Abstract:
Bush thickening is amajor concern to farmers of arid and semi-arid rangelands; reactive intervention remains the
norm. Herewe compared some of the short-termecological implications of chemical and physical removal of the
bush encroacher Acacia mellifera in the central Highland savanna of Namibia.We selected 21 invaded sites, 7 had
been chemically cleared, 7 had been physically cleared and 7 had never been cleared. Fromeach site,we recorded
grass species composition, as well as the densities of A. mellifera, the undesired perennial shrub Pechuel-loeschea
leubnitziae and a non-targeted tree Acacia erioloba, 24–30 months post-treatment. We fitted one-way ANOVA
models to test for the effect of treatment on grass species richness and density of targeted and non-targeted
tree species. A canonical correspondence analysis was used to determine how treatment affected grass species
composition. While both treatments reduced the density of the bush encroacher, P. leubnitziae effectively replaced
A. mellifera in chemically treated sites, where die-back presumably happened faster and nutrient and
water competition decreased more rapidly. In such sites, perennial grass species were effectively outcompeted
by P. leubnitiziae.
