Forest Ecology and Management 211 (2005) 318–328
www.elsevier.com/locate/foreco
Dynamic oak-scrub to forest succession: Effects of
management on understorey vegetation, humus forms and soils
Beate Strandberg a, Søren M. Kristiansen b,*, Knud Tybirk a,1
a
National Environmental Research Institute, Department of Terrestrial Ecology, Vejlsoevej 25, DK-8600 Silkeborg, Denmark
b
Department of Earth Sciences, University of Aarhus, Ny Munkegade building 520, DK-8000 Aarhus C, Denmark
Received 25 February 2004; received in revised form 2 November 2004; accepted 21 February 2005
Abstract
Active management for preservation of conserved ecosystems is receiving increased attention, as management probably is
the most important factor for the temporal and spatial distribution of understorey vegetation, and probably humus forms and soil
nutrient cycling as well. The present study investigates this issue on well-drained sandy soils in the ancient woodlands of Hald
Ege, Denmark, which was preserved in 1915. Four types of management have continued since then: (i) managed, pure oak, (ii)
non-managed, beech-oak, (iii) grazed oak and (iv) coppiced oak stands. Data consisted of two independent present-day data sets
from all types of management, and one comparison between data from 1916 and now. Relations between forest type and possible
explanatory variables, such as land-use history and characteristics of forest, humus layer, soil and understorey, were studied
using principal component (PCA) and correspondence (DCA) analyses. Results showed that grazing mammals have kept the oak
forest in a state resembling the pre-preservation stage with respect to both vegetation and humus forms. Here, light penetration to
the forest floor during the entire growing season supported a diverse flora and a moder or mull-type of decomposition. The nonmanaged plots were in contrast succeeded into a dark beech-oak forest with thick humus layers and a drastic decrease in
understorey species number. The present analysis hence supports the theory that management is necessary to conserve oakscrubs and open woodlands from successional changes of herbaceous forest vegetation, humus forms and understorey
vegetation.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Coppice; Fagus silvatica; Forest grazing; Plant succession; Quercus spp.; Species richness
* Corresponding author. Present address: Department of Agroecology, Danish Institute of Agricultural Sciences, P.O. Box 50, DK8830 Tjele, Denmark. Tel.: +45 8999 1655; fax: +45 8999 1619.
E-mail address: [email protected]
(S.M. Kristiansen).
1
Present address: National Environmental Research Institute,
Department of Wildlife Ecology and Biodiversity, Kalø, Grenåvej12, DK-8410 Rønde, Denmark.
1. Introduction
Interactions of vegetation and soil have often been
described, and effects of forest tree species and
understorey vegetation on pedogenesis are under a
temperate climate recognised on acid soils (Berendse,
1998; Binkley and Giardina, 1998; Miles, 1985; van
0378-1127/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2005.02.051
B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
Breemen and Finzi, 1998). The properties of different
tree species influence the litter decomposition and soil
nutrient cycling, which in turn influence the understorey vegetation. Oak (Quercus spp.) trees are found
to create islands of enhanced fertility through organic
matter incorporation and nutrient cycling (Dahlgreen
et al., 1997). Beech (Fagus silvatica) on the other
hand, decreases surface soil pH significantly and has
leaves that decompose more slowly leading to a mortype of decomposition on poor soils (Brahy et al.,
2000).
Many studies of understorey vegetation in temperate forests analyse external factors influencing the
vegetation such as acidification, eutrophication or
various forest management intensities (Brunet et al.,
1996; Falkengren-Grerup, 1995; Härdtle et al., 2003;
Rubio et al., 1999). The single factor most severely
affecting the vegetation of present-day managed forest
is believed to be forest management (Vejre and
Emborg, 1996). Traditional management techniques,
such as coppice and forest grazing, have great
conservation interest and are receiving increased
attention (e.g., Putman, 1996).
Most Danish oak-scrubs are young and are
presently slowly changing into oak forest as traditional
woodmanship has ceased. The scrubs, therefore, are
conserved by active management, such as grazing,
coppice and selective cutting. Presently, oak-scrub
management has been included in the recent Danish
forest law revision. Such conservation management,
however, is likely to influence both vegetation, humus
forms and soil nutrient cycling. This is important as
the few remaining natural ancient woodlands, on
undisturbed soils, may give us some very interesting
information of the ‘‘natural’’ stage of soil development.
The interactions of soil/humus form development,
forest succession and management have not been
explored before in the context of conservation
strategies on well-drained sandy soils. This paper
focuses on these interactions and addresses the
following questions: (i) does the secondary oak forest
succession without management cause a mor-type
decomposition after invasion of beech and canopy
closure and (ii) can management measures such as
grazing and coppice maintain a mull-type of decomposition and high species diversity after canopy
closure when oak continues to dominate?
319
2. Materials and methods
2.1. Study area
The study took place in the ancient woodlands of
Hald Ege in Central Jutland, Denmark (568250 N,
98400 E). This site is unique as it was studied already in
the late 19th century by Müller (1884) and again in
1916 (Olsen, 1938). Hald Ege is situated in a glacial
landscape formed during the cease of the last Ice Age,
and is one of the least disturbed Danish forests on
well-drained sandy soils. The forest has formerly been
used for grazing and forest products, but no signs of
cultivation are found since the Bronze Age, where the
eastern part of the forest was cultivated (Worsøe,
1981). The major part of the forest was preserved in
1914–1915, and the rest in 1942. In 1916, the forest
formed an open oak-scrub or woodland with strong
indications of former grazing and coppice of
individual trees.
Since the preservation different management have
been applied. Smaller parts in the centre were kept
untouched to follow the forest succession. These
parts are referred to as ‘non-managed’. In most parts
of the forest beech and coniferous species were cut
away every decade in order to preserve the typical
oak-scrub/forest. We term this type of management
‘oak management’. During the 1930s, coppicing of
oak trees took place in smaller parts. These parts are
referred to as ‘coppiced’. Besides, smaller parts,
referred to as ‘previously grazed’, have been grazed
until approximately 1970, and finally, parts of the
forest, denoted ‘grazed’, are presently grazed
extensively by horses. The site and history have
been described in detail by Tybirk and Strandberg
(1999).
A soil investigation of Hald Ege by Kristiansen
and Greve (2003) revealed that parent material and
soil types were rather uniform: the parent material
was all-over quartzose, fluvio-glacial medium sand,
with less than 5% material > 2-mm. Only the
northern most parts at sites 3, 4 and 18 (Fig. 1)
had a contrasting parent material, as a loamy sandy
till was underneath a 20–40-cm thick layer of sand. In
general, Kristiansen and Greve (2003) found Podzols
on sands under ‘non-management’, Arenosols under
‘oak management’, ‘coppiced’ and ‘previously
grazed’, and Luvisols and Cambisols in loamy sand
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B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
making plant-soil interpretations difficult in these
ancient woodlands.
2.2. Sampling sites
Fig. 1. Map of the present-day Hald Ege forest. The 34 sample sites
in the ‘extended data set’ are indicated with type of management
(oak management, non-managed, coppiced, grazed and previously
grazed) on the plot. The ‘basic data set’ consists of sample sites 1–
17, 23 and 24, and the ‘historic data set’ consists of sample sites 1–
17.
under oak management. The spatial distribution was
nevertheless only partly explained by the site factors
as several patches with Podzols were found under
‘oak-management’. Soils were very similar to
descriptions made in 1879 (Müller, 1884), reflecting
that the soil probably retain features of past soilforming factors. Soil morphologies may thus no more
be in agreement with present pedogenic processes,
Seventeen sample sites (sample sites 1–17; Fig. 1)
were investigated by Olsen in 1916 (Olsen, 1938).
These sample sites were re-analysed in 1995 and the
results presented in Tybirk and Strandberg (1999). In
1995, two sample sites located within the previously
grazed (sample site 24) and presently grazed (sample
site 23) parts were also analysed. The data from these
19 sample sites (the ‘basic data set’) covered the span
of soil and management types in the forest. At these
sites, a range of soil, vegetation and environmental
parameters were analysed. The three management
types: coppiced, previously grazed and grazed were
only represented by one sample site each in the ‘basic
data set’. To analyse the effects of management in
detail, the ‘basic data set’ was supplemented by an
additional sampling (‘extended data set’: additionally
sampling sites 18, 19, 21, 22, 25–34; Fig. 1)
representing the different management strategies.
From these additional sampling sites, collected in
1997, only vegetation was analysed (Table 1). To
analyse the influence of management on the vegetation
over time, the vegetation data from 1916 were
analysed together with the ‘extended data set’, giving
a total of 50 samples. These data are referred to as ‘the
historical data set’.
All sample sites were located within homogeneously looking parts of the five different managements, which included a visual assessment of site
factors as micro-topography, canopy density, understorey vegetation composition, humus forms, soil
disturbances, etc.
Table 1
Management types applied in the study area
Management type
Management type
‘Basic data set’a
‘Extended data set’b
Non-managed
Oak management
Coppiced
Grazed
Previously grazed
Untouched since 1916, now with beech dominance
Beech and coniferous species are removed every 10 years since 1916
Indication on maps of coppice in the 1930s
Presently extensively grazed by horses
Indications of grazing until approx. 1970
3
13
1
1
1
3
15
3
6
6
19
33
Number of plots
a
b
Number of sites with soil and vegetation data. The plots are identical to the ‘historic data set’.
Number of sites with vegetation data.
B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
2.3. Sampling of vegetation, soil and
environmental data
The methodology used for analysis of vegetation
was identical to that by Olsen (1938). At each sample
site, frequencies of field and bottom layer species were
calculated by the Raunkiær method (Raunkiær, 1910)
based on rooted presence/absence in 25 randomly
located circles of 0.1 m2 within a homogeneous area
of 50–100 m2. All registrations were carried out in late
June. Vascular plant nomenclature follows Hansen
(1991) and for mosses Andersen et al. (1976). Soil
classification is according to FAO (1998).
Soil samples were taken in May 1997 at the 19
basic sample sites. Five-metres long soil profiles were
dug to 40-cm at each site in order to investigate spatial
variation of humus forms and top-soil morphologies.
A bulked top-soil sample (0–10 cm) was obtained by
mixing 10 sub-samples. Description and sampling of
humus types were done in these trenches and classified
according to Jabiol et al. (1995). Mull represents here
the most fertile humus forms with fast incorporation of
organic matter into the mineral soil, mor represents
soils where organic matter decomposition is very slow,
and moders are intermediate between these two. The
degree of humus decomposition was characterised and
grouped into five categories (0–4): Mor (0), Eumoder
to Dysmoder (1), Hemimoder (2), Oligo- to Amphimull (3) and Mesomull (4). The poorest humus type,
Mor (0), was not represented among the sampling sites
but only found in non-managed areas outside the
sampling sites.
Light penetration through the canopy was measured
at the 19 basic sample sites. Assuming that Olsen (1938)
measured light inside and outside the forest as
simultaneously as possible with a simple light meter,
we did the same using a Marolux digital light detector.
Light penetration in percentage of full light was
calculated based on 4–6 measurements outside and 16
measurements inside the forest at each sample site. At
each plot, all measurements were taken within 10 min.
These measurements are considered rough, but useful
and comparable, estimates of light penetration.
Laboratory analyses were performed as described
in Kristiansen and Greve (2003). Briefly, air-dried, 2mm sieved material was analysed by the following
methods. pH was determined on uncrushed material in
1:1 soil:liquid ratios (w/v) in 1 M KCl with a glass/
321
calomel electrode. On crushed material, total carbon
was determined by dry combustion and weighing of
the evolved CO2, total nitrogen by the Kjeldahl
method, and total phosphorus by spectrophotometry
after ignition (550 8C) and extraction with 1 M HCl.
2.4. Statistical analyses
Principal component analyses (PCA) were performed on the environmental data in the ‘basic data
set’ to study the interrelationship between environmental variables and their grouping into complexgradients (terBraak, 1987). All three data sets were
analysed by indirect gradient analysis using detrended
correspondence analysis (DCA) (Hill and Gauch,
1980). The coenoclines of DCA ordination of the
‘basic data set’ were interpreted by vectors of the
environmental variables showing their direction of
steepest increase. Correlations between environmental
variables and the two first axes were tested by
Spearman’s rank correlation. The statistical software
package PC-ORD (McCune and Mefford, 1995) was
used for these analyses.
The identification of significant differences in
understorey vegetation under different management
was done on ‘the extended data set’ and ‘historical
data set’ by aid of an ANOSIM permutation test
(Clarke and Green, 1988). The ANOSIM test
procedure locates significant differences among
predefined groups of samples on basis of Bray–Curtis
similarity indices (Bray and Curtis, 1957). The
statistical software package PRIMER (Clarke and
Warwick, 1994) was used for this analyse. The
predefined groups were the five different types of
management in the study areas (Table 1).
3. Results
3.1. The ‘basic data set’
When grouping the sample sites according to the
type of management (Table 2), some of the most
important trends are readily recognised. At the nonmanaged sites, little light penetrated to the forest floor,
only few understorey species occurred and all sites
were strongly podzolised. These sites had soil C/N
ratios above 20, low degree of decomposition and thus
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B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
of understorey species was positively correlated.
Percentage of light and management formed a second
complex-gradient significantly ( p < 0.001) correlated to the second biplot axis. Percentage of light was
negatively correlated, whereas management was
positively correlated. The amount of phosphorus
and pH in top-soils showed no significant correlations.
The DCA ordination (Fig. 2) of the ‘basic data set’
had eigenvalues for the first three axes of 0.520, 0.162
and 0.082, respectively. The first axis explained 63.7%
of the species–environment relation. Fig. 2 reveals
significant negative correlation of the first axis with
thickness of organic layer ( p < 0.001) and positive
correlation with soil pH ( p < 0.01). These two
parameters are expected to be inversely correlated,
and it is noteworthy that species number ( p < 0.001)
and light ( p < 0.05) also are positively correlated with
the first axis. At the right-hand side of the diagram, we
find the previously grazed and grazed plots together
with the most species diverse plots on soils with the
highest degree of humus decomposition. Percentage of
light ( p < 0.01) and number of species ( p < 0.05)
were significantly and negatively correlated to the
second axis.
a thick organic layer. The oak-management sites
formed a broad group reflecting the highly variable
acid soils ranging from soils with a mull-type
decomposition to unfertile moders, mostly dominated
by Vaccinium myrtillus. The sample sites 3 and 4 were
located in the northern part of the forest under which a
sandy loamy subsoil was found. This resulted in
enhanced availability of water and nutrients at these
sites, and presumably caused the richest flora to be
found here. The coppiced, previously grazed and
presently grazed sites were only represented by one
site each, which gave no possibility to generalise. The
degree of decomposition, however, indicated a mulltype of decomposition at these sites where the sandy
parent material also was found.
The PCA ordination of the environmental parameters had eigenvalues of the first two axes of 4.355
and 1.272, and 70.3% of the variance was explained
by these axes. The soil C/N ratio, thickness of organic
layer, degree of decomposition and number of
understorey species formed a complex-gradient and
showed significant ( p < 0.001) correlations to the
first biplot axis. The top-soil C/N ratio, thickness of
organic layer and degree of decomposition were
negatively correlated to the first axis, whereas number
Table 2
Environmental data from the ‘basic data set’ sites
Management
typea
Sample
site
Light
penetration (%)
Number of
understorey species
Total P
(mg P kg soil1)
Ph
(KCL)
C/N
Thickness of
organic layer (cm)
Decomposition
typeb
N
N
N
O
O
O
O
O
O
O
O
O
O
O
O
O
C
G
P
9
10
12
1
2
3
4
5
6
8
11
13
14
15
16
17
7
23
24
0.8
0.9
0.8
1.7
7.4
8.5
5.3
5.3
7.1
6.6
8.5
5.8
5.6
7.9
2.6
8.0
4.0
8.5
3.8
3
5
1
9
12
24
16
14
12
11
9
7
9
16
5
9
12
17
16
72
81
59
177
89
186
183
182
476
165
161
117
260
83
304
177
334
275
207
2.95
2.99
2.84
3.29
2.90
3.82
3.33
3.07
3.02
2.74
2.90
2.90
2.80
3.48
2.75
2.68
3.36
3.36
2.99
25
23
22
16
21
15
16
20
12
23
20
25
21
19
20
25
20
15
18
8.7
8.7
8.1
5.4
5.7
3.0
4.4
5.4
4.1
8.3
8.0
9.0
8.8
5.4
10.4
10.0
6.4
2.8
3.8
2
1
1
4
3
4
4
4
4
2
2
2
2
2
2
2
4
4
4
a
b
Management type: O, oak-management; N, non-managed; C, coppiced; G, grazed; P, previously grazed.
The soil organic matter decomposition was grouped into five categories (0–4) ranging from mor to mull humus forms.
B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
Fig. 2. Detrended correspondence analysis of the vegetation data in
the ‘basic data set’. Vectors of the species number and the environmental variables: organic layer thickness, pH and light are showing
their direction of steepest increase. The type of management is
indicated on the plot.
Based on this analysis, the various management
types clearly influences understorey and soil parameters. Especially the group of non-managed plots
(plots 9, 10, 12) formed a distinct group in the DCA
biplot (Fig. 2).
3.2. The ‘extended data set’
When including a number of additional plots
selected for their management strategy, the picture
becomes clearer. The DCA ordination of the ‘extended
data set’ (Fig. 3) had eigenvalues for the first three axes
of 0.560, 0.237 and 0.109, respectively. Except for the
coppiced sites, the type of management formed distinct
groups in the ordination although oak management
overlapped with both coppiced and previously grazed
sites. The grazed plots were significantly different from
the managed, un-grazed plots in other ways with the
previously grazed plots forming a distinct and
significantly different group in between non-managed
323
Fig. 3. Detrended correspondence analysis of the vegetation data in
the ‘extended data set’. The type of management are indicated in the
plot and groups of sample sites with identical management are
encircled.
( p < 0.01) and the grazed plots ( p < 0.01) (Table 3).
Thus, to generalize, two groups occurred: un-grazed
and grazed, with an interesting position of the
previously grazed sites.
As mentioned previously, oak-management was the
basic type of management of the forest, and the oak
management plots covered a wide variety of soil types
and therefore different plant communities. Oak
management could be dominated by V. myrtillus,
and Deschampsia flexuosa forming a relatively
homogenous vegetation on more fertile soils. Where
V. myrtillus did not dominate, a number of codominant
understorey species occurred, such as Oxalis acetosella, Maianthemum bifolium, Melampyrum pratense, Stellaria holostea, Anemone nemorosa, Holcus
mollis, Trientalis europaea and the mosses Pleurozium
schreiberi and Hypnum cupressiforme. The coppiced
plots did not differ significantly from these general
patterns, whereas the non-managed plots differed by
having very few species: V. myrtillus and D. flexuosa
and few mosses. The grazed plots, on the other hand,
Table 3
Differences in understorey vegetation between groups of sample sites under different management strategies
Oak management
Coppiced
Non-managed
Grazed
Coppiced
Non-managed
Grazed
Previous grazed
n.s.
p = 0.002
n.s.
p = 0.001
p = 0.012
p = 0.012
n.s.
n.s.
p = 0.012
p = 0.002
The ANOSIM permutation test was based on the ‘extended data set’; n.s.: not significant.
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B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
contained several species absent, or rarely found, in
the rest of the management strategies, such as Luzula
campestre, Holcus mollis, Agrostis spp., Festuca
rubra, whereas mosses were less common. Unlike
in the grazed plots the species V. myrtillus, Lonicera
periclymenum, Luzula pilosa and Trientalis europaeus
were common in the previously grazed plots.
3.3. The ‘historical data set’
To complete the analysis, the data from Olsen (1938)
were included to give indications of development
through time. The DCA ordination, including all 50
plots (Fig. 4), had eigenvalues for the first three axes of
0.525, 0.240 and 0.167, respectively. The 1916 part of
the data set formed a group fully separated from the
1995 data. Within the recent data, the five management
types were located as in Fig. 3. Olsen (1938) identified
three different types of soil/humus forms: humid mull,
dry mull and mor, and they also formed distinct groups
in the ordination. It is striking that the presently grazed
plots are rather similar to the humid mull plots of 1916.
The differences between groups of sample sites,
five management groups in the recent data set and
three soil groups in the 1916 data set, were tested by
the ANOSIM test procedure (Table 4). The 1916 soil
groups were significantly different from one another
and they were also significantly different from all 1995
management groups. Among the recent data, the oak
management group neither differed significantly from
the coppiced group nor from the group of previously
grazed sites. The latter two groups did not differ
significantly. In other words, the 1995 sites could be
Fig. 4. Detrended correspondence analysis of the vegetation data in
the ‘historical data set’ with the sample sites 1–17 (Olsen, 1938)
below the full line. These sample sites are indicated as previously
grazed. The types of management of the sample sites 1–34 analysed
in this paper are indicated on the plot. The ‘historical data set’ is
grouped into three categories on basis of soil development, whereas
sites analysed in 1995 are group on basis of management strategy.
separated into three clearly distinct groups of sample
sites: non-managed, managed (oak management,
coppiced, previously grazed sites) and grazed.
4. Discussion
4.1. Management effects on soils and humus layers
The data analyses reveal that the various management types influences on, or interacts with both humus
Table 4
Differences in understorey vegetation between groups of sample sites in the ‘historical data set’ analysed by the ANOSIM permutation test
1916 Data
1916
Humid mull
Dry mull
Mor
1995
Oak management
Coppiced
Non-managed
Grazed
n.s.: not significant.
1995 Data
Dry mull
Mor
Oak management
Coppiced
Non-managed
Grazed
Previous grazed
p < 0.008
p < 0.002
p < 0.001
p < 0.001
p < 0.004
p < 0.001
p < 0.03
p < 0.02
p < 0.006
p < 0.03
p < 0.02
p < 0.006
p < 0.005
p < 0.004
p < 0.001
p < 0.005
p < 0.004
p < 0.001
n.s.
p < 0.002
n.s.
p < 0.001
p < 0.01
p < 0.01
n.s.
n.s.
p < 0.01
p < 0.002
B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
forms, top-soil properties and understorey vegetation
succession. The plots left unmanaged during the 80
years have become dominated by dense beech canopy.
Little light (and probably less precipitation) penetrated the canopy and consequently few species were
found and a thick organic layer accumulated. These
sample sites were significantly different from all other
sites with respect to both humus form and vegetation.
Also, the presently grazed plots that had a mull-type of
decomposition and a number of plant species, not
found or rarely found under other management
strategies, was significantly different. In the oakmanaged plots, the understorey vegetation varied
highly probably reflecting the variety of site properties
from mull-type to moder-types of decomposition.
These results are in accordance with the findings of
Elgersma (1998), Nielsen et al. (1987b), and Dahlgreen et al. (1997) that the properties of the dominant
tree species influences soil organic matter decomposition rates. This in turn influences the understorey
vegetation, humus forms and may result in enhanced
soil nutrient cycling underneath oak trees. Consistent
with the findings that beech on poor soils decreased
surface soil pH significantly and had slowly decomposing leaves leading to a mor-type of decomposition
(Brahy et al., 2000), it was previously found that the
non-managed beech-oak part was located on Podzol
soils only in Hald Ege (Kristiansen and Greve, 2003).
Under the managed parts of Hald Ege, such a
correlation between soil types and vegetation was
not established.
4.2. Forest management effects on understorey
vegetation
Changes in understorey species during the last
century have also been attributed to increased atmospheric deposition (Falkengren-Grerup, 1995; Brunet
et al., 1996), but other factors may as well influence
the ground flora profoundly (Hermy et al., 1993;
Härdtle et al., 2003). For instance, decreased light
penetration was the most important factor influencing
vegetation changes in Hald Ege during the last 80
years although decreases in disturbance level also
played a role (Tybirk and Strandberg, 1999). Nevertheless, the intention of keeping the oak-scrub from
changing into a species-poor beech forest seemed to
function, as the present data reveal that management
325
strategy seems to be most important (Figs. 2–4;
Tables 3 and 4). From a conservational point-of-view
it is especially interesting that grazing mammals kept
the forest at a stage resembling mostly the oak-scrub/
forest of 1914 with respect to both vegetation and
humus forms. This is probably because Hald Ege was
grazed until the preservation in 1914–1915, and all
plots could therefore be considered previously grazed
when Olsen (1938) did his investigation in 1916.
Dahlgreen et al. (1997) found that grazing in an oak
forest decreased the thickness of A and AB horizons,
but were concerned about the sustainability of such
forest grazing because it reduces the potential for oak
regeneration and development of an understorey
vegetation. This signifies that grazing may be used
as temporary forest treatment—sometimes periods of
no grazing are necessary for the regeneration of the
forest. Forest grazing in this case gives higher floristic
diversity, but indeed the grazing creates many other
niches and spatial heterogeneity for other types of
organisms (Putman, 1996).
4.3. Changes in diversity and soil decomposition due
to succession—formulation of a hypothesis
This paper has analysed and discussed various
aspects of changes occurring in a hypothetical
succession from heathland ! oak-scrub ! oak forest
and finally ! beech dominated forest. The last three
steps have been treated in this and a previous study
(Tybirk and Strandberg, 1999), but all steps have
previously been investigated (e.g., Nielsen et al.,
1987a, 1987b; Kristensen and Henriksen, 1998; Rode,
1999; Sørensen and Tybirk, 2000).
This leads us to propose the following hypothetical
sequence of ground flora and organic matter decomposition changes occurring through this succession
(Fig. 5). On a hypothetical time scale (centuries)
former heathland on poor sandy soils will gradually
change into oak-scrub and open oak-scrub/forest as
the trees are ageing. Finally, it may succeed into dark
oak/beech forest if management cease. Once a forest
climate has been created, understorey V. myrtillus may
become dominant initiating a mor-formation in the
soil and further ousting other understorey species.
This has been found in Hald Ege and other Danish
oak-scrubs (Sørensen, 1998; Tybirk and Strandberg,
1999). Dense clones of V. myrtillus may leave little
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B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
or do we want to preserve the process of succession
from heathland towards a mixed natural forest?
4.4. Implication on soil genesis?
Fig. 5. Hypothetical figure of changes in soils and understorey
vegetation occurring in the succession from heathland to beech
dominated forest on poor sandy soils. Along the time-axis heathland
changes gradually into oak-scrub and finally into beech dominated
deciduous forest. The data on soil organic matter decomposition and
species number presented in this paper forms basis of the full lines
with indication of the management types: grazing, oak management
and non-managed.
space for other species and may reduce the regeneration possibilities for competing species, probably
through interactions in the humus form (Ponge, 2003).
When the secondary forest succession reaches the oakbeech stage V. myrtillus cannot survive any longer,
probably due to decreased light, reduced water
availability and strong beech litter accumulation.
The second axis in Fig. 5 can be either an indication
of floristic diversity or soil fertility expressed by soil
pH, C/N ratio and thickness of organic layer. Both
heathlands and beech forests are characterised by few
species, relatively low pH, thick humus layer and
consequently high C/N. Intermediate succession stages
of oak-scrub and open oak forest have higher floristic
diversity and higher soil nutrient availability. The figure
indicates a further theoretical development as the mixed
deciduous forest is ageing. A dynamic mosaic-cycle
forest type may establish with temporal oscillating
understorey diversity and organic matter turnover.
Based on this, the central question for conservation
of such secondary forest successions is basically: where
on this hypothetical scale do we want to keep the
ecosystem? Ideally, all stages could be represented in an
area. The reasons for maintaining the various types may
be historical, nostalgic or optimal biodiversity conservation reasons. Another question could arise from
this analysis: do we want to conserve the oak-scrub
structure and the associated species in a certain stage—
The model proposed in Fig. 5 may also have
profound effects on soil if some environmental
thresholds are exceeded. The reason is that keeping
a forest at a certain successional stage for a long
period, soil characteristics may be influenced as
understorey vegetation and humus forms are connected with soil genesis via soil biota and soil solution
chemistry. For example, older successional stages
with mixed beech, oak and birch (Betula spp.) forests
have been shown to enhance podzolisation (Aaby,
1983), while traces of depodzolisation (the conversion
of podzolic soils into non-podzolised soil types) occur
in early successional stages (Nielsen et al., 1987a,
1987b), or after deforestation (Barrett and Schaetzl,
1998). In other words, we propose that long-term
forest management may cause a more or a less
podzolised soil, depending on site factors as susceptible nutrient-poor parent materials and climatic
conditions.
Such slow plant-soil interaction can also explain
why the spatial distribution of soils in Hald Ege was
only partly explained by parent material variations
under oak management (Kristiansen and Greve, 2003),
as evidence of former, stronger podzolisation are
retained in sub-soils for at least 60 years (Nielsen et al.,
1987a, 1987b). The proposed model can only be
hypothetical in Hald Ege as temporal and spatial effects
are difficult to separate in such ancient woodlands.
Other studies under similar climatic conditions may
support the proposed pattern (Vejre and Emborg, 1996;
Bernadzki et al., 1998; Härdtle et al., 2003), whereas
others from deeper South European soils do not (Rubio
et al., 1999). Such a dynamic behaviour of soil genesis
following forest succession/management is nevertheless in accordance with the theory recently proposed by
Ponge (2003) that alternating phases of ecosystem
stability are controlled by humus forms.
5. Conclusion
Our data indicate that leaving the forest without
management may decrease the floristic diversity and
B. Strandberg et al. / Forest Ecology and Management 211 (2005) 318–328
litter decomposition rates. The works on grazed oak
forests indicate clearly that grazing, at least as a
temporary forest treatment, is likely to reverse oak
forest aging and litter decomposition rates by
maintaining the forest in a species rich open stage.
The central thesis of this paper is accordingly that by
conservational management we can maintain or obtain
certain site characteristics.
Acknowledgements
Fussingø State Forest District is thanked for
permission to conduct research in the forests.
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