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.
