Browsing by Subject "Siberian moth (Dendrolimus sibiricus)"

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  • Jin, Qi (Helsingfors universitet, 2013)
    The optimal harvesting for a set of even-aged Dahurian Larch (Larix gmelinii) stands located in Aershan area of the northeast of Inner Mongolia, China, are studied. The effects of catastrophic pest outbreaks (i.e. Siberian moth) on the optimal harvesting plan are also studied, and the comparison on these two cases, namely deterministic and stochastic, are analyzed. The simulation is based on an individual-tree diameter growth model, an individual-tree height model, and model for the tree mortality for the coming 5-year period. Combined with the simulation system, the optimization model modified from Hyytiäinen et al. (2005) is able to find the number of thinnings, intensity of thinning, type of thinning, subject to given rotation lengths. In even-aged management, the objective variable is the bare land value with 3.5% discount rate. In addition, a scenario approach is applied when simulating the effects of catastrophes, i.e., pest outbreaks. Stochasticity here is represented by a set of scenarios. The timing of an insect outbreak is random. In order to know the frequency of insect outbreak, an exponential model is applied. The numerical results indicate that the probability that an outbreak at epidemic level will occur within an interval of 5 years is about 0.39. Within a 10-year interval the probability is about 0.63. It is nearly certain that an outbreak at epidemic level occurs within 45 years. The optimal solutions are presented separately for deterministic and stochastic cases. For the deterministic case, the results indicate that high bare land values were associated with stands of high basal area, tree diameters and height. Typically, the higher the mean annual increment and the site quality, the higher the bare land value. Meanwhile, the results show that the optimal rotation may vary considerably (40-58 yrs) at 3.5% interest rate depending on the initial stand state. In the stochastic case, considering the effect of catastrophe of pest outbreak, numerical results show that the optimum roation is shortened and the mean values of bare land value are about 14.8% to 25.6% lower compared with the deterministic case.