Rotation-end financial performance of vegetation control on Eucalyptus smithii in South Africa

Abstract

Control of competing vegetation during eucalypt regeneration is important but the cost-benefit of varying levels of control is not well understood. A trial was initiated to quantify the impact of five vegetation control treatments on Eucalyptus smithii R.T.Baker. to determine the potential loss in growth and differential costs against which this growth loss could be linked. Five treatments were developed to suit the predicted vegetation load at the site and varied according to weeding intensity (high, moderate and low weeding) or area around the tree that was weeded (no vegetation control, a 2 m row weeding and complete vegetation control). The vegetation control treatments were imposed at planting and maintained until canopy closure (16.4 months). Tree growth was monitored throughout the rotation and this, together with the cost of the various establishment and weeding operations, were used to make treatment comparisons. Weed growth was rapid following planting, with competition-induced divergence in tree growth occurring from 52 d. Rotation-end volume for the Weedfree check (414 m3 ha^–1) and Row weeding treatment (394 m³ ha^–1) were significantly different from the Weedy check (319 m³ ha^–1), with the Moderate (374 m³ ha^–1) and Low (371 m³ ha^–1) weeding intensity treatments intermediate but not significantly different from each other, nor from the other treatments. The financial performance (expressed as bare land value [BLV] with 6% discounting) of the Weedfree check outperformed the other treatments and was 37% higher than the Weedy check. The BLVs of the Moderate and Low weeding intensity treatments were similar to each other, indicating that these treatments were both feasible in terms of financial performance. However, the 2 m Row weeding had c. 10% higher BLV than the Moderate and Low weeding intensity treatments, and could be considered as a viable alternative to the Weedfree check. Sensitivity analysis conducted on the data in terms of local or exogenous risks indicated that between the treatments, differences in response to either local or global market risks were minor. Thus, small changes in cost and price levels, or larger changes in applicable discount rate, would not alter the ranking of the vegetation control treatments, with the Weedfree check (High weeding intensity) being the best in terms of financial performance, and the Weedy check the worst.

Keywords: bare land value, competition, Eucalyptus smithii, internal rate of return, merchantable volume, weed management