A non-linear mixed-effects model to predict cumulative bole volume of standing trees

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Abstract
For purposes of forest inventory and eventual management of the forest resource, it is essential to be able to predict the cumulative bole volume to any stipulated point on the standing tree bole, while requiring measurements of tree size that can be made easily, quickly and accurately. Equations for this purpose are typically non-linear and are fitted to data garnered from a sample of felled trees. Because the cumulative bole volume of each tree is measured to numerous upper-bole locations, correlations between measurements within a tree are likely. A mixed-effects model is fitted to account for this within-subject (tree) correlation structure, while also portraying the sigmoidal shape of the cumulative bole volume profile.