Terrestrial ecosystems of Kostomukshsky strict nature reserve, as a key element of the Green Belt of Fennoscandia, are mainly represented by forest communities. The typological spectrum, quantitative ratio, spatial distribution and internal structure of forest coenoses are discussed in connection with the landscape characteristics of the study area. The reserve‘s forests are most typical of the north taiga subzone of East Fennoscandia. Dynamics of the forest communities is analysed in relation to identified patterns of the fire regime in the past millennia. Severity and consequences of past human impact on the forest cover are assessed.