Defoliation patterns of three grass species in sourveld grazed by cattle and sheep

Abstract

A point‐based technique was used to determine the effects of grazing, due to stocking rate and cattle‐to‐sheep ratio, on the defoliation pattern of three grass species. At each of 100 systematically located points per grazing treatment the nearest plant of each of three target species was recorded as being in one of five defoliation categories which ranged from ungrazed to severely, but uniformly, grazed. Each treatment was sampled at the end of each of three consecutive grazing seasons. The data for each species were subjected to log‐linear and canonical correspondence analyses. In these analyses the proportional composition of defoliation categories was the dependent variable and stocking rate, cattle‐to‐sheep ratio and year were the independent variables. The results indicated that (1) stocking rate had an overriding effect on defoliation pattern; (2) ratio had a lesser but significant influence on the defoliation pattern of all three species; (3) similar defoliation patterns may be achieved at different cattle:sheep ratios provided that the stocking rate is adjusted; (4) the grazing capacity concept must be reconsidered to account for the differing impacts of grazing by cattle and by sheep on individual grass plants; and (5) the sampling technique applied in the study provided meaningful information on the defoliation pattern of the target species.

Additional keywords:

• Alloteropsis semialata
• cattle:sheep ratio
• grazing capacity
• Themeda triandra
• Tristachya leucothrix