Structure, composition and community ordination of tropical monsoon forest within the Makalu Barun Conservation Area of eastern Nepal
Zomer, Robert; Carpenter, Chris; Ustin, Susan L.; Ives, Jack D.
Low elevation forest vegetation within the river gorges of eastern Nepal is an important repository of biological diversity. Much of this biodiversity is currently threatened. Forests fragments along the bottom of the deep riparian corridors form networks of biological refugia within a highly utilized and disturbed zone. Remnant forests found on steep and inaccessible slopes provide important resources, both for local subsistence agriculturalists and wildlife species, some of which are threatened. Preservation of these forests, both within the Makalu Barun Conservation Area, and throughout the Himalayan region more generally, presents an important conservation challenge. Results summarize field studies conducted in the Makalu Barun Conservation Area of east Nepal from 1991 to 1994. Ecological and botanical data were collected within 30 (400 m2) quadrats and at a series of georeferenced ground control points along the Arun River and several of its tributaries. Five community types, within three major forest formations, were delineated by TWINSPAN analysis. Importance Value Index (IVI) was calculated for all tree species within each community. A direct gradient analysis of the distribution of dominant species along an elevational transect is modeled based upon a Gaussian distribution of IVI's. Dynamics and structure are described, including population age structure of the most abundant species. Forest community distribution is modeled relative to measured site topoclimatic variables and estimated anthropogenic use. Elevation, slope-position, aspect, and anthropogenic use-levels correspond (p < 0.05) to community composition, based upon a canonical correspondence analysis (CCA) of relative species abundance. Comparison of TWINSPAN groupings with the CCA ordination exhibits general agreement, showing a definitive separation of communities along topoclimatic and use gradients.