The effect of environmental factors on the regeneration of Quercus semecarpifolia Sm. in Central Himalaya, Nepal

Poor regeneration of oak forest has been observed in north America and Eurasia. In the Himalaya it has mainly been explained by anthropogenic pressures. This study analyses the regeneration of two Quercus semecarpifolia Sm. forests (2-3000 m a.s.l.), where one forest has almost nil disturbance and the other has different degrees of canopy disturbance. The relationships between biotic and abiotic environmental variables and the number of Quercus semecarpifolia seedlings and saplings (i.e., recruits < 10 cm Diameter at Breast Height (DBH)) were analysed by means of Generalized Additive Models (GAM). The two forests were compared with respect to size-class distributions of mature trees (i.e., > 10 cm DBH), and the number of recruits. The size-class distributions indicate that regeneration is most reliable in the nearly undisturbed forest. Most recruits were found under high canopy cover and high potential radiation. Canopy disturbance has a negative effect on the number of seedlings. Seedlings seem to prefer a pH of around 6, Loss-on-Ignition between 20 and 30 %, and total nitrogen between 2 and 3 %. In general, there were very few plots with saplings, and there was not a clear relationship between the number of saplings and the soil variables. The size-class diagrams indicate a lack of young trees in the disturbed forest, and it is hypothesized that fire may inhibit recruits reaching the canopy phase.