Structural analysis of veteran trees and their neighbors in Hyrcanian forest types (Case study: Baharbon district of the Kheyroud Forest)

Document Type : Research Paper

Authors

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

2 Forest and Rangeland Research Devision, Kermanshah Province Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization, Kermanshah, Iran.

3 Department of Statistics and Mathematics, Gonbad-Kavoos University. Gonbad-Kavoos, Iran.

10.22059/jfwp.2026.401213.1367

Abstract

Introduction: Old-growth trees are recognized as key components of the functioning, stability, and biodiversity of natural forests, especially in the Hyrcanian forests. This study aimed to analyze the structural characteristics and spatial distribution patterns of Oriental beech (Fagus orientalis) old-growth trees and their neighboring trees in two different forest types (pure beech and mixed beech with other species) in the Baharbon district of Kheyroud Forest, northern Iran.
Method: Old-growth beech trees were identified based on diameter at breast height (DBH > 100 cm). A total of 47 sample plots (0.5 ha in the mixed type and 1 ha in the pure type) were established around old-growth trees. Within each plot, all trees with DBH > 7.5 cm were measured, and their species were recorded. Structural attributes, including mean DBH, dominant height, dominance index, diameter and height differentiation indices, species mingling index, and uniform angle index (for spatial pattern), were calculated. In total, 310 structural groups in the pure beech type and 411 groups in the mixed type were analyzed. An independent t-test was used to compare the indices between the two forest types.
Results: Oriental beech was the dominant species, with 256 old-growth trees in the pure type and 138 in the mixed type. In terms of vegetative dimensions, alder (Alnus subcordata) had the largest size in the pure beech type (mean DBH = 103.4 cm, mean height = 40.8 m). Hornbeam (Carpinus betulus) was the second most frequent species in the mixed type (153 trees) but had smaller dimensions. The uniform angle index indicated a relatively regular distribution pattern in both types. The species mingling index was significantly higher in the mixed type. The independent t-test revealed that only species mingling and height differentiation showed statistically significant differences (P ≤ 0.05) between the two forest types. Other indices, including diameter differentiation, dominance, and the uniform angle index, did not differ significantly.
Conclusion: The results emphasize that the mere presence of old-growth beech trees does not create strong structural differentiation at the horizontal level. Instead, the key differences between pure and mixed beech types are reflected in qualitative stand features, vertical competition for light (expressed by height differentiation), and neighborhood species diversity (expressed by the mingling index). In other words, while the spatial distribution pattern of old-growth trees is similar in both types, the vertical structure and species composition surrounding them differ significantly. These findings are crucial for conservation-oriented management of Hyrcanian forests, suggesting that preserving old trees alone is insufficient; attention must also be paid to the ecological context, including species diversity and vertical interactions. 

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References

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Forest and Wood Products
Volume 79, Issue 1
June 2026
Pages 19-34

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