Biology ETDs

Publication Date



Within grasslands, precipitation, fire, nitrogen (N) addition, and extreme temperatures influence community composition and ecosystem function. The differential influences of these abiotic factors on Chihuahuan Desert grassland communities was examined within the Sevilleta National Wildlife Refuge, located in central New Mexico, U.S.A. Although fire is a natural disturbance in many grasslands, fire during drought temporarily increased forb cover and decreased grass cover for several years. The seasonal timing of fire was not important, rather community recovery was more influenced by the persistent drought conditions. N deposition is increasing worldwide due to human activities, and although additional N increases productivity and decreases diversity in most terrestrial systems, community responses were variable in Chihuahuan Desert grasslands. During above-average precipitation, N addition greatly increased aboveground productivity but did not influence belowground productivity or community composition. During average or below-average precipitation, no effects of N addition on the grassland community occurred. Although human activities provide grasslands with extra N, soil microorganisms help plants naturally acquire N. The activity of soil microbes, and in turn nutrient availability for plants, responded to rainfall events and the proximity to plants and varied throughout the monsoon growing season. Lastly, shrub encroachment is converting grasslands to shrublands and may possibly be reversed by extreme climate events. Following an extreme cold event at the boundary between Chihauhuan Desert grass- and shrublands, shrubs were damaged but not killed by cold temperatures. Therefore a single cold event might not be influential enough to reverse shrub encroachment. Many factors, including fire, N addition, and shrub encroachment, influence Chihauhaun Desert grasslands, but the magnitude of influence is strongly regulated by precipitation. Some factors, such as fire seasonality and N addition, were not influential during drought and only changed communities when water limitations were alleviated, while other factors, such as extreme cold temperatures, influence communities regardless of soil water status. As humans continue to change abiotic factors and natural environments, it is important to understand how plant communities respond to changing conditions.

Project Sponsors

Research was funded in part by National Science Foundation grants to the University of New Mexico for Long-term Ecological Research, Research Experience for Undergraduates, Doctoral Dissertation Improvement, and Rapid Response Research, a grant from the USDA Forest Service National Fire Plan, the U.S. Department of Energys Office of Science through the Western Regional Center of the National Institute for Climate Change Research, T & E Inc., and several Alumni and Graduate Student Scholarships from the University of New Mexico Graduate Student Association, Department of Biology, and Biology Grad Student Association.




desert grassland, plant community ecology, climate change, fire, N deposition, extreme climate event, extracellular enzyme activity

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Advisor

Collins, Scott L.

First Committee Member (Chair)

Sinsabaugh, Robert L.

Second Committee Member

Marshall, Diane L.

Third Committee Member

Ford, Paulette L.

Fourth Committee Member

McLaren, Jennie R.