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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	[Vegetation structures in the habitats of capercaillie Tetrao urogallus in the Fichtelgebirge]
Auteurs :	Andreas von Hessberg, Auteur ; Carl Beierkuhnlein, Auteur
Type de document :	Article
Dans :	Ornithologischer Anzeiger (39(2-3) September, 2000)
Article en page(s) :	159-174
Résumé :	Within the palaearctic-boreal range of the capercaillie, many Central European populations are considered to be very endangered. In the Fichtelgebirge (Northeastern Bavaria), the native population declined during the past years and is considered to be very endangered currently. Despite the critical status, there is little knowledge about habitat structures and habitat use in the Fichtelgebirge. In this study, we analysed the forest and vegetation structures within the remaining range of the capercaillie in the Fichtelgebirge, which was determined by some 170 direct and indirect evidences within the past years. The results, however, render only a temporary assessment of the habitat use which obviously varies within a season. Forest stands appeared to be most attractive with more than 50 % pines (Pinus sylvestris). By contrast, there were only few records from locations consisting of more than 20 % deciduous trees. The majority of the pine stands is growing on soils originating from phyllites which are abundant in quartz. On this soil type, blueberry (Vaccinium myrtillus) is obviously not replaced by grass species. This dwarf shrub is an important habitat structure for the capercaillie. In the Fichtelgebirge, the birds prefer areas where blueberry covers more than 60 % of the field layer, and where the shrub grows higher than 35 cm. There is a positive correlation between blueberry abundance and light intensity in the forest stand. Therefore, the density of forest edges with higher trees is one main factor for blueberry abundance. There were significantly more capercaillie records in areas with a density of tall tree edges exceeding 1 km/ha. The density of edges is correlated with the quantity of tree trunks per area and the age of the trees. Both factors are influenced considerably by forest-management. The density of edges has also an impact on the competitiveness of the grasses: especially Calamagrostis villosa is able to restrain the blueberry massively. Also, the quantity of dead wood (covering the ground, standing dead wood) was assessed. A ground cover of dead wood exceeding 50 fm/ha reduced the abundance of the blueberry. In some forest stands, the total stock of dead wood reached up to 20 % of the total wood biomass. Besides an analysis of the spatial dimension (vegetation structure), the investigation focused also on the temporal dimension (forest succession). For the latter, we used the statistical distribution of the stem diameters of dead and living trees. Old and large (in diameter) trees were completely absent. The anthropogenic influence on succession cannot be overlooked. Since these criteria currently do not apply to the Fichtelgebirge, the capercaillies are driven off into areas with younger successional stages which represent a minor habitat quality. These suboptimal habitats sometimes showed a high abundance of blueberry, but the density of edges was too low in most of the studied areas. Our proposals for an improvement of the habitat structures and habitat quality aim at the rescue of the capercaillie population by short-term habitat improvements.

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