tree model

Hyrcanian forests are the most valuable forests in the north of Iran and industrial harvesting occurs only in this area. It is a productive region near the southern coast of Caspian Sea. In these forests mixed beech stands mostly shown uneven-aged structure that is managed under selection system. In order to determine the priority of uneven aged method not only from an ecological view, but also from other views, especially in economical view compared to other methods, should be prove this important by tools or methods. The growth models enable the simulation of stand development in alternative management schedules and select finally the best method. Nowadays sivicultural tendency has been applied here. 768.4 ha unmanaged forest of Gorazbon district in Kheyroud educational-experimental forest was studied using 258 permanent sample plots. The models were used to optimize the stand structure and the alternatives in which various initial stands should be converted to the optimal uneven-aged structure. The model set consists of individual-tree diameter increment model, individual tree height model, survival model, and a model for ingrowth. The models indicate that the annual volume increment of the forests ranges from 2.5 to 7 m3ha-1a-1 in uneven-aged management, depending on species composition. The models and analysis of this study indicate that the uneven aged forest is more practical and superior than other methods (young even-aged stand, mature even-aged stand, and two-storied stand) in forest conversation and economically wood production.

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.