The development of a taper model and a diameter at breast height to total height model to predict user defined roundwood assortment volumes in Sitka spruce first thinning plantations in Ireland.

Abstract

A taper equation and a diameter at breast height (DBH) to total height model were developed for Sitka spruce (Picea sitchensis (Bong.) Carr.) trees of first thinning stage in Ireland. The use of the models may be of benefit to forest practitioners who require information on the volumes of specific assortments prior to harvest, particularly where the practitioners wish to define the dimensions of these assortments themselves, such as in the wood energy sector. The models could be implemented into a tool for practitioners, once further field trials are undertaken to estimate the degree to which errors are propagated. To develop the models, data were collected from 433 trees on five private forest sites in Ireland. The Kozak (2004) variable exponent taper equation was parameterised using the data. This taper equation utilises total height as an input, and therefore an estimate of total height per tree was required. A Chapman Richards equation was parameterised to predict total height from DBH. Using the equations together, the volumes of 90 sample trees were predicted, and then compared to actual measurements. The equations predicted the full stem length volume with a standard error estimate of 0.0098 m3 per tree, and a bias of 0.00003 m3 per tree.