ارزیابی خردزیستگاه‌های درختی در مراحل تحولی راشستان‌های قطعه شاهد کلاردشت

Background and objectives: Sustainable management of forest ecosystems requires the application of biodiversity indicators. Tree-related Microhabitats (TreMs) can play these roles because they host specialized species that are directly or indirectly dependent on them and are generally more abundant and diverse in natural forests or forests that have not been managed for decades. TreMs are structures on living or dead trees that provide a specific habitat or habitat essential for at least part of the life cycle of species or species communities for development, nutrition, or shelter. They exhibit a wide range of structures (such as dendrotelms, Woodpecker cavities, insect galleries and bore holes, etc.) that are essential for many animal, plant, or fungal species, and several species are highly dependent on these specific microhabitats. Some, such as cavities, can host multiple species. The aim of this project was to identify and evaluate TreMs and compare their characteristics at different development stages in the less disturbed heathlands of the control compartment in the Kelardasht region.

Methodology: This study was conducted in district one of control compartment of Langa forest management plan in watershed no. 36 (Kazemrood). Developmental stages were identified in the control compartment based on Korpel's definitions at 2009. In each development stage, the initial, optimal and decay, one sample plot (100×100 m) were selected with four sides in the four geographical directions. Diameter at breast height of all tree species in each plot were measured. TreMs were identified based on the European Union's Integrate+ guide, including eight general forms (cavities, injuries and wounds, bark, deadwood, deformation /growth form, epiphytes, nests and other), 20 groups (woodpecker cavities, trunk and mould cavities, branch holes, dendrotelms and water-filled holes, insect galleries and bore holes, bark loss / exposed sapwood, exposed heartwood / trunk and crown breakage, cracks and scars, bark pockets, bark structure, dead branches and limbs / crown deadwood, root buttress cavities, witches broom, cankers and burrs, fruiting bodies fungi, myxomycetes, epiphytic crypto- and phanerogams, nests, sap and resin run and microsoil) and 64 subgroups, in the three sample plots.
Results: In the initial, optimal and decay developmental stages, 40.6, 6.2 and 16.8% of trees lacked any microhabitats, respectively. The highest number of microhabitats was observed in the initial stage (13) on a beech tree with a diameter at breast height (d.b.h.) of 98 cm, in the optimal stage (9 microhabitats) on a Cappadocian maple tree with a d.b.h. of 43 cm, and in the decay stage (10 microhabitats) on a hornbeam tree with a d.b.h. of 56 cm. Of the 20 microhabitat groups studied, no nests were seen in any of the developmental stages. Most microhabitats showed the highest abundance with a slight difference in the optimal stage, except the dendrotelms. The trend of changes in the frequency of other TreMs was approximately similar in all development stages, except the dendrotelms. Although the frequency of epiphytes on tree trunks showed a similar trend in all three development stages, the frequency in the initial stage was significant compared to the other two stages. Except for the dendrotelms, other microhabitats showed the highest abundance with a slight difference in the medium diameter class of the optimal stage, the medium diameter class of the decay stage, and the small diameter class of the optimal stage, respectively. The highest number of dendrotelms was counted in the large (32), small (23) and very large diameter (16) classes of the initial stage, respectively. Interestingly, the greater abundance of insect galleries and bore holes was observed in the small diameter class of the decay stage (9) compared to other diameter classes in other stages. On average, 16.03 % (43.9 trees) of trees per hectare belonged to cavities, 11.2 % (5.5 trees) to injuries and wounds, 8.03 % (22.3 trees) to barkof tree-related microhabitats, 3.02 % (8.7 trees) to dead branches and limbs / crown deadwood, 19.29 % (52.7 trees) to deformation /growth form, 12.72 % (33 trees) to epiphytes, and 24.2 % (3.3 trees) to other microhabitats (sap and resin run and microsoil). On average, the frequency of trees with 5 or more microhabitats in the three development stages was 18.6%. On average, 1.2 microhabitats were identified per tree in the all development stages. The abundance of TreMs varied by tree species.
Conclusion: The rate of formation of tree microhabitats varies greatly among different tree species, locations, and diameters of trees, as well as the type of forest management. Although the frequency of tree microhabitats increased with increasing diameter at breast height, some microhabitat groups showed high rates in small diameter trees. Therefore, tree conservation for biodiversity should concern trees of all sizes. For this purpose, in addition to large trees that host more than 5 microhabitats, protection of small diameter trees with specific microhabitats should also be considered. Therefore, in order to protect biodiversity, it is necessary to value not only forest stands and trees that have a more microhabitats, but also trees that have a high probability of forming microhabitats in the future due to the species or local environmental conditions. In this regard, adding quantitative microhabitat formation models to forest stand dynamics simulators is essential to better consider biodiversity conservation in forest management.