TREE SPECIES DIVERSITY AND QUANTIFICATION OF ABOVE GROUND CARBON STORAGE OF ROOFTOP GARDEN IN DHAKA CITY

Abstract

In the current context of increasing urbanization and a related increase in greenhouse gas emissions, rooftop gardens are alternatives means in mitigating climate by its potential Carbon (C) sink. This work was aimed at estimating the aboveground carbon stock and tree diversity in the areas of DAE projected four metropolitans viz. Mirpur, Mohammadpur, Gulshan and Tejgaon of Dhaka city. The data of 63 rooftop gardens were analyzed; a total of 883 trees were sampled and 32 different tree species under 21 families were identified and recorded on the basis of tree diversity and Carbon stock. It was found that large rooftop gardens had 31 different types of species where mean number of trees per hectare was 586.97, medium rooftop gardens had 29 different types of species where mean number of trees per hectare was 616.86 and small rooftop gardens had 16 different types of tree species where mean number of trees per hectare was 701.45. The Shannon Wiener index was used to assess the tree diversity per rooftop garden and it ranged from 1.45 to 3.79 with a mean value of 2.74. The carbon estimations were done using allometric equations for small sized trees with diameter at breast height (DBH) as predictor variable for biomass. Size of the tree, diameter at breast height (DBH) and tree species diversity data were analyzed. As the few samples of the monitored population was smaller than 1.3 m and destructive measurements was not possible, root collar diameter (RCD) was recorded and corrected to be used in the allometric model. Among the rooftop garden categories large area gardens had the highest carbon stock 3.071 Mg ha -1 (ranges from 1.65 Mg ha -1 to 4.66 Mg ha ) and lowest carbon stock 1.867 Mg ha -1 was found in small rooftop gardens (ranges from 1.18 Mg ha -1 to 2.83 Mg ha -1 ). Among the five major dominating species the highest amount of carbon was stored by Mango (20.37 Mg) followed by Guava (16.84 Mg), Jujube (13.84 Mg), Sapota (12.34 Mg) and Carambola (11.32 Mg). The results of the study show that rooftop farming of Dhaka city has a diverse tree species that could contribute significantly by reducing carbon in the atmosphere.