Savanna browse production. 1: Determinants and measurement

Abstract

With the rapid expansion of wildlife ranching and conservation in South African savannas and the resultant increase in multi-species grazing and browsing systems, information on browse production potential is essential for determination of carrying capacity. This study, conducted on three game reserves in the northern Zululand coastal plains of KwaZulu-Natal, explored the biotic (measurable tree dimensions, and tree species) and abiotic (climatic and soil) factors influencing the rate and quantity of quarterly browse production of seven key savanna tree species (Acacia nilotica [Vachellia nilotica], Carissa bispinosa, Dichrostachys cinerea, Euclea divinorum, Gymnosporia senegalensis, Spirostachys africana and Ziziphus mucronata). Available canopy volume, mean maximum daily temperature and tree species were the most significant determinants of browse production. Available canopy volume proved to be the most reliable predictor of browse production per species and per tree, with quarterly browse production being greater on trees with larger available canopy volumes (up to a threshold). Browse production differed significantly between quarters. Growing season onset occurred during the sampling period prior to the rainy season when mean maximum daily temperatures peaked. Quarterly browse production was greatest in evergreen E. divinorum, followed by the semi-deciduous species, S. africana and Z. mucronata.

Keywords:

• available canopy volume
• browser carrying capacity
• CART
• growing season
• tree guild