Aboveground production and species richness of annuals in Chihuahuan Desert grassland and shrubland plant communities

Abstract

Precipitation variability and shrub encroachment in response to global environmental change are likely to affect both richness and aboveground net primary production (ANPP) of annual plants in arid and semi-arid ecosystems in the northern Chihuahuan Desert, especially given the grazing history and desertification potential of this aridland region. Using a nine-year dataset (1999–2007), we examined the spatial and temporal variation in annual plant communities in grass- and shrub-dominated vegetation, and evaluated the relationships between species richness and ANPP with seasonal and annual precipitation and soil moisture. We found that species richness and ANPP varied among seasons and between years in both grass- and shrub-dominated areas. Cryptantha crassisepala, Plantago patagonica, and Phacelia integrifolia were the most common species found in both communities in both seasons, and Chamaesyce serrula, C. serpyllifolia, and Kallstroemia parviflora were more common in summer only. We found that species richness in summer was significantly correlated with summer precipitation and summer soil moisture in both communities, but summer ANPP was significantly correlated with summer precipitation and soil moisture only in shrubland. However, richness and ANPP of winter annuals were significantly correlated with winter precipitation and winter soil moisture in shrubland and grassland. Our results demonstrate that temporal variation in rainfall can be as important as annual total amounts for plant performance, and that response to temporal dynamics varies among species but not between grass- and shrub-dominated communities. We conclude that desert annuals provide a highly dynamic system for understanding the processes that influence plant species composition and abundance, and that desert annual systems will likely be highly impacted by shrub encroachment along with increases in precipitation variability as a consequence of anthropogenic climate change.