Recent vegetation shifts in the French Alps with winners outnumbering losers

1. Quantifying the impact of global change on biodiversity is a central focus of ecological research, essential for guiding policy decisions and conservation management strategies. Mountain ecosystems, recognized as early indicators of climate change impacts and centres of exceptional biodiversity, can provide critical insights into these biodiversity shifts. However, accurately assessing biodiversity changes remains challenging due to limitations in data quality, particularly regarding coverage over adequate temporal scales and fuzzy sampling strategies. 2. Here, we analysed more than 11 million expert-verified occurrence records of 4250 plant species from the French Alps collected over the past 30 years. Using a robust detection framework to statistically correct spatiotemporal biases, we quantified changes in species distributions, identifying winners (species expanding their range) and losers (species contracting their range). 3. Our results indicate that approximately one-third of alpine plant species have significantly expanded their distribution, while about 13% experienced range declines since the '90s. Although species responses did not strongly correlate with their floristic characteristics or IUCN status, expanding species were typically characterized by high colonization ability (ruderal), rapid growth (acquisitive strategies) and tolerance to higher temperatures (thermophilic). Despite a weak overall phylogenetic signal, winners or losers were disproportionately represented in some families and genera. 4. Synthesis. This study advances our understanding of recent biodiversity changes in mountain ecosystems, laying the groundwork for identifying underlying drivers and supporting targeted future conservation initiatives.