Temporal stability of biomass in annual plant communities is driven by species diversity and asynchrony, but not dominance

Aims: Primary biomass production is a fundamental process for ecosystem functioning. Yet, little is known on the mechanisms driving temporal stability of biomass production in annual plant communities, particularly when subjected to highly variable environments and undergoing temporal changes in species composition. We aimed to disentangle the relative importance of biomass production, species diversity, dominance and asynchrony of species fluctuations as drivers of biomass stability in mediterranean and semi-arid annual plant communities. Location: Mediterranean (31°42′ N; 35°03′ E) and semi-arid (31°23′ N; 34°54′ E) sites, Israel. Methods: Above-ground biomass and species abundance were monitored in 15 plots of 250 m² per site during eight consecutive years. Relationships between stability drivers and community stability were studied at the regional (between sites) and local (within sites) spatial scales. Results: Community biomass stability (mean biomass/SD) increased from the semi-arid to the mediterranean site concomitantly with higher biomass production, richness, and evenness. Differences in stability between sites were due to opposite effects of site conditions on the mean and SD of community biomass, leading to higher stability in the mediterranean site. Within sites, species asynchrony was the key driver of stability at the local spatial scale. Richness and biomass production affected stability indirectly through asynchrony, but in different ways at each site. At the mediterranean site, these factors had indirect negative effects on stability by reducing asynchrony, but did not rescind a positive effect of asynchrony on community stability. At the semi-arid site, biomass production had indirect positive effects on stability through asynchrony, while richness had no effect on asynchrony and stability. Stability was not driven by species evenness in either site. Conclusions: Our study provides new insights into the complex control of biomass stability in the dynamics of mediterranean and semi-arid annual plant communities, with different mechanisms driving stability across the regional vs local spatial scales.