Assessing topographic controls on vegetation characteristics in Chittagong Hill Tracts (CHT) from remotely sensed data

The study aimed at assessing multi-scale correlation between vegetation characteristics and topographic parameters in Chittagong Hill Tracts (CHT), Bangladesh. Traditional shifting cultivation and its associated activities are considered unsuitable practices in CHT, therefore, the alternative land use systems e.g. agroforestry, tree farming, and afforestation are more suitable and sustainable in the region. We assessed the topographic controls on vegetation indices (NDII, NDVI, and EVI and their corresponding characteristics) to identify the potential sites for alternative land use practices. The result shows that NDII, EVI, and NDVI values vary 48%, 27%, and 23%, respectively, relative to their respective mean values. The soil moisture decreases with higher slope and elevation having the coefficient (R2) values of − 0.17 and − 0.19, respectively because the underlying soil cannot retain rainwater as run-off are comparatively faster in higher elevation and slope. Elevation and slope exert influence on all vegetation characteristics under consideration. Soil moisture is negatively paired with NDVI (R2 value of − 0.04) indicating, interestingly, that soil moisture content does not influence vegetation water content. Aspect has no significant correlation to any of the vegetation indices (R2 is ~ 0.02 in all cases) and, hence, while selecting sites for alternative agricultural practices, the topographic parameter of aspect can be ignored. NDII and EVI are significantly correlated more with elevation than slope. Thus, the potential site for the biomass or vegetation which retains moisture content should be in an area that is more susceptible to elevation followed by slope. In contrast, NDVI is significantly correlated with the soil moisture, slope, and altitude. Therefore, to get a generalized vigor of vegetation of higher green leaf content, primary production, chlorophyll content, and green leaf biomass, one must consider a combination of elevation and slope, as well as soil moisture, in CHT while selecting the potential sites for alternative agricultural practice.