Changes of structural attributes mixed beech stand in different tree stories Shastkalateh forest, Gorgan

Structure of forest ecosystems undergoes changes in the temporal and spatial scale that this changes cause development. Development process is very slow and takes place in long term in this unites. For evaluation of this changes are used density, canopy and mixing amount. Structural attributes, show the ecological diversity and sustainability of forest ecosystems well. We conducted this study to compare changes in the structural attributes of density and canopy with diversity of tree species between different stories, as well the relationship these variables with diversity indices, between two periods of inventory in fixed location and natural environment where external factors have the least proportion in stand development.

Permanent sample plot with an area of 16 ha is located at 770-920 elevation and Northwest and west directions in 32 compartment, district one Shast Kalateh forest. Inventory was carried out using 100 % sampling method with 1 ha sample plot. Differences from 2003 to 2023 quantitative attributes of density, canopy and biodiversity indices were measured with standard method and compared through ANOVA in different stories.

The density of trees in the investigated plot reduced from 306.31 to 275.44 trees per hectare in 2003 and 2023. Only, Beech (Fagus orientalis Lipsky) species increased in density during this period. The highest frequency of tree individual belonged to under story in 2003, but in 2023, it was transferred to middle story. The average crown coverage percentage reduced from 86% to 70%. The highest amount of canopy percentage assigned to middle and upper stories. The average of Shannon's heterogeneity in 2003 in three story was (1.32, 1.29, 0.72) and in 2023 (0.49, 0.53, 0.58) respectively. The Shannon Wiener diversity index provided a better judgment of the species diversity in the investigated plot than other indices.

The investigated plot is a Mixed beech stand in which Beech shade tolerance species is dominant. Mixing more tree species while increasing diversity at different levels will bring stability of forest ecosystems. The results of this research showed that the indices of species diversity are only one of the methods of interpretation and evaluation of forest ecosystems and other characteristics should also be paid attention to. The periodic monitoring of this indices correctly shows changes trend of forest ecosystem. The results of used indices can be basis of evaluation and comparison with similar forest. Keywords: Structure dynamics, Diversity, Tree strata, Mixed beech stand