This paper presents the results of investigations on natural forest regeneration in Norway spruce (Picea abies L. Karst.) monocultures in the Ukrainian Beskids with the use of FORKOME model prognostic possibilities. Different variants of regeneration methods are presented. Selective cutting with planting was determined as the most effective: spruce selective cutting with simultaneous planting of target species: beech (Fagus sylvatica L.) and fir (Abies alba Mill.) with admixture of ash (Fraxinus excelsior L.). Beech and fir biomass increases rapidly over the first 20 years -then it stabilizes. After another 20-30 years the initial form of beech forest is recognizable and it is possible to speak about an increase of beech forest, which in the course of time achieves a higher degree of similarity to natural stand. In the Ukrainian Beskids the potential forest stand consists of beech and fir (Dentario glandulosae-Fagetum).

Results of investigation of fir forest dynamics in the Bieszczady Mountains using a FORKOME (FORest KOzak MEnshutkin) model in response to climate changes are presented. The model was verified in field trials in 1998–2001 in a fir forest in forest district Procisne in the Bieszczady Mountains (Poland). Prediction of tree biomass and tree number was made for the next 600 years. The simulation demonstrated beech domination when mean annual temperature increases by 2°C while with a decrease in temperature by 2°C fir becomes dominant in the examined area. Both one simulation run and Monte Carlo simulation showed comparable results in statistical analysis. The results of FORKOME model simulations enable to set a thesis that forest succession may be used for evaluating the level of climate-change influence on forest ecosystems. Presented results indicate great usefulness of the model while investigating various subjects, especially concerning climate changes, which may have both theoretical and practical importance.