Perennial grass response to 10-year cattle grazing in the Mendoza plain, mid-west Argentina

Basal area (cm2 m−2) and density (plants m−2) for total, undesirable, intermediate and preferred perennial grasses were monitored in 1990 and in 2000 in response to two grazing strategies (yearlong continuous and rotational) and four grazing intensities (ungrazed; light, moderate and heavy grazing). Grazing intensity had a significant effect on basal area of perennial grasses. Basal area and density for all the grass groups tended to be higher in 2000 than in 1990 for all grazing intensities but the grazed treatments did not show significant differences in basal area and density increases from 1990 to 2000 for all the mentioned grass groups. Several hypotheses could be advanced to explain the limited grass response to treatments. The stocking rates applied may have been too light to cause significant effects. Grasses appear to be resistant under the grazing intensities used and the annual drought occurring during 7 of the 9 last years of the study. Given the history of heavy grazing in this environment, it is possible that what has been observed is natural temporal variation in basal area and plant density.