Community Structure and Regeneration of Sub-alpine Abies spectabilis (D.Don) Mirb. Forest in Langtang National Park, Central Nepal

Abstract

Community structure and regeneration of Abies spectabilis (D.Don) Mirb was studied in Abies spectabilis forest located between Chandanbari and Lauribina area (3100-4000m) of Langtang National Park, Central Nepal. Vegetation sampling was done by quadrat method, and the sample quadrats were located by systematic random sampling method. Nine vertical transects running parallel to each other were defined within the study area and the quadrats were located along the transects. Altogether 80 quadrats were sampled. Canopy cover, litter and grazing/trampling damage in each quadrat were determined by visual estimation. Soil samples were collected from each quadrat from its four corners and their physicochemical characteristics were analyzed. Number of woody plant species, number of individuals of each tree species, diameter at breast height (DBH) of each individual tree, number of seedlings and saplings of tree species were recorded in each quadrat. Various community attributes (e.g. importance percentage, species diversity) and population characteristics (e.g. life table, density- diameter curve) were analyzed. Soil was slightly acidic with soil pH value 6.35. Soil carbon and soil nitrogen were 7.24% and 0.44% respectively. Twenty five woody species were recorded from the forest. Abies spectabilis was the dominant tree species with the highest importance percentage (84%) and Rhododendron campanulatum was the co-dominant species (5%). Simpson’s Index of Dominance (0.75) was more than Shannon Wiener’s Index (0.63). Species diversity of the forest was relatively low, which might be due to anthropogenic factors such as cattle grazing, fire wood collection and logging. Total tree density declined with increasing elevation between 3100 m and 3550 m but it increased from 3550 m towards treeline (4000 m).Density-diameter curve for all tree species combined was nearly reverse J- shaped, indicating sustainable regeneration. But the curve for Abies spectabilis alone deviated slightly from the typical reverse J-shape with lower density of the smallest size class than of the next size class. Mortality of seedlings was 98% and only 2% of seedlings developed into saplings. Very high mortality of seedlings might be due to high disturbance (grazing/trampling) by livestock. Therefore, regeneration of Abies spectabilis was not sustainable.