Lasting effects of long-term climate disturbance on grassland community structure under two levels of drought

Background/Question/Methods

The magnitude and frequency of drought is expected to increase in the US Great Plains under future climate regimes. Although semiarid systems are considered resistant to water limitation, the ability of these systems to recover after extended periods of intense drought has not been tested. The objective of our research was to determine if the severity level of long-term drought affects the resilience and recovery of a drought-tolerant grassland. In the semiarid shortgrass steppe of Colorado, USA, we examined changes in vegetation cover and tiller density over the course of an 11-year drought manipulation experiment in plots that received 25% and 50% of ambient growing season precipitation. At the end of the 11^thgrowing season, we removed the drought manipulation shelters and monitored changes in plant community composition and tiller density during the first three years of recovery. 

Results/Conclusions

We found that 11 years of drought resulted in large reductions in total plant cover and cover of the dominant species, Bouteloua gracilis in plots that received 25% and 50% of ambient growing season precipitation. During the first several years of drought, severity did affect the plant community response, yet by the end of the 11-year drought differences between drought treatments were not significant. While total cover and cover of B. gracilis were reduced under long-term drought compared to ambient conditions, there was no difference between the two drought treatments. Under recovery, growing season precipitation was near the long-term average, but, the plant community was slow to respond. Total canopy cover and cover of the dominant species remained reduced in the drought treatments in both drought severities, but we did observe a persistent reduction in B. gracilis tillers in the most severe drought treatment, indicating that drought severity may have a lasting impact on recruitment of the dominant species. Our results suggest that during shorter-term droughts, severity may affect recovery of the plant community, while in longer-term droughts, recovery patterns may be similar, regardless of drought severity.