Simulating browse production and response of Acacia karroo to defoliation II. Evaluation of browse management systems and strategies

Abstract

To assess management implications, a model was used to simulate the response of Acacia karroo to a wide range of different climatic patterns and defoliation regimes. The model predicts that if poor growing conditions initiate growth later in spring than normal, total season growth and harvest is significantly reduced. In comparison, cooler overall temperatures throughout the season reduce growth less markedly. Results indicate that increasing the number of camps in a pastoral system increases the total amount of A. karroo that can be harvested. The model illustrates, in general terms, the limits and constraints of increasing the number of camps, varying the length of stay in each and varying the length of the rest period before the next occupation at different stocking rates. It also indicates the increases in A. karroo harvests that can be expected with different management strategies. The most important prediction of the model was the large increase in productivity that could be expected by sparing or very light use early in the growing season. Even if it is possible to reduce stock in times of drought, this was shown to be of very little benefit.

‘n Model is gebruik om die reaksie van Acacia karroo oor ‘n wye reeks van verskillende klimaatsomstandighede en moontlike ontblaringstelsels te simuleer sodat die invloed daarvan op bestuur geskat kan word. Die model voorspel dat indien swak groeitoestande, gedurende die lente, groei later as wat normaalweg ‘n aanvang laat neem, totale seisoenale groei en oesopbrengs betekenisvol verminder word. In vergelyking hiermee word groei minder verlaag deur algehele koue temperature gedurende die seisoen. Die resultate het aangetoon dat, indien the hoeveelheid kampe in ‘n landelike sisteem vermeerder word, die totale aantal A. karroo wat benut kan word, ook vermeerder. Die model illustreer, in algemene terme, grense en beperkinge daarvan om die aantal kampe te vermeerder, om die tydperk van benutting in elke kamp te wissel en om die lengte van die rusperiode te wissel voordat die kamp weer benut word, teen verskillende veeladings. Dit dui ook op die vermeerdering in die geoeste A. karroo wat verwag kan word onder verskillende bestuurstelsels. Die belangrikste bevinding van die model was heelmoontlik die groot toename in wat verwag kan word indien daar slegs ‘n ligte produktiwiteit benutting vroeg in die groeiseisoen plaasvind. Selfs al was dit moontlik om vee vroegtydig te verminder in droogtetye, het dit maar ‘n klein invloed getoon.

Additional index words:

• Browsing
• goats
• simulation model