Tree species composition and diversity in relation to anthropogenic disturbances in broad-leaved forests of Bhutan

Abstract

We assessed the impact of anthropogenic activities such as selective felling and resource extraction on plant diversity and forest structure in the broad-leaved forests of Bhutan. The forest area was grouped into three zones according to human influence: settlement-agriculture, semi-disturbed, and natural forest. A total of 140 plant species were identified. Maximum species richness of trees (8 species/plot) was recorded in natural forests and least in the settlement-agriculture zone (3 species/plot). Shannon (1.73 ± 0.62) and Simpson diversity (5.49 ± 2.97) indices were highest for the natural forest zone as compared to the semi-disturbed (0.92 ± 0.74, 2.70 ± 2.05) and settlement-agriculture zones (0.74 ± 0.74, 2.24 ± 2.13). The density and basal area of trees decreased from 373 N ha−1 and 37.9 m2 ha−1 in the natural forest zone to 114 N ha−1 and 5.7 m2 ha−1 in the settlement-agriculture zone. The diameter distribution revealed a lack of commercial tree species in the higher dbh classes from the settlement-agriculture and semi-disturbed zones due to selective felling. Increasing accessibility and anthropogenic activities caused the reduction in biodiversity of the watershed. Selective felling and resource extraction created gaps which were colonized by non-timber species and this may change the forest structure.