| 1. |
- Fagerberg, Nils, 1972-
(författare)
-
Individual-tree-selection in uneven-sized Norway spruce stands in southern Sweden : Developments of tools for simulation and optimization
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Individual-tree-selection (ITS) is a continuous cover forestry method that aims to utilize the uneven-sized stand structure through optimized individual tree selections. ITS is an interesting management alternative to rotation forestry in terms of production of multiple benefits and forest owner profitability. With regard to Fennoscandia, ITS is currently only practiced to a limited extent, partly because of a scarcity in knowledge and skills among all stakeholders, but also due to the shortage of scientific guidelines for how optimized tree selections are performed in practice. Thus, the aim of the thesis is to develop tools for optimizing practical ITS recommendations for Norway spruce.Tree position data for model fitting were collected from five trial sites in southern Sweden, one of which was documented with terrestrial laser scanning to get crown shape data for knot size modelling. A method that optimizes the target diameter dependent on the discount rate and the degree of the local competition exposed to the subject tree, was developed. Technically, a defined adaptive control function was optimized with full system stochastic simulation and with expected present value as the objective function variable. Since the quality of the optimization is dependent on the quality of the models in the simulation, priority was given to the evaluation and development of the central models. Available individual tree growth models were tested and evaluated with tree data from long term uneven-sized trial plots. Furthermore, new individual-tree distance-dependent growth models were developed for uneven-sized Norway spruce. A modelling framework, for prediction of the largest knot size per stem height section, was developed to provide means of simulating log quality depending on impact from local tree competitors.The results indicated that the thinning intensity in uneven-sized stand structures may be used to actively control the transition point where smaller diameter classes are subjected to suppressed growth. The evaluation of the Swedish individual-tree growth models which are included in the HEUREKA forest simulator, showed underestimation of large trees and overestimation of small trees. The underestimation is smaller or absent in denser forests for diameter classes above 40 cm. The new distance-dependent growth models are presented in two versions, one with and one without crown ratio as a predictor. The new growth models facilitate the testing of spatial decision criteria in ITS optimization. From the results of the ITS optimization, field operators can choose either a fixed level target diameteror a flexible target diameter that is adaptive to the degree of local competition surrounding the subject tree. Optimal fixed target diameters at breast height range from 33 cm to 23 cm depending on discount rate (1–3 %). A decision support structure for ITS is proposed.
|
|
