Semiarid ecosystems have experienced significant changes during the last two centuries as a result of both changes in land management policies and global climate change.  Overgrazing, altered fire regimes and precipitation patterns, and increased atmospheric deposition have altered resources and affected biodiversity and ecosystem functioning.  Shrub encroachment and desertification are amongst the transformations that arid and semiarid ecosystems have been undergoing.  Millions of dollars are being spent on management and restoration efforts, though there is much uncertainty with regards to what future climate scenarios hold and what their effects on biodiversity and ecosystem function will be.  Therefore it is important for us to further our understanding of how these ecosystems respond to such extrinsic drivers as fire and atmospheric deposition so that we can predict future changes in community structure and ecosystem function. 

We are conducting two long-term studies that investigate the effects of seasonal fire and atmospheric deposition (nutrient co-limitation) on the plant community and ecosystem function in Chihuahuan Desert grassland. 

Results/Conclusions

Cover and species richness of different life forms (grasses, forbs, shrubs) were affected differentially by season of fire and nutrient deposition, as was soil chemistry.  Net primary production was primarily limited by nitrogen, but also by phosphorus and potassium.  Given the extreme year-to-year variability in precipitation in this system, more long-term data are needed before we can interpret these results conclusively.