Das Auerhuhn Tetrao urogallus im Alpinen Lebensraum: Verbreitung, Bestand, Lebensraumansprüche und Förderung

Die Alps are the stronghold of the Capercaillie population in Central Europe. Here, mountain forests still provide habitat for an estimated total population of 32,250–35,700 birds. However, overall population has decreased remarkably during the last century. In Switzerland for example, a regression of the occupied area has been observed in the peripheral and lower regions of the national distribution area resulting in a population loss of at least 55% in 30 years. Decreasing habitat quality and increasing human disturbance are considered to be the main limiting factors for the endangered population status of Capercaillie in Switzerland. Since 2008, the species is receiving significant support by the national Capercaillie Action Plan that aims to conserve a viable population for the future. Based on a habitat and a patch occupancy model, conservation areas of first and second priorities have been delineated. There, species-specific forestry measures are taken to increase the overall habitat quality. Timber harvest and the consecutive reduction of standing stock as well as the zonation of Capercaillie core areas to reduce human disturbance in the most sensitive zones are the most important measures. Analysis of habitat use at the forest stand scale revealed an optimal canopy cover of 40–60 percent, a heterogeneous distribution of trees, a well-developed ground vegetation cover with Vaccinium and a minimal amount of lowbranched spruce trees and other hiding structures as essential habitat elements. Special forest reserves are optimal instruments to conserve and promote habitat suitability at a scale relevant for local populations. In one study area, we developed a systematic planning method for habitat assessment and management. Based on both, an area-wide map of forest stands and stand-specific habitat quality, we assessed the actual and target profile of eleven test stands representative for the vegetation types and development stages of the entire reserve. Habitat measures were then derived from the comparison of the two profiles and the expected natural development of each stand. The range of the measures taken includes thinning for regeneration, the creation of flight and escape aisles, the partial clearing of the proximity of roosting trees, the regulation of young growth in favor of conifers, the planting of silver firs, forest edge improvements, increasing the number of laying logs and erecting root-plates. The procedure has proved its practicability during the first years of management. However, only a success control regarding the development of habitat suitability and the population response of the species will show how effective the management method is. The newly developed principle of habitat reference areas that has been applied for the first time will provide valuable support for such a task in the near future.
Keywords: Capercaillie Tetrao urogallus, Alps, forestry measures, habitat requirements, population size, species conservation, Switzerland.