Timing is important : seasonality of precipitation influences ecosystem properties and response to grazing

Abstract

Water availability and grazing are both strong drivers of grassland community structure and function. We know that water limited ecosystems, can be very sensitive to temporal changes in precipitation, influencing important properties including primary production, carbon and nutrient cycling and plant and microbial species composition. However, little is known about how the timing of water availability interacts with grazing. I conducted a global meta-analysis to investigate the importance of precipitation seasonality in determining broad-scale patterns of plant community response to grazing. I focused on the relative importance of climatic factors compared with grazing variables in influencing the effects of grazing on plant species composition and primary production. Locations with more summer precipitation experienced greater grazing-induced changes in species composition. Species composition was more responsive to grazing covariates, whereas production was more responsive to climatic variables, particularly the length of the growing season. I explored potential mechanisms for this pattern by conducting a trait study at a climate change experiment on the Tibetan Plateau. Shifting the timing of water availability toward the winter altered community-level plant traits associated with grazing avoidance and tolerance, and grazing sometimes acted as a feedback. Together, these results provide compelling evidence that the timing of precipitation can interact with grazing to drive changes in plant community structure and function. In light of climate changes that may shift the timing of precipitation in many systems worldwide, these effects are increasingly important to understand.