Graduate Thesis Or Dissertation
 

A study of optimal timing and intensity of silvicultural practices : commercial and precommercial thinning, fertilization and regeneration effort

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  • One traditional problem in forest management is to find the optimal stand level management regime. Four important silvicultural practices including precommercial thinning, commercial thinning, fertilization and regeneration harvest are considered jointly in this study. The partial analyses, i.e. considering some of the silvicultural practices, are also discussed. The inability to account for diameter acceleration in the two-dimensional dynamic programming technique is overcome by using a three-dimensional dynamic programming network with biometric relationships from DFIT. The continuous growth is fitted into a discrete dynamic programming network by using the "neighborhood" concept. The descriptors used are stand age, number of trees and basal area. The effect of the size of the state space of dynamic programming is discussed and a basal area interval between four to 20 square feet is suggested when the tree interval used is 15. Commercial thinning is considered every ten years and captures anticipated merchantable mortality. Precommercial thinning is considered at age ten. Different intensities of precommercial thinning can be considered jointly with other silvicultural practices. Three levels of fertilization, i.e. 400 pounds, 200 pounds and zero pounds of nitrogen per acre, are applied every ten years after commercial thinning. An extra dimension representing different levels of fertilization is eliminated by computations and using the neighborhood concept. The forward recursive relation of dynamic programming finds the best management regime for different rotations as the solution progresses. Precommercial thinning accelerates diameter growth and will affect later commercial thinning entries. Commercial thinning lengthens rotation and fertilization increases site capacity and raises optimal stocking level. The solution technique developed also finds the optimal management for different initial stand conditions. Plantation is solved by assuming that it is equivalent to a stand precommercially thinned at age two. The impact of individual silvicultural practices and their interactive effects are derived. Under the revenue and cost assumptions used, it is found that fertilization has the highest economic impact, commercial thinning is the second and precommercial thinning is the last, when silvicultural practices are considered individually. The highest total effect of two silvicultural practices is precommercial thinning and commercial thinning. Commercial thinning and fertilization is the second and precommercial thinning and fertilization is the last. Precommercial thinning and commercial thinning has the highest interactive effect, commercial thinning and fertilization is the second and precommercial thinning and fertilization is the last which is negative. The interactive effect of precommercial thinning, commercial thinning and fertilization is positive, that is to say, when these practices are applied together, the total effect is larger than the sum of individual effects. The techniques developed and discussed give practical answers to questions of stand level optimization with complex cost, revenue and growth model silvicultural interactions.
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