Optimizing thinnings and rotation of Scots pine and Norway spruce mixtures

The study describes a simulation-optimization system which uses spatial mod els for diameter and height growth, crown ratio and tree mortality for Scot s pine and Norway spruce mixtures. The optimal one- and two-thinning regime s of six initial stands with varing species composition were solved by usin g nonlinear optimization. The soil expectation value (SEV) at 3 % interest rate was used as a management objective. The regimes are determined by taki ng into account the stand basal areas before the thinnings, the removal per centages for small, medium-sized and large pines and spruces, and the stand basal area before the final felling. The greatest SEV (8900 FIM ha(-1)) wa s attained with the initial stand where the proportion of pines was 65 % of the number of the stems. In the two-thinning regime, the first thinning wa s conducted at the age of 39 years when the stand basal area was 37 m(3)ha( -1) and the dominant height was about 15 m. After the thinning, the basal a rea was 27 m(3)ha(-1). Spruces were thinned from below, but both small and large pines were removed. The second thinning was 8 years later and much he avier: the stand basal area was decreased from 35 m(3)ha(-1) to 18 m(3)ha(- 1) by removing both small and large pines and spruces. When the optimal two -thinning regime was compared to the regime presented by Forest Centre Tapi o, the loss of SEV was about 30 % (6070 FIM ha(-1)) in the case of thinning s from below, and about 20 % (7250 FIM ha(-1)) in the case of thinnings fro m above.