Broader niches revealed by fossil data don’t reduce estimates of range loss and fragmentation of African montane trees

Abstract

Aim: Many species’ climate tolerances are broader than those estimated from current native ranges. Indeed, some Afromontane trees’ niches are up to 50% larger after incorporating fossil data. This expansion could reduce estimates of species’ future range loss due to climate change but also implies strong non-climatic limitations on species’ current ranges. One such limitation is land use, which fossil data suggest influences Afromontane tree distribution, preventing these trees from occupying warmer conditions than they currently do. We aim to assess the degree to which the broader climatic tolerances revealed by fossil data buffers projected range loss from climate and land use for Afromontane trees. Location: Africa. Time period: Last 21,000 years. Major taxa studied: Afromontane trees. Methods: We used species distribution models informed by both current and fossil distributions to project future ranges under climate and land-use projections. Results: We found that projected range reductions are only slightly ameliorated by incorporating fossil distributions and these improvements diminish further under severe land use or climate change scenarios. Taxa that are less impacted by climate are more impacted by intense land use. Depending on the severity of climate and land use, the geographic extent of Afromontane tree species’ ranges will contract by 40-85% and the trees will completely be lost from large portions of Africa. We projected that the surviving species’ ranges will become increasingly fragmented. Main conclusions: Maintaining Afromontane ecosystems will require mitigation of both climate and land-use change and protecting areas to optimize connectivity. Our findings caution that species with climate tolerances broader than their current range might not necessarily fare better under strong changes in climate or land use.