Biomass Characterization and Allometric Model Development for Aboveground Carbon Stock of Benguet Pine (Pinus kesiya)

Abstract

Experts generally agree that allometric models generated from destructively sampled trees is the most accurate and direct method of estimating carbon stock. However, carbon sequestration studies in the Philippines generally used generic mixed species models; thus, this study was conceptualized – to generate a more accurate and direct estimate of the aboveground carbon and organic matter content of Benguet pine (Pinus kesiya). A total of 24 best–fit allometric models were generated for total aboveground carbon and organic matter content and its different compartments based on 15 destructively sampled trees. These models have high r2 and adjusted r2 values of 0.79 to 0.99 and are thus deemed highly accurate in estimating the carbon stock and, subsequently, the carbon sequestered by Benguet pine forest. Diameter at breast height (D) was found to be the primary predictor variable and total tree height (H) as the secondary predictor variable. Tree biomass was also characterized in terms of biomass partitioning pattern, wood–bark proportion and organic matter content. The main trunk contains the bulk (60 to 77%) of the aboveground biomass, followed by branches, needles and twigs, respectively. However, in small pines, needles have greater biomass than the branches. Larger pines generally have greater wood proportion than smaller trees while the bark is greatest on the basal portion and decreases apically in trunk sections. High OM ranging from 72 to 99% were recorded in the different components with higher percentages in woody components than in needles and bark; and in smaller pines than in larger ones. Having these species–specific allometric models and a clear understanding on biomass and carbon distribution in Benguet pine could help local forest managers accurately account for pine forest carbon stock and guide them on how to enhance the pine tree’s carbon sequestration capacity.