Importance of climate‐induced tree species composition changes in forecasting the amount of reachable habitat for forest birds

Abstract

AbstractAimBird and tree species distributions will shift along with future climatic conditions through direct effects related to species responses to bioclimatic variables. In addition, tree species composition changes should indirectly drive changes in forest bird habitats. Here, we predicted the effects of climate changes on the amount of reachable habitat for forest birds and teased apart the role of the indirect effects.LocationFrance.MethodsWe projected tree and bird species distributions (2020 and 2050) using generalized additive models which accounted for climatic conditions at a large scale (France) and local environmental conditions at regional scale. The projections combined two scenarios of climate changes (RCP 2.6 and 8.5) and two scenarios of forest management (increase in either deciduous or coniferous stands). We modelled the amount of reachable habitat with landscape graphs and the equivalent connectivity index (EC) for five birds associated to the main forest types of the study area. To differentiate the sources of EC change between 2020 and 2050, we compared two future landscape graphs including only the indirect effect, or the direct and indirect effects of climate changes.ResultsFor birds with low and intermediate thermal maxima, climate‐based distributions were nearly stable over time (absence of direct effects), EC change was only attributed to indirect effects. In contrast, for bird species with high thermal maximum, EC change was mostly driven by direct effects (more favourable climatic conditions) and little by indirect effects.Main conclusionsUsing an innovative modelling framework that bind species distribution and connectivity models with climate and land use changes in forest, we showed that EC dynamics could be completely due to climate‐driven changes in tree species composition. Our results highlight the importance of accounting for the indirect effects of climate changes, especially in forests where major shifts in tree species composition are expected.