Research note: Quantification of the effects of defoliation on grass vigour

Abstract

The quantification of defoliation effects on grass vigour is important in understanding veld response to differential management. Effect of grazing on vigour can be determined by measuring regrowth during the season following grazing and comparing treatments with an undefoliated control. In this study, veld was defoliated at varying intensities and frequencies. During the following season, regrowth was measured on all treatments to quantify any residual treatment effects on vigour. Comparisons between measuring yield per tuft and yield per unit tuft basal area of this regrowth revealed marked discrepancies between the methods. These findings were in agreement with previously reported studies. In addition, differences between the mean tuft basal areas were found between treatments. Differences in vigour may reflect a change in tuft area as well as amount of growth per unit tuft area. Quantification of residual effects of grazing on plant vigour should thus logically be done using techniques based on plant yields, rather than on the basis of yield per unit tuft basal area. Techniques are available for the measurement of regrowth of all species present using quadrats, and this measure, expressed as species yield per unit land area, gives extra significance to the results.

Additional index words:

• Grass productivity
• measuring grass regrowth
• residual effects of grazing