Ecological determinants of stability in dryland plant communities

Community stability is often presented as crucial for sustaining ecosystem services under environmental change. Yet, its determinants (dominance, asynchrony in species fluctuations, averaging effect of species diversity) have rarely been disentangled in natural systems, and their contributions across climates remain unclear. We disentangled the determinants of stability in 40 winter annual communities comprising 178 populations across four climates (arid, semi-arid, Mediterranean, mesic-Mediterranean) and two microhabitats (open areas and under perennial shrubs) over 13 yr in a dryland biodiversity hotspot. Asynchrony in species fluctuations and the averaging effect of species diversity emerged as the strongest stabilizing mechanisms. Asynchrony consistently stabilized communities across climates, independent of species richness, challenging the 'Insurance Hypothesis'. The averaging effect was weaker in desert and mesic-Mediterranean climates, suggesting biodiversity may not always determine stability. These findings stress the need to separate compensatory dynamics into asynchrony in species fluctuations and the averaging effect of species diversity to better predict community stability over time under increasing climatic variability.