Introduction: The study of the habitat value of old trees is crucial, as they are key factors in the structural heterogeneity of natural forest stands and play significant ecological and habitat roles. This research aims to investigate the microhabitat value of thick, old trees within the pure oriental beech type in the Baharbon district of the Kheyrud Forest.
Material and methods: Using forest cruising in a pure beech stand, 30 veteran trees were randomly identified and examined. Variables such as tree species with microhabitats and the types of observed microhabitats-including Wood pecker cavity, trunk base rot hole, buttress root concavity, canker, micro soil, trunk cavity, branch hole, crack in the bark, nest, stem fungi, crack in the stem and dead wood-were recorded. The frequency and microhabitat value of the veteran trees were then analyzed.
Results: The results of the study indicated that the stem gall microhabitat had the highest frequency among the observed microhabitat types, accounting for 22.16% of the total 1,530 recorded instances. In contrast, the branch cavity with 0.65% had the lowest frequency. The distribution of microhabitats among the three tree species -Acer velutinum Boiss., Fagus orientalis Lipsky., and Alnus subcoradata C.A.Mey - was 53.79%, 27.12%, and 19.08%, respectively. The highest frequency of microhabitats for Acer velutinum and Alnus subcoradata was associated with the stem gall, at 22.16% and 21.91%, respectively. In contrast, for Fagus orientalis, the highest frequency was observed for the large trunk cavity, at 17.83%. The lowest frequency of microhabitats for all three species- Acer velutinum, Alnus subcoradata , and Fagus orientalis -was associated with nesting sites, at 0.60%, 1.02%, and 0.72%, respectively. The branch cavity was entirely absent in beech. The highest frequency of various microhabitat elements was observed in - Acer velutinum within the macro class, with nine recorded instances. In contrast, the lowest frequency was observed in alder within the mega class, with only two instances. Additionally, the highest frequency of microhabitat elements in the mega class was recorded in Acer velutinum, with 11 instances. Conversely, the lowest frequency within the mega class was again observed in alder, with only two instances. Analysis of the frequency of habitat tree types using ANOVA at a 99% confidence level (p < 0.01) in pure beech stands revealed a statistically significant difference among the 12 studied groups.
Conclusion: The present study highlights the unique role of veteran trees-particularly Carpinus betulus and Alnus subcordata species-in the formation and diversity of forest microhabitats. These trees, due to their specific physiological, structural, and genetic characteristics-such as thick bark, wide crowns, heartwood decay, and gall formation-host a variety of habitat components critical for numerous organisms, including saproxylic species, birds, and epiphytes. The findings also suggest that focusing specifically on veteran trees, rather than conducting a general assessment of trees with microhabitats, may yield different results compared to some previous studies. In this study, the maple species was identified as the most prominent macrohabitat tree and, due to its high diversity of habitat features, has the potential to be considered a "macrohabitat tree." Therefore, in management programs-such as logging and exploitation operations-special attention should be paid to the habitat value of veteran trees and their role in the sustainability of forest stands.