Patterns of plant selection by grazing cattle in two savanna grasslands: A plant's eye view

Abstract

The amount of grazing experienced by individual tufts of the most abundant perennial grasses of two Transvaal savannas was monitored at regular intervals for two growing seasons. In general, Setaria incrassata and Themeda triandra were heavily grazed, Bothriochloa insculpla and Aristida bipartita were lightly grazed, and Heteropogon conlortus and Digitaria eriantha were intermediate. Tufts with a greater amount of moribund material were less heavily grazed. The smallest tufts of all species were the most lightly grazed, although the most heavily‐grazed tufts were on occasion intermediate in size rather than being the largest. A tuft had an increased likelihood of being heavily grazed if it had previously been heavily grazed, both within a growing season and for two successive growing seasons. A spatial pattern of grazing was evident, as individual species were less heavily grazed at different locations within the paddocks. The influence of species identity on the amount a tuft was grazed was not absolute but rather quantitative and conditional on the level of other variables. Tuft size and the amount a tuft had been previously grazed generally had a greater influence on the amount a tuft was grazed during an individual grazing event than species identity, location or moribund material. Species selection is possibly, in part, a consequence of selection for plant structure which optimizes intake.