Wednesday, November 15, 2006

Mesquite Tree Removal Changes Soil Nutrient Cycling Processes in Semi-Arid Ecosystems.

Eileen Finnerty-rae and Tom Thompson. Univ of Arizona, PO Box 210038, Tucson, AZ 85721-0038

The principal economic use of semi-arid grasslands in North America is commercial livestock production.  Woody plant encroachment in grasslands is a significant problem for land managers due to reduction in herbaceous plant populations and difficulties associated with livestock handling. The expansions of mesquite (Prosopis velutina) in southwestern Arizona, and attempts to control or remove mesquite have been well documented.  However, removal of woody plants may affect the distribution and quantities of biological and nutrient resources within the soil. In addition, changes in C and N cycling caused by mesquite removal may change amounts of C and N sequestered in these soils. Although limited long-term data regarding the affects of mesquite removal on C and N sinks are available, it is important to understand both the long and short-term effects of mesquite removal in order to make informed land management decisions. We investigated the effects of mechanical removal of mesquite at two separate semi-arid grassland sites south of Tucson, AZ. We evaluated the effects of mesquite removal on soil temperature and moisture, C and N pools, N2O and CO2 fluxes, N mineralization rate, specific microbial population components, and activities of selected enzymes. These factors were studied to develop a more comprehensive understanding of short-term changes in C and N dynamics and microbial populations following mesquite removal.