests in Europe’s temperate region reported evidence of
wind disturbance, ranging in size from several to hundreds
of hectares (Svoboda & Pouska 2008; Svoboda et al. 2010,
2012; Zielonka et al. 2010; Panayotov et al. 2011;
Cada
et al. 2013). This study provides additional evidence that
stand-replacing disturbances are part of the natural distur-
bance regime in P. abies forests.
Although we found strong evidence of stand-replacing
disturbances within stands, there was less evidence that
such events were synchronized throughout the entire
landscape. Several periods (e.g. from 1800 to 1830 and
1900 to 1930) with high-severity disturbance were com-
mon to only three out of six study sites. Within stands,
however, plots that recorded damage during these periods
of high-severity disturbance were often clustered in space
(see Fig. 5). Previous studies have documented clustered
patterns of high-severity disturbances in landscapes where
windstorms were the most severe disturbance agent
(Frelich & Lorimer 1991; Foster & Boose 1992; Kulakow-
ski & Veblen 2002; D’Amato & Orwig 2008; Fraver et al.
2009). The prevalence of wind as a disturbance agent
could potentially explain lower synchronicity in stand-
replacing events in this study, given its patchy nature
within a landscape (Panayotov et al. 2011). Nevertheless,
even in mountainous regions with complex topography,
windstorms can cause stand-replacing disturbances over
large continuous areas up to thousands of hectares
(Kulakowski & Veblen 2002; Zielonka et al. 2010). Fur-
thermore, it is well documented that damage caused by
windstorms can vary considerably across landscapes, due
to variability in the storm itself, as well as interactions
with forests and landscape features (e.g. Foster & Boose
1992; Frelich & Reich 1995; Kulakowski & Veblen 2002;
Panayotov et al. 2011; Stueve et al. 2011). The relation-
ship between physiographic features and the spatial pat-
tern of disturbance was analysed without straightforward
results. Altitude and land form were correlated with the
ordination gradient, but only in Calimani. The low num-
ber of plots covering a range of physiographic conditions
over the landscape is likely a limitation of this aspect in
our study. Several other studies have found a relationship
between disturbance history and topographic exposure,
especially when focusing on the effects of windstorms
(Sinton et al. 2000; Kulakowski & Veblen 2002; D’Amato
& Orwig 2008; Panayotov et al. 2011). In the Rila
Mountains of Bulgaria, for example, Panayotov et al.
(2011) report increasing likelihood of wind-throw on par-
ticular slope aspects and with increasing altitude in P. abies
forests.
Many of the plots throughout the studied landscape
did not show evidence of severe disturbance, but rather a
history of low- and intermediate-severity disturbances. A
good example is the 19501980 period in Giumalau,
when a significant number of plots showed light to mod-
erate disturbance with considerable spatial variation
throughout the stand (see Fig. 4). Tree mortality during
periods of light and moderate disturbances could result
from several processes. For example, moderate severity
wind damage or bark beetle outbreaks can cause a range
of mortality patterns at the stand scale, from scattered,
single trees to small patches of catastrophic damage
(Woods 2004; Worrall et al. 2005; Nagel & Svoboda
2008). Fungal colonization of old trees could also cause
direct mortality or indirectly increase vulnerability to
wind or bark beetle attack (Worrall et al. 2005). Based on
our results, moderate severity disturbance events that
remove 2040% of the canopy in a given decade affected
a similar portion of the landscape, as did extreme distur-
bances. Similarly, Stueve et al. (2011) suggest that the
Fig. 5. Non-metric multidimensional scaling (NMDS) ordination of
disturbance histories from the Calimani landscape, based on a matrix of
decadal disturbance rates. Individual stands are designated in the
ordination (see Table 1). Isolines show the gradient in the disturbance
index (DI, see Methods). The DI increases in all directions from a low in the
centre of ordination space (minimum possible value 3forlow-
disturbance severity), such that plots with higher DIs were located away
from this central space (maximum possible value 0 for high-disturbance
severity). Vectors show passively projected physiographic characteristics
of plots and the DI index, where only those with r²>0.1 are shown. The
vector orientation shows the direction of the gradient, and its length is
proportional to the correlation between the variable and the ordination.
Journal of Vegetation Science
396 Doi:10.1111/jvs.12109 ©2013 International Association for Vegetation Science
Landscape-level disturbance in Picea forests M. Svoboda et al.
aggregate damage of intermediate severity disturbances is
similar to that of large, catastrophic events that occur
very infrequently in forested landscapes of the Great
Lakes region, USA. Taken together, these findings suggest
that periodic disturbances that cause intermediate sever-
ity damage at stand scales may be an important compo-
nent of the disturbance regime in temperate forest
regions.
Our results therefore highlight the considerable vari-
ability in disturbance severity in both space and time over
the studied landscape. That is, we documented a contin-
uum of canopy damage ranging from small-scale gap
dynamics, to localized damage from intermediate severity
disturbance, and to stand-replacing events over large
areas of individual stands. Notably, previous studies in
P. abies forests of Europe’s temperate zone have reported
a range of disturbance severities at the stand level. For
example, some studies have reported gap dynamics (Hole-
ksa & Cybulski 2001; Panayotov et al. 2011; Szewczyk
et al. 2011), while others have reported stand-replacing
disturbances (Zielonka et al. 2010; Panayotov et al. 2011;
Svoboda et al. 2012). However, when disturbance pat-
terns are evaluated at the landscape scale, as in this study,
the entire range of disturbance severity can be found
within a given landscape. This heterogeneity in distur-
bance severity at local and regional scales has also been
documented in temperate forests of North America,
where large areas of primary forests occur (e.g. Frelich &
Lorimer 1991; Foster & Boose 1992; Veblen et al. 1994;
Bergeron 2000; D’Amato & Orwig 2008; Fraver et al.
2009).
Disturbance agents: windstorms or bark beetle
outbreaks
Because dendrochronological methods alone cannot iden-
tify the agents of historical disturbance pulses documented
in this study, we searched all available historical archives
for information on the occurrence and severity of distur-
bances during the last 200 yrs in the study region (Fig. 6,
Appendix S7). Historical data suggest that windstorms and
bark beetle outbreaks were the most likely causes of the
disturbance peaks found in this study. Strong windstorms
that caused widespread damage were reported throughout
the time period covered with our disturbance chronolo-
gies, and were more frequent than reported bark beetle
outbreaks, which suggest that wind may have been a more
important disturbance agent during the past two centuries.
(Fig. 6, Appendix S7). Peaks in disturbance severity
detected in this study (18001830, 18201850, 18401870,
19001930 and 19501980) coincided with the distur-
bances reported in the historical data. However, because
of the limited geographic precision of the reported histori-
cal disturbances, the connection between individual
windstorms and bark beetle outbreaks is difficult to make.
Another limitation is that the reliability of historical data
decreases further back in time. Nevertheless, there is clear
evidence that strong windstorms occur in the region nearly
every decade, often several times during a given decade.
Consistent with this finding, recent work suggests that Cal-
imani and Giumalau are located within regions of Roma-
nia with the highest occurrence and risk of wind
disturbance (Popa 2007).
Fig. 6. Historical disturbances in Romania for the period covered in this study, summed per decade (as midpoints). We include here only severe
disturbances with a regional impact on mountain forests. In many cases no details were available regarding the exact location and extent of damage.
Information compiled from Avram (1983), Ichim (1988) and Popa (2007, 2008).
Journal of Vegetation Science
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M. Svoboda et al. Landscape-level disturbance in Picea forests
Methodological considerations
Our analyses highlighted two important methodological
issues related to the reconstruction of past disturbances.
The first relates to gap recruitment, which was the domi-
nant pathway of canopy accession in our study; ca. 80% of
trees showed this pattern (see Fig. 2, Table 1). Similar pat-
terns were reported by Svoboda et al. (2012) and Panayo-
tov et al. (2011) in other P. abies forests in Europe’s
temperate zone. These findings have important implica-
tions for disturbance history reconstruction. Specifically,
relying solely on releases from suppression to reconstruct
past disturbances could potentially underestimate distur-
bance rates. A second methodological concern is associated
with protracted periods of gap recruitment following dis-
turbances. Several previous studies suggest that recruit-
ment of P. abies regeneration might span several decades
following disturbance (Holeksa et al. 2007; Panayotov
et al. 2011; Szewczyk et al. 2011; Svoboda et al. 2012). In
addition to the slow growth of P. abies seedlings and sap-
lings in mountain environments, there are a number of
possible explanations for the prolonged recruitment period
seen in the disturbance reconstructions. This pattern could
be the resultof successive canopy disturbances over several
decades, a combination of advance regeneration and
newly established seedlings, a lack of sufficiently decayed
dead wood for seedling establishment, or factors that influ-
ence the survival and growth of regeneration, such as
browsing, late frost and heavy snow or ice damage in post-
disturbance cohorts. In closed-canopy stands with little to
no advance regeneration, seedling establishment and
recruitment following stand-replacing disturbance could
be particularly slow (Rammig et al. 2006; Svoboda et al.
2012). Recognizing these long periods of post-disturbance
recruitment is important for interpreting disturbance histo-
ries. That is, quantifying disturbance severity by decade,
which is the most common approach (Frelich & Lorimer
1991), would underestimate disturbance severity in cases
when post-disturbance regeneration occurs over several
decades. Similarly, long establishment periods for distur-
bance severity assessment have been used in sub-alpine
forests in several other regions (Veblen et al. 1994;
Kulakowski & Veblen 2006; DeRose & Long 2012).
Conclusions
Of the two growth rate criteria used to assess past distur-
bance, gap recruitment was by far the most common, rep-
resenting 80% of disturbance evidence overall.
Importantly, this recruitment occurred over quite pro-
tracted time periods, which spanned at least three decades
following disturbance. We identified a range of disturbance
severities over the landscape, including periods with the
stand-replacing events, as well as periods with low- and
intermediate-severity disturbances. More than half of the
plots across the studied landscape experienced high- to
extreme-severity disturbances, although they were not
always spatially and temporally synchronized across stands
and landscapes. Plots indicating high-severity disturbances
were often clustered in space; while this tendency was less
clear for moderate- and low-severity disturbances. Stand-
replacing disturbances were detected in areas up to
1020 ha, and were likely caused by windstorms. Histori-
cal evidence suggests that windstorms played an important
role in shaping these forests, while the role of bark beetle
outbreaks remains unclear. Intermediate- and low-severity
disturbances also played an important role over a large part
of the landscape, highlighting the considerable spatial and
temporal variation in disturbance severity throughout the
landscape. Thus, when the disturbance regime was appro-
priately evaluated at the landscape scale, as in this study,
the entire range of disturbance severity was revealed
within this landscape.
Acknowledgements
This study was supported by Czech Science Foundation
project GACR P504/10/1644. J. Rejzek, M. Mikol
a
sandV.
Trotsiuk were supported by the Czech University of Life
Sciences, student project CIGA 20114310. We would like
to thank M. Valtera, J. Lehej
cek,
C. Streer, S. Kosobud, K.
Svobodov
a, M. Reitschmiedov
a, L. Mat
ej
u, M.
Cern
ıkov
a
and C. Voln
y for assistance in the field. Comments by
anonymous reviewers have greatly improved the manu-
script. We thank the C
alimani National Park authorities,
especially E. Cenus
ß
a and local foresters, for administrative
support and assistance in the field.
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Supporting Information
Additional supporting information may be found in the
online version of this article:
Appendix S1. Examples of plot-level disturbance
chronologies.
Appendix S2. The disturbance history reconstruc-
tion of old canopy trees in stand C1.
Appendix S3. Non-metric multidimensional scaling
(NMDS) ordination of disturbance histories from the
Giumalau landscape, based on matrices of decadal distur-
bance rates.
Appendix S4. Maps showing the altitude of plots in
Giumalau (G1) and Calimani C1.
Appendix S5. Maps of disturbance index (DI) values
for plots in Giumalau (G1) and Calimani (C1).
Appendix S6. Land form maps of plots in Giumalau
(G1) and Calimani (C1).
Appendix S7. Historical disturbances (windstorm
and bark beetle outbreak) in Romania for the period cov-
ered by this study.
Journal of Vegetation Science
Doi: 10.1111/jvs.12109©2013 International Association for Vegetation Science 401
M. Svoboda et al. Landscape-level disturbance in Picea forests
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Understanding the processes shaping the composition of assemblages at multiple spatial scales in response to disturbance events is crucial for preventing ongoing biodiversity loss and for improving current forest management policies aimed at mitigating climate change and enhancing forest resilience. Deadwood-inhabiting fungi represent an essential component of forest ecosystems through their association with deadwood decomposition and the cycling of nutrients and carbon. Although we have sufficient evidence for the fundamental role of deadwood availability and variability of decay stages for fungal species diversity, the influence of long-term natural disturbance regimes as the main driver of deadwood quantity and quality has not been sufficiently documented. We used a dendroecological approach to analyse the effect of 250-years of historical natural disturbance and structural habitat elements on local (plot-level) and regional (stand-level) species richness of deadwood-inhabiting fungi. We used data collected from 51 study plots within nine best-preserved primary spruce forest stands distributed across the Western Carpathian Mountains. Historical disturbances shaped the contemporary local and regional species richness of fungi, with contrasting impacts of disturbance regime components at different spatial scales. While local diversity of red-listed species has increased due to higher disturbance frequency, regional diversity of all species has decreased due to higher severity historical disturbances. The volume of deadwood positively influenced the species richness of deadwood-inhabiting fungi while canopy openness had a negative impact. The high number of observed rare species highlights the important role of primary forests for biodiversity conservation. From a landscape perspective, we can conclude that the distribution of species from the regional species pool is-at least to some extent-driven by past spatiotemporal patterns of disturbance events. Natural disturbances occurring at higher frequencies that create a mosaic forest structure are necessary for fungal species-especially for rare and endangered taxa. Thus, both the protection of intact forest landscapes and forest management practises that emulate natural disturbance processes are recommended to support habitats of diverse fungal communities and their associated ecosystem functions.
... Recent dendroecological studies on European primary Picea forests show that increasingly common high-severity disturbances are not only a result of climate change and should be reinterpreted considering legacy effects (resulting in increased susceptibility e.g., Schurman et al., 2018). In contrast with the literature on stand scale natural disturbance reconstructions (e.g., Szewczyk et al., 2011), recent landscape level studies show that large scale natural disturbances historically occurred in primary (unmanaged) forest landscapes (Svoboda et al., 2014;Janda et al., 2017). This study contributes to the conception that bark beetle outbreaks, even in their unprecedented magnitude, are acting as a natural disturbance agent in temperate conifer mountain forest (e.g., Kulakowski, 2016). ...
Article
Temperate mountain forests have experienced an increase in frequency and severity of natural disturbances (e.g., droughts, fires, windstorms and insect outbreaks) in recent decades due to climate and environmental change. Outbreaks of bark beetles have caused significant dieback of conifer forests in Central Europe and it is essential to model and predict the potential severity of future bark beetle outbreaks. However, to predict future bark beetle activity, historical baseline information is required to contextualize the magnitude of current and potential future outbreaks. A fossil beetle record from a forest hollow in the Tatra Mountains, Slovakia; one of the best-preserved national parks in Central Europe, was produced to identify insect outbreaks during the last millennia. Sub-fossil bark beetle re-mains were compared with parallel pollen and charcoal to assess whether peaks in conifer bark beetle remains correspond with indications of disturbance documented in historical or sedimentary fossil records. Three peaks in bark beetle remains were detected (1) post-2004, (2) AD 1140-1440, and (3) AD930-1030. The abundance of speciesPityogenes chalcographusandPityophthorus pityographus in the two top samples can be linked directly to large bark beetle outbreaks in the High Tatra Mountains after 2004. P. chalcographus and P. pityographus are also the abundant species in the second peak (AD 1140e1440) while the third peak (AD 930e1030) consists of the species Polygraphus poligraphus. The most prominent conifer bark beetle in Central Europe, Ips typographus, was found to be present in most of the samples but always at very low numbers. It is plausible that P. chalcographus and P. pityographus fossils might be useful proxies for past conifer bark beetle outbreaks in Central Europe, as they occur together with fossils of I. typographus but appear to be well-preserved. A significant correlation was found between primary bark beetles and macroscopic charcoal densities in the sediment, highlighting the complex interactions between disturbance agents, bark beetles and fire, in this long-term regime of natural disturbances. Our 1400-year disturbance record shows how bark beetle outbreaks have been an important component of the regional natural disturbance regime for over a millennium and have intensified with increasing anthropogenic activity. Bark beetle outbreaks are likely one of the drivers promoting the future ecological stability of the temperate conifer ecosystem over decades to centuries.
... Previous studies show that wind has been an important natural disturbance factor in many parts of Europe during the past 300 years (Zielonka and Malcher, 2009;Panayotov et al., 2011;Svoboda et al., 2012Svoboda et al., , 2013Janda et al., 2014;Trotsiuk et al., 2014;Pettit et al., 2021), although there is considerable variability in disturbance regimes between various regions and forests (managed vs old-growth forests). It has been suggested that strong wind severity and frequency has increased during the past century and that this has been accompanied by increases in both the area affected and volume of damaged trees (Gregow et al., 2017). ...
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Windstorms are one of the most important disturbance factors in European forest ecosystems. An understanding of the major drivers causing observed changes in forests is essential to improve prediction models and as a basis for forest management. In the present study, we use machine learning techniques in combination with data sets on tree properties, bioclimatic and geomorphic conditions, to analyse the level of forest damage by windstorms in the Sudety Mountains over the period 2004–2010. We tested four scenarios under five classification model frameworks: logistic regression, random forest, support vector machines, neural networks, and gradient boosted modelling. Gradient boosted modelling and random forest have the best predictive power. Tree volume and age are the most important predictors of windstorm damage; climate and geomorphic variables are less important. Forest damage maps based on forest data from 2020 show lower probabilities of damage compared to the end of 20th and the beginning of 21st century.
... Recently, TRW data have been successfully applied to predict future forest growth and climate responses (Charney et al. 2016;Dorado-Liñán et al. 2019). TRW data have also been used to reconstruct regimes of windthrow, bark beetle, storm and other disturbance regimes (Veblen et al. 1994;Svoboda et al. 2014). Explaining relationships between climate and disturbance dynamics (Hart et al. 2014) forms the basis to parameterise models of disturbance dynamics under climate change (Temperli et al. 2015;Thom et al. 2017). ...
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Models to predict the effects of different silvicultural treatments on future forest development are the best available tools to demonstrate and test possible climate-smart pathways of mountain forestry. This chapter reviews the state of the art in modelling approaches to predict the future growth of European mountain forests under changing environmental and management conditions. Growth models, both mechanistic and empirical, which are currently available to predict forest growth are reviewed. The chapter also discusses the potential of integrating the effects of genetic origin, species mixture and new silvicultural prescriptions on biomass production into the growth models. The potential of growth simulations to quantify indicators of climate-smart forestry (CSF) is evaluated as well. We conclude that available forest growth models largely differ from each other in many ways, and so they provide a large range of future growth estimates. However, the fast development of computing capacity allows and will allow a wide range of growth simulations and multi-model averaging to produce robust estimates. Still, great attention is required to evaluate the performance of the models. Remote sensing measurements will allow the use of growth models across ecological gradients.
... Whereas fine-scale disturbances dominate the natural forest dynamics of deciduous upland forests of Central Europe [7][8][9][10], several studies have highlighted the importance of large-scale, stand-replacing events for conifer mountain forest ecosystems [11][12][13][14][15]. More recently, a mixed-severity disturbance regime, predominantly driven by gap dynamics with infrequent severe stand-replacing events, has been documented for some mixed mountain forest ecosystems [8,13,[16][17][18][19][20]. Though fine-scale processes have been abundantly studied in Central European forests, the long-term dynamics of mountain sites following high-severity disturbances needs further investigation, particularly in respect to tree-species coexistence, spatial patterns, tree-soil interactions and factors controlling mortality. ...
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The driving forces of tree mortality following wind disturbances of mountain mixed European temperate forests belongs among issues not comprehensively resolved. Hence, we aimed to elucidate the key factors of tree resistance to historical severe disturbance events in the Boubínský Primeval Forest, one of the oldest forest reserves in the Czech Republic. By using spatially explicit tree census, dendrochronological and soil data, we study spatial and temporal patterns of past disturbances and mathematically compared selected characteristics of neighboring trees that were killed by a severe storm in 2017 and those that remained undisturbed. The tendency of trees toward falling was primarily driven edaphically, limiting severe events non-randomly to previously disturbed sites occupied by hydromorphic soils and promoting the existence of two spatially-separated disturbance regimes. While disturbed trees usually recruited in gaps and experienced only one severe release event, surviving trees characteristically regenerated under the canopy and were repeatedly released. Despite the fact that disturbed trees tended to reach both lower ages and dimensions than survivors, they experienced significantly higher growth rates. Our study indicates that slow growth with several suppression periods emerged as the most effective tree strategy for withstanding severe windstorms, dying of senescence in overaged life stage. Despite the selective impact of the Herwart storm on conifer population, we did not find any difference in species sensitivity for most characteristics studied. We conclude that the presence of such ancient, high-density wood trees contributes significantly to the resistance of an entire stand to severe storms.
... Disturbances are an essential component of forest dynamics that significantly affect forest biodiversity and species composition (Schelhaas et al., 2003;Svoboda et al., 2014). In natural forests, the varying spatial and temporal extent of disturbances and their severities create a mosaic of forests with alternating structural complexity throughout the landscape (Sommerfeld et al., 2018). ...
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Aim Natural disturbances influence forest structure, successional dynamics, and, consequently, the distribution of species through time and space. We quantified the long-term impacts of natural disturbances on lichen species richness and composition in primary mountain forests, with a particular focus on the occurrence of endangered species. Location Ten primary mountain spruce forest stands across five mountain chains of the Western Carpathians, a European hotspot of biodiversity. Methods Living trees, snags, and downed logs were surveyed for epiphytic and epixylic lichens in 57 plots. Using reconstructed disturbance history, we tested how lichen species richness and composition was affected by the current forest structure and disturbance regimes in the past 250 years. We also examined differences in community composition among discrete microhabitats. Results Dead standing trees as biological legacies of natural disturbances promoted lichen species richness and occurrence of threatened species at the plot scale, suggesting improved growing conditions for rare and common lichens during the early stages of recovery post-disturbance. However, high-severity disturbances compromised plot scale species richness. Both species richness and the number of old-growth specialists increased with time since disturbance (i.e. long-term uninterrupted succession). No lichen species was strictly dependent on live trees as a habitat, but numerous species showed specificity to logs, standing objects, or admixture of tree species. Main conclusions Lichen species richness was lower in regenerating, young, and uniform plots compared to overmature and recently disturbed areas. Natural forest dynamics and its legacies are critical to the diversity and species composition of lichens. Spatiotemporal consequences of natural dynamics require a sufficient area of protected forests for provisioning continual habitat variability at the landscape scale. Ongoing climatic changes may further accentuate this necessity. Hence, we highlighted the need to protect the last remaining primary forests to ensure the survival of regionally unique species pools of lichens.
... This was done after discussing with data contributors the criteria and categories used for constructing their datasets, which we then mapped onto our definition framework. Depending on the datasets, these criteria included: (1) forest age or structural variables 19,23,36 , (2) legal designation 25 or year since onset of protection 37 , (3) time since last anthropogenic disturbancee 38 , or (4) the lack of human impacts and infrastructures 39 . ...
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Primary forests, defined here as forests where the signs of human impacts, if any, are strongly blurred due to decades without forest management, are scarce in Europe and continue to disappear. Despite these losses, we know little about where these forests occur. Here, we present a comprehensive geodatabase and map of Europe’s known primary forests. Our geodatabase harmonizes 48 different, mostly field-based datasets of primary forests, and contains 18,411 individual patches (41.1 Mha) spread across 33 countries. When available, we provide information on each patch (name, location, naturalness, extent and dominant tree species) and the surrounding landscape (biogeographical regions, protection status, potential natural vegetation, current forest extent). Using Landsat satellite-image time series (1985–2018) we checked each patch for possible disturbance events since primary forests were identified, resulting in 94% of patches free of significant disturbances in the last 30 years. Although knowledge gaps remain, ours is the most comprehensive dataset on primary forests in Europe, and will be useful for ecological studies, and conservation planning to safeguard these unique forests.
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Natural disturbances strongly influence forest structural dynamics, and subsequently stand structural heterogeneity, biomass, and forest functioning. The impact of disturbance legacies on current forest structure can greatly influence how we interpret drivers of forest dynamics. However, without clear insight into forest history, many studies default to coarse assumptions about forest structure, for example, whether forests are even or unevenly aged. The aim of this study was to analyze the effects of past disturbances on the current diameter distributions of Norway spruce (Picea abies (L.) Karst.)-dominated landscapes throughout the Carpathian Mountains. Our dendroecological dataset comprises tree cores from 339 plots (7,845 total tree cores), nested within 28 primary forest stands, known to vary greatly in the severity of historical disturbances. Our analyses revealed that historical disturbances had a strong and significant effect on the current diameter distribution shapes at the plot level. We demonstrated that mixed-severity disturbance regimes were more frequent and create a complex pattern of diameter distributions at the plot and stand scale. Here, we show that high severity disturbance was associated with unimodal diameter distributions, while low and moderate severity was associated with the reverse J-shaped distribution. This is a result of complex disturbance patterns, with structural biological legacies. Our results will have important management implication in the context of tree size heterogeneity, biomass storage, and productivity as influenced by natural disturbances. Lastly, these results demonstrate that structural changes may arise as consequences of changing disturbance regime associated with global change.
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This study examined relationships among forest landscape dynamics, environmental factors (climate and landforms), and disturbance history in forests dominated by Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and Pacific silver fir (Abies amabilis) in the Bull Run basin in northwestern Oregon and evaluated the findings in a broader geographic context. Three sets of analyses were conducted: mapping of historical windthrow disturbance patches in the 265-km2 Bull Run basin over the past century and analysis of their relationships with meteorological conditions, landforms, and vegetation; comparison of forest structure and species composition as a function of mapped windthrow and wildfire disturbance history in 34 1-ha vegetation survey plots in Bull Run; and canonical correspondence analysis of environmental factors and forest overstory species composition in 1637 vegetation plots in the Mount Hood and Willamette National Forests. Nearly 10% of the Bull Run basin has been affected...
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Duncan, R.P. (1989). An evaluation of errors in tree age estimates based on increment cores in kahikatea (Dacrycarpus dacrydioides). New Zealand Natural Sciences 16: 31-37. Twelve kahikatea (Dacrycarpus dacrydioides) discs were used to assess the likely errors associated with estimating tree age from growth ring counts in increment cores. Two major sources of error were examined: (1) Failure of the increment core to pass through the tree's chronological centre. A geometric model is developed for estimating the distance to the chronological centre in cores where the arcs of the inner rings are visible. The mean percentage error from 84 cores that passed within 50 mm of the chronological centre was ± 35% corresponding to a mean absolute error of ± 21 years. The majority of this error is due to growth rate differences between the missing radius and the measured part of the core. (2) Missing rings. The average age underestimate from 48 cores due to missing rings was 13%. A significant correlation between radius length and age under estimate (r = 0.81) suggests that sampling along the longest radii will reduce this error. The average age underestimate due to missing rings from cores located along the longest radii of the twelve samples was 3%.
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Norway spruce (Picea abies L.) is an important tree species with a remarkable natural range throughout Europe and Asia, ranging from the Balkan Peninsula to Siberia in the north and from the French Alps in the west to the Sea of Okhotsk in the east. Wherever it occurs, it is a key component of both natural and managed forests. Norway spruce is the most economically valuable conifer in Europe, producing high-quality timber and wood products. This book presents a concise and comprehensive review of the biology, ecology, and management of Norway spruce. It integrates classic and contemporary literature (more than 2000 works cited in the text), highlighting basic research and forestry practices in central and eastern Europe. The topics include anatomy and morphology, physiology and nutrition, reproductive biology and genetics, and ecology. In addition, it examines mycorrhiza, diseases and pests as well as silviculture and wood products. In the light of increasing threats to forest health from air pollution, climate change, and insects and disease, it provides an essential information source to those concerned with the ecology, conservation, and management of the species.
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Landscape pattern is generated by a variety of processes, including disturbances. In turn, the heterogeneity of the landscape may enhance or retard the spread of disturbance. The complex relationship between landscape pattern and disturbance is the subject of this book. It is designed to present an illustrative analysis of the topic, presenting the perspectives of several different disciplines. The book includes conceptual considerations, empirical studies, and management examples. Important features include: hypotheses about the spread of disturbance and the effects of scale changes in landscape studies; the multidisciplinary approach; and the explicit focus on the landscape level. The intended audience comprises graduate students, academics, and professionals interested in landscape ecology. The reader will receive a state-of-the-art treatment of a current topic in landscape ecology.
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Ecologists are aware of the importance of natural dynamics in ecosystems. Historically, the focus has been on the development in succession of equilibrium communities, which has generated an understanding of the composition and functioning of ecosystems. Recently, many have focused on the processes of disturbances and the evolutionary significance of such events. This shifted emphasis has inspired studies in diverse systems. The phrase "patch dynamics" (Thompson, 1978) describes their common focus. The Ecology of Natural Disturbance and Patch Dynamics brings together the findings and ideas of those studying varied systems, presenting a synthesis of diverse individual contributions.
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Background: In forests subject to stand-replacing disturbances, conventional models of succession typically overlook early-seral stages as a simple re-organization/establishment period. These models treat structural development in essentially 'relay floristic' terms, with structural complexity (three-dimensional heterogeneity) developing primarily in old-growth stages, only after a closed-canopy 'self-thinning' phase and subsequent canopy gap formation. However, is it possible that early-successional forests can sometimes exhibit spatial complexity similar to that in old-growth forests - i.e. akin to an 'initial floristic' model of structural development? Hypothesis: Based on empirical observations, we present a hypothesis regarding an important alternative pathway in which protracted or sparse forest establishment and interspecific competition thin out tree densities early on - thereby precluding overstorey canopy closure or a traditionally defined self-thinning phase. Although historically viewed as an impediment to stand development, we suggest this process may actually advance certain forms of structural complexity. These young stands can exhibit qualities typically attributed only to old forests, including: (1) canopy gaps associated with clumped and widely spaced tree stems; (2) vertically heterogeneous canopies including under- and mid-stories, albeit lower stature; (3) co-existence of shade-tolerant and intolerant species; and (4) abundant dead wood. Moreover, some of these qualities may persist through succession, meaning that a significant portion of eventual old-growth spatial pattern may already be determined in this early stage. Implications: The relative frequency of this open-canopy pathway, and the degree to which precocious complexity supports functional complexity analogous to that of old forests, are largely unknown due to the paucity of naturally regenerating forests in many regions. Nevertheless, recognition of this potential is important for the understanding and management of early-successional forests.
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Natural forest age dynamics is often more or less cyclic, with profound temporal changes in stem density and tree size, tree age structure, deadwood frequency and the abundance of canopy gaps. We investigated the response of ground and epiphyte vegetation to the natural forest age dynamics of an old-growth spruce forest focussing on (1) the influence of stand age-related shifts in forest structure and related changes in soil conditions on the diversity and composition of plant communities, (2) differences in the species turnover of cryptogamic epiphytes and ground vegetation in relation to forest age development, and (3) the importance of later (advanced) forest development stages for characteristic epiphyte communities.