The importance of near-natural stand structures for the biocoenosis of lowland beech forests
Susanne Winter, Martin Flade, Heiko Schumacher, Eberhard Kerstan and Georg Möller Brandenburg State Agency for Large Protected Areas, Tramper Chaussee 2, D-16225 Eberswalde, Germany
winter@wzw.tum.de; martin.flade@lua.brandenburg.de; hschuma@fh-eberswalde.de;
georg-christian.moeller@t-online.de
Abstract
A ‘Research and Development Project’ in Brandenburg (Germany) running from 1999 to 2003 aimed to define nature conservation standards for the management of lowland beech forests. The avifauna, saproxylic beetle fauna, ground beetles, saproxylic fungi, and the stand structures were investigated in twelve managed near-natural beech forests, and in six that had been unmanaged for 12 to more than 100 years near-natural beech forests to identify bioindicators for near-natural forest stands, which maintain the typical biocoenosis of beech forests. Some selected spotlight-like results are presented in this paper.
The results show, for example, striking differences in stand structures between near-natural beech stands and managed forests, close dependence of bird species on silviculture influences and effects of forest developmental phases on ground beetles of beech forests. For instance, near-natural stands are much more structured, richer in dead wood (10–20 times of the volume of managed forests) and are characterised by a much higher abundance of breeding birds, especially wood- inhabiting and beech forest indicator species, as well as some saproxylic fungi species. Saproxylic and ground beetles are characteristic of deciduous forests.
Some examples for bioindicators of natural or near-natural beech forests are:
1 High number of special tree structures (e.g. trees with severe crown damage, large cavities, clefts in the stem, scratches and bark bags with/without mould), which are typical attributes of ancient forests and a suitable structural indicator.
2 The Middle Spotted Woodpecker Dendrocopos mediuswas identified as a valid indicator for mature beech forests with old trees. The occurrence of D. mediusdepends on two typical stand structures: a) rough bark structures (typical for old beech trees >200 years), and b) dead wood in parts of the stems or branches of standing trees.
3 Carabus glabratusis suggested as a bioindicator among the ground beetles.
4 Fungi species of the genus Pluteusare significantly more frequent in unmanaged forests.
5 The number of individuals of saproxylic beetle species which are not captured in the managed forests is three times higher than in >50 year-old unmanaged beech forests.
Keywords: lowland beech forest, natural beech forest, nature conservation standard, bioindicator for naturalness,Fagus sylvatica,stand structure, avifauna, saproxylic beetles, saproxylic fungi, Carabidae, ground beetles
1 Introduction
The potential natural global distribution of beech forests with dominant Fagus sylvaticaL. is restricted to Europe with a focus on western, western-central and southern parts. In the southern and warmer part of the potential natural distribution area, beech forests are located in (sub)mountainous to subalpine regions, whereas in the northern area it is mainly a low- land to submountainous forest type. Lowland beech forests are potentially distributed in a narrow belt from northern France and southern Great Britain over the northern part of Germany, Denmark and southern Sweden to northern Poland (BOHNand WEBER2000).
Germany has a high responsibility for the conservation of beech forest as it contains the core area of global beech forest occurrence. Our project focuses on the lowland beech forests because of their currently restricted distribution. At present, lowland beech forests are scarce and extremely fragmented. The two largest continuous lowland beech forest tracts of 3500 and 6500 hectares are located in the Schorfheide-Chorin Biosphere Reserve, state of Brandenburg, north-east Germany.
Besides the small and fragmented area of actual occurrence, the lowland beech forests have been severely altered by silviculture (e. g. young trees, in general with a maximum age of 160 years). There are no virgin lowland beech forests left.
In practice it seems impossible to protect the whole biocoenosis of beech forests (FFH- guideline 1992, appendix 1), including 7000 animal species and 4000 plant species (BERTSCH
1947) by simply creating unmanaged reserves (‘total reserves’). Although in Germany larger unmanaged lowland beech forest reserves (which are not ancient forests!) were established in 1990, e. g. parts of the Jasmund and Müritz National Parks and in the Schorfheide-Chorin Biosphere Reserve. The proportion of strict reserves in the total forest area is less than 1 %.
Considering the limited dispersal potentials of many saproxylic beetles and fungi, it is obvious that the protection of the entire lowland beech forest biocoenosis can only be guaranteed or succeeded by implementing maintenance and conservation measures as part of normal beech forest management.
The goal of the Research and Development Project (1999–2003) at the Brandenburg State Agency for Large Protected Areas was to define nature conservation standards for the management of lowland beech forests (FLADEet al.2004; WINTERet al.2002, 2003). The main question was how to manage lowland beech forests without disturbing the typical bio- coenosis. To answer this, the main studies had to find out the differences between managed and unmanaged forests and the importance of near-natural stand structures for the bio- ceonoses of lowland beech forests. Some exemplary results of this comparison are presented in this article.
There are three major topics:
1 To identify the differences between near-natural beech stands and managed forests.
2 To analyse the impacts of the stand structure on the biocoenosis.
3 To identify bioindicators for conservation-sound beech forest management.
2 Study sites and methods
The avifauna, saproxylic beetle fauna, ground beetles, saproxylic fungi, vegetation and the stand structures were investigated in twelve differently managed near-natural beech forests, and in six that had not been managed for 12 to more than 150 years. All stands were older than 120 years. The study plots were located in the north-eastern part of Germany. Most of
them were in the northern part of Brandenburg with four in Mecklenburg-Vorpommern (Fig. 1). The area of study sites was about 40 ha each. This plot size could not be achieved in two of the near-natural sites (r2 Heilige Hallen24.9 ha, tree stand ~350 years old,r3 Fauler Ort 13.6 ha, >350 years old) and the two shelterwoods (w4 Haussee 11.4 ha and w6 Klaushagen17.4 ha).
Fig. 1. Location of the study sites in north-east Germany.
Fifteen study plots belong to the Galio odorati-Fagetum (FISCHER1995). Four of them are mixed with the Luzulo-Fagetum caused by the rich-structured relief and the soil changes of this young moraine landscape, which was shaped by the Vistula glaciation (LIEDTKEand MARCINAK1995). The vegetation of one unmanaged study site represents the richer part of the Galio odorati-Fagetum with Mercurialis perennis, Hepatica nobilisand Paris quadrifolia.
Two managed sites and one ~20 years unmanaged study site belong to the Luzulo-Fagetum.
The study sites are divided into three subdivisions, which are marked with different letters: 1. managed forest = w (abbreviation of the German word “Wirtschaftswald”), 2. from 10 to 20 years undisturbed forests = k (abbreviation of “kurzzeitig ungenutzt” – shortly unmanaged), 3. 50 years or more undisturbed forest = r (abbreviation of long-term reference study plot). Study site Serrahn r1was unmanaged for ~50 years and Heilige Hallen r2and Fauler Ort r3for an unknown time but more than 100 years.
2.1 Stand structure
Our field studies were divided into grid point studies and full-coverage studies. At grid points (100 m × 100 m in r-study plots, 100 m ×200 m in w- and k-study plots), detailed parameters of the stand were measured.
1 20 “Special Tree Structures” (STS) were recorded in a circle of 12.62 m radius (500 m2).
The 13 selected STS referred to in this paper are: 1. trees with severe crown damage (more than 50 % of the crown is lost), 2. secondary crown trees (almost dead stems with one or more big lateral branches, developed after break-down of the primary crown), 3. living trees with completely broken crowns, 4./5. large cavities with/without mould, 6.
cavities of large woodpeckers (Green Picus viridisand Black Woodpecker Dryocopus martius), 7. clefts in the stem, 8. open bark gaps (scratches) and 9./10. bark bags with/with- out mould, 11.–13. trees with tinder fungus Fomes fomentarius, with Fomitopsis pinicola or other fungi (for definitions see WINTER2005). As an example of the results we take the STS “bark bags with mould” with the following definition of its structure: The bark of a tree is partially lifted and filled up with mould between the bark and stem; the lifted bark has a width and height of 5 cm ×5 cm minimum, and a minimum depth of 2 cm.
The choice of special tree structures is mainly based on knowledge of habitat needs of saproxylic insects and fungi (KOCH1989; MÖLLER1991, 1993, 1994; KÖHLER1996) as well as bats (MESCHEDEand HELLER2000) and birds (BEZZEL1986, 1992; FLADE1994, GLUTZand BAUER1994). The results presented are based on data from STS of living trees.
2 Dead wood volume was calculated according to the length and middle diameter, measured for standing dead trees 7 cm or more in diameter at 1.3 m breast height (without bark 6 cm diameter) and for lying dead trees 15 cm or more in diameter at the thicker end and 7 cm (without bark 6 cm) or more in diameter at the thinner end.
3 The forest development phases were mapped extensively in the study sites following the method of TABAKU(2000) with small modifications by WINTER(2005).The forest cycle was divided into eight development phases: regeneration, grow-up, early optimum, middle optimum, late optimum, terminal, breakdown phases and gaps. Additionally, fens, bogs and open water (small lakes) were mapped.
2.2 Breeding birds
The recording of breeding birds and their abundance was according to the ‘extended territory mapping’ methodology (FLADE1994; BIBBYet al.1995, DO-G 1995). The avifauna of several study sites was mapped in up to four subsequent years (1998–2001).
The bird population density has a natural dynamic or variation. Local changes could be caused by weather conditions (like severity of winters), time and intensity of tree-fructi- fication as well as shooting, droughts or other impacts during migration and wintering (BEZZEL1982; GATTER2000). To achieve comparability of data gathered in different years, an annual reference index value for eastern Germany calculated by SCHWARZand FLADE (2000) and FLADEand SCHWARZ(2004); data of the DDA Monitoring Programme = the German Common Birds Census) was used. This index is based on some hundred bird moni- toring plots which are surveyed by standardised methods and shows the large-scale annual population changes of breeding birds in the whole of Germany as well as in sub-regions.
Local data on abundance were multiplied with the corresponding East-German population index to be able to consider the general annual changes in species populations.
Calculation of preference index: A preference index was used to analyse whether birds either prefer or avoid distinct forest development phases. Using a GIS, the number of bird registrations in each forest development phase was summarised. The expected number of registrations was calculated as an area proportion of the development phase and pro- portional share of all registrations of the respective bird species. Finally, the preference
index for each bird species and development phase was calculated as follows: preference index = number of bird records/expected number of records –1.
2.3 Saproxylic fungi
In eight study sites (five w-, one k- and two r-sites), all wood-inhabiting fungi species with fruit bodies >4 mm diameter were registered in transects of one to two ha per study site. In study sites with very low abundance of suitable habitats for saproxylic fungi, a transect was taken which was a little longer than in well-structured stands. These transects had a width of 25 m. In the years 2000 to 2002, the fungi were mapped on five visits per study site in a semi- quantitative way. Additional to the species name, the substrate of the fungi and the number of growing locations (‘findings’) were registered. The number of fruit bodies was not relevant, but the substrate units were. One saw-stump, one standing/fallen tree or branch was regarded as one unit. Heaps of brushwood and fallen dead crowns were also regarded as a single unit.
The scientific names of the saproxylic fungi according to GERHARDT(1997) and ad- ditionally to JÜLICH(1984), MOSER(1978) and BREITENBACHand KRÄNZLIN(1984) are used.
2.4 Saproxylic beetles
Saproxylic beetles (and some other important saproxylic insect taxa, not included in this paper) were recorded at nine study sites (3 r-sites, 1 k-site and 5 w-sites) at five selected, representative grid points each (see section 2.1). At each sample point, a bark beetle trap, a crown trap (KÖHLER2003) and one or two (depending on the breast height diameter of the chosen tree) lime strips (rings), were installed for a full reproductive season (early May to late August). Additionally, all special structures (dead wood and STS) providing habitats for saproxylic insects were investigated by ‘hand and lamp trapping’ and ‘meshing samples’ over the whole study site. Data analysis was performed separately for the whole data set of the study site and exclusively for the data of the standardised grid point samples (the latter was important in order to compare numbers of individuals between different study sites and to correlate the trapping results with stand structure data). Indicator species for natural beech forests were classified according to the following categories: a) species which were recorded in several individuals and at (mostly) several sample points in the long-term unmanaged study sites (r-sites), but were absent in the managed study sites (w-sites), and b) species which were significantly more abundant at sample points in r-sites compared to the w-sites.
2.5 Ground beetles – Carabidae
For the recording of ground beetles, the standard pit trap method (BARBER1931) was used.
Ethylenglycol was used as the trapping liquid. In every study site, five traps were installed at selected grid points (see 2.1) from the beginning of the vegetation period (early spring) up to the end of November. In every development phase (including gaps) which was represented in the grid points of each study site, at least one was chosen to place a pit trap. Since the maximum number of different development phases represented by grid points was five per study site, a selection of development phases was not necessary. The pit traps were emptied every fortnight (15 times during the vegetation period).
3 Exemplary results
3.1 Stand structure 3.1.1 Dead wood volume
The difference in occurrence of dead wood in managed and unmanaged forests was surpris- ingly large (Fig. 2). The r-sites (142–244 m3per ha) had an approximately 10 to 15 times high- er dead wood volume than w-sites (2.7–34 m3per ha, within a section area of 10 hectares up to 78 m3 per ha). The k-sites (unmanaged for 12–20 years) did not yet show clear differences from the w-sites (Fig. 2). Dead wood pieces were not only much more abundant in the r-sites, but were also on average twice as long and much thicker than in w-sites.
managed unmanaged
<20 years
unmanaged
>50 years 0
50 100 150 200 250
dead wood volume [m3/ha]
Fig. 2. Dead wood volume in managed and un- managed lowland beech forests (mean volume [m3/ha] + standard error.
3.1.1 Occurrence of Special Tree Structures (STS)
A certain time after direct human impact has ceased, forests develop distinct differences to managed forests: e.g. smaller patches of development phases and development of late optimum, terminal and breakdown phases (= ageing phases, LEIBUNDGUT 1993; KORPEL
1995; TABAKU2000). In unmanaged forests, the qualitative diversity is, with 10 to 13 special tree structure types per study site, significantly higher (p <0.001) than in managed forests (3–8 special structure types per study site). In r-study sites, the number of STS is twice as high as in w-study sites (Fig. 3). The mean in long-time unmanaged forests is 156 STS/ha and in managed forests 76 STS/ha. If the structure of open bark gaps is excluded (promoted in managed forests by felling and harvesting, and in unmanaged forests by falling trees), the number of STS in r-study sites is almost three times higher than in w-study sites. This shows that managed forests are much more uniform in structure.
In the following, one STS and its importance for the lowland beech forest biocoenosis is presented:
Bark bags with mould form from dead bark on dead or living trees. The bark is partially lifted and filled up with mould between bark and stem. This STS was registered with a width and height of 5 cm ×5 cm minimum, and a minimum depth of 2 cm. The mould consists of decayed wood, chitin parts from insects, and animal excrement. The bark bags with mould were variously used as nesting sites by treecreepers Certhia brachydactyla, C. familiaris (GLUTZand BAUER1993), and as breeding sites or roosts for bats (e. g.Barbastella bar- bastellus, Myotis bechsteini,MESCHEDEand HELLER2000). Insects use them as both hiding places and breeding nests. In particular, species of the Dermestidae and Alleculidae prefer to live in the mouldy, nutritious bark bags (MÖLLER 2000). So too do species of the Histeridae which capture fly larvae in the bark bags. Another typical inhabitant of bark bags in the crown of trees is Dictenidia bimaculata.
This small STS was not found in most of the managed forests, whereas in the r-study plots it was found regularly. This STS is a good indicator for ageing structures on living trees (Fig. 4). In all w-, k-study sites and in Serrahn r1bark bags are less common than in >100 year-old unmanaged beech forests.
Fig. 3. Special tree structures in managed and unmanaged lowland beech forests (number/ha) and share of open bark gaps of the total number.
250 200 150 100 50
w1 w2 w3 w6 w7 w8 w9 w10 w11 w12 study plots bark gaps
number/ha
all the other STS
w13 k1 k2 k3 k4 r1 r2 r3
0
Fig. 4. Bark bags with mould in managed and unmanaged lowland beech forests (number/ha).
10 8 6 4 2
w1 w2 w3 w6 w7 w8 w9 w10 w11 w12 study plots
number/ha
w13 k1 k2 k3 k4 r1 r2 r3
0
3.2 What impact does the stand structure have on the biocoenosis?
3.2.1 Breeding birds
In the unmanaged forests Heilige Hallen r2and Fauler Ort r3,60–120 territories/10 ha were found (Fig. 5). This is significantly more than in all other study sites (p <0,001, Mann- Whitney-U-Test). Because of the still very homogeneous structure, the briefly unmanaged k-study sites do not have more territories/10 ha than the managed sites.
The calculation of the preference index for the habitat use of birds according to the forest development phases resulted in pronounced differences (Fig. 6).
The breakdown phase is the most favourable phase for breeding birds. The early optimum and terminal phase as well as gaps are also preferred by birds, but less than the breakdown phase. Birds avoid the regeneration and middle optimum phase. It is not surprising that forest birds occur less often in fen mires, bogs and forest lakes, which are not development phases, but occur frequently in lowland beech forests.
23 of the 37 recorded bird species of lowland beech forests preferred the breakdown phase (preference index >1). The differences in the abundance between w- and r-study sites are mainly caused by the lack of this phase in managed forests.
One of the ‘wood-inhabiting’ species, which qualifies as an indicator species of beech forests, the Red-breasted Flycatcher Ficedula parva,avoids the breakdown phase. It prefers to forage in dark dense beech forest stands with high air humidity. Additionally, it needs small cavities and clefts for nesting. These habitat needs are fulfilled in the terminal phase, where F. parvahas been recorded most often. All other indicator species of beech forests (according to FLADE1994, modified) prefer the terminal and/or breakdown phase.
High breeding-bird abundances in r-study plots and preferences for ageing phases already indicate the rich and diverse supply of habitat structures in near-natural lowland beech forests. The ecological value and importance of near-natural stand structures is also exemplified by the Middle Spotted Woodpecker (Dendrocopos medius), which is mainly
120
100
80
60
40
20
w1 00 w2 01
w3 00 w4 99
w6 00 w7 99
w8 99 w9 98
w10 98/02 w12 98–02 w11 99
abundance (territories/10 ha)
w13 01 k1 00
k2 98/01
k3 98 r1 99–00 r2 98–01
r3 98–01 0
Fig. 5. Abundance of breeding birds (territories/10 ha) in unmanaged and managed lowland beech forests; w = managed, k = shortly and r = long time unmanaged lowland beech forests; for study sites with more than one mapping season: average values. Minimum and maximum abundance is shown for study sites with more than one year of research.
distributed in central and south-eastern Europe. Germany has about 20 % of the world population (FLADE1998). In our study sites, the occurrence of D. mediuscan be divided into three categories (Fig. 7):
1 In six w- and two k-study sites the species is missing.
2 In six managed beech forests D. mediusoccurs, but in four of them this is caused by the occurrence of oaks, which have a share of <10 % of the total number of stems.
3 The long-time unmanaged r-study sites Heilige Hallen r2and Fauler Ort r3show more than one territory/10 ha, although almost no oaks occur. The same was the case in the k1- study site ‘Stechlin’.
2.0
1.5
1.0
0.5
0.0
–0.5
preference index
mosaic structure
I II III IV V VI VII VIII IX
I regeneration II grow-up phase III early optimum phase IV middle optimum phase V late optimum phase
VI terminal phase VII breakdown phase VIII gaps
IX fen/bog/water
Fig. 6. Preference index of breeding birds according to different forest development phases, and including wetlands.
3.0 2.5 2.0 1.5 1.0 0.5 0
w1 00 w2 01
w3 00 w4 99
w6 00 w7 99
w8 99 w9 98
w10 98/02 w11 99
w12 98–02
w13 01 k1 00 k2 98/01
k3 98 r1 99–00 r2 98–01
r3 98–0
territories/10 ha
Fig. 7. Occurrence of Middle Spotted Woodpecker Dendrocopos medius(territories/10 ha) in lowland beech forests. w = managed, k = shortly and r = long-term unmanaged lowland beech forests; for study sites with more than one mapping season: average values.
3.2.2 Saproxylic fungi
The number of saproxylic fungi species (126 in total) varies in the study sites between 68 and 86. Most species were found in the forests Heilige Hallen r2and Fauler Ort r3,unmanaged for more than 100 years. The fewest were observed in one of the managed beech forests (Fig. 8). Slightly more species were found in unmanaged lowland beech forests than in managed stands, but the difference is not significant. Regarding the total number of findings (localities) there were slightly, but also not significant, fewer localities in r-sites than in w-sites (Fig. 9).
The occurrence of 22 species shows significant differences between managed and unman- aged lowland beech forests. Only three (Ascocoryne sarcoides[Fig. 10],Trametes hirsutaand T. versicolor) of them are more abundant in managed forests. Eight out of 19 species, which are more frequent in the r-study sites,Heilige Hallen r2and Fauler Ort r3,belong to the genus Pluteus (Fig. 11). Some species like Hericium coralloides (Scop.:Fr.) Gray,Pluteus romellii(Britzelm.) Sacc. and P. umbrosus(Pers. ex Fr.) were exclusively recorded in r-study sites.
Fig. 8. Species number (mean + standard deviation) of saproxylic fungi found in managed, less than 20 and more than 50 years unmanaged lowland beech forests.
Fig. 9. Total number of growing units (localities) of species registered in managed and unman- aged lowland beech forests (Box-Whisker-Plot, showing median and quartiles).
managed unmanaged
<20 years
unmanaged
>50 years 65
70 75 80 85 90 95
number of species per study site
managed unmanaged
900 1200 1500 1800 2100 2400 2700 3000 3300
total number of localities of species
Fig. 10. Occurrence of Ascocoryne sarcoides in managed and unmanaged lowland beech forests.
Fig. 11. Occurrence of eight species of genus Pluteusin managed, less than 20 and more than 50 years unmanaged lowland beech forests.
managed unmanaged >50 years 0
10 20 30 40 50
Ascocoryne sarcoides [mean number of records per study site]
managed unmanaged <20 unmanaged >50 0
10 20 30 40 50 60 70
mean number of Pluteus species in study sites
Pluteus cervinus Pluteus hispidulus Pluteus nanus Pluteus petasatus Pluteus phlebophorus Pluteus romellii Pluteus salicinus Pluteus umbrosus
3.2.3 Saproxylic beetles
In the unmanaged forests nearly 200 beetle species occur which were not recorded in the managed forests (whole data set, including investigation of STS on the whole study site). The total number of individuals of these beetles is very high (>1200). In managed forests fewer than 400 individuals of beetle species without a record in the unmanaged forests were found (Fig. 12), despite five w-sites, but only four (on average smaller) k- and r-sites were studied.
This result, along with the strong correlation between indicator species number and dead wood volume found in the standardised grid sample plots, (Fig. 13, right) confirms the enor- mous importance of old-growth stands.
In managed beech forests, no significant correlation between the amount of dead wood in grid sample plots (circles of 500 m2) and the number of individuals of indicator species was found (Fig. 13, left), whereas the unmanaged beech forests show a strongly significant cor- relation between these two parameters (R20.41, p <0.01).
Fig. 12. Number of beetles species and recorded individuals of these species which occurred in only one of the study sites exclusively; w = managed, k = briefly unmanaged and r = long-term unmanaged low- land beech forests; right: summarised data for managed and long-term unmanaged study plots.
1400 1200 1000 800 600 400 200 0
Number of …
individuals species
w12 w1 w5 w10 w9 k2 r1 r2 r3 managed
unmanaged
Fig. 13. Correlation between the number of individuals of saproxylic indicator beetle species and dead wood, left: managed, and right: >50 years unmanaged lowland beech forests; both in sample plots (circles) of 500 m2.
dead wood [m2/500m2] 20 10
0
number of individuals
2500 2000 1500 1000 500 0
dead wood [m2/500 m2]
30 20
10 0
2500 2000 1500 1000 500 0
number of individuals
Altogether, we identified 131 beetle species (out of 711 species with 155 000 individuals in total) that significantly prefered unmanaged lowland beech forests, which we classify as indi- cator species for the naturalness of stands. Species number and number of individuals of these indicator species (recorded in the grid sample plots) correlate significantly not only with various dead wood parameters (besides total volume also e. g. number of objects, volume of standing and fallen dead wood, basal area), but also with the forest development phases, abundance of STS and number of STS types.
3.2.4 Ground beetles
Ground beetles are influenced by changed stand structures in the ageing period (WINTER
et al.2002; WINTER2005). In long-term unmanaged lowland beech forests, many more indi- viduals of so-called mesophilic forest ground beetle species (according to MÜLLER- MOTZFELD 2001) were recorded than in managed forests (Fig. 14). As one example, the occurrence of Carabus glabratusis shown (Fig. 15 and 16).
Carabus glabratus is trapped significantly more often in unmanaged than in managed forests (Fig. 15). This is because it favours the breakdown phases which occur much more often in unmanaged than in managed forests. On average, more than three individuals of C.
glabratuswere found in pit traps located in the ageing phases. In all the other development phases, summarised in two columns in Figure 16 (grow-up phase and optimum stage, KORPEL1995), a maximum of 0.5 individuals/pit trap only was recorded.
Fig. 14. Captures of mesophilic forest ground beetle species (MÜLLER-MOTZFELD 2001) in managed,
<20 years and >50 years unmanaged lowland beech forests.
managed unmanaged
<20 years
unmanaged
>50 years 30
40 50 60
ground beetles of mesophilic deciduous forest [individuals per 5 pit traps]
managed unmanaged
1 2 3 4
individuals per trap
Fig. 15. Captures of Carabus glabratusin man- aged and unmanaged lowland beech forests [mean number of individuals per trap].
4 Discussion
This paper presents only an exemplary sample out of the entire results of a comprehensive research project, which aimed to identify nature conservation standards for the management of lowland beech forests (FLADEet al.2004; WINTERet al.2002, 2003, 2005). We focus on a selection of pronounced differences between managed and unmanaged forests here.
Considering the fact that all study sites consist of ‘mature’ beech stands more than 120 years old, the clear differences between managed and long-term unmanaged forests in various parameters like dead wood volume, special tree structures, and composition of different parts of the biocoenosis are striking. The natural ageing of lowland beech forests up to the breakdown phase causes an increase in structural and species diversity as well as an increase in the number and abundance of species typical for lowland beech forests. As shown in the investigations on breeding birds, saproxylic fungi, saproxylic beetles and ground beetles (Winter et al.2002), and also in more detailed ecological studies on foraging habitat use of typical beech forests birds (such as the European Nuthatch Sitta europaea,Red-breasted Flycatcher, and Middle Spotted Woodpecker; HERTEL 2001), strong-dimensioned dead wood, the development of ageing phases and special tree structures are keystones for the occurrence of typical and threatened beech forest species. According to ERNST and HANSTEIN(2001), dead wood and special structures of old living trees also play an essential role in the diversity of lichens.
The Middle Spotted Woodpecker Dendrocopos mediuswas identified as a valid indicator for mature beech forests without any share of oaks. Occurrence depends on two typical stand structures: a) rough bark structure (typical for old beech trees >200 years old) and b) dead wood forming part of the stems or branches of standing trees (see above; GÜNTHER
and HELLMANN1997; HERTEL2001, 2003). Whilst young beeches have an unsuitable and smooth bark, old trees develop the necessary rough bark with scratches and clefts.
Additionally, all breeding cavities of the Middle Spotted Woodpecker (n = 20) were located in standing dead wood (dead trees or dead branches of living trees), which occurs much more often in unmanaged than in managed forests.
development stage
breakdown optimum
grow-up
number of individuals (mean)/trap
3.5 3.0 2.5 2.0 1.5 1.0 0.5
0.0 Fig. 16.Carabus glabratus in dif-
ferent forest development phases [number of individuals per trap].
Among the saproxylic fungi, the Icicle fungusHericium coralloidesis thought to be a suit- able indicator for conservation-sound beech forest management. This fungus grows on dead wood in a progressed stage of decay and, under suitable conditions, fructificates every year.
The species is easy to recognise because of its typical fruit body. Registration of this fungus in the course of habitat type mappings and certification procedures is possible. The indicator value is also described by SCHMID and HELFER (1995): “Unfortunately, you cannot find Icicle fungus very often in the forest for simple economic reasons. The fungus does not put up with saw-stumps or broken branches. It needs dead stems of strong dimensions as habitat. Nowhere else is it able to build its fruit bodies. These large stems have an enormous timber value and thus are rarely left for the Icicle fungi in the forest. To make a taxation of this fungus could be regarded as worthless.” This fact gave the fungi a ranking in the Red List of Brandenburg (MUNR 1993).
Strong-dimensioned dead wood contains more micro-climatic and decomposition stages than smaller stems. Besides the Icicle fungus, some species of the genus Pluteus,especially P. umbrosus, indicate old-growth forests (NUSS 1999) because it grows exclusively in the final phase of the decomposition of these strong-dimensioned stems.
The high abundance of Ascocoryne sacroidesin managed forests can be explained by its occurrence on fallen small and damp branches, e.g. brushwood and crown breakage in man- aged forests, and on the cutting surface of tree stumps (MICHAEL et al. 1986). The two Trametesspecies T. hirsutaand T. versicolorare more abundant in managed forests because of their preference for light forest stands (DERBSCHand SCHMITT1987; KERSTAN2003). A relatively low density of these species in unmanaged forests was also found by ADAMCZYK
(1995).
According to our results, the ground beetle Carabus glabratusshows a clear preference for the ageing phases of beech forests, but according to the literature it is not a stenope silvicol species (KOCH 1989; WACHMANN et al. 1995).C. glabratusdoes not depend upon beech forests; it finds suitable habitats in coniferous or mixed forests, too (BARNDT et al.1991;
MÜLLER-MOTZFELD2001). Nevertheless, other authors have recorded C. glabratusonly in extended and old forests (LOHSE1954; DÜLGE1992). ASSMANN(1994) and ASSMANNet al.
(2001) described the species as an indicator for historical old-growth forest. Whether C.
glabratusis a suitable indicator for near-natural beech forests cannot be decided on the basis of our investigation. Further detailed studies are necessary.
These results show that the occurrence of typical structures of the ageing phases in man- aged forests determines whether there is a deterioration of the typical biocoenosis, and thus is crucial for the maintenance or loss of natural biodiversity.
Acknowledgements
This study could not have been undertaken without the Federal Agency for Nature Conservation in Bonn, Germany, which financed our research project, and Silvia Dingwall for improving the English.
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Accepted May 19, 2005
