Persistence of desertified ecosystems: Explanations and implications

Abstract

Studies of rainfall partitioning by shrubs, responses of shrub-dominated ecosystems to herbicide treatment, and experiments using drought and supplemental rainfall were conducted to test the hypothesis that the shrub-dominated ecosystems that have replaced desert grasslands are resistant and resilient to disturbance. Between 16 and 25% of the intercepted rainfall is channelized to deep soil storage by stemflow and root channelization. Stemflow water is nutrient enriched and contributes to the "islands of fertility" that develop under desert shrubs. Drought and rainfall augmentation experiments during the growing season after 5 consecutive years of summer drought found that (1) growth of creosotebushes, Larrea tridentata, was not significantly affected, (2) perennial grasses and forbs disappeared on droughted plots, (3) nitrogen mineralization increased in the short term, and (4) densities and biomass of spring annual plants increased on the droughted plots. Doubling summer rainfall for 5 consecutive years had less-significant effects. Coppice dunes treated with herbicide in 1979 to kill mesquite (Prosopis glandulosa) had the same frequency of occurrence of the shrub as the untreated dunes when remeasured in 1993. These data indicate that the shrub-dominated ecosystems persist because they are resistant and resilient to climatic and anthropogenic stresses.

Effects of long-term cattle exclosure on vegetation and rodents at a desertified arid grassland site

“…Restoration attempts have often involved removal of livestock but typically perennial grass recovery has not been observed even after 20 years following livestock removal (e.g. Brown, 1950;Gardner, 1950;Glendening, 1952;Smith and Schmutz, 1975;West et al, 1984;Roundy and Jordan, 1988;Skarpe, 1990;Laycock, 1991;Kelt and Valone, 1995;Whitford et al, 1995). These observations have led to the development of alternate stable state models that predict no recovery of perennial grasses over time-scales relevant to management following livestock removal because of presumed changes in soil properties (Walker et al, 1981;Westoby et al, 1989;Schlesinger et al, 1990;Friedel, 1991;Lockwood and Lockwood, 1993;Archer, 1996;Rietkirk et al, 1996.…”

Desertification processes due to heavy grazing in sandy rangeland, Inner Mongolia

“…In arid and semi-arid areas, wind erosion and heavy grazing, which are common problems in sandy rangeland (Hennessy et al, 1986), are the principal mechanisms of land degradation (Okin et al, 2001). Once soil is exposed due to heavy grazing, wind erosion occurs immediately in sandy rangeland (Whitford et al, 1995). Wind erosion and heavy grazing are the main causes of sandy desertification in desert areas (Okin et al, 2001).…”

Plant effects on nitrogen retention in shortgrass steppe 2 years after 15N addition

“…However, substantial live root biomass, with the capacity for nutrient uptake, exists in the small openings (<20 cm diameter) between plants (Hook et al 1994). In addition, processes such as the erosional redistribution of soil, and the concentration of biomass (and therefore litterfall) around plants leads to the formation of "resource islands" in semiarid and arid systems (Schlesinger et al 1990;Hook et al 1991;Whitford et al 1995;Burke et al 1998).…”