Plant species dynamics in the Southern Tall Grassveld under grazing, resting and fire.

Abstract

An analysis of temporal changes in botanical composition in a long-term grazing trial indicates that species dynamics in the Southern Tall Grassveld of Natal are determined by the specific combination of grazing, mowing and fire impacts. Species composition of a grazing systems trial was recorded at intervals during 16 years, and in the 14 years following the removal of herbivores, during which time the experimental area was burnt periodically. Site trajectories in ordination space facilitated the assessment of the nature, magnitude and rate of species composition change under various combinations of impacts. Under rotational grazing and mowing, botanical change was minimal, both during the grazing and the subsequent rest and fire phases of the trial. It is suggested that the interruption of continuous grazing at a high stocking rate by a seasonal rest (rotational resting) promoted the invasion of the sward by Aristida junciformis. This also occurred in the continuously-grazed treatment at a high stocking rate when stock were removed from the treatment and periodic burning was introduced. It appears that swards dominated by A. junciformis remain stable under a rest and burning regime.

Keywords: area; aristida junciformis; botanical composition; burning; composition change; continuous grazing; fire; grassveld; grazing systems; herbivores; mowing; natal; recovery; rotational grazing; sheep grazing; site trajectories; south africa; southern tall grassveld; species composition; state-and-transition model; stocking rate; temporal changes