Deadwood Structure and Species Diversity in Managed Stands of the Hyrcanian Forests

Deadwood is a fundamental structural and functional component of forest ecosystems, influencing biodiversity, nutrient cycling, and natural regeneration. Despite its ecological significance, coarse woody debris (CWD) stocks in managed forests are often markedly reduced compared with natural stands. This study quantified the diversity, density, and volume of both standing and fallen deadwood across six selectively managed forest sites in the Hyrcanian region of northern Iran—Chehel-Chay, Beliran, Do-Hezar, Se-Hezar, Zilakyrood, and Faryrood. Using full inventories within 2500 m² plots, all CWD ≥ 7.5 cm diameter was measured, classified by species, diameter class, decay stage, and structural type. Species diversity (α-, β-, and evenness indices) was calculated, and differences in CWD characteristics among sites were tested with ANOVA, PERMANOVA, SIMPER, and canonical correspondence analysis. Generalized linear mixed models were additionally employed to evaluate environmental and management drivers of CWD density and volume. Results revealed substantial variability in CWD profiles across sites, with Faryrood consistently exhibiting the highest density and volume of both snag and log, particularly for Fagus orientalis and Carpinus betulus . Diameter-class distributions and decay-stage frequencies also differed significantly, reflecting contrasting disturbance histories and management intensities. Multivariate analyses identified elevation, slope, and management history as the primary predictors of CWD composition. Overall, the study provides critical benchmark values for CWD in managed Hyrcanian forests and demonstrates that current management regimes influence both the quantity and structural diversity of deadwood. These findings highlight the importance of integrating deadwood retention targets into close-to-nature silvicultural planning to maintain habitat quality and support long-term ecosystem functioning.