Browsing by Subject "dynaaminen optimointi"
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(2013)This study analyzes the optimal harvesting of single species uneven-aged Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and birch (Betula pendula Roth. and B. pubescens Ehrh.) stands, in addition to mixed species stands with all three species. The analysis is based on an economic description of uneven-aged forestry using a size-structured transition matrix model and a single-tree model. The optimization problem is solved in its general dynamic form using gradient-based interior point methods. Similar analysis on uneven-aged birch, Scots pine and mixed species stands in Nordic conditions has not been published. Increasing the harvesting interval decreases the average annual volume yield. Assuming natural regeneration, this suggests that volume yield is maximized by uneven-aged rather than even-aged management. The present value of stumpage revenues is maximized after saw timber and pulpwood prices, interest rate, and a 15-year harvesting interval are included. The economically optimal solution with a 3% interest rate produces an annual yield of 1.9, 5.5 and 2.9 cubic meters (m3) for Scots pine, Norway spruce, and birch respectively in single species stands at site with average productivity. At less productive sites, the mixed species stand is heavily dominated by Norway spruce regardless of interest rate. At more productive sites on the other hand, increasing interest rate increases species diversity. Both the optimal volume yield and net present value maximization solutions converge to unique species- and site-type-specific steady-states with constant harvests. The transition matrix model typically used in optimization studies is computationally less demanding than the single-tree model, but the differences in optimal solutions are more remarkable than earlier studies show. Additionally, it appears that the investmentefficient optimization model may result in steady-state solutions that significantly differ from the correct solutions.
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(2013)The purpose of this study was to define economically optimal stand structures and harvesting cycles for uneven-aged Scots pine (Pinus sylvestris L.) in Finland. According to a recent proposal by Ministry of Agriculture and Forestry, uneven-aged management will be included in the new Forest Act as an alternative for future forest management in Finland. Uneven-aged management is also planned to be included in the Forest management practice recommendations by the year 2014. However, only little knowledge exists on optimal uneven-aged management in Finland, particularly on uneven-aged Scots pine. This thesis aimed at filling the gap in knowledge regarding economically optimal management of uneven-aged Scots pine. So far, economic studies on uneven-aged Scots pine have been conducted only in a static optimization framework, where optimal stand structure is constrained with a classic “reversed-J” diameter distribution, and transition cuttings are limited to one single harvest. In this work, stand structures and harvesting cycles were optimized for maximum volume yield and maximum stumpage revenues by applying both static and dynamic optimization. Until now, no dynamic optimization has been conducted on uneven-aged Scots pine. Static optimization was applied for different growth sites from mesic sites in Southern Finland (MT1300) to sub-xeric sites in Central Finland (VT1100). Mesic sites in Southern Finland were also optimized in a dynamic framework. A density-dependent individual tree model with latest ecological growth models was applied in optimization. The large-scale nonlinear problems were solved by means of numerical computing with discrete-time formulations. Present value of stumpage revenues was maximized applying 1% and 3% discount rates. Economically optimal harvesting cycle became 40 years in Southern Finland (site MT1300), and even longer at more northern and less fertile site types. Results imply that it is not economically optimal to manage Scots pine with a traditional selection method with short harvesting cycles, but rather with a heavy harvesting regime including low after cut basal areas. When maximizing present value of stumpage revenues, optimal after cut basal areas in Southern Finland were as low as 5 m2 (1% discount rate) and 3.2 m2 (3% discount rate) per hectare. A proposal of Ministry of Agriculture and Forestry suggests minimum after cut basal areas of 10–11 m2 per hectare for Southern Finland, which clearly exceed the optima of this study. Contrary to the existing results for uneven-aged Scots pine, economically optimal stand structure did not follow the classic reversed-J diameter distribution.
Now showing items 1-2 of 2