COS 89-2 - Drought and disturbance interact to reduce diversity and richness in three dryland plant communities

Background/Question/Methods

Intense droughts and human disturbances occur across many terrestrial ecosystems, but their direct and interactive effects on individuals, communities, and ecosystems remain largely unknown. Research in both land use and climate change ecology has a rich history, but there is a paucity of studies that combine both drivers. Nevertheless, the data that do exist suggest the interactive effects of multiple global change drivers cannot be understood or predicted from assessments of single drivers alone. Using experimental manipulations to isolate the effects of drought, physical disturbance, and their interaction, we conducted a full-factorial field experiment (n=10 per treatment/site) in three dryland ecosystems in the Great Basin, Mojave, and Chihuahua deserts to address our guiding question:



What are the effects of drought and disturbance on plant species abundance, composition, and diversity?



Using non-destructive methods, we recorded species identity for all species within our experimental manipulations. We utilized parametric statistical frameworks to fit experimental outcomes within our research question.

Results/Conclusions

The co-occurrence of drought and physical disturbance reduced species richness and diversity across all three study systems, with negative synergistic effects observed in all three desert sites. Across all sites, drought reduced richness (-27%) and drought and disturbance combined reduced richness (-25%), however, unexpectedly, physical disturbance alone had no effect. Further, although all treatments reduced Shannon’s diversity (drought -59%, disturbance -65%, drought and disturbance -75%) there was a negative synergism between the drivers we imposed, reducing species richness and diversity in plant communities beyond single drivers alone. NMDS ordination of each dryland plant community indicated that the changes in diversity were driven by an increase species turnover, rather than nestedness, suggesting that our experimental treatments caused a loss of sensitive species as opposed to replacement by species previously not found in the local assemblages.

Our results suggest there is large potential for negative synergisms between drought and disturbance in dryland ecosystems, but the severity of negative impacts is contingent on the resistance to global change drivers possessed by species present within the community. Taken together, our cross-site findings support current knowledge of dryland productivity’s sensitivity to precipitation and offer new perspectives into dryland ecosystem sensitivity to multiple types of disturbance.