FOREST STRUCTURE AND REGENERATION OF Betula utilis D. DON IN MANASLU CONSERVATION AREA, Nepal
Forest structure and regeneration of Betula utilis (D. Don) was studied in Betula utilis forest located in Samagaun area (3500 – 4000 m) of Manaslu Conservation Area. Vegetation sampling was done by quadrat method. Five vertical transects running parallel to each other were defined within the study area and the paired quadrats (10 m × 10 m) spaced horizontally about 100 m apart was sampled at every 100 m elevation increment from 3500 m up to 4000 m. Altogether 40 quadrats were sampled to determine the Importance Value Index (IVI) of tree species, distribution pattern of seedlings and saplings, and soil attributes. Regeneration was assessed by density - diameter curve. Number of tree species, number of individuals of each tree species, diameter at breast height (DBH) and height of each individual tree, number of seedlings and saplings of tree species were recorded in each quadrat. Twelve soil samples were taken for laboratory analysis. Four tree species were recorded from the forest. Betula utilis was the dominant tree species with the highest Importance Value Index (173.22) in mixed Betula forest and 262.96 in Pure Betula forest and Abies spectabilis was the co – dominant species (65.95) in mixed Betula forest while Rhododendron campanulatum was the co-dominant species (37.03) in pure Betula forest. Simpson’s Index of Dominance was more than Shannon Wiener’s Index. Species diversity of the forest was relatively low, which might be due to anthropogenic factors such as cattle grazing, fire wood collection and logging. Density of Betula utilis was increased with increase in altitude where as density of other tree species were decreased with increase in altitude. Mixed Betula forest at lower elevation was young. The density diameter curve of the tree population of Betula utilis both on mixed and pure forests deviated slightly from the typical reverse J shaped structure and hence did not show the sustainable regeneration. The sapling density was higher than seedling density. The distribution of seedlings and saplings were not uniform among the sampling plots. There were no saplings on 25% of the plots and seedlings on 60%. In lower elevation saplings of Abies spectabilis and Larix himalaica were higher than of Betula utilis. If not severely disturbed, mixed Betula forest may be replaced by Abies spectabilis.