Browse production and offtake by free-ranging goats in an arid zone, Kenya

Degradation of woody plants in arid zone ecosystems is often blamed on brow sing by free-ranging goats in and around settlements. However, lack of empi rical evidence makes such a notion misleading to the management of tree reg eneration. Five techniques were compared for the monitoring and estimation of browse offtake from young Acacia tortilis by free-ranging gears and the techniques were used to estimate goat relative stocking density in Kenya, a n arid zone, from 1986-1990. The findings showed that A. tortilis uses comp ensatory browse production expressed through twig growth and herbivory tole rance to modify goat browsing pressure. Goat browsing did not result in dif ferent tree growth rates between the browsed and the unbrowsed treatments. Browsed trees produced more twigs than unbrowsed trees. The browsed twigs p roduced greater net cumulative twig growth than the unbrowsed, suggesting t hat goat herbivory stimulates browse production. Twig availability declined as trees grew out of reach of goats (i.e. > 150 cm). The five techniques e stimated variable relative stocking densities at higher browse offtake, but provided comparable values when the browse offtake declined. The findings also showed that free-ranging goats adjusted browsing pressure in response to the decline in available browse and browsing efficiency, as opposed to i ntensifying browsing pressure as commonly believed. These results highlight the futility of establishing fixed stocking densities in arid environments where variability of browse production is great. Rather, resource managers may be obliged to calculate stocking densities yearly or seasonally. (C) 1 999 Academic Press.