Assessing selected microhabitat types on living trees in Oriental beech ( Fagus orientalis L.) dominated forests in Iran

On the selected sites in the investigated Oriental beech ( Fagus orientalis L.) dominated forests in Iran with an extensive individual tree selection system, tree microhabitats (MH) are more influenced by tree level factors such as tree species and DBH than by plot level factors such as plot basal area or size and species diversity. Despite the ecological importance of tree microhabitats for biodiversity, there is a lack of information about the occurrence of microhabitat features in Hyrcanian forests in Northern Iran. The aims of this study were to assess selected MH types on living trees in forests managed with an individual tree selection system and forests unmanaged since at least 30 years and to study the effect of tree and plot level factors on their occurrence. A total of 120 circular sample plots were used to collect tree level microhabitat information at six different sites in Oriental beech forests in Iran. Pairs of managed and recently unmanaged forests were located at six sites. Generalized linear mixed models were employed to analyze (i) the effect of management on microhabitat occurrence, and (ii) to explain the occurrence of microhabitats at tree level. There was no significant difference in total number of assessed microhabitats per ha in forests managed with a low-intensity management regime with individual tree selection versus recently unmanaged forests (no management intervention for at least 30 years). Stem cavity with decay was by far the most frequent microhabitat type in managed (16.5 per ha) as well as in recently unmanaged forests (14.2 per ha). Hornbeam and oak trees have a higher probability to host microhabitats (bark loss, woodpecker cavity, and stem cavities) than the dominant oriental beech. Suppressed trees indicated by basal area of larger trees have a lower probability to show bark loss and conks of fungi. Models of microhabitat occurrence on trees have potential to support the development of management guidelines to foster biodiversity.