Urban forests as carbon reservoirs: comparative assessment across Delhi-NCR

Rapid urbanization and population growth in the Delhi-National Capital Region (NCR) have resulted in the loss of green cover, deterioration of air quality, and intensification of the urban heat island effect. Urban forests serve as important nature-based solutions by acting as carbon (C) sinks; however, site-specific information on biomass and C storage in semi-arid tropical megacities remains limited. This study assessed tree biomass, C density, and carbon dioxide equivalent (CO₂eq) across four urban forest sites in Delhi-NCR: Sanjay Van, Mandir Marg Ridge Forest, AcSIR Headquarters (Ghaziabad), and Aravali Biodiversity Park (Gurugram). Vegetation sampling was conducted using three plots per site, with three 20 m × 20 m (400 m²) subplots established within each plot. Tree height and diameter were measured, and biomass was estimated using species-specific allometric/volumetric/pantropical allometric equations. The relationship between biomass and basal area was evaluated using Pearson's correlation analysis. Sanjay Van exhibited the highest biomass (108.71 Mg ha^-1) and C density (50.01 Mg ha^-1), whereas Aravali Biodiversity Park showed the lowest values (34.51 Mg ha^-1 biomass and 15.87 Mg ha^-1 C). A strong positive correlation was observed between basal area and total biomass (r = 0.78, p < 0.001; n = 36). Differences among sites were primarily associated with variations in species composition, stand structure, and local environmental conditions. Uncertainties in biomass estimates mainly arose from sampling variability, the use of allometric equations developed under different ecological conditions, and belowground biomass estimation based on fixed root-to-shoot ratios. This study provides baseline information on the C sequestration potential of urban forests and highlights the importance of conserving mature stands, restoring degraded areas with native species, and integrating long-term C monitoring into urban planning.