A Site-growth Study of Eucalyptus grandis in the Mpumalanga Escarpment Area

Abstract

A site-growth study was conducted on Eucalyptus grandis on the granitic soils of the Mpumalanga escarpment area. The objectives were twofold, namely to identify those site factors that can be related to the growth of the species, as well as the development of a statistical site-growth model for the quantitative evaluation of sites for tree growth performance. An integrated approach was followed using multiple regression analysis, incorporating attributes on topography, climate and physical and chemical soil characteristics, with Site Index at 20 years (SI₂₀) as the dependent variable. The study revealed that the growth of E. grandis is mainly influenced by factors controlling available soil moisture, together with the organic carbon content of the topsoil. A statistically significant site-growth model was developed, although the model showed bias by overpredicting at low potential sites and underpredicting at high potential sites. This could be ascribed to the use of a growth model (for standardising on growth data to SI₂₀) that was developed in a geographically different area. Suitable site-specific growth models are not yet available for the study area.