Tree-related microhabitat characteristics in hemi-boreal production forests: The role of DBH and stand heterogeneity
Gailenė Brazaitytė, Michael Manton, Žydrūnas Preikša, Vitas Marozas, Gediminas Brazaitis
Abstract
Tree-related microhabitats (TreMs) support a multitude of forest-dwelling species by providing food and shelter. Although the primary goal of forest management remains wood production, modern practices prioritise multifunctionality which promotes biodiversity, and non-timber benefits. This requires the development of biodiversity indicators and evidence-based benchmarks. Focussing on mature hemi-boreal production forests, this study explores tree- and plot-level microhabitat characteristics by analysing (I) abundance and occurrence of tree-related microhabitats, (II) richness of tree-related microhabitat types, and the impacts of (III) diameter at breast height (DBH), and (IV) stand heterogeneity. In total, we surveyed 76 production forest stands of different dominant tree species. Results showed TreMs occurred on 23.2 % of the surveyed trees. The number of TreMs per tree ranged from zero (76.8 %) to one (18.8 %) and two (3.4 %), while three to six microhabitats were observed rarely (1 %). Tree species was a significant factor for TreM occurrence, varying from 17.3 % to 71.9 % of TreM trees in deciduous species, to less than 10 % in coniferous Scots pine and Norway spruce. The most common TreM types were deformations / growth forms (26.5 %) and epiphytes (25 %). Results revealed that the probability of TreM occurrence increased significantly with DBH in Scots pine, silver birch, small-leaved linden, European aspen, pedunculate oak, and Norway maple, with a mean critical threshold of 51.5 cm DBH for deciduous species, whereas the critical thresholds for the two coniferous species, and black alder were not found. On the plot-level, richness of TreM types had significant positive correlation with tree species richness ( r = 0.39, p < 0.02), and heterogeneity of basal area ( r = 0.29, p < 0.001) and DBH ( r = 0.3, p < 0.001). This study reveals that in mature hemi-boreal production forests TreM characteristics are influenced by tree species, DBH and stand structural diversity. Our results suggest that deciduous species are more significant contributors to biodiversity through microhabitat provision compared to conifers. In production forests, both TreM trees, and potential TreM trees with larger diameters should be retained during commercial harvests.