Topographical influence on recent deforestation and degradation in the Sikkim Himalaya in India; Implications for conservation of East Himalayan broadleaf forest

Context Land-cover change in tropical mountains is a significant concern for the loss of biodiversity and ecosystem function. In the eastern Himalaya, knowledge on the factors driving these changes is currently inadequate to development conservation and management plans. Objectives: We computed land-cover change over a 23-year period for the Sikkim Himalaya in India for the elevation range 800-2800 m using Landsat satellite data and an extensive set of ground measurements of vegetation types and other landuse. We then tested how these land-cover changes may be influenced by topography, mediated through decisions on landuse. Methods: We carried out supervised classification using 'Random Forests', and ensemble-based classification algorithm that is robust and accurate. We then used linear discriminant analyses to test which of seven common topographical variables can be used to discriminate the different land-cover types. Results: The primary forest in the 800-2200 m elevation range was warm broadleaf forest, whereas the primary forest in the elevation 2200 m-2800 m was Fagaceae dominated forest. Forest cover declined by over 30% in warm broadleaf forest, and primary forest declined by 16% overall, with concomitant increases in secondary forest and agriculture. Elevation was the strongest discriminant of landuse, followed by slope and aspect, presumably reflecting peoples' choice on landuse based on topography. Conclusions: Tropical montane forests continue to decline in the Sikkim Himalaya, particularly at lower elevations. Topographical factors determine landuse decisions by local communities.