Competition in thinned Silvertop Ash ( Eucalyptus sieberi L. Johnson) stands from early coppice growth

Abstract

Vigorous development of coppice shoots on the stumps of thinned trees may inhibit the growth of retained trees. This study examined the effects of thinning intensity and site quality on coppice growth in 18–23-year-old regrowth stands of Eucalyptus sieberi L. Johnson (Silvertop Ash), located in the Eden Region of southeastern New South Wales, Australia. To assess competition between coppice and the retained stand 2–3 years after thinning, basal area, leaf area, sapwood area and foliage nutrient concentrations were determined for both stand components, coppice and retained trees. Coppice contributed between 0.1 and 33% of the basal area and 1.6 and 83% of the leaf area of the regrowth stands, after thinning had removed between 27 and 88% of the basal area. The proportion of total stand basal area occupied by coppice shoots increased with thinning intensity. At the lowest of three different site qualities, coppice basal area was inversely related to the overstorey basal area, sapwood area and leaf area. However, in stands growing at the medium and high site qualities, these relationships were weak. At the high site quality, coppice basal area was much lower than in stands of lower site quality. Restricted coppice development at the high site quality may be genetically determined. The specific leaf area was higher in the coppice leaves (6.7 m 2 kg −1) than in leaves from the overstorey (3.7 m 2 kg −1). The foliage concentrations of P, K, Mg and Ca were also significantly higher in coppice leaves than in leaves from the overstorey. The stomatal area of coppice leaves was higher than in leaves from overstorey trees, indicating a higher potential transpiration in the coppice. Assuming similar sap flow rates for the coppice and the overstorey component, the coppice may contribute up to 53, 32 and 17% of stand transpiration at the low, medium and high site quality, respectively. Our results show that control of coppice development may benefit retained trees on medium- to low-quality sites.