Deforestation and degradation in tropical mountains is a global concern for the loss of biodiversity and ecosystem function. The eastern Himalayan forest ecosystems in India have seen significant transformations in recent decades, but the ecological and socioeconomic drivers of these changes are poorly understood. We studied recent forest transformations, tree diversity, and socioeconomic factors in the elevation range 500-3200m in the Teesta River Basin of the Eastern Himalaya in India. We assembled Landsat Satellite data covering two decades, sampled tree diversity using 147 plots of 0.1 ha each, and conducted questionnaire sample surveys at 10 locations covering >1000 households accounting for >5000 individuals for quantifying socioeconomic attributes. We used extensive ground measurements of forest composition and structure to classify Landsat data and study forest transformation over time. We used the decision-tree based algorithm ‘randomForests’ for landcover classification, and predictions of species diversity and tree size diversity for the landscape. Socioeconomic surveys yielded data on land holdings, forest resource dependence, incomes, governance, institutional arrangements, and observations of environmental change. We tested how forest transformations may be correlated with topography, mediated through decisions on landuse by local communities, and how forest resource dependence and governance may be driving forest transformations.
Results/Conclusions
During 1990-2013, forest cover declined by over 30% in the mid elevation (800-2200m) ranges, which has the most species rich broadleaf forest. There was 16% decline in forest cover overall, which was associated with increases in area under agriculture and secondary forest. Although agricultural expansion has now ceased, transformation of primary forest to secondary formations appears to continue. While environmental factors explained about half the variation in tree species abundances among sites, Shannon’s species diversity and Shannon’s size diversity were poorly related to the environmental variation, indicating that landuse history was an important factor. In terms of land holding the primary forest at low and middle elevations were privately owned, while at higher elevations primary forest was in protected areas. Most of primary forest was present at higher elevations and steeper slopes, indicating peoples’ choice and influence on forest transformation. Most of the incomes were from agriculture and forest resources contributed less than half the incomes. Over 90% of respondents said they have witnessed increases in temperature, incidence of crop disease, and water stress for drinking and agriculture, and have resorted to changing cropping patterns. However such changes have not led to increase in conflicts over access to land or resources.