Model details are found in Table 2. Crown size is an important measure of tree vigour. A tree’s crown reflects the cumulative

level of competition over the past and the potential for a released tree to utilize available resources such as increasing growing space. Accordingly, many single-tree growth models use crown size (usually crown ratio or crown length) as a predictor of height and diameter check details increment, as well as tree mortality. Changing tree and stand characteristics over the course of a growth projection necessitates a model to update the estimate of crown size. The most common way is to use a function to estimate crown size directly using correlated tree size and stand characteristics. The advantage is that resulting relationship predicts the crown size for the next growing period from current tree and stand conditions. This procedure

is appealing when only one-time observations of crown size are available, the usual situation with forest inventory data. If crown size has been observed repeatedly for at least two successive periods on the same individuals, then the change in crown size can be predicted directly, again relying on a relationship between crown increment and tree and U0126 order stand characteristic (Hasenauer and Monserud, 1996). BWIN, Prognaus, and Silva use a model for crown size; change in crown size is used by Moses ( Table 3). A measure of competition is a surrogate for the ability of a tree to compete for scarce resources, such as light, water, and nutrients. A measure of competition or stand density is a key independent variable in most height and diameter increment functions, as

well as the model for mortality. The competition measure can either include spatial information (distance-dependent) or not (distance-independent). Some tree growth models explicitly include the change in the competition situation before and after thinning, to address an additional species-specific response to crown release. A distance-dependent measure of competition is used Etofibrate by Moses and Silva. Even though a distance-dependent variant of BWIN exists, our application of BWIN and Prognaus used distance-independent measures of competition. Details on the competition indices can be found in Table 4. The data for simulations in this study come from 69 permanent research plots that were established in pure and mixed stands of Norway spruce and Scots pine. Plots are located in two study areas in the northern (Litschau) and southern (Arnoldstein) part of Austria. In Litschau, 23 plots were observed for 30 years (1977–2007); in Arnoldstein, 46 plots were observed for 15 years (1993–2008). The plots were established to provide a data basis for a distance-dependent tree growth model. In Litschau trees were released in 1982 using the A-value according to Johann (1982); thinning intensity varied from light to heavy thinning. Details can be found in Hasenauer et al. (1996).