Processes of desertification by goats overgrazing in the Tamaulipan thornscrub (matorral) in north-eastern Mexico

During the period of October 1995 to October 1996 a single overgrazing episode was monitored to determine the effects of overgrazing by goats on leaf cover in five vertical strata. Soil bulk density, infiltration rates, organic matter content, and the concentration of soil macronutrients within the Tamaulipan thornscrub (matorral) of north-eastern Mexico were assessed. Variance, covariance, and principal component analyses of the data suggest that leaf cover and soil bulk density were affected by overgrazing. There were no statistically significant differences in infiltration rates, organic matter content, or macronutrients. This may be the result of the large spatial variability associated with these parameters or the short time period in which these parameters were monitored. Changes in plant species composition, vegetation cover, and soil compaction were identified as early responses to overgrazing within this ecosystem. The importance of identifying early indicators of overgrazing and the need for future research are discussed.