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

Species distributions are shifting under global change, with mountain ecosystems among the most vulnerable. In such landscapes, ability to track changing conditions is limited, threatening narrowly distributed species. As a mountain biodiversity hotspot in southwestern Europe, the Pyrenees harbors many such species, making it a key case study for climate vulnerability assessments.

This study implements a bioclimatic niche modeling pipeline to evaluate climate change impact 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 bioclimatic niche suitability, using an ensemble modeling approach integrating five algorithms (MaxEnt, Generalized Linear Model, Generalized Additive Model, Gradient Boosting Machine, and Random Forest). Their future spatiotemporal dynamics were projected under four climate scenarios (Shared Socioeconomic pathways 126, 245, 370, 585) for four successive periods spanning 2021 to 2100.

By 2100, 69% of endemic species are projected to lose over 75% of their bioclimatic niche, and half to face complete losses under high-emission scenarios. Only two species may gain suitable areas, highlighting the need for species-specific conservation strategies. Bioclimatic niches are projected to shift by ∼180 m upslope and ∼3 km in latitude on average, with areas of highest multi-species suitability, referred to as bioclimatic hotspots, becoming restricted to elevation above 2000 m. These trends intensify after 2041-2060 period, 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 projected by the century’s end and high elevation refugia emerging as key conservation priorities. Anticipating these shifts and integrating them into conservation planning will be crucial to mitigating high-elevation biodiversity loss in a rapidly changing world.