|Whitford, Walter - US-EPA|
|Turanzas, Gustavo - NEW MEXICO STATE UNIV|
|Meza, Ernesto - NEW MEXICO STATE UNIV|
Submitted to: International Symposium and Workshop on Desertification in Developed Countries
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 1994
Publication Date: N/A
Technical Abstract: Desertification in much of the southwestern US and northern Mexico has resulted in the replacement of perennial grasslands with desert scrublands. Scrublands dominated by C3 shrubs exhibit long-term persistence, resist control efforts, and are resilient in areas where control and revegetation with grasses have been attempted. Experiments using 5 consecutive years of fsummer drought using "rain-out" shelters and 5 consecutive years of approximately doubling the summer rainfall resulted in no significant changes in annual net above-ground primary production of creosotebush in either of the treatments. There were significant changes in species composition and above-ground net primary production of spring annual plants and some reduction of perennial grasses and forbs in droughted plots. There were small changes in decomposition rates and nitrogen mineralization potential but no quantitative differences in the soil microfauna. Studies of shrub water budgets demonstrated that between 6% and 25% of the intercepted rainfall was translocated to deep soil storage by stemflow and root channelization. Nutrient minerals in stemflow water on creosotebush were 5 to 10 times more concentrated in stemflow than in throughfall and bulk precipitation. These data demonstrate that once shrubs are established, islands of resource enrichment of water and nutrients develop under the shrubs. The result is self-reinforcing systems that are resistant to disturbance, even climatic change. The data from these studies suggest that management of desertified landscapes in North America should focus on maintaining the residual grasslands and on the economic uses of the shrub-dominated ecosystems.