Forest development on the Schwaegalp in the 20th century and its significance for the habitat of capercaillie (Tetrao urogallus L.)
2006
Fritsche, B. (ETH Zentrum, Zuerich (Switzerland). Departement Umweltwissenschaften, Professur Waldoekologie) | Bollmann, K. | Graf, R.F. | Bugmann, H.
Capercaillie populations declined significantly during the 20th century. The loss of suitable habitats in montane and subalpine forests is considered the main reason for this negative trend. Aerial photographs of 1932/35, 1960 and 1999 and a statistical model were used to analyse the changes in capercaillie habitat at the Schwägalp (a region north of the Säntis, cantons of AI, AR and SG). From these data sources we extracted information on changes in forest area and forest structure variables relevant for capercaillie. To supplement our study, we intended to use data from vegetation maps and forest management plans. Such data, however, were inconsistent or not available at the required small scale. The parameters degree of canopy cover, variability of canopy cover and slope explained a significant part of the variance in our habitat model. Evidence of the occurrence of capercaillie was frequent in forest stands with intermediate canopy cover, high variability of canopy cover and moderate slopes. We also found an increase in forest area and a slight loss of suitable habitat. This loss, however, cannot alone explain the decline of the capercaillie population at the Schwägalp. Other factors not taken into account in this study must have adversely affected the population. We suggest that the decline of capercaillie population has multifactorial causes and was driven by the loss of suitable habitats and increased incidences of human disturbances and predation.
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