The effect of harvesting operations, slash management and fertilisation on the growth of aEucalyptusclonal hybrid on a sandy soil in Zululand, South Africa

Abstract

Harvesting operations during clearfelling and extraction of timber from commercial plantations result in many processes that may affect long-term site productivity such as soil compaction and residue manipulation. The objective of this work was to evaluate the effects of various harvesting operations and fertiliser applications on soil physical properties and the subsequent growth of a Eucalyptus clonal hybrid ( Eucalyptus grandis x camaldulensis ) on the sandy soils of the Zululand coastal plain in northern KwaZulu- Natal. Increases in bulk density and penetrometer soil strength and decreases in aeration porosity were recorded on plots where a wheeled harvester had been used and on extraction roads, but these were not of a sufficient magnitude to limit tree growth. Available water capacity increased on the compacted plots. At six years of age there were no significant differences in stand volume between the plots harvested by different methods or between fertiliser treatments, nor was there any interaction between the treatments. However, a significant response to fertilisation was evident after one year. In contrast to the other treatments, trees in plots subjected to the wheeled harvesting operation did not respond to fertilisation, suggesting that an early release of nutrients occurred, caused by the breakdown and incorporation of slash in the topsoil. Key Words: Harvesting impacts; soil compaction; Zululand; soil physical properties; Eucalyptus grandis x camaldulensis; long-term site productivity Southern African Forestry Journal No.203 2005: 15-26