Quantitative characteristics of natural regeneration of woody species in managed stands of Hyrcanian forests, Iran

 
Background and objectives: Natural regeneration is considered one of the most important factors affecting the survival and sustainability of natural forests. Understanding the diversity, distribution, and status of natural regeneration of woody species provides important insights into the ecological health and services of forest ecosystems and helps predict future forest sustainability. Considering the ecological and productive importance of Hyrcanian forests, it seems necessary to conduct a comprehensive study on the status of natural regeneration in these forests. Therefore, the aim of this study is to investigate the quantitative status of natural regeneration of woody plant species in managed stands of Hyrcanian forests in northern Iran.
Methodology: To carry out this study, four forest landscapes in the Hyrcanian forest were selected, including Fariroud - Zilkiroud (watersheds 22 and 23) in Gilan Province, Dohezar - Sehezar (watersheds 33 and 34) and Beliran (watershed 53) in Mazandaran Province, and Chehel Chai (watershed 92) in Golestan Province. Using a systematic random sampling method, small sample plots of 4 m² were selected at the intersection of a 150 × 200 m² inventory grid, totaling 34,723 sample plots (Fariroud 5,345 sample plots, Zilkiroud 4,377, Dohezar 5,185, Sehezar 7,522, Beliran 6,847 and Chehel Chai 5,447) to investigate regeneration. All seedlings and saplings within the sample plots were counted, and their quantitative characteristics were measured. In each forest habitat, the quantitative status of species regeneration including tree species type, growth stages, growth form, number of regenerations, collar diameter and seedling height were identified and measured. Natural regeneration in each habitat was classified into three classes of collar diameter: less than 2.5 cm, 2.5-7.5 cm, and 7.5-12.5 cm, and three height classes of less than 30 cm, 30-130 cm, and more than 130 cm by woody species. Graphs and analyses were performed in Excel and SPSS 26.
Results: The highest and lowest regeneration frequencies of woody species were beech (Fagus orientalis Lipsky) (38.03%) and oak (Quercus castaneifolia C.A.Mey.) (0.95%), respectively. Also, the class of collar diameter less than 2.5 cm had the highest frequency (74.13%), and the class of collar diameter 7.5-12.5 cm had the lowest frequency (9.3%). The height class less than 30 cm had the highest frequency (69.38%), and the height class greater than 130 cm had the lowest frequency (10.35%). Comparison of the frequency percentage of species with a collar diameter of less than 2.5 cm showed that the highest and lowest frequencies were in the Zilkiroud and Chehel Chai habitats, respectively. The highest frequency percentage of species with a collar diameter of 2.5-7.5 cm was in the Zilkiroud habitat, and the lowest was in the Sehezar habitat. By comparing the frequency percentage of thickets with collar diameter 7.5-12.5 cm, the highest frequency was observed in the Fariroud habitat and the lowest in the Sehezar. Comparison of the natural regeneration frequency of different woody species showed that the highest percentage of regeneration frequency in Chehel Chai habitat was for oak (72.87%), in Beliran habitat for maple (Acer velutinum Boiss.) (40.61%), in Fariroud habitat for hornbeam (Carpinus betulus L.) (29.31%), and in Dohezar, Sehezar, and Zilkiroud habitats with frequencies of 60.59, 90.5, and 53.54%, respectively, for beech. The results of one-way analysis of variance (ANOVA) indicate a significant difference in seedling species diversity among different forest stands in terms of height and collar diameter with a probability of 95%.
Conclusion: The managed stands of the western Hyrcanian forests (Fariroud - Zilkiroud forest landscape) have more young seedlings (collar diameter less than 7.5 cm) compared to the managed stands of the eastern Hyrcanian forests (Chehel Chai forest landscape), and the managed stands of the eastern Hyrcanian forests (Chehel Chai forest landscape) have more regeneration seedlings with a collar diameter of 7.5-12.5 cm and a height of more than 130 cm. This indicates the establishment of favorable regeneration in the eastern Hyrcanian forests and the presence of unfavorable environmental factors in the western Hyrcanian forests.