Non-destructive assessment of carbon sequestration in Aquilaria malaccensis plantation in Sri Lanka

Abstract

Carbon sequestration by plants has the potential to significantly address global environmental challenges, including accumulation of greenhouse gases in the atmosphere, which leads to climate change. This study is one of the first in-situ, non-destructive investigations of carbon sequestration in A. malaccensis plantations in Sri Lanka, addressing a critical gap in local and regional data. A total of 125 trees aged between 4 and 8 years were sampled from Sadaharitha Plantations Limited, Ayagama, Rathnapura. Tree height and diameter at breast height (DBH) were measured using a laser distance meter and measuring tape, respectively, while timber volume was estimated using geometric methods (Cylindrical Volume Method). Biomass was calculated using species-specific wood density (320 kg/m³), and carbon content was estimated based on an established carbon fraction (40.35%). This study focused on developing and validating allometric models for estimating aboveground biomass and carbon storage in agarwood trees categorized by age. Essential variables such as tree height (H), diameter at breast height (D) and timber volume were measured to develop regression models, which were then assessed for accuracy using metrics including R-squared (R2), RMSE, and percentage error. Among the models tested the Logarithmic function: Log [Above ground Carbon content (kg)] = -0.819 + 1.5513Log [ Tree Diameter at 1.5m height (cm)] + 1.056Log [ Total Tree Height (m)] was identified as the best fitting model for estimating aboveground carbon content. This model achieved a high accuracy with R² = 96.68%, RMSE = -18.71, and percentage error = 2.79%, indicating strong predictive capability and minimal deviation from observed values. The study showed a significant positive correlation between tree growth parameters and carbon content, highlighting the potential of agarwood as an effective species for carbon sequestration. The carbon sequestration potential of agarwood (50.80 tons CO₂/ha over an 8-year lifespan) was compared with that of rubber (286.26 tons CO₂/ha over 30 years) and teak (664.27 tons CO₂/ha over 50 years) to determine the most effective plantation for carbon fixation. Despite its lower overall carbon sequestration, agarwood is considered the best crop for short-rotation systems due to its higher annual carbon fixation efficiency, although teak remains more effective for long-rotation plantations aimed at maximum long-term carbon storage. These models provide valuable insights for climate change mitigation strategies. Planters may also increase their income through carbon crediting of cultivating agarwood trees. By measuring tree height and DBH, the model allows for accurate estimation of aboveground carbon content in Aquilaria malaccensis plantations without destructive sampling. It is a practical and cost-effective tool for plantation managers and policymakers to track carbon stocks, verify carbon credits, and guide sustainable plantation development.