Being an annual plant in a water-limited Mediterranean-alpine mountain; the case of rare-endemic and threatened Arenaria nevadensis

Mountain ecosystems are proving to be particularly vulnerable to the effects of global change, with Mediterranean high mountains standing out as among the most susceptible regions worldwide. The impact of climate change on biota operates across key levels: metabolism, phenology, evolution, and spatial distribution. Monitoring species within these ecosystems is crucial to establish early warning indicators for effective mitigation and adaptation strategies. Within this context, annual plants, like the critically endangered species Arenaria nevadensis endemic to Sierra Nevada, could offer advantages as indicators due to their rapid life cycles and dependence on water sources.This study aims to investigate the impact of climatic change on this specific annual, endemic, and threatened species while assessing its potential as an indicator for shifting snow patterns affecting alpine biota. Analyzing data collected between 2005 and 2021 from four populations of Arenaria nevadensis alongside hydro-meteorological data revealed notable variations in population parameters linked to climatic fluctuations. Factors such as precipitation and snowpack significantly influenced plant size, reproductive potential, and population size, with neighboring populations showing distinct responses to climatic variations.The observed unpredictability in population trends across consecutive years underscores the climatic stochasticity inherent in Mediterranean mountains, particularly Sierra Nevada. Forecasts of decreased precipitation and increased temperatures are expected to diminish snowpack depth and duration, posing a severe threat to this critically endangered species. Conservation efforts should prioritize managing higher elevation populations and exploring new suitable habitats for restoration or assisted migration.While Arenaria nevadensis demonstrates promise as a climate change indicator owing to its short life cycle, restricted distribution, and sensitivity to climatic shifts, comprehensive understanding of its germination ecology, seed bank role, and reproductive biology remains lacking. Addressing these knowledge gaps is crucial to enhance its effectiveness as an indicator species.