A case of high tree diversity in a sal (Shorea robusta)-dominated lowland forest of Eastern Himalaya: Floristic composition, regeneration and conservation

A seasonally dry, Sal (Shorea robusta)-dominated forest in the Eastern Hima layan lowlands of the Mahananda Sanctuary, Darjeeling had a far greater spe cies richness (87 species in greater than or equal to 10 cm and 69 species in greater than or equal to 30 cm girth class) and diversity than other sal forests in India. Euphorbiaceae, with 8 species, was the most speciose fam ily followed by Lauraceae, Meliaceae and Leguminosae. Dispersion of species was either clumped or random, and only two species were uniform. Rare spec ies (less than or equal to 1 stem ha(-1)) constituted 36% of the flora and were randomly distributed. Tree species dominated the flora with 87.3% shar e. Mixed dominance of species groups prevailed in the forest, i.e. large, m edium and small trees and shrubs shared stand density in nearly equal propo rtions, but climbers were less abundant. Among five most abundant species, none was a large tree. However, four of the five species accumulating maxim um basal area were large trees. All the girth classes showed a multi-specie s dominance, with 21 species in mature ( greater than or equal to 180 cm gi rth), 40 in elder (greater than or equal to 90 to < 180 cm), 55 in young ( greater than or equal to 30 to < 90 cm), and 68 in juvenile class ( greater than or equal to 10 to < 30 cm). Six species were available only in seedli ng layer (greater than or equal to 30 cm height to < 10 cin girth). Thus of all 93 species, 20.4% showed good regeneration, 10.8% fair, 30.1% poor and 17.2% lacked regeneration. The remaining 21.5% species seem to be reappear ing. While high-grade timber species were poorly regenerating, shrubs and c limbers were regenerating well. Despite legal protection, this diverse sal forest continually experiences anthropogenic interference by the inhabitant s on fringes. Rare species that contribute maximum to the tree diversity ar e at high risk of local extinction.