Relationship of Tree Stand Heterogeneity and Forest Naturalness

The aim of our study was to investigate if compositional (tree species richness) and structural (vertical structure, age-structure, patterns of canopy closure) heterogeneity of the canopy layer is related to individual naturalness criteria and to overall forest naturalness at the stand scale. The naturalness values of the assessed criteria (tree species composition, tree stand structure, species composition and structure of shrub layer and forest floor vegetation, dead wood, effects of game, site characteristics) showed similar behaviour when groups of stands with different heterogeneity were compared, regardless of the studied aspect of canopy heterogeneity. The greatest difference was found for criteria describing the canopy layer. Composition and structure of canopy layer, dead wood and total naturalness of the stand differed significantly among the stand groups showing consistently higher values from homogeneous to the most heterogeneous group. Naturalness of the composition and structure of the shrub layer is slightly but significantly higher in stands with heterogeneous canopy layer. Regarding other criteria, significant differences were found only between the homogeneous and the most heterogeneous groups, while groups with intermediate level of heterogeneity did not differ significantly from one extreme. However, the criterion describing effects of game got lower naturalness values in more heterogeneous stands. Naturalness of site characteristics did not differ significantly among the groups except for when stands were grouped based on pattern of canopy closure. From the practical viewpoint it is shown that purposeful forestry operations affecting the canopy layer cause changes in compositional and structural characteristics of other layers as well as in overall stand scale forest naturalness.