Rainfall variability and animal production in the semi‐arid savanna of Southern Africa

Abstract

Ecological systems in the semi‐arid savanna of southern Africa are subject to an erratic moisture supply. This results in large and unpredictable fluctuations in plant production and changes in plant cover and botanical composition, notably in the herbaceous layer. With rapidly increasing pressure on the land there is an urgent need to define land use procedures which will give maximum production over the years and which will minimise stress on livestock and the vegetation during droughts. Present knowledge is inadequate for this purpose, and there is a strong case for comprehensive study of the effects of rainfall fluctuations on plant and livestock production, botanical composition and soil cover.

The feasibility of developing models to estimate plant production from simple meteorological, soil‐water and plant growth parameters is indicated. It is shown how such models could be used in conjunction with empirical relations between stocking pressure and gain per animal, and stocking pressure and intake, to simulate fluctuations in animal and plant production over a long period of years. With such a model a variety of management options could be examined with particular emphasis on the critical seasons in which plant growth is at a minimum.

Uittreksel

Ekologiese stehels in die droë bosveldstreke van suidelike Afrika is deur onreëlmatige vog beïnvloed. Die uitslag is groot verskille in plantproduksie en verskille in plantbedekking en botaniese samestelling van veral die kruidagtige laag. Aangesien die snelheid waarmee die druk op die land besig is om toe te neem, is dit dringend nodig dat grondbenutting‐stelsels gedefineer word om optimale produksie op ‘n standhoudende basis te verseker, en om gevaarlike druk op beide vee en plante gedurende tye van droogte te vermy. Huidige kennis is nie voldoende nie, en omvattende studies is nodig om die invloed van onreëlmatige reënval op plantegroei, diere‐produksie, botaniese samestelling en grondbedekking te bestudeer.

Die moontlikhede om modelle te ontwikkel, om plantproduksie vanaf sekere weerkundige, grondwater en plantgroei parameters te voorspel, is aangedui. Dit word bewys dat sulke modelle, in verbinding met empiriese verwantskappe tussen vee‐druk en produksie per dier, en vee‐druk en weidingsinname, gebruik kan word om veranderinge in diere‐ en plantproduksie oor die jare te simuleer. Die modelle kan ‘n verskeidenheid van bestuurmetodes toets, met klem op kritiese seisoene wanneer plantegroei minimaal is.