The effect of past grazing intensity on the vigour of Themeda triandra and Tristachya leucothrix

Abstract

Tuft vigour of important sourveld grasses was indexed by measuring the regrowth, during a full season's rest, of tufts of Themeda triandra Forssk. and Tristachya leucothrix Nees, which (1) had not been grazed, (2) had been leniently, or (3) had been severely grazed during the previous two growing seasons. A sequential harvesting technique was applied and regrowth was expressed in terms of above‐ground herbage‐mass accumulation and etiolated growth. Patterns of regrowth were similar for both species. Severe grazing during the previous two years significantly reduced topgrowth yields during the first 27 to 31 weeks of rest compared to tufts which had previously been leniently or not grazed. Etiolated growth was greater on leniently and ungrazed tufts than on severely grazed tufts for 13 to 15 weeks after the commencement of spring growth, whereafter there were no significant differences. The regrowth patterns of tufts for all intensities of defoliation suggests that the vigour of severely grazed tufts of both species had been restored by the end of a full growing season's rest. However, a need for further studies into the efficacy of a growing season's rest is indicated.

Additional index words:

• Cattle
• sheep
• season‐long rests