资源环境科技发展态势分析平台

Final crop stand density is an important determinant of plantation value. A relatively simple model, based on productivity indices, has recently been developed that can spatially optimise final crop stand density Sept, of the widely planted plantation species Pinus radiata D. Don for stands grown for structural grade timber. When applied to New Zealand this model shows Sept to be ca. 100 stems ha(-1) higher than the current final stand densities. Using a comprehensive set of model simulations, the objectives of this research were to (i) examine the accuracy of predictions of SOP, from the simple model and (ii) determine the potential economic gain of thinning structural grade regimes to optimal stand densities.

Simulations included 15 combinations of the metrics Site Index and 300 Index that cover the productivity envelope occupied by New Zealand plantations and assumed a rotation age of 28 years. For each combination of Site Index and 300 Index, simulations included Sept and eight stand densities that were 200, 150, 100 and 50 stems ha(-1) lower and higher than Sept.

Composite financial metrics, weighted by the proportion of the plantation estate in each productivity class, showed marked increases from stand densities 200 stems ha(-1) lower than Sept to Sept which levelled off above S. t. This levelling off after Sept suggests that the simple model provides an accurate estimate of Sept. Gains in gross value, net value, internal rate of return and net present value that could be realised through increasing stand density by 100 stems ha(-1) were, respectively, $5183 ha(-1) ($77,891-$83,074 ha(-1)), $2319 ha(-1) ($28,740-$31,059 h(a-1)), 0.44% (8.05-8.49%) and $294 ha(-1) ($108-$402 ha(-1)). When scaled up to the plantation estate potential gains in net and gross value that could be realised through thinning to Sept were respectively, $1.7 and $3.8B, which when discounted back to the current time equate to respective gains of $156 and $349 M.