Growth and yield models for uneven - aged and mixed broadleaf forest (Case study: Gorazbon District in Kheyroud Forest, North of Iran)

Hyrcania is a productive region near the southern coast of Caspian Sea. Her forests are mostly uneven-aged beach-dominated hardwood mixtures. There is increasing willingness to treat these forests without clear-felling, following the ideas of continuous cover management. However, lack of growth and yield models have delayed this endeavor, and no instructions for uneven-aged management have been issued so far. 768.4 ha virgin forest of Gorazbon district in Kheyroud educational- experimental Forest was sampled using 258 permanent sample plots in which two inventories was done. This study developed a set of models which enable the simulation of stand development in alternative management schedules and select finally the best method. The models were used to optimize the stand structure and the way in which various initial stands should be converted to the optimal uneven-aged structure. These models firstly developed without site index and age. The model set consists of individual-tree diameter increment model, individual tree height model, survival model, and a model for ingrowth. Logistic model fitted with binary logistic regression analysis was used to model the probability of survival. Non-linear mixed-effects modeling was used in height and diameter increment modeling. The predictors used in survival and increment modeling described the influence of tree size, competition and species. A common model was fitted for all species, using indicator variables to account for any species effects. Competition was described by stand basal area and basal area in larger trees. Competition variables were not included in the tree height model since they would result in instantaneous (and illogical) changes in predicted tree height in simulated thinning treatments. Within the models individual-tree diameter increment model, individual tree height model, survival model had high accuracy, Fagus orientalis and Quercus casaneifolia species had highest incremental diameter between species. In the end, using of growth models have advantages and disadvantages in planning and forest management that aware of this importance can be taken correct and logical decisions.