Predicted effects of climate change on indicator species of structural and biological diversity inmountain forests: towards adaptive forest management in the face of environmental uncertainty
Auteurs : Bollmann (Kurt), Braunisch (Veronika) et Arlettaz (Raphaël)
Année de publication : 2014
Publication : rapport de projet
Résumé :
The general goal of the study was to predict the impact of climate change on the distribution and realized niches of four species of conservation concern and to assess the mitigation potential of adapted forestry measures. We used four cold-adapted mountain forest bird species with complementary habitat needs: Hazel grouse (Bonasa bonasia), Capercaillie (Tetrao urogallus), Pygmy owl (Glaucidium passerinum) und Three-toed woodpecker (Picoides tridactylus). In particular, we investigated the following questions: (1) How do climate, landscape and vegetation explain the distribution of the model species? (2) To what extent climate change and climate induced vegetation changes will affect habitat quality? (3) Can these changes be compensated ormitigated by adaptive habitat management?We analysed the presence of the model species in 300 grid cells of 1km2 along an altitudinal gradient in four biogeographic regions, in particular Black Forest, Swiss Jura, Northern Pre-Alps, and Eastern Central Alps. Field work has been carried out by one scientific assistant (coordinator), four master students, one bachelor student, and two technical field assistants. They formed four field teams of two persons each. Species presence was modeled as a function of climate, landscape and vegetation information under current climate, and then extrapolated to 2050, assuming the moderate IPCC16 scenario A1B. We used two modelling approaches at two spatial scales: first, we predicted species occurrence at the landscape scale (comprising the whole study area of Switzerland and Baden-Württemberg, Germany) by considering only climate and landscape information. In the second approach, we analyzed species occurrence at the local scale by also integrating vegetation structure. Results indicate that climate explains a considerable part of the species’ occurrences on both the landscape scale and within the eco-climatic niche of the species. Climate change predicts a decline in occurrence for all four species, ranging from –22% (Three toed woodpecker) to –41% (Capercaillie). Respective figures for Pygmy owl and Hazel grouse are –26% and –30%. These declines are partly caused by climate-induced vegetation changes which decrease the occurrence probability of all four species, particularly at the low-altitudinal margins of their current distribution. Negative effects could be compensated only partly by modifying and improving single, species-specific vegetation factors with habitat management measures. However, a full compensation could only be achieved if several factors would be changed directionally and in concert. In the Three-toed woodpecker, for instance, such a compensation would include an increase of standing dead wood within the species home range, itself containing a minimal amount of Norway spruce (Picea abies) with heights of 15 m or more.Our results illustrate that the often simplified cause-effect relationship between climate change and species occurrence has to be considered more specifically. The prediction of large-scale species distribution models is not a suitable basis for strategic decisions in cases of trade-offs between species conservation and climate change, since they neglect climate-induced vegetation changes. Our study shows that an adapted habitat management that focuses on a relatively small set of decisive vegetation variables can mitigate indirect negative effects of climate change on mountain forest species. However, it partly requires working against the climate change-induced dynamics of vegetation development, and is as such also in competition with other ecosystem services.