Do Gibbons Live in Dense Forest? A Case Study from Upper Brahmaputra Valley, Assam, India

Abstract The present study aimed at predicting the potential habitat of Western Hoolock Gibbon (Hoolock hoolock) in the upper Brahmaputra river valley, Assam and to identify the conservation priority areas for systematic conservation of the species taking canopy cover into account. We used the maximum entropy algorithm for the prediction of the potential habitat of Gibbons using its current distribution with 19 environmental parameters as primary predictors. Spatio-temporal analyses of the habitat were carried out using satellite-based remote sensing and GIS techniques for two decades (1998–2018) along with Terra Modis Vegetation Continuous Field product to examine the land use land cover (LULC), habitat fragmentation, Normalized Difference Vegetation Index (NDVI) and tree cover percentage of the study area. To identify the conservation priority area, we applied a cost-effective decision-making analysis using systematic conservation prioritization in R programming. The model predicted an area of 6025.1 km2 under high potential habitat, and a major part of it was found to overlap with the dense forest (80.04%) followed by moderately open forest (73.90%) and open forest (65.82%). The LULC change matrix showed deduction of forest areas in the predicted high potential habitat during the study period, while agricultural class showed an increasing trend. The fragmentation analysis indicated that the number of patches and patch density increased from 2008 to 2018 in the ‘very dense’ and ‘dense’ canopy regions of the gibbon habitat. Based on the conservation priority analysis, 640 km2 area has been proposed to conserve a minimum 10% of the gibbons’ habitat. The current analysis revealed that in Upper Brahmaputra Valley most of the areas under dense forest and dense canopy have remained intact over the last two decades, at least within the high potential habitat of gibbons independent of the degree of area change in forest, agriculture and plantation.