Data from nutrients and herbivores impact grassland stability across spatial scales through different pathways

Nutrients and herbivores are well-known drivers of grassland
diversity and stability in local communities. However, whether they interact to
impact the stability of aboveground biomass and whether these effects depend on
spatial scales remain unknown. It is also unclear whether nutrients and
herbivores impact stability via different facets of plant diversity including
species richness, evenness, and changes in community composition through time
and space. We used a replicated experiment adding nutrients and excluding
herbivores for 5 years in 34 global grasslands to explore these questions. We
found that both nutrient addition and herbivore exclusion alone reduced
stability at the larger spatial scale (aggregated local communities; gamma
stability), but through different pathways. Nutrient addition reduced gamma
stability primarily by increasing changes in local community composition over
time, which was mainly driven by species replacement. Herbivore exclusion
reduced gamma stability primarily by decreasing asynchronous dynamics among
local communities (spatial asynchrony). Their interaction weakly increased
gamma stability by increasing spatial asynchrony. Our findings indicate that
disentangling the processes operating at different spatial scales may improve
conservation and management aiming at maintaining the ability of ecosystems to
reliably provide functions and services for humanity.