Response of Colophospermum mopane to different intensities of tree thinning in the Mopane Bushveld of southern Africa

Abstract

In the Mopane Bushveld, Colophospermum mopane is viewed as a threat due to its ability to suppress the herbaceous layer. The objective of this study was to investigate the re-establishment of C. mopane over a 19-year period on seven plots thinned to different tree densities. Thinning was completed during 1989 and measurements done annually from 1990 to 1995 and again during 2008. Absolute tree densities (plants ha⁻¹) increased in the low tree density plots, whereas in the high tree density plots the tree densities declined. Changes in leaf phytomass of the C. mopane trees were more pronounced than changes in absolute tree densities and growth of the remaining trees mainly occurred as increases in canopy diameter, rather than increases in tree height. Growth of established trees displayed an exponential increase in growth with declining tree density demonstrating the suppressive effect of inter-tree competition on the growth of individual trees. A trend towards an equilibrium appears to exist where some self thinning occurred in the dense plots, opposed to increases in the number and size of trees in the thinned plots. Considering the benefits of trees (soil enrichment and food to browsing herbivores), tree thinning rather than tree clearing is recommended.