Authors analyze a 44-year record of herbaceous vegetation change for three contrasting grazing regimes, within a semi-arid savanna, to evaluate the relative contribution of confined livestock grazing and climatic variability as agents of vegetation change. Analysis of these long-term data indicate that both grazing and climatic variability are important agents of herbaceous vegetation change in this semi-arid savanna. Grazing intensity had a significant, directional effect on the relative composition of short- and mid-grass response groups and response group composition was significantly correlated with time since the various grazing regimes were established. Therefore, Fuhlendorf et al. failed to reject hypothesis one that grazing would produce a directional and proportional change in the relative composition of short- and mid-grass response groups. In contrast to grazing intensity, interannual precipitation was not significantly correlated with response group composition. However, interannual precipitation significantly correlated with total plant basal area, while time since precipitation of grazing regimes was not, but both interannual precipitation and time since imposition of grazing regimes were significantly correlated with plant density. Vegetation change was reversible even though the herbaceous community had been maintained in an altered state for 60 years by intensive livestock grazing. However, 25 years were required for the mid-grass response group to recover following the elimination of grazing and recovery occurred intermittently. The occurrence of both directional and non-directional vegetation responses within this system were largely a function of (1) the unique responses of the various community attributes monitored and (2) the distinct temporal responses of these community attributes to grazing and climatic variation. This interpretation supports previous conclusions that individual ecosystems may exist in equilibrial and non-equilibrial states at various temporal and spatial scales.
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