Comparison of structural complexity index (SCI) in the developmental stages of Hyrcanian mixed beech forests

The structural complexity of forest stands is one of the most important characteristics of natural forests. Changes in the forest stand structure through the development of stands cause complexity in the stand structure. We conducted this research to quantitative analysis of structural complexity in the three stages of stand development in the Hyrcanian forests. Three one-hectare study areas were selected within developmental stages (Totally 12 hectares) and after forest inventory, the structure complexity index was calculated for each stage. We employed ten variables including stem per hectare, mean of diameter at breast height (DBH), coefficient of variation of DBH, diameter Gini coefficient, number of trees with a diameter larger than 100 cm at breast height, the ratio of the number of trees in different stories, the faction of canopy gaps, amount and volume of dead woods and tree size variation to calculate this index. The mean and median complexity index was 65.46 and 66.15. the highest value obtained in the terminal (transition) stage was equal to 84.17 and the lowest was 49.3 in the initial stage. The structure complexity significantly was higher in the terminal stage, meanwhile based on the Tukey test, the difference between the initial (58.85±3.33) and optimal stage (61.39±4.23) was not significant. Considering the role of diversity and complexity of forests structure on forest ecological functions like maintaining biological diversity, it is necessary to consider complexity in all interventions and forest tending operations. Also, we proposed the forest complexity enhancement besides maintaining biodiversity should consider as the most important goal of forest management plans.