Modelling carbon stock in a tropical urban forest: Insights from i-Tree Eco and pantropical allometric equations in Chattogram City, Bangladesh

ABSTRACT Quantifying carbon stocks and sequestration in urban forests is essential for understanding their contribution to the global carbon cycle. Despite increasing attention to urban carbon accounting, limited studies have examined tropical urban forests using the i-Tree Eco Model, particularly in rapidly urbanizing cities such as Chattogram, Bangladesh. This study aimed to estimate carbon stocks in Chattogram’s urban forests using the i-Tree Eco Model, validated with pantropical allometric equations. Field data were collected from 208 circular plots (totaling 8.4032 ha; each 0.0404 ha) across three urban zones: Trees, Built-up with Trees, and Others. Total carbon stock estimated by i-Tree Eco (229,330 t) was 16.6% lower than that from the Chave equation (275,002 t) and 21.3% lower than the Brown equation (291,520 t). Carbon density estimates from i-Tree were 17–28% lower than pantropical equations, although differences were generally not statistically significant (p ≥ 0.05) under two-tailed tests with varying assumptions for belowground biomass allocation and carbon conversions. Carbon density varied significantly among the three zones (p ≤ 0.05), with the Trees zone showing the highest values (41.26–52.57 t C ha⁻¹) and the Others zone the lowest. This variation reflects differences in tree size and density. Moreover, carbon density showed strong positive correlations with stand structural attributes e.g. dbh, basal area. The total annual carbon sequestration by Chattogram’s urban forests was estimated at 33,240 t CO₂, emphasizing their role in mitigating atmospheric carbon. These findings provide valuable insights into the carbon storage potential of urban forests and underscore their importance for climate change mitigation and strategic urban forest management in tropical cities.