Relative proportion of dominant tree species across diameter classes in less-disturbed mid-elevation forests of the western Hyrcanian region

Document Type : Research Paper

Authors

1 Department of Forestry, Faculty of Natural Resources, Lorestan University, Khorram Abad, Iran.

2 Department of Forest Sciences and Engineering, Faculty of Natural Resources, Sari Agricultural Sciences and Natural Resources, Sari, Iran.

3 Department of Forestry and Forest Economics, Faculty of Natural Resources, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

4 School of Forestry, Northern Arizona University, Flagstaff, Arizona, USA.

10.22059/jfwp.2025.400354.1363

Abstract

In uneven-aged forests, analyzing the relative proportion of species across diameter classes provides a clearer understanding of their ecology than simply examining diameter distribution. This study was conducted in the relatively undisturbed Gorazbon District of the Kheyrud Educational and Research Forest (prior to logging in 2009) to investigate tree species composition and the relative proportion of species across different diameter classes. Data were obtained through complete enumeration over 770 ha, and all trees with diameter at breast height (DBH) greater than 7.5 cm were grouped into seven 25-cm diameter classes. Results showed that Carpinus betulus was the most abundant species (50.3%), but its relative proportion declined sharply with increasing diameter, indicating its comparatively short lifespan, high decay rate, and weak competitive ability in later successional stages. In contrast, Fagus orientalis (31.3% of all trees) dominated the large-diameter classes, constituting more than 60% of trees above 85 cm DBH, confirming its long-lived, climax characteristics. Quercus castaneifolia displayed a U-shaped pattern, with notable presence in both smaller and larger diameter classes. The analysis of relative proportions revealed that species do not necessarily follow the same behavior along the successional pathway. These findings demonstrate that merely observing declining diameter distribution is insufficient to uncover ecological differences, lifespan, and spatial competitiveness among species. Instead, analyzing relative proportions within diameter classes provides a deeper understanding of survival dynamics. The results can serve as a foundation for developing predictive models of species composition, optimizing tree-marking practices, and formulating sustainable harvesting guidelines for the Hyrcanian forests.

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Main Subjects

References

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Forest and Wood Products
Volume 78, Issue 3
November 2025
Pages 333-346

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