Determinants of the occurrence of a native encroacher species, Pechuelloeschea leubnitziae (wild sage), in the eastern Okavango Delta, Botswana

Abstract

Although indigenous to southern Africa, Pechuel-loeschea leubnitziae is considered a problematic weed as it forms dense monotypic stands in the grasslands and woodlands of the Okavango Delta, Botswana, and is associated with veld degradation and a dominance of shade-tolerant, poor-quality grass species. Generalised linear modelling was used to determine the effect of the following environmental conditions on the likelihood of occurrence of P. leubnitziae: type of land use, vegetation type, burning history, total woody species density, soil pH and soil texture. There was no difference in P. leubnitziae presence under wildlife, large livestock and small livestock land use (p = 0.227). Only vegetation type (p < 0.001) and total woody species density (p < 0.001) significantly affected P. leubnitziae occurrence, with the species being rare in dense mopane woodlands and most likely to occur in mixed thornveld and mixed broadleaf woodland, although this likelihood decreased with increasing total woody species density. A single burn had no effect on P. leubnitziae occurrence, but repeated burning should be investigated as a means to reduce the vigour and recoppicing success of P. leubnitziae.

Keywords: burning, land use, problem plants, tree density