Effectiveness of community management on the carbon sequestration capacity of mangroves in the Negombo Estuary, Sri Lanka

Mangroves perform several important functions and provide a wide range of services from an ecological, social, and economic point of view at the local and regional level. Although scientific explanations on the ecological importance of mangroves have emerged recently, evidence that livelihood resource extractions and community-based, traditional developing activities performed from long history. Due to the limited information found to be on ecological services rendered by the traditional mangrove cultivation and management practices, the present study focused on quantifying the ecological services, especially the carbon sequestration capacity of a community- managed mangrove area at Negombo estuary, Sri Lanka. Kadolkele was selected to represent the natural and relatively undisturbed mangrove stands, and Wedikanda represented the man-made/ cultivated mangrove stand at Negombo estuary. Above- and below-ground biomass of mangrove trees was estimated using an allometric method. The average annual biomass increment was calculated using five years of data from the same study plots at two study sites.  Mean annual biomass increments and their percentages were recorded,13.54 ±0.47 Mg ha-1y-1 (9.24%) and 12.02 ±0.14 Mg ha-1y-1 (8.98%) for Kadolkele and Wedikanda, respectively. Average annual total organic carbon (TOC) accumulation rates were revealed, 7.19 ±0.25 Mg ha-1y-1 and 6.56 ±0.07 Mg ha-1y-1 for Kadolkele and Wedikanda, respectively. Generally, the highest biomass and TOC increments were recorded in the areas near the estuarine shoreline, and a decline trend was observed towards the landward. Based on the five-year total woody growth, the annual carbon sequestration capacities were 7.71 ±1.29 Mg C ha-1 y-1 and 6.90 ±1.18 Mg C ha-1 y-1 for Kadolkale and Wedikanda, respectively. A statistically significant difference was not observed (p > 0.05) between the values of biomass and TOC increments of the study areas. Results revealed that the carbon sequestration capacity of mangrove areas managed with traditional ecological knowledge is comparable to that of natural mangroves. Cultivated mangrove stands exhibit similar primary productivity to natural stands, thereby demonstrating the positive contribution of mangrove cultivation to overall ecosystem productivity and carbon assimilation.  This indicates the significance of traditional wisdom in mangrove cultivation management methods.