Evaluation of three objective point‐sampling techniques to measure utilization of karoo bushes

Three techniques to measure utilization of karoo bushes were evaluated. Precision, accuracy and consistency were measured on three species at different times and levels of utilization. The percentage‐cover technique was less sensitive and less efficient than the percentage‐edible‐strikes and percentage‐twigs‐grazed techniques. It required samples that were 25% larger than those needed for the other two techniques to achieve equivalent levels of precision. For any single technique, precision was consistent for different species. Provided samples exceeded 30 bushes all techniques were consistent over time. No improvement in accuracy was measured for samples greater than 20 bushes. While similar levels of accuracy were achieved on the three species, the lack of consistency of the percentage‐cover technique for different levels of utilization, limits the usefulness of the technique. To estimate utilization of a single species using any of the techniques with adequate precision and accuracy, approximately 25 minutes with two operators was required.     

Exploring the potential of the descending‐point method to measure utilization in karoo veld

Abstract

The descending‐point method of vegetation survey proved effective in measuring meaningful plant cover changes during a grazing period. No significant changes in basal cover or plant height were detected. Changes in canopy spread and canopy cover could only be used to detect changes in utilization at levels lighter than 50 % and 70 % respectively. Selective utilization between species implies that it may be extremely difficult to achieve a specified level of utilization in practice. Therefore, in karoo veld, resting may be considered a more practicable veld management strategy than attempts to achieve a specific utilization intensity. The descending‐point method is time‐consuming in determining canopy cover. Thus, methods based on more effective point sampling, within the canopy spread, may be more appropriate for this purpose.