Almost nothing left to lose: Suitable habitat for glacial relicts strongly declines under future climate and land use scenarios

Species distributions is shifting, along elevational and latitudinal gradients, likely reflecting the influence of climate change. Yet, land use also influences plant species distribution. This makes it challenging to pinpoint the primary driver and their respective contributions to the change. Glacial relicts, small populations of arctic-alpine species at the margin of their ecological range are considered reliable indicators of climate change impact. The habitats where they occur are also usually threatened by land use. They are thus an ideal system to study the effect of these two key drivers. We used four vascular plant species (Trifolium spadiceum, Traunsteinera globosa, Gentiana lutea and Bellidiastrum michelii) from wet and cold environments, and used species distribution models to study the effects of climate change on their ranges, incorporating high-resolution environmental data on climate, topography, and geology, alongside species occurrence data from long-term monitoring in SW-Germany. The resulting suitability maps were masked with land use maps, to assess the additional effects of land use. To obtain projections of potential future distributions we additionally modelled distribution under future climate and land use scenarios. Across various future climate scenarios, the suitable area for all species decreased by an average of 60 % on average due to climate change. Land use alone, significantly reduces suitable space, decreasing it by an average of 72 % under current and future climate and land use change scenarios. Despite the severe susceptibility to climate change, our findings reveal an additional, equal or even stronger influence of land use on the distribution of glacial relicts that will precipitate their decline. Ultimately, our findings can facilitate development of conservation strategies essential for the preservation and sustainable management, that are crucial for preserving not only glacial relict populations but also the overall biodiversity in these areas.