Comparison of herbaceous cover and regeneration diversity in pure beech, pure hornbeam, and mixed beech-hornbeam stands (Case study; Darabkola educational-research Forest, Mazandaran)

 Biodiversity is one of the most important indicators of the sustainability of forest ecosystems, which is affected by stand mixture. Vegetation composition and diversity data are the most important basic information for recognizing the natural capacity and targeting for the principled management of forest habitats. On the other hand, the correct understanding of the regeneration status in the forest is the most important The components in predicting the future of the forest are in terms of structure and composition of tree elements. The aim of this study was to compare the diversity of herbaceous cover and regeneration in pure beech, pure hornbeam and mixed stands in Darbakola educational and research forest of Sari.

 For this purpose, the inventory was performed by randomized systematic method with grid dimensions of 75 × 100 meters and in each stand, 25 sample plots with an area of 400 square meters were implemented and the diameter and height characteristics of the trees were collected. To study biodiversity, names of herbaceous species and the type and number of regenerations were collected in 2×2 meter micro sample plots in four quarters and the center of the sample plots in two stages (May and September). Diversity indices of Shannon and Simpson richness indices of Margalf and Manhenick and evenness Owens and Burger Parker diversity indices were used to study the biodiversity of regenerations and grass cover. One-way analysis of variance was used to compare quantitative characteristics of biomass and biodiversity between habitats and to compare the means by SNK test in SAS software environment and to draw graphs using Excel-2010 software. Past software was used to study biodiversity.

 The results of the present study showed a higher density of beech regeneration in all three studied stands. The highest total number of regeneration was observed in mixed habitat (4040). The highest indices of diversity, richness and regeneration evenness were observed in pure hornbeam and the lowest in pure beech. Regarding herbaceous cover, no significant difference was observed between diversity indices among different stands, while the average of these indices was higher at the beginning of the growing season than at the end of the growing season. Therefore, stand mixture has more tangible effects on regeneration diversity than herbaceous cover, and herbaceous cover diversity is more affected by the during the growing season than type of stand mixture.

 Based on the results of the present study, the future composition of the studied populations will be affected by the dominant species of beech. Also, due to the species diversity in the mixed habitat, the highest total number of regeneration and forest density will be related to this stand. Regarding the grass cover, the higher average of diversity indices at the beginning of the growing season than at the end of the growth season, indicates that the environmental conditions are better in terms of temperature and soil moisture in this season. Therefore, mixing has more noticeable effects on regenerative diversity than grass cover and the difference in grass cover diversity is more affected by the time period of the growing season.