Modelling habitat suitability of the critically endangered Agarwood (Aquilaria malaccensis) in the Indian East Himalayan region

Agarwood (Aquilaria malaccensis) is a critically endangered species on the IUCN red list globally. It is highly valued for its aromatic wood, popularly called agar, which has been overexploited in its natural range. The natural habitat of Agarwood is also drastically changing due to anthropogenic activities, and the tree is no longer in existence in the wild except in some intact forest patches. In the Indian East Himalayan region, Agarwood is planted in indigenous agroforestry and communal lands. Here, species distribution modelling (SDM) was used to establish Agarwood's current and future habitat suitability under two representative climate change scenarios (RCP4.5 and RCP8.5). We implemented an ensemble of five SDM models, including two regression and three machine learning methods, using datasets from 82 locations. The results revealed that of the total area of 269,159 km(2 )of the Indian East Himalayan region, 2282 km(2 )is currently highly suitable. However, it is predicted to decrease by 34.28% under RCP4.5 and 14.64% under RCP8.5 by 2050, whereas 44.88% of the highly suitable area would reduce under RCP4.5 and 27.18% under RCP8.5 by 2070. Under the current climate scenario, the state of Assam has a substantial area potentially suitable for Agarwood, representing 99.21% of the state's land area (2264 km(2 )). However, there will be a tremendous loss of suitable habitats in future climate change scenarios. Our study highlights that precipitation of the driest quarter, precipitation of the warmest quarter and mean temperature of the driest quarter were the most influential bioclimatic variables. In addition, sand, clay content and organic carbon density were critical predictors of the distribution of Agarwood. This study has provided baseline data on the potentially suitable habitat of the species to guide the formulation and implementation of policies and practices for the conservation of Agarwood in the Indian East Himalayan region.

Automated summary

This study examines the current and future habitat suitability of Agarwood in the Indian East Himalayan region using species distribution modelling. The results indicate a decrease in suitable habitats for Agarwood in the future due to climate change. Precipitation and temperature variables, as well as soil characteristics, were found to be critical predictors of Agarwood distribution.