Climate variability reduces biomass stability in species-rich grasslands, depending on management.

Climate change threatens grassland biomass stability, but combined effects of climate variability and grassland management have rarely been analyzed, constraining our ability to predict management-dependent responses. In a large field experiment in Central Germany, we assessed temporal stability of aboveground biomass and potential underlying mechanisms (dominance, asynchrony, and averaging) in non-fertilized species-rich grasslands over nine years (2015-2023). The grasslands were exposed to ambient or simulated future climate following regional projections (higher temperature and altered seasonal precipitation pattern) and were managed by mowing or sheep grazing. While the future climate treatment showed little effects, high background climate variability increased biomass variability due to lower stabilization by asynchrony and averaging, which was more pronounced in meadows than in pastures. The lower biomass resistance to extreme summer droughts and the higher recovery afterwards in meadows compared to pastures was likely attributable to higher amounts of biomass removed by mowing than by grazing. However, stabilization by the diversity-associated averaging effect, which generally contributed most to biomass stabilization, was lower in pastures compared to meadows at peak biomass production in spring, due to declining species diversity with the lower biomass removal by grazing. Accordingly, we conclude that grassland management with low biomass removal can enhance biomass resistance to climate variability, but this may be offset in the long term by species loss and reduced stabilization through the diversity-associated averaging effect.