Urban forests baseline and ecosystem benefits of a tropical metropolis: case of Dhaka, Bangladesh.

Dhaka, one of the world’s most crowded megacities, is undergoing rapid urban development that has led to an alarming and fast decline of urban forests and trees. Urban trees provide critical services to city landscapes, including the provision of shade, reducing air pollution through absorption of air pollutants, managing wastewater runoff and surface water, and absorbing carbon dioxide from the atmosphere. There is very little information on the extent, characteristics, and ecological value of Dhaka’s urban trees, which limits policymakers in designing sustainable measures that protect urban trees for the future. To address this information gap, we conducted Dhaka’s first-ever urban tree inventory that provides robust baseline data to set and monitor goals for improving urban tree cover and access to urban tree benefits. We used the i-Tree Eco modeling tool to estimate the economic value of selected ecosystem services urban trees provide. We found that the tree cover in Dhaka is currently below 11%, which is much lower than its potential as a tropical city. There are 1.3 million trees, or about one tree per 7 people. The inventory identified 110 tree species belonging to 33 families in Dhaka, and more than 60% of the tree species are exotic. Overall, urban trees provide an estimated USD 6.74 million per year in ecosystem benefits and store an additional estimated USD 3.19 million worth of carbon. The overall tree diversity is considered moderate to high based on several diversity indices. The three most dominant species of Dhaka are Mangifera indica, Swietenia mahagoni, and Cocos nucifera. This new baseline information equips policymakers to guide urban greening strategies and monitor progress towards city-level tree cover goals.