Summary 

The results of field studies on saproxylic beetles carried out in 10 nature forests in the northern Rhineland (Nordrhein-Westfalen, Germany) from 1986 to 1996 are presented and compared with other German reserves. In an introductory part, a general description and analysis of the saproxylic beetle fauna of Germany is given, which can serve as a reference for both this study and future research. 

Saproxylic beetles are defined as both xylophagous species which need ligneous stems of trees and shrubs for reproduction and (non-xylophagous) species whose reproduction is dependent on either necrotic or rotting stems of trees and shrubs or other organisms thriving in these habitats. 

For Germany, 1,371 species of saproxylic beetles are identified and recorded both in a database and in an appendix with the following parameters: habitat preference (wood, bark, wood humus, nests, wood fungi, sap exudation), biotope preference (dense woodland, sunny woods with low tree density), affinity for deciduous or coniferous trees, food and feeding habit, body size, general distribution, distribution in Germany, and degree of endangering; in addition, it is indicated if a species visits flowers, inhabits the first successional stage of dead wood, or has specific host plant affinities. 

These parameters are used in various combinations for the description and analysis of the saproxylic beetle fauna of Germany. The most important figures and results, which are discussed in detail in the introductory part, are as follows: 

• From the south to the north, species number decreases by approximately 60%. 
• Only 13% of the species are restricted to a specific tree or shrub genus. 
• Saproxylic beetles are habitat specialists: 468 species are lignicolous, 401 are corticolous, 241 live in wood humus, 29 in nests, 151 are confined to wood fungi, and 12 to sap exudations. 
• 32% of the species occur in sunny open woodland. 
• The fauna is primarily composed of widespread species, montane Central European elements, of South European-Mediterranean, and of North European-Siberian elements. 
• 54 species are extinct, 211 critical, 272 endangered, and 274 are vulnerable. Beetles confined to wood humus and species with a distribution just reaching Central Europe from the west, south, and east are particularly threatened. 

In the 10 nature forests, a total of 172,321 specimens and 1,551 species of beetles were sampled. 492 of the species, between 143 and 264 per site, were xylophilous. The study sites are compared with respect to species diversity, ecological, biogeographical, and faunistic characteristics of the recorded species, and referred to the known fauna of Nordrhein-Westfalen. This comparison shows that lignicolous and thermophilous species as well as beetles restricted to coniferous woods and endangered species are underrepresented. 

Species number and composition significantly depend on the geographical location and on altitude, but also on the impact of preceding management, which was assessed through the management history of the sites and through various structural characteristics. The number of fungicolous species is exclusively correlated with the species number of wood fungi present. The species community of nature forests is characterized by a low degree of evenness, apparently the result of the presence of numerous small populations of rare and endangered species. 

For a comparative evaluation of the results of German nature forest research in the recent past, the species lists of 45 forest reserves and of 84 additional sites were analyzed. Using a database with 45,854 datasets on 3,183 beetle species, among them 1,025 specialized saproxylic species, further comparisons were possible. The current state of nature forest research in different German regions (Bundesländer) is discussed in detail. The species numbers of all study sites are presented in a table with special reference to ecological parameters. 

Up to today, 828 saproxylic beetle species have been recorded in German forest reserves. Differences in species numbers are a result of the sampling methods and sampling intensity applied in the sites. In addition, they are explained by the altitude and the management history of the reserves, as well as by the history of the occurrence of dead wood in the forests. In the most important reserve, the "Urwald von Taben", 1,149 beetle species were recorded. Among the 449 saproxylic species, 153 were endangered and 65 species exclusively occurred in this site. The fauna of dense forests differs significantly from that of various open anthropogenic biotopes. Moreover, nature forests are inhabited by a higher average number of saproxylic species than reference managed forests. 

In the concluding chapter, aspects of faunal changes and methodical problems of nature forest research are discussed. The increase in species number due to continuous immigration (approximately 50%) and more extensive research is quantitatively exemplified in the fauna of the northern Rhineland. First records - more than 161 species in the past 50 years - primarily refer to species from other faunal regions as well as to endangered and to small beetles. Several examples show that species can extend their range over distances of several hundred kilometres; consequently, the absence of suitable habitats is the most significant barrier limiting the dispersal of species with isolated relict populations. 

An analysis of the life history, habitat reqirements, and the distribution of those species that have gone distinct shows that their extinction was not so much caused by forest management as by natural fluctuations of the range of distribution. The occurrence of critical species, in contrast, is confined to isolated old forests, so that their conservation is within the responsibility of forestry. 

Among the immigrants to the northern Rhineland, the majority of the numerous inhabitants of coniferous woods are not endangered, widespread, and they occur in common biotopes and habitats, so that they are of little significance for conservation concepts for the saproxylic beetle fauna; there is almost no overlap with the beetle fauna of coniferous woods in the mountain ranges in southern Germany. 

Various sampling methods and hypotheses regarding the saproxylic beetles of tree tops are presented and discussed with respect to their significance for nature forest research. Based on a study of the Hienheimer Forst near Kehlheim/Bayern, differences in species numbers between the fauna of tree tops and near-ground habitats are shown. The fauna of wood fungi is in tree crowns almost absent, and for the lignicolous species the differences were insignificant. Only the heliophilous species were more often observed in the tree-tops than in near-ground habitats. Future research projects on the composition and significance of the saproxylic fauna of tree-tops are suggested. 

Finally, traditions of dead wood management traditions are considered and the mapping of potential relict localities of saproxylic beetles is recommended. In conclusion, issues such as the amount of dead wood in forests, the absence of dead wood in managed forests, and the necessity of an extension of the nature forest reserve programme are commented on.

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