Predicting spatiotemporal bioclimatic niche dynamics of endemic Pyrenean plant species under climate change: how much will we lose?

Species distributions are shifting globally due to environmental and anthropogenic pressures, with mountain ecosystems among the most vulnerable. In such landscapes, the ability of species to track changing conditions is limited, placing narrowly distributed species at risk. As a mountain biodiversity hotspot in southwestern Europe, the Pyrenees harbor many such species, making it a key case study for climate vulnerability assessments. This study implements a multi-species bioclimatic niche modeling pipeline to evaluate the impacts of climate change on endemic Pyrenean plant species by 2100. Objectives are to (i) map current bioclimatic niche suitability (ii) forecast its future spatial dynamics, and (iii) identify potential climate refugia for conservation. Species occurrences were combined with 19 bioclimatic variables (1x1 km resolution) to characterize current bioclimatic niche suitability, using an ensemble modeling approach integrating five algorithms (MaxEnt, Generalized Linear Model, Generalized Additive Model, Gradient Boosting Machine, and Random Forest). Its future spatiotemporal dynamics were predicted under four climate scenarios (Shared Socioeconomic pathways 126, 245, 370, 585) for 2021-2100 period (2021-2040, 2041-2060, 2061-2080, 2081-2100). By 2100, nearly all endemic species are predicted to experience severe bioclimatic niche contractions, with half facing complete losses under high-emission scenarios. However, one species may gain suitable areas, highlighting the need for species-specific conservation strategies. Bioclimatic niches are predicted to shift upslope by ~180 m, with hotspots becoming increasingly confined to refugia above 2000 m. These trends intensify after 2060, reflecting escalating climate pressures as the century progresses. Our findings highlight the profound threat climate change may pose to endemic Pyrenean flora, with widespread bioclimatic niche losses predicted by the end of the century and high elevation refugia emerging as key conservation priorities. Our modeling framework provides a systematic approach for anticipating shifts and informing conservation planning to mitigate high-elevation biodiversity loss in a rapidly changing world.