Seedling Potential Attributing Ecological Variables: Trees Species Diversity along an Elevational Gradient in the Temperate Hill Forest, Central Nepal

Present research examined the tree diversity and their regeneration patterns along an elevation gradient in the temperate hilly forest, Central Nepal. Data were collected from 300 sample plots of 10 x 10 m 2 each. A total of 10 elevation bands of 100 m difference sampled from 1365 to 2450 m asl. A random sampling method was used to collect information in three seasons, winter, pre-monsoon and post monsoon seasons. Circumference at breast height (CBH) was used to broadly categorize the plant species into trees, saplings and seedlings. Present study found nearly ninety percent tree species were at regenerating stage. The tree species richness ranged from 12 to 25 with density of 350 to 1200 individuals per hectare. Species richness of tree and sapling showed statistically significant unimodal pattern, peaked at mid-elevation. Elevation showed a strong and positive linear relationship with the seedling density (Deviance = 0.99, p < 0.001) and significant hump shaped relationship with sapling density (Deviance = 0.95, p < 0.001). Similarly, elevations showed statistically significant negative hump shaped relationship with all tree, sapling and seedling's Simpson indices (Deviances = 0.89, 0.87 and 0.57). The highest values of the Shannon-Weiner index and lowest value of the Simpson index were found at mid-elevation for all growth forms. In the study area, 49% tree species found in a good renewal status, 32% were in fair renewal, and 11% at a poor regenerating condition. Nevertheless, 4.3% tree species were reported as non-regenerating stage and 4.3% were newly introduced species. Hence, the regeneration status of the study area was considered as fairly good since sapling (78.5%) > seedling (10.6%) ≤ mature (10.9%). Among tested environmental variables elevation, annual mean rainfall, aspect, slopes, pH, N and annual mean temperatures were the most influential factors in regeneration of trees species.