Structural dynamics of deciduous mixed stands in the Hyrcanian forests, northern Iran

Forest structure as an effect of forest dynamics can be used to characterize biophysical processes, biodiversity and ecosystem functions. This study examines the structural components of old-growth forest stands located in the Caspian forests, north of Iran. We measured forest-related attributes in five plots located in the Kheyrud Forest, Mazandaran Province, Iran in 2004 and 2014, respectively. The mean stand density was of 338.6 tree ha-1, the mean volume was of 389.2 m3 ha-1, and the volume of deadwood accounted for 34.1 m3 ha-1. The mean stocking volume per hectare was for beech: 3.95; hornbeam: 7.00; oak: 1.39; maple: 0.60 and other species: 2.55 m3 ha-1. Meanwhile, the mean volume of the felled trees, other cuttings, snags and logs were 31.3, 1.1, 12.6, and 21.5 m3 ha-1, respectively. The mean abundance of gap size on small (<200 m2), intermediate (200-500 m2), and large (>500 m2) classes were calculated as 53.5, 37.9, and 14.1%, respectively. No significant difference in size gap distribution was detected over 10 years, neither any gap size class. The coarse woody debris (CWD) percentage from total deadwood volume varied from 67% to 93%, whereas the fine woody debris (FWD) amount was estimated ranged between 7 and 33%. No significant differences between 2004 and 2014 was found for CWD and FWD. Comparison of spatial pattern results of tree species in 2004 and 2014 implies that there were no significant changes in the mingling index, uniform angle index, or diameter differentiation at species and stand levels, except oak and maple species that showed a significant change in diameter growing. In other words, despite the harvesting of the trees, spatial pattern indices have not changed significantly. These results indicate the performance of ecological forestry programs by foresters in the Hyrcanian Forest stands and their increasing consideration to the ecological principles of the forest. The results are useful in the sense that they characterize the stand structure components which are fundamental to performing silvicultural treatments based on the emulation of natural forest structural dynamics.