Two-level optimization approach to tree-level forest planning

Background:Laser scanning and individual-tree detection are used increasingly in forest inventories.As a consequence,methods that optimize forest management at the level of individual trees will be gradually developed and adopted.Results:The current study proposed a hierarchical two-level optimization method for tree-level planning where the cutting years are optimized at the higher level.The lower-level optimization allocates the trees to the cutting events in an optimal way.The higher-level optimization employed differential evolution whereas the lower-level problem was solved with the simulated annealing metaheuristic.The method was demonstrated with a 30 m30 m sample plot of planted Larix olgensis.The baseline case maximized the net present value as the only management objective.The solution suggested heavy thinning from above and a rotation length of 62 years.The baseline problem was enhanced to mixed stands where species diversity was used as another management objective.The method was also demonstrated in a problem that considered the complexity of stand structure,in addition to net present value.The objective variables that were used to measure complexity were the Shannon index(species diversity),Gini index(tree size diversity),and the index of Clark and Evans,which was used to describe the spatial distribution of trees.The article also presents a method to include natural advance regeneration in the optimization problem and optimize the parameters of simulated annealing simultaneously with the cutting years.Conclusions:The study showed that optimization approaches developed for forest-level planning can be adapted to problems where treatment prescriptions are required for individual trees.