Evaluation of tree-related Microhabitats (TreMs) in the developmental stages at control stand of Kelardasht beech forests

Background and Objective: Sustainable management of forest ecosystems requires the use of appropriate biological indicators to assess forest ecological conditions. Tree-related microhabitats (TreMs) are among the most important of these indicators because they provide essential habitats for numerous animal, plant, and fungal species and are generally more abundant and diverse in natural forests or forests subject to minimal management interventions. These structures, which develop on living trees or standing deadwood, include water-filled tree holes, woodpecker cavities, insect galleries, and various other specialized structures that are important for the survival, feeding, and reproduction of many species. The aim of this study was to identify, assess, and compare tree-related microhabitats across different developmental stages of relatively undisturbed beech stands in the reference compartment of the Kelardasht region.
Material and Methods: The study was conducted in the reference compartment of Series 1 of the Langa Forest Management Plan, located in Watershed No. 36 (Kazemrud). Developmental stages were identified in the reference compartment based on Korpel's definitions in 2008. One 1-ha sample plot (100 × 100 m) was established in each of the initial, optimal (peak), and disintegration (decay) developmental stages, with the plot sides oriented along the four cardinal directions. Tree species and diameter at breast height (DBH) were measured and recorded for all trees within each plot. Tree-related microhabitats were identified according to the European Union's Integrate+ classification guide, comprising eight broad forms (cavities, injuries and wounds, bark, deadwood, growth forms/deformations, epiphytes, nests, and other microhabitats) and 20 groups, including woodpecker cavities, trunk cavities, branch cavities, water-filled tree holes, insect galleries, bark loss, stem and crown breakage, cracks and wounds, bark tears, bark structures, dead branches, dendrotelms, branch aggregations, cankers, fruiting bodies of wood-decaying fungi, non-specific fungal structures, cryptogams, nests, sap flows, and dendromicrohabitats associated with fine debris.
Results: In the initial, optimal, and decay developmental stages, 40.6%, 6.2%, and 16.8% of trees, respectively, lacked any tree-related microhabitat. The highest number of microhabitats recorded on a single tree was 13 on a beech tree with a DBH of 98 cm in the initial stage, 9 on a maple tree with a DBH of 43 cm in the optimal stage, and 10 on a hornbeam tree with a DBH of 56 cm in the decay stage. Of the 20 microhabitat groups examined, nests were not observed in any developmental stage. Except for water-filled tree holes, all other microhabitat groups occurred at their highest frequencies, with only minor differences, in the optimal stage, and their patterns of variation across developmental stages were generally similar. Although moss cover followed a similar pattern across all three developmental stages, its frequency was higher in the initial stage. Moreover, except for water-filled tree holes, the highest frequencies of microhabitats were generally recorded, with slight differences, on medium-diameter trees in the optimal stage, medium-diameter trees in the decay stage, and large-diameter trees in the optimal stage. The highest numbers of water-filled tree holes were recorded in the initial stage, particularly among large-diameter (32), small-diameter (23), and very large-diameter (16) trees. Insect galleries and wood-borer cavities were most frequent among small-diameter trees in the decay stage (9), exceeding their frequency in the other developmental stages. On average, 16.03% of trees (43.9 trees) had cavities, 2.11% (5.5 trees) had injuries, 8.03% (22.3 trees) had bark-related microhabitats, 3.02% (8.7 trees) had dead branches and crown structures, 19.29% (52.7 trees) had stem deformations, 12.72% (33 trees) hosted epiphytes, and 2.24% (3.3 trees) had other types of microhabitats. The mean number of microhabitats was 2.1 per tree, while 18.6% of trees hosted five or more microhabitats.
Conclusion: The formation of tree-related microhabitats varies according to tree species, site conditions, tree diameter, and forest management regime. Although microhabitat abundance generally increases with increasing DBH, some microhabitat groups may occur at high frequencies on small-diameter trees. Therefore, biodiversity conservation should encompass trees across a broad range of size classes. Particular attention should be given to retaining large-diameter trees supporting more than five types of microhabitats, as well as small-diameter trees bearing unique microhabitats. In addition, trees with the potential to develop microhabitats in the future should be incorporated into conservation planning.