Long-term vegetation trends and productivity under conservative and light grazing on Chihuahuan Desert rangelands: Application to Swaziland beef cattle production.

摘要

Knowledge of the relationships between stocking rate and plant production is fundamental to sustainable management of grazed rangelands. Vegetation changes were evaluated over an 11-year period (1995-2005) on grazing excluded, light grazed and conservative grazed areas on the Chihuahuan Desert rangelands of south central New Mexico. Soil organic carbon and nitrogen were evaluated during the last 2 years of the study. During the study period, grazing use of primary forage species averaged 30% and 38% on light and conservative grazed rangelands, respectively. Standing crop of total vegetation and perennial grasses showed large fluctuations among years due to variable rainfall. There were no differences in species and species groups in autumn standing crop and basal cover among grazing excluded, light and conservative grazed rangelands. Basal cover for black grama, the dominant decreases grass in the Chihuahuan Desert, declined from 1995-1997 to 2003-2005. However, rate of decline did not differ between light and conservative grazed rangelands. Forage standing crop was higher on shallow soils (less than 40 cm) than deep soils both during wet and dry years. Both mesquite canopy cover and mesquite density were higher in deeper (40 cm or more) than shallow soils.;There were no differences in soil organic carbon and nitrogen among grazing excluded, light and conservative grazed areas. Drought exerted overriding influence in vegetation trends and rangeland ecological condition. Light to conservative grazing involving 30-38% use of current year's growth of key forage species did not adversely affect standing crop, soil organic carbon and nitrogen compared to grazing exclusion on the Chihuahuan desert rangelands.;Principles of light to conservative grazing levels involving 25 to 35% use of key forage species have a potential to restore deteriorated rangelands in Swaziland and consequently improve the country's beef cattle productivity.