|Köhler, F (1996a):
forests and managed forests. Comparative studies of the beetle fauna (Coleoptera)
in the forest reserve Kermeter (North Rhine Westfalia, Germany). - Schriftenreihe
LÖBF/LAfAO NRW (Recklinghausen) 6, 1-283.
A total of 1,218 species of Coleoptera was recorded on the four study sites. Including previous studies, all 1,331 beetle species presently known from the "Kermeter" are systematically listed. Between 695 and 804 species were recorded per study site, the figures for the nature forests being on average 9.4 % higher than those for the managed forests. Compared with other local faunas of the Rhineland, species richness is lower at higher altitudes of the Eifel. Among German nature forest reserves, however, the number of recorded species is highest in the nature forests of the "Kermeter" due to high study intensity.
In a syneccological analysis the species assemblages of soil beetles including special microhabitats as well as of planticolous and saproxylic beetles of the "Kermeter" are described; examples of realized assemblies are provided. Based on this analysis the unmanaged nature forests and the managed forests are compared, the results are discussed and, when possible, prognoses regarding the future development are made. In view of the relatively short period since the establishment of the nature forests, striking differences regarding the beetle fauna were not to be expected. Nevertheless, differences and tendencies were observed, the most important of which are compiled below.
Regarding the species composition of the beetle fauna of the forest litter layer, no major qualitative differences were found. A quantitative analysis, in contrast, showed higher population densities in the nature forests, which were independent of the depth of the litter layer and which are interpreted as an effect of shading, lower rate of desiccation and stronger growth of fungi. As the trees advance in age, habitat heterogeneity at the tree-base of the beeches increases, and consequently also the number of beetle species associated with tree-bases.
The epigeic fauna of special biotopes, such as wetland biotopes and clearings, is of heterogeneous species composition, independent of management status. The same applies to special habitats. Differences between the sites result from the respective availability of such microhabitats as rotting matter (carrion, dung, debris) and fungi. Only the number of species associated with birds- and mammals-nests was observed to be 70 % higher in nature forests. An advanced age of the forest results in an increase of habitat diversity and the availability of potential nesting sites for small mammals and birds.
In the planticolous beetles there is a correlation between the number of plant and of beetles species present on the study sites. Nearly 90 % of the plant species recorded prefer anthropogenic biotopes such as waysides, meadows and deforested areas, whereas dense, natural or semi-natural beech forests are consequently inhabited only by a low number of phytophagous beetle species. Human forest management results in a heterogeneous clearing of woodland areas and, therefore, an increase in habitat and species diversity. The corresponding species assemblages, only exceptionally including rare or endangered phytophages, generally represent the fauna typical of deforested biotopes of mountain ranges. No differences between managed forests and nature forest reserves were observed, since the periphery of the latter, too, is exposed to considerable anthropogenic influences.
In the saproxylic beetles there was a pronounced correlation between habitat availability and the number of species and specimens collected, independent of the inhabited structures. In particular, however, it was observed that nature forest reserves strongly contribute to the protection and future development of the saproxylic beetle fauna. In the "Kermeter" the following current tendencies were found regarding the different structures of rotting wood and their respective species compositions:
The mostly xylophagous wood beetles (lignicolous species) are represented in nature forest reserves at lower species numbers, since the partially cleared managed forests are additionally inhabited by thermophilous wood beetles which prefer more strongly insolated habitats. Furthermore, in the managed forests a greater variety of habitats is available for wood beetle species visiting flowers. When the nature forests are increasingly cleared at a more advanced age of the beech stands, however, the species spectrum is expected to be similar to that of managed forests. Because of the generally reduced number of species in mountain ranges due to less favourable climatic conditions, the results may not apply to low altitude woodland.
Regarding the number of species and specimens of bark beetles, the four study sites were highly similar, due to extensive availability of suitable habitats on all sites and low dependence on the presence of dead wood. The only differences observed are caused by species occurring on spruce; in both managed forest sites spruce stands were considerably larger, and consequently also the populations of corresponding bark beetles, In the long run, however, when forest maintenance plans are put into practice, the bark beetle fauna of managed forests is expected to approximate that of the nature forest reserves.
Xylodetriticolous beetles as characteristic species of the advanced stages of nature forests are of particular significance when assessing the state of forests. On account of the relatively short tradition of nature forest reserves, differences between managed and nature forests cannot, as yet, be observed at a general level. There were, however, striking differences between the intensively managed "Lohrbachkopf" and all the other sites. In contrast to beech, rotting coniferous wood was of little significance for the protection and preservation of the xylodetricolous beetle fauna.
The availability of dead wood, the presence of fungi and the number and density of beetle species associated with saproxylic fungi are correlated. Consequently, in the nature forest reserves with a larger supply of rotting wood, more species and and a distinctly greater number of specimens were recorded. Like the xylodetricolous beetles, the species associated with saproxylic fungi are strongly dependent on the presence of large dead wood and old trees. In the future the mode of forest management is expected to yield clear differences regarding these two beetle assemblages.
Faunistically, the "Kermeter" is characterized by a very large number of species, nearly 40% of them rare or very rare. In spite of traditionally high faunistic activity in the area, almost 100 species were first or re-records (after 50 years) for the Eifel. Seven species were for the first time recorded for the Rhineland, a further four species had not been recorded for 50 years. Seven of these species are first records for North Rhine-Westphalia. Ecologically, the highest proportion of rare species (60 %) was observed in the saproxylic beetles. In the nature forest reserves, the proportion of rare beetle species was slightly higher with regard to all habitat preferences. Records of particular faunistic significance are commented on in detail.
A comprehensive account of the methods used, the specific results and the experiences regarding the trap methods (pitfall traps, trunk eclectors, window traps, air and soil bait traps, glue rings) and manual sampling techniques (square sampling, soil sieving, net catches, "Klopfschirm" catches in the vegetation and at dead wood, dead wood sieving, manual catches) is given.
It is principally recommended to use manual sampling techniques in addition to trap methods in faunistic and ecological studies. Especially highly specialized species are often only caught accidentally in traps; therefore, in the absence of further manual techniques differences between study sights and study periods may be distorted or obscured. In view of the great number of species, the rarity of many stenotopic beetles and the oscillations of populations, only a study period of at least two years is adequate.
Based on an ecological evaluation of efficiency, combinations of methods and different concepts regarding the study in forests of the beetle fauna of the soil, plants, rotting wood and other decaying matter are suggested. For an investigation of the beetle fauna associated with dead wood, window traps, the sieving of rotting wood as well as glue rings as a less expensive substitute for the trunk eclectors are recommended as cardinal methods. When studies only saproxylic beetles are conducted, the additional use air bait traps and manual sampling of rotting wood and the vegetation may be of valuable assistance.
For a study of the planticolous fauna in nature forest reserves manual net and "Klopfschirm" catches are primarily recommended. Even without the trunk eclector catches 97 % of all planticolous beetles in the "Kermeter" would have been recorded. The epigeic beetle fauna is best investigated quantitatively with pitfall traps and square sampling. For a qualitative faunistic recording, sieving of the litter layer and microhabitats as well as the use of pitfall traps in special habitats are recommended. Extreme habitats that cannot be studied with pitfall traps or by sieving should be sampled manually. For an investigation of the beetles of decaying matter, a forest habitat particularly rich in species, bait traps, sieving and manual catches are most efficient.