Effect of altitude and disturbance on structure and species diversity of forest vegetation in a watershed of central Himalaya

The Phakot watershed of Central Himalaya harbours two forest types; Anogeissus latifolia subtropical dry deciduous forest (600 - 1200 m asl) and Quercus leucotrichophora moist temperate forest (1500 - 1900 m asl). We assessed the disturbance level in these forests and analyzed its effect on species composition and diversity. Three levels of disturbance (undisturbed, moderately disturbed and highly disturbed) were identified within both the forest types on the basis of canopy cover, tree density and light attenuation. The canopy cover and light attenuation were higher in the Quercus leucotrichophora forest as compared to the Anogeissus latifolia mixed forest. Asteraceae was the dominant family at all disturbance levels in both forest types. Tree density was higher in the Anogeissus latifolia mixed forest, while shrub and herb density was high in Quercus leucotrichophora forest as compared to the Anogeissus latifolia mixed forest. A sharp decline in tree density and basal area was recorded with increasing disturbance level in both the forests. Species richness (number of species per unit area) of trees, shrubs and herbs declined with disturbance, except for the highly disturbed Anogeissus forest which was more species rich than the undisturbed or moderately disturbed forest.