Using ecological forest site mapping for long-term habitat suitability assessments in wildlife conservation—Demonstrated for capercaillie (Tetrao urogallus)

Although key factors for vegetation composition and structure, site and soil condition have received little attention as predictors of habitat suitability in wildlife ecology to date. Using the example of capercaillie (Tetrao urogallus), an indicator species for open, well-structured forest habitats, we evaluated the potential use of ecological forest site mapping for the identification of areas where the preferred vegetation structures are supported by the prevailing soil conditions. These are sites that we, therefore, expected to be of long-term relevance to the species.Employing an expert model, we evaluated data from the state's forest site and soil condition database including soil texture, soil type, humus type, nutrient status and hydrological regime. The data were aggregated to a soil condition index (Is), quantifying the potential to support capercaillie-relevant vegetation types. First, we assessed the correlation of Is with the current vegetation conditions in the study area. Subsequently, we evaluated the short-term (15 years) and long-term (100 years) changes to the capercaillie distribution with respect to Is at different spatial scales and calculated a threshold for the prediction of long-term capercaillie presence.Although the vegetation structure in the study area was largely influenced by forestry, Is was correlated with all investigated vegetation structure variables that determine habitat suitability for capercaillie. Soil condition proved to be an important indirect predictor of long-term capercaillie inhabitation, performing best when considering an area exceeding the size of a large capercaillie home range. The long-term range contractions corresponded significantly with the spatial pattern of suitable soil conditions, the short-term development demonstrated a similar trend. The results indicated an ongoing retreat from degenerating secondary habitats, created by historic land use techniques on sites with low Is, to sites with high Is values, which should be considered when defining priority areas for conservation. Forest ecological site mapping provides detailed, area-wide data that allow for a spatially explicit evaluation of the vegetation development. Therefore, it can facilitate the integration of conservation targets in forest management, for species dependent upon specific vegetation conditions.