Röjningsförbandets betydelse för avverkningsekonomin i södra Sverige
The aim of this work is to demonstrate how the net present value (NPV) at the time of the first thinning depends on the spacing after pre-commercial thinning, and show how net value from first thinning in same stand is influenced.
This study is performed with models based on non-distant dependent growth models for single trees. Two different growth models have been used, one for cleaning (pre-commercial thinning) and one for thinning. The first one yields stem density distributed over diameter classes. In the second one, (the thinning model), it is possible to choose when thinning should be done, the thinning method, thinning grade and numbers of thinning. Growth functions that are not influenced by thinning are applied. The models have also been used in project ?Hugin?.
The rate of interest used at the calculations, the silviculture and quality aspech are also discussed.
The conclusion of this project is that it might be reasonable with more information about the importence of different spacings for the NPV under different rates of interest. According to the results in this study, it also might be conceivable to make a reduction of recommended stem density before first thinning in ?The Royal Boards? (Skogsstyrelsens) template for thinning?, (when rate of interest is 2 %), especially for spruce.
The reduction of recommended stem density before first thinning is in the region of:
Pine
T20: 0
T24: 100
T28: 500
Spruce
G24: 500
G28: 600
G32: 600
G36: 600
This study do not consider that a lower stem density gives higher cleaning cost.