Increased rainfall variability reduces biomass and forage quality of temperate grassland largely independent of mowing frequency

Abstract

Climate models indicate that global warming will stimulate atmospheric exchange processes and increase rainfall variability, leading to longer dry periods and more intense rainfall events. Recent studies suggest that both the magnitude of the rainfall events and their frequency may be as important for temperate grassland productivity as the annual sum. However, until now interactive effects between land management practice, such as mowing frequency, and rainfall variability on productivity and forage quality have not been studied in detail. Here, we present the data from a field experiment (EVENT II) in which a Central-European grassland was subjected to increased spring rainfall variability (low, intermediate and extreme rainfall variability without any change to the rainfall amount) and increased mowing frequency (four times compared to twice a year). We assessed biomass production, forage quality parameters, root-length and shoot–root ratio. Enhanced spring rainfall variability reduced midsummer productivity and the leaf N and protein concentrations of a target species, but did not exert any long-term effects on biomass production and forage quality in late summer. However, the increased spring rainfall variability reduced aboveground net primary productivity by 15%. More frequent mowing increased productivity in the first year of the study, but decreased productivity at the end of the second year, showing a decline in the potential for overcompensation after a history of more intense mowing. Generally, more frequent mowing decreased the shoot–root ratio and increased the concentration of leaf N. Increased mowing frequency neither buffered, nor amplified the adverse effects of rainfall variability on productivity, but made leaf N concentrations in early summer more responsive to altered rainfall patterns. These results highlight the fact that even relatively small and short-term alterations to rainfall distribution can reduce production and forage quality, with little buffering capacity of altered mowing frequency. Comparisons with productivity data from the first year of the study, in which both, rainfall distribution and rainfall amount were modified, demonstrate the crucial role of sufficient moisture (annual rainfall amount) for grassland resilience: in this first year, negative effects of extreme rainfall variability lasted until the end of the year. To conclude, increased rainfall variability under climate change will likely affect agricultural yield in temperate meadows. Management strategies to buffer these effects have yet to be developed.