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Abstract
A long-term study of grasslands has revealed that primary production in more diverse plant communities is more resistant to and recovers more fully from drought. According to the diversity-stability hypothesis, species differ in their traits, and more diverse ecosystems are more likely to contain species that can withstand environmental perturbations. Alternatively, the species-redundancy hypothesis suggests that many species are so similar that ecosystem functioning is independent of diversity once the major functional groups are present. During the 11-year study of successional and native grasslands in Minnesota, the most severe drought of the past 50 years occurred (1987-1988). A curvilinear relationship was observed between drought resistance and plant-species richness before the drought. These results, therefore, support the diversity-stability hypothesis and lend further urgency to calls for the conservation of biodiversity.