Species diversity, regeneration and early growth of Sal forests in Nepal

Forest disturbance has been the subject of intense research for many years, but the synergistic effects of various disturbance factors on the forest vegetation are not well documented, particularly in Sal forests. In this thesis, the nexus between a bundle of inherent disturbances of varying intensities and the diversity and/or regeneration of Nepalese Sal forests was examined. In addition, the effects of a single disturbance factor – tree fall gaps – on species diversity, regeneration and early growth of Sal forest were assessed. The intensity of the combined inherent disturbances in each of the studied forest was calculated, and was found to have differing effects on various aspects of the forest vegetation. The total stem density of saplings and poles increased with increasing disturbance intensity, to a certain level, while most of the tree species in the community showed changing dispersion patterns along the disturbance gradient. Socially preferred tree species displayed high regeneration performance in forests subjected to moderate level of disturbance. Tree fall gaps favored regeneration by increasing the density of seedlings of some socially preferred tree species (including Sal) and promoted the maintenance of high species diversity. However, neither overall species diversity nor regeneration positively correlated with gap size, suggesting that the maintenance of species diversity and regeneration in gaps are related more strongly to several other attributes of gaps than gap size. Generally, forests subjected to moderate level of disturbance maintained species diversity and enhanced regeneration performance, which in turn was coupled with the regeneration strategy of dominant tree species – in line with the Intermediate Disturbance and Recruitment Limitation Hypotheses. In conclusion, the findings signify that moderate level of disturbance may be touted as a management tool for Sal forests.