Browsing by Subject "kokoluokkarakenteinen malli"

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.