The prediction of growth and wood quality parameters for plantation grown Pinus radiata D. Don. in New Zealand

Most of the wood harvested in New Zealand comes from plantations of the exotic species Pinus radiata D. Don. Because forest yield exceeds demand much of the expanding forest production is available for export. Analysis of the export potential for forest products has shown that wood quality will be important to market success. Yet there is concern that intrinsic properties will decline after 1985 with an inevitable reduction in rotation age. This work develops parameters which link silviculture to the two most important intrinsic properties, wood density and tracheid length. Both of these properties vary more or less regularly with geographic region. Within individual trees values depend on wood-age (= rings from pith). The properties of a stand of trees can be assessed if volume per tree can be partitioned into wood age categories. The parameter suggested here as best indicating wood quality whilst also having relevance to silviculture is volume of mature-wood, that is volume of wood age greater than ten years. A replicated spacing/thinning trial of 75, 0.06ha plots provided the data source. Models were developed to predict the wood quality parameter. Diameter growth is projected for a plot by means of an individual tree, distance dependent model based on multiple linear equations. Height is predicted from age and diameter by a system of homologous non-linear equations and volume per tree by a function of diameter squared and height. From diameter, height and age, mean wood age is predicted using a multiple linear equation and the distribution of volume by wood age is predicted using the Weibull function. The distribution is applied to each tree and totalled for the stand. Comparing results at a fixed age for a wide range of silvicultural regimes reveals that silviculture has a greater influence on wood quality than hitherto believed.