What drives temporal stability of biomass production? Testing the roles of species diversity, dominance, asynchrony and spatial scale in annual plant communities

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
in communities 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 semiarid annual plant communities. Location:
Mediterranean (N31o42’; E35o03’) and Semiarid (N31o23’; E34o54’) sites,
Israel. Methods: Aboveground biomass and species abundance were monitored
in 15 plots of 250m2 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 (temporal mean/SD) increased
from the Semiarid to the Mediterranean site concomitantly with higher
biomass production, richness, and evenness, but was not associated with
changes in species synchrony. 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 Semiarid 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 semiarid annual plant communities,
with different mechanisms driving stability across the regional vs. local
spatial scales.