Silvicultural effects on the productivity and wood quality of eucalypt plantations

Abstract

The productivity of most forest plantations is less than their physiological potential as defined by the prevailing climate, because the supply or capture of light, water and nutrients is less than optimal. However, maximum growth does not equate to maximum wood value. The silvicultural challenge is to design and use management regimes that achieve target growth rates and wood quality by manipulating resource supply, capture or use. It has been and remains possible to identify and ameliorate factors limiting growth, sometimes on a large scale, e.g. by soil cultivation, residue management, fertiliser, weed control, irrigation, coppice management, thinning and pruning. This review examines some of these silvicultural practices for eucalypt plantations. During the past two decades, an increase in research on silvicultural practices in relation to soil and plant processes has improved our understanding of their effects on tree growth and wood quality, and on non-wood values including the potential for adverse on- or off-site effects. Eucalypt silviculture usually targets high growth rates and short rotations. High growth rates, and to some extent low nutrient-use efficiencies of eucalypts, lead to high nutrient demand and a high potential for nutrient depletion if management does not facilitate nutrient conservation. A detailed examination of nutrient management is presented. We indicate how silvicultural information is incorporated into current empirical- and process-based systems of productivity prediction, and identify potential improvements to these models. Silvicultural options are included adequately in some empirical models, and some process-based productivity models adequately cater for pruning and thinning, but process-based predictions of other silvicultural options, e.g. cultivation, slash retention, fertiliser, weed control and pest management, remain in their infancy.