Year-to-year variations in rainfall are projected to increase as the climate warms, with uncertain consequences for ecosystem structure and function. Results from a rainfall manipulation experiment suggest that more variable rainfall regimes will lead to more diverse grassland communities, which can buffer concomitant declines in dominant plant productivity.

In a six-year rainfall manipulation experiment, Laureano Gherardi and Osvaldo Sala, of Arizona State University, assessed the effect of interannual variations in rainfall on plant functional diversity and productivity in a desert grassland in New Mexico. Plant functional diversity increased with rainfall variance, underpinned by a reduction in the relative abundance of perennial grasses (the dominant plant functional type) and an increase in the abundance of rarer plant functional types, such as shrubs, annual grasses and forbs. The contrasting responses of dominant and rare species seemed related to the fact that dominant species did better in terms of productivity under modal rainfall regimes, whereas rare species did better under very wet conditions.