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Reinforcementcapacityofpotentialbuffer
zones:Foreststructureandconservation
valuesaroundforestreservesinsouthern
Sweden
ArticleinForestEcologyandManagement·July2005
DOI:10.1016/j.foreco.2005.03.028
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Forest Ecology and Management 212 (2005) 333–345
www.elsevier.com/locate/foreco
Reinforcement capacity of potential buffer zones: Forest structure
and conservation values around forest reserves in southern Sweden
Maria Thorell, Frank Götmark *
Animal Ecology, Department of Zoology, Göteborg University, Box 463, SE 40530 Göteborg, Sweden
Received 15 September 2004; received in revised form 22 February 2005; accepted 30 March 2005
Abstract
Buffer zones may reinforce protected areas and are often recommended, but have rarely been systematically studied in
temperate forests. Globally, temperate broadleaved forest is considered to be the most disturbed biome, with small, scattered
natural fragments. In theory, it is often assumed that nature reserves have heavily exploited surroundings. We tested this
assumption using a random sample of 49 small reserves (forest area 5–225 ha) that lacked buffer zones. We expected two major
outcomes: either a sharp decline in conservation value from the forest reserves to the surroundings, or a gradient of decreasing
value from the reserves and outwards. Basic structural indicators of red-listed forest species were studied in the reserves, in their
potential buffers (200 m wide), and in non-protected forests outside the buffers. On average, southern broadleaved deciduous
forest covered 37% of the forested area in the reserves, 18% in the potential buffers and 5% in non-protected forest outside the
buffers. The density of large living trees (>40 cm diameter at breast height, dbh) was 30 stems per woodland hectare in the
reserves, decreasing to 15 in the buffers, and to 10 outside the buffers. Similar, but less marked gradients, were found for dead
standing trees and downed dead wood. The diversity of trees and shrubs indicated relatively high conservation values in the
buffers. Valuable reserves had valuable potential buffers, as conservation values of the reserves were positively correlated with
those of the buffers. Our results show that heavy exploitation of surroundings cannot a priori be assumed for nature reserves. The
results are encouraging for preservation of temperate forest biodiversity, since small reserves seem to be reinforced by their
surroundings, but we suggest that protection by law or by other means is necessary to maintain the conservation values of
potential buffer zones for the future.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Conservation strategy; Reserve surroundings; Matrix; Dead wood; Deciduous broadleaved trees
1. Introduction
* Corresponding author. Tel.: +46 31 7733650;
fax: +46 31 416729.
E-mail addresses: [email protected] (M.Thorell),
[email protected] (F. Götmark).
Nature reserves and other protected areas (hereafter
‘reserves’) are cornerstones for the preservation of
biodiversity. In order to function successfully, reserves
need to be combined with appropriate management of
the surrounding landscape, and therefore zoning is
0378-1127/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2005.03.028
334
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
often recommended (Noss and Cooperrider, 1994;
Harwell, 1997; Norton, 1999). In particular, buffer
zones around reserves are viewed as important
(Jongman, 1995; Groom et al., 1999; Shafer, 1999).
Buffer zones have a two-fold purpose; to reinforce
reserves by, e.g., increasing the size of area
considered, and to eliminate or reduce negative
influence on the reserves from their surroundings
(Batisse, 1997; Groom et al., 1999; Shafer, 1999).
Reserve species may find supplemental habitat in
buffer zones, but buffer zones may also be core area
for other species, and become core area for new
species if habitat or climate changes (Groom et al.,
1999). The buffer zone concept includes a component
of local stewardship, in particular in biosphere
reserves, providing incentives for landowners and
residents to be involved in conservation planning
(Nepal and Weber, 1994; Richards, 1996; Kremen
et al., 1999). The need for buffer zones is most evident
for small reserves (Shafer, 1995), which have high
proportion of edge habitat (Matlack and Litvaitis,
1999) and small populations vulnerable to extinction.
At a global level, temperate broadleaved deciduous
forest has the highest degree of human disturbance
(Hannah et al., 1995). Almost no forest in Europe or
southern Scandinavia is undisturbed, and most seminatural forests are small and scattered (Peterken, 1996;
Halkka and Lappalainen, 2001). Old trees and large
dead trees, important for many forest species, have
largely disappeared (Samuelsson et al., 1994; Keddy
and Drummond, 1996; Peterken, 1996). Protection of
forest biodiversity has high priority in many countries,
but only a small proportion (6.3%) of the European
forest is protected in reserves (cf. Soulé and Sanjayan,
1998). About 95% of the reserves are smaller than
1000 ha (Halkka and Lappalainen, 2001) and the
mean size is usually less than 100 ha (Nilsson and
Götmark, 1992; von Bücking, 1997).
Nature reserves, in particular forest reserves, are
usually viewed as fragments surrounded by heavily
modified habitat, like arable fields or forest plantations
(e.g., aerial photographs in Shafer, 1995, 1999;
McIntyre and Hobbs, 1999; reviewed by Haila,
2002). It is possible, however that land owners and
others involved manage the surroundings of reserves
in a different way than areas further away from the
reserves. Ask and Carlsson (2000) found that nonindustrial private forest owners (n = 29) in southern
Sweden (i) had no or low requirement for timber yield
on 7% of their forest land, (ii) that these stands had
conservation values above the average, and (iii) that
they were located closer to woodland key habitats
(forest areas with conservation values; Gustafsson et al.,
1999) than were randomly selected stands. It is also
possible that reserves have been established in landscapes where conservation values generally are high
compared with other landscapes, so that the surroundings of reserves are not heavily modified habitat.
Studies of conservation values in existing reserves
and in their potential buffer zones are needed to
evaluate possibilities for buffer zones to reinforce the
reserves. Here, we examine if potential buffers
reinforce small temperate forest reserves in southern
Sweden that lack buffers. Reinforcement is defined as
the degree to which potential buffer zones strengthen
reserves by resembling them in habitat types of
interest to conservation. High resemblance between
reserves and buffer zones should imply that (1) buffers
are relatively efficient in terms of function and (2)
buffers increase the effective size of reserves (for most
small forest reserves, an increase in area would
reinforce biodiversity values). We used habitats and
microhabitats (forest types, tree species, large trees,
and dead wood) as indicators of conservation value,
testing the null hypothesis of no difference in forest
conservation value between reserves and potential
buffers. Based on the alternative hypothesis of lower
conservation value outside the reserves, we predicted
either (1) a sharp decline in average conservation value
at reserve boundaries, with heavily modified habitats
(e.g., production forest, plantations) bordering the
reserve or (2) a gradient with decreasing conservation
value from the reserve boundaries and outwards. A
sharp decline in values just outside reserves should be
detectable in our potential buffers that we also
compared with forest outside the buffers, farther
away from the reserves.
2. Material and methods
2.1. Forest ecosystems and forest protection in
southern Sweden
The forest in southern Sweden (Fig. 1) is a transition
between boreal forest in central and northern Sweden
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
335
Fig. 1. South Sweden with counties and nature reserves studied in five of the counties.
and temperate forest in continental Europe (Esséen
et al., 1997; Nilsson et al., 2001). Under natural
conditions, forest in the southern study area (Halland,
Skåne, and Blekinge counties, Fig. 1) would consist of
species-rich broadleaved deciduous forest (hereafter
‘southern deciduous forest’) and some Scots pine
(Pinus sylvestris), whereas forest in Bohuslän and
Älvsborg (Fig. 1) would include southern deciduous
forest but more coniferous forest (Scots pine, Norway
spruce Picea abies, with birch Betula pendula, B.
pubescens, and aspen Populus tremula). Southern
deciduous forest includes oak (Quercus robur and Q.
petrea), beech (Fagus sylvatica), common ash (Fraxinus excelsior), wych elm (Ulmus glabra), Norway
maple (Acer platanoides), lime (Tilia cordata), gean
(Prunus avium) and hornbeam (Carpinus betulus)
(Gustafsson and Ahlén, 1996).
In Sweden, currently about 80% of the tree volume
consists of Scots pine and Norway spruce, and 10% of
birch (NBF, 2000). More than 50% of the Swedish redlisted forest species are found in southern deciduous
forest (Berg et al., 1994; Gustafsson and Ahlén, 1996).
These species experience a deficit of old living trees
and dead trees, and light conditions are judged
important for many of them (Berg et al., 1994; Jonsell
et al., 1998; Ranius and Jansson, 2000).
Based on number and total area, nature reserves
dominate forest protection in Sweden (see Götmark
and Nilsson, 1992; Nilsson and Götmark, 1992; SEPA,
1997a; Fridman, 2000), but in southern Sweden only
about 1% of the forest is protected (SEPA, 2003a).
Currently, the strategy in Sweden is (i) to establish
new, or enlarge current reserves, (ii) to establish
habitat protection areas (generally less than 5 ha), (iii)
to sign nature conservation agreements with forest
owners, (iv) to encourage setting aside forest
voluntarily by forest owners themselves, and (v) to
take biodiversity in consideration during forestry
practices (Gustafsson and Ahlén, 1996; Nilsson et al.,
2001; SEPA and NBF, 2003). In addition, SEPA
(2003b) recommends ‘protective zones’, but inside the
forest reserves.
2.2. Study area and selection of forest reserves
for field studies
The study area is a lowland (0–200 m a.s.l.) mosaic
landscape (forest, arable land and pasture, lakes,
336
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
wetlands, exposed bedrock, urban areas, and an
elaborated road network) where the forest is mainly
owned by non-industrial private forest owners (78% of
the forest owners). Land owners often combine
forestry with agriculture (NBF, 2000; Götmark
et al., 2000) and forest properties are usually small
(73%, <400 ha).
In June 1997, there were 383 nature reserves
containing at least 1 ha of forest in the five counties
selected for studies (Fig. 1, SEPA, 1997b). Basic data
on all 383 forest reserves were collected from files,
maps, and aerial photographs in offices of the County
Administrations. The objectives of most of the
reserves were to protect biodiversity and recreational
values related to nature. The 383 reserves were
relatively small, with a median land area of 46 ha. The
median forest area was 22 ha, so the reserves also
contained other habitat types (see below).
For our study of potential buffer zones, we
classified the reserves into categories (A, B and C)
depending on the position of the forest in relation to
the reserve boundary. In A-reserves, the forest in the
reserve extended to the boundary along more than
20% of the perimeter. Such forest was judged
susceptible to edge effects (Olsen, 1988; Murcia,
1995) and buffer zones were considered to be
appropriate. B-reserves had forest located on islands,
or the forest extended to the boundary along less than
20% of the perimeter. This forest was judged to be
buffered by the surrounding habitats near or in the
reserve, and in little need of a buffer zone. C-reserves
protected either a bog or a lake where a strip of forest
had been included around the bog or lake as buffer
zone. As forest protection was not the objective of Creserves, they were excluded from the study. The 383
reserves comprised 297 A-reserves, 64 B-reserves,
and 11 C-reserves (another 11 reserves omitted due to
classification problems).
For further sampling, we selected A-reserves with a
forest cover of 5–225 ha (n = 198). Buffer zones
should be needed especially for forest reserves of
intermediate size, where buffers would not constitute a
too large or too small proportion of the total reserve
area. Our potential buffer (see below) for a 10 ha
reserve would be four times larger in size than the
reserve; for a 100 ha reserve, the buffer would be of
the same size as the reserve. The 198 A-reserves were
divided into four size categories: 5–20 ha (79
reserves), 21–50 ha (76 reserves), 51–100 ha (30
reserves), and 101–225 ha (13 reserves). From each
size category, we randomly selected 25% of the
reserves, but stratified by county such that the number
of reserves selected in each county reflected its
proportion of the 198 reserves. We obtained in total 49
reserves (for general data for each reserve, see Thorell,
2003).
2.3. Collection and treatment of data
We studied the 49 reserves in the field August–
November 1997 and May–October 1998. Line
transects (300–400 m long, 25 m wide, and perpendicular to the reserve boundary) extended from the
reserve’s interior to 200 m outside the reserve
boundary (Fig. 2). The width of the potential buffer
zone (200 m) was based on reported edge effects (see
Murcia, 1995; Gascon et al., 2000, and especially
Olsen, 1988, relevant to the study area). Buffer zones
may vary in width along the boundary of a reserve
(e.g., Wenjun et al., 1999) but our aim was to examine
changes in conservation value with distance from
reserves and we therefore used the design shown in
Fig. 2.
We collected data in each 25 m 25 m quadrat
along the line transects (Fig. 2). On average, we
sampled 10 transects per reserve (S.D. 4, n = 49).
Fig. 2. Schematic drawing of reserve, its potential buffer zone and
transects along which data were recorded in quadrats (see text). The
transects reached 100 m (small reserves) or 200 m (large reserves)
into reserves, and were separated by a distance of 200 m (small
reserves) or 400 m (large reserves) along the reserve boundaries.
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
Depending on the size and shape of the reserves, the
transects extended 200 m (17 cases), 100 m (27 cases),
or less than 100 m (5 cases) into the reserves’ interior
parts. If another reserve abutted the sampled reserve (5
cases) we excluded transects along the boundary part
with the adjacent reserve; thus, potential buffers only
included non-protected land. For reserves with less
than 50 ha of forest, 200 m separated the transects,
while in reserves with forest area larger than 50 ha,
400 m separated the transects along the reserve
boundary.
In quadrats along the transects in each reserve and
potential buffer, we quantified abundance of habitat
types, forest types, tree and shrub species, large trees,
dead wood, and variation in light regime (canopy
openness) for large trees and dead wood. Thus, we
quantified basic indicators of conservation value for
stands in temperate forests (see Berg et al., 1994;
Keddy and Drummond, 1996; Lindenmayer et al.,
2000; Nilsson et al., 2002). Habitats were visually
assessed (percentage cover in quadrat, 25 m 25 m,
along transect) as woodland (synonym for forest),
agricultural land, wetland, settlement, infrastructure
(roads, power-lines), other terrestrial habitat, and open
water (pond, stream). We recorded six forest types,
based on the definitions of the Swedish National
Forest Inventory; NFI): coniferous forest (>70%
canopy cover of conifers), southern deciduous forest
(>70% canopy cover of southern deciduous trees),
other deciduous forest (>70% canopy cover of
deciduous trees but with <70% southern deciduous
trees), mixed forest (30–70% coniferous trees),
clearcut (including young forest <1.5 m high), and
other woodland (e.g., abandoned agricultural land
with saplings). Barren rock, soil, or sand covering
<50% of quadrat were considered part of the
predominant habitat; otherwise they were recorded
as other terrestrial habitat.
We recorded species occurrence of trees/shrubs
>1.5 m high. Q. petrea and Q. robur were recorded as
‘‘oak’’, and B. pendula and B. pubescens as ‘‘birch’’.
Species were classified as native or exotic according to
Jonsell (2000), supplemented by Hultén (1971) and
Mossberg et al. (1992). Species richness is the total
number of species (taxa) recorded in a reserve or buffer,
i.e., occurrence in at least one quadrat. Species
frequency is the proportional occurrence in all quadrats
of a reserve or buffer zone (e.g., a tree that occurred in
337
all quadrats along transects in a reserve had the
frequency 100%). For large (40.9–83 cm diameter at
breast height, dbh) and ‘giant’ (>83 cm dbh) trees, we
recorded number of stems in each quadrat. Giants were
very rare and were pooled with large trees (also
presented separately, see below). Light regime (canopy
openness) for large tree trunks and dead wood was
classified as ‘closed’ (canopy completely, or almost
closed), ‘open’ (no canopy cover around tree, at least
within a radius approximately equal to the trunk length
of the tree), or ‘intermediate’ (light regime between
‘closed’ and ‘open’).
We measured two components of coarse dead wood;
logs (downed dead trees) and snags (standing dead,
sometimes broken trees, included if 1.3 m high). We
only recorded snags and logs 16 cm in diameter (dbh,
or corresponding to dbh). A log unit was defined as at
least 8 m, with shorter logs measured as proportions of
8 m (thus, a 3 m piece was a 3/8 or 0.38 log unit; a 9 m
log was 1.0 log unit). This procedure was used to
estimate densities of logs of approximately normal
length, since cut pieces were quite common. Standing
dead wood was measured as one unit regardless of
height. We also classified logs into four stages of decay.
Stage 1 had all branches left, and sometimes leaves or
needles. Logs with only parts of the branches and most
of the bark left, were in stage 2. Logs in stage 3 had no
bark or branches left, while stage 4 logs had soft wood
mostly covered with bryophytes. Stage of decay was
measured only in 1998 (n = 33 reserves).
For non-protected land outside buffers (>200 m
from reserve boundaries), we obtained estimates of
indicators from the Swedish National Forest Inventory
(NFI; J. Fridman, personal communication). The NFI
is based on small plots in a grid system covering
Sweden; procedures in NFI and calculation of
standard error for estimates are explained in Fridman
(2000). We used NFI data from 1994 to 1998,
combining all plots in non-protected forest for the five
counties. Thus, the NFI data gave one overall estimate
(S.E.) for each indicator analysed. The estimates
were computed from a different sampling design,
unsuitable for our statistical analysis and so not used in
tests; however, as the NFI estimates were based on
several thousand plots, estimates are reliable, with low
S.E. (see below).
Reserves (n = 49) and potential buffer zones
(n = 49) were sample units in the statistical analyses.
338
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
Table 1
Habitat and forest types in reserves, potential buffer zones, and other non-protected land in the study area
Category
Reserve (%)
Potential buffer
zone (%)
Other non-protected land in
the study areaa (%)
Habitat type
Forest
Agricultural land
Wetland
Human settlement
Infrastructureb
Other terrestrial habitat
Open water
82.6
10.9
1.1
0.8
1.6
2.7
0.3
(2.5)
(3.9)
(0)
(0.4)
(0.3)
(1.0)
(0.1)
56.1
26.4
3.4
5.9
3.3
4.2
0.8
(3.9)
(4.0)
(1.3)
(1.6)
(0.4)
(1.2)
(0.2)
51.6
27.6
3.0
7.5
1.6
0.3
8.4
Forest type
Southern deciduous
Coniferous
Mixed
Other deciduous
Clearcut/other woodland
36.9
25.8
17.5
16.9
2.9
(5.0)
(4.2)
(2.6)
(2.7)
(0.8)
17.0
36.9
20.2
20.2
5.7
(2.0)
(3.8)
(2.7)
(2.8)
(0.9)
5
69
6
11
8
(0.8)
(0.7)
(0.2)
(0.4)
(0.1)
(0.1)
(0.6)
(0.6)
(0.8)
(0.4)
(0.6)
(0.4)
Measurements are mean (S.E.) as percentage of transect area (reserves, buffers) or percentage of non-protected land area (from the Swedish NFI,
National Forest Inventory). For habitats: n = 49 reserves/buffers, for forest types: n = 49 reserves and n = 46 buffers (three buffers lacked forest).
a
Estimate of standard error (S.E.) based on the sampling design of NFI; see Section 2, and Fridman (2000) for sampling and calculations.
b
Mainly roads and aerial power-lines.
The Wilcoxon matched pairs signed ranks test was
used to analyse differences between forest reserves
and their potential buffers. For habitat and forest types,
statistical tests were only performed on the major type
(we used proportions; their sum is always 100%, and
thus, they are not statistically independent). Statistical
tests were two-tailed in these analyses, but one-tailed
tests are possible as our alternative hypothesis
specified an outcome in one direction, i.e., lower
conservation values outside reserves (hence, p-values
reported below may be divided by two).
Using Spearman’s rank correlation (rs), we examined similarity in indicator value between reserves and
potential buffers, and thus, whether reserves with high
conservation values had buffers with corresponding
high values. For these analyses, two-tailed tests were
appropriate, and we give two-tailed p-values below.
3. Results
3.1. Habitat types, forest types, and tree
species frequencies
We found a higher mean proportion of forest in the
reserves (83%) than in the potential buffers (56%) and
in other non-protected land (52%; Table 1). The
difference between the reserves and the potential
buffers in forest proportion was significant
( p < 0.0001), but we found no significant correlation
between forest proportions in reserves and their
associated buffer zones (rs = 0.34, p = 0.17). For
agricultural land (Table 1), the mean proportion was
Table 2
Tree and shrub species richness, measured as occurrence in at least
one transect quadrat in reserves (n = 49) and potential buffer zones
(n = 49)
Mean no. of species (S.E.)
All trees
Resident trees
Alien trees
Southern
deciduous trees
Other deciduous trees
Trees with berries
and fruitsc
All shrubs
Resident shrubs
Alien shrubs
a
b
c
Difference
pa
Reserve
Potential
buffer zone
14.6 (0.7)
14.3 (0.6)
0.6 (0.1)
16.0 (0.8)
14.9 (0.7)
1.1 (0.2)
4.1 (0.3)
4.2 (0.3)
n.s.
3.5 (0.1)
4.8 (0.3)
3.6 (0.1)
5.4 (0.4)
n.s.
0.05
8.1 (0.5)
7.8 (0.5)
0.3 (0.08)
9.2 (0.6)
8.0 (0.5)
1.2 (0.2)
n.s.
n.s.
n.s.
Wilcoxon matched-pairs signed rank test.
Not significant; p > 0.05.
Native species.
0.009
n.s.b
0.02
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
339
Table 3
Mean number of large trees (>40.9 cm dbh), snags (standing dead trees, 16 cm diameter), and logs (downed dead trees, 16 cm) per woodland
hectare in reserves (sample size, n = 49), buffers (n = 46, three buffers lacked forest), and other non-protected forest in the study area; and mean
number of logs (16 cm) in four decay stages per woodland hectare in reserves (n = 32) and buffers (n = 29, three buffers lacked forest)
Category
Large trees
Snags
Logs
Logs, by decay stagec
Stage 1
Stage 2
Stage 3
Stage 4
a
b
c
Reserve vs. buffer zone pb
Mean no. per woodland hectare (S.E.)
Reserve
Potential buffer zone
Other non-protected landa
30.5 (2.7)
9.7 (1.2)
16.6 (2.2)
14.6 (1.4)
7.1 (1.0)
13.0 (1.8)
10.0 (0.6)
4.7 (0.4)
9.3 (0.9)
<0.0001
0.16
0.07
No
No
No
No
>0.2
>0.2
0.02
0.04
1.8
2.2
4.0
4.3
(0.3)
(0.4)
(0.8)
(1.0)
1.8
2.0
2.0
2.0
(0.4)
(0.4)
(0.4)
(0.4)
data
data
data
data
Estimate of standard error (S.E.) based on the sampling design of NFI; see Section 2, and Fridman (2000) for sampling and calculations.
Wilcoxon matched-pairs signed rank test.
Stage 4 is most decayed (see Section 2); note different sample size for these data.
lower in reserves (11%) than in potential buffers
(26%) and other non-protected land (28%).
With respect to forest types, the reserves and their
potential buffer zones had relatively high proportions
of forest types valuable for conservation, compared to
other non-protected forest which was dominated by
coniferous forest (Table 1). The mean proportion of
southern deciduous forest was highest in the reserves
(37%), and decreased gradually over the buffer zones
(17%) to other non-protected forest (5%); the
difference between reserves and buffers was significant ( p < 0.0001). The mean proportion of other
deciduous forest and the mean proportion of mixed
forest was relatively similar in the reserves and in the
potential buffers, but the mean proportions of both
forest types were markedly lower in other nonprotected forest (Table 1).
For the reserves and their matched potential
buffers, we found strong positive correlations in the
proportion of southern deciduous forest ( p < 0.0001),
other deciduous forest, and mixed forest (Fig. 3). We
also found significant correlations in tree species
frequencies in reserves and buffers for three common
deciduous trees (Fig. 4); oak, rowan (Sorbus
aucuparia), and birch.
3.2. Tree and shrub species richness
We found significantly more tree species (taxa) in
the potential buffers than in the reserves, but the
difference was no longer significant when only resident
tree species were included (Table 2). Species richness of
southern deciduous trees and of other deciduous trees
was similar for reserves and buffer zones, but native tree
species with berries and fruits, important components
for biodiversity, were significantly more common in the
buffers. Shrub species richness was similar in reserves
and buffers (Table 2). No data were available for other
non-protected forest, but its markedly higher proportion
of coniferous forest implies that tree and shrub species
richness is lower there (for areas of similar size as the
reserves and buffers). On average, we surveyed a larger
area in the buffers than in the reserves (longer transects,
see Section 2), which might influence species richness
estimates. However, for neither reserves nor buffers
analysed separately did we find any correlation between
tree or shrub species richness and the surveyed forest
area in transects; area therefore should not be a
confounding factor.
3.3. Large trees, snags and logs
The mean densities of large trees, snags and logs
per woodland hectare were highest in the reserves,
decreased in the potential buffer zones, and declined
further in other non-protected forest (Table 3). The
density of large trees (>40.9 cm dbh) was twice as
high in reserves compared to buffers ( p < 0.0001).
Densities of snags and logs tended to be higher in
reserves than in buffers, but the differences were not
340
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
Fig. 3. Relationships between reserves and potential buffer zones
in proportions (%) of three forest types (of surveyed woodland
area in transects): southern deciduous forest, other deciduous
forest, and mixed (deciduous–coniferous) forest. The sample size
for both reserves and buffers is 46 (three buffers lacked forest).
Indicated in each graph is line for linear regression, and Spearman’s correlation coefficient with test (no tests were done for
other deciduous and mixed forest, as the proportions were not
statistically independent).
Fig. 4. Relationships between reserves and potential buffer zones
for species frequencies of oaks, birches and rowan (proportions of
quadrats along transects where the species was found). The sample
size for both reserves and buffers is 46 (three buffers lacked forest).
Indicated in each graph is line for linear regression, and Spearman’s
correlation coefficient with test.
significant in two-tailed tests (Table 3, one-tailed tests
are possible, see Section 2). We found significant
correlations ( p < 0.01) between reserves and their
buffer zones in densities of large trees, snags, and logs
(Fig. 5).
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
341
conditions. The result was similar for other nonprotected forest, except for relatively high proportion
of logs in open conditions (20%), perhaps due to clearcutting there.
We found higher densities of logs in more advanced
stage of decay (in stages 3 and 4) in the reserves than in
the potential buffers, whereas densities of logs in stages
1 and 2 were similar in reserves and buffers (Table 3).
4. Discussion
Fig. 5. Relationships between reserves and potential buffer zones
for large trees, snags (standing dead trees), and logs (downed dead
trees) per woodland hectare along transects (n = 46; three buffers
lacked forest). Indicated in each graph is line for linear regression,
and Spearman’s correlation coefficient with test.
We recorded giant trees (>83 cm dbh) in 21
reserves (39 trees) and 11 buffer zones (23 trees). The
mean density of giants in reserves was 0.39 trees per
hectare (S.E. 0.09, n = 49) and in buffers 0.23 trees
per hectare (S.E. 0.10, n = 49). In other nonprotected forest, giants were absent or occurred in
extremely low density.
Large trees, snags, and logs were mainly recorded
in closed and intermediate light conditions in both
reserves and buffers (Table 4). Only 4–13% of the
large trees, snags, and logs were found in open light
Our basic indicators of forest conservation value
suggest that forest in potential buffer zones is not as
heavily exploited by forestry as forest in other nonprotected areas. We found no sharp decline in
conservation values outside the reserves, but instead
we found gradual decline from inside the reserves to
other non-protected forest in the counties. This
suggests that the surroundings of small forest reserves
are not heavily modified, as is often assumed.
Moreover, we found that reserves with high forest
conservation values generally had buffers with high
values. Given reports on intense forestry in Swedish
unprotected forests (e.g., Berg et al., 1994; NBF, 2000;
Fridman, 2000), our results were not only surprising
but also encouraging.
The forest in the reserves may be classified as seminatural forest that only by time will develop the
characteristics of old-growth forest (Peterken, 1996).
Densities of large trees and coarse dead wood were
clearly lower than in old-growth forests in Europe
(Nilsson et al., 2001, 2002). Nevertheless, the reserves
and their potential buffers contained much valuable
southern deciduous forest, as well as many relatively
large trees. Fridman (2000) found that the volume of
dead wood was significantly higher within than outside
nature reserves in Sweden; for southern Sweden
analysed in his study, the tendency was similar, but
not significant. In our study, the densities of snags and
logs were relatively similar in reserves and buffers, but
higher than in other non-protected forest in the counties.
There are at least three possible explanations for the
relatively high conservation values in the potential
buffer zones. First, the reserves may have been
established in forest areas that had high or relatively
high conservation values. When the buffers were
compared with 200 m wide zones around control areas
342
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
Table 4
Light regime (canopy openness) for large trees, snags and logs in woodland, classified at trunks into open, intermediate and closed condition
(n = 49 reserves and n = 46 potential buffers; three buffers lacked forest)
Trunks per woodland
hectare (mean (S.E.))
Reserve
(%)
Trunks per woodland
hectare (mean (S.E.))
Potential buffer zone
(%)
Other non-protected
foresta (%)
Large trees
Closed
Intermediate
Open
15.2 (1.8)
13.1 (2.3)
1.2 (0.3)
51.5
44.4
4.1
7.5 (1.1)
5.9 (0.7)
1.0 (0.2)
52.1
41.0
6.9
47.2
49.8
3.0
Snags
Closed
Intermediate
Open
4.0 (0.8)
4.6 (0.9)
1.3 (0.3)
40.4
46.5
13.1
3.4 (0.8)
3.1 (0.5)
0.8 (0.2)
46.6
42.5
10.9
44.4
41.9
13.7
Logs
Closed
Intermediate
Open
7.7 (1.3)
7.2 (1.3)
1.5 (0.4)
47.0
43.9
9.1
5.9 (1.0)
5.5 (0.9)
1.6 (0.4)
45.4
42.3
12.3
41.0
38.9
20.1
a
Data from the Swedish National Forest Inventory, in which light is measured at ground level. From these data, degree of light exposure on
trunks and dead wood was estimated as percentage of all trunks surveyed.
of non-protected forest (selected to match each
reserve, of the same size and shape), areas of ‘national
interest for nature conservation’ (designated in
legislation) made up a significantly higher proportion
of the land in the buffers of the reserves than in the
buffers of the control areas (Thorstensson, 2001). This
suggests that land valuable for conservation tend to be
aggregated around the nature reserves. Second, forest
near reserves might be situated on ground that is more
inaccessible for forestry than other non-protected
forest. In our study area, forest in the reserves
contained more steep ground than forest in the nonprotected control areas mentioned above (Reinhardt,
2001). Thus, topography might contribute to the
observed results. Finally, non-industrial private forest
owners that own most of the forest in south Sweden
and forest near many of the reserves (Götmark et al.,
2000), may have avoided forestry or cutting near the
reserves for practical, environmental, or aesthetical
reasons. We have no direct evidence for this
explanation, but it is a possibility (cf. Ask and
Carlsson, 2000 who found that some forest owners
avoid cutting in small stands of conservation value).
Agricultural land (fields and pastures) was on
average more common in potential buffers than in
reserves. Especially in Skåne, in the south (Fig. 1),
intensive agriculture predominates in the landscape,
and the woods (reserves) were sometimes isolated
‘forest islands’. Restoration of deciduous woodland
is probably needed in buffer zones containing much
arable land. In the middle and northern parts of the
study area, fields and pastures were usually smaller
than in Skåne (Kling, 2001), and they might be
beneficial to buffer zones. For instance, semi-natural
pastures (woodland pastures) may be very rich in
vascular plants, insects, and birds (Götmark, 1992;
Pärt and Söderström, 1999; Gärdenfors, 2000). Old
sun-exposed deciduous trees in such semi-open areas
are habitat for many red-listed cryptogams and
insects (Gärdenfors, 2000), species that may be
dependent upon forest disturbance (Berg et al., 1994;
Jonsell et al., 1998; Ranius and Jansson, 2000). We
generally found few large trees in open conditions.
To create habitat for red-listed cryptogams and
insects, forest management in reserves and buffer
zones may include thinning around some larger
deciduous trees.
5. Management and conservation implications
Our results are encouraging for the preservation of
forest biodiversity in so far as the potential buffer
zones contained relatively high conservation values,
especially outside forest reserves of higher quality.
Therefore, at present we judge that the reinforcement
M. Thorell, F. Götmark / Forest Ecology and Management 212 (2005) 333–345
capacity of potential buffer zones is relatively high for
nature reserves in our study area. However, for
surroundings of nature reserves in Sweden there are
few specific restrictions on forestry and other forms of
land use. We recommend that buffer zones around
existing forest reserves are considered in the study
region but further studies are needed on how to
implement buffers to reinforce reserves, and to involve
stakeholders in a positive way. Forest owners in
potential buffers around reserves (n = 17 reserves)
showed interest for forest conservation, but generally
asked for economical support if buffers would imply
restrictions on cutting (Götmark et al., 2000). One
possibility, already in use in Sweden, is nature
conservation agreements where forest owners are
financially supported by the state for conservation
measures, e.g., for planting deciduous trees and
retaining large trees and dead wood on their land.
Another opportunity for creating buffer zones is
development of the legal land use plans in municipalities (Thorell, 2003). In some cases, conflicts over
land use in a buffer zone may be so frequent that it
becomes inefficient (Groom et al., 1999). Any laws or
rules for buffer zones should allow flexibility, such that
buffers would not be mandatory for all reserves. For
reserves with very high values in potential buffers, we
suggest that enlargement of the reserves should have
higher priority than creation of buffers (Thorell, 2003).
In conclusion, this study of temperate forest reserves
and their potential buffer zones shows that one cannot
assume a priori that nature reserves have heavily
exploited surroundings. The forest in potential buffer
zones had relatively high conservation value, when
compared with reserves and other non-protected forest.
These potential buffers reinforce their reserves by
relatively high buffering capacity, and by increasing the
effective size of reserves. In a longer perspective,
valuable habitats in the potential buffers probably need
to be protected. The generality of our results should be
tested in other regions to evaluate buffering capacity of
the surroundings of reserves, and our systematic
method for studying reserves may then be useful.
Acknowledgements
This study was mainly financed by grants from the
former Swedish Council for Planning and Coordina-
343
tion of Research (FRN), and the Research Council
(VR) to F.G. Additional funding was received from
Verner von Heidenstams fond, Sökjers stipendiefond,
Kungliga Skogs- och Lantbruksakademien, Adlerbertska forskningsfonden, Wilhelm och Martina
Lundgrens vetenskapsfond, Collianders stiftelse, Paul
och Marie Berghaus donationsfond, and Stiftelsen
Olof Ahlöfs fond. We thank Kristina Jungbark, Åsa
Persson, Erik Heyman, Karin Rystedt, and Uno Unger
for their assistance with field work, and Jonas Fridman
for providing data from the Swedish National Forest
Inventory (Riksskogstaxeringen). We also thank
Conny Askenmo, Thomas Elmqvist, Ragnar Lagergren, anonymous referees, and especially Craig Shafer
for critical reading and valuable comments on the
manuscript.
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