Research Note: Tests for inducible thorn defences against herbivory must consider plant growth strategies

Abstract

Rainfall variability is a major determinant of system dynamics and profitability of livestock enterprises in arid and semi-arid environments. Range managers consequently require detailed information on the financial and ecological implications of various stocking strategies in order to formulate viable management systems. Data collected over seven seasons (1986-1993), from a series of extensive grazing trials in the semi-arid savanna of KwaZulu-Natal with cattle stocked at three rates (0.17, 0.23 and 0.30 LSU ha^-1) were used to develop a bioeconomic stocking model (LOWBEEF). The model comprised two biological sub-models (BEEF and GRASS), and an integrated economic component. The BEEF sub-model related seasonal live mass gain to stocking rate and rainfall. The GRASS sub-model related residual herbage at the end of summer to summer stocking intensity, range condition (indexed as the sum of proportions of three key forage species.

Keywords:Themeda triandra, Panicum maximum and P. coloratum) and rainfall. The period over which supplementary feeding would be required to maintain cattle mass was related to residual summer herbage mass. The biological sub-models were linked to an economic component model (ECON) to reflect the influence of various environmental and economic parameters on profitability.

African Journal of Range & Forage Science, Vol. 13(2), pp. 67-71