Untersuchungen zur optimalen Steuerung der Waldentwicklung

Abstract

This study deals with the optimisation of the forest development in even-aged spruce and uneven-aged pine stands. The aim of this research is the generation, evaluation and optimization of management options for even-aged spruce stands and uneven-aged pine stands. To achieve this goal it is necessary, in the first place, to utilize the research results in the area of forest growth. First, the development of the basal area in pure spruce stands was examined. Two different types of basal area models were analysed and compared: The path invariant algebraic difference form models (PID models) and the differential equations models for the estimation of the annual basal area increment (DIF models). Among the analysed PID models the equations of Schumacher (1939) and Souter (1986) showed the best performance according to the criteria of the MRES (mean residuum) and RMSE (root mean square error). Although according to their good performance both models can be recommended for estimating basal area, the model of Schumacher has the advantage that only one parameter and two independent variables (age and basal area) are required.Among the analysed DIF models the equation of Rodríguez Soalleiro (1995) showed the best results according to the criteria of the correlation coefficient and the RMSE (root mean square error).Using a forest of 38 spruce stands as an example the problem of the management optimization was investigated. Several management alternatives for each stand were generated with the management simulator Jakta. The economic criterion forest value was used for option evaluation. Finally, the optimal space-time pattern of thinnings for the whole forest was determined using the software package JLP for linear programming. A sensitivity analysis for the optimal solution was carried out, considering the timber price and interest rate changes. A variation of the wood price of ±20% and two different interest rates (i = 1% und i = 7%) were explored.To analyse the growth of uneven-aged pine stands a matrix stand growth model was developed. This model was applied to simulate different management options for uneven-aged stands. According to the economic criterion of the land expectation value a cutting cycle of 5 years and a growing stock of 133 m3/ha showed the best economic results. In this case the land expectation value amounts to 6083,82 €/ha. The comparison between continuous forest management and rotation forest management showed that on the good sites the land expectation value of the rotation system is around 48% higher than if the continuous forest system were applied; but on poor sites the land expectation value of the continuous forest system is slightly higher than what can be expected under rotation management.