Building allometric models to estimate above-ground and below-ground biomass of mahogany sapling.

There are large areas of big-leaf mahogany (Swietenia macrophylla King) afforestation and reforestation plantations for reducing carbon dioxide due to climate change in Taiwan. In Taiwan, out of the total area of mahogany plantations of approximately 2982.00 ha, 125.40 ha is in national forests and 232.00 is at the Hsin-Hua Experimental Forest Station. Biomass is a plant attribute that accumulates over time. It is an important indicator of growth and is used in analysis and management processes. Above-ground biomass is the key parameter in many allometric relationships. However, there are few studies on below-ground biomass estimations of mahogany, for it is difficult to excavate and quantify these portions. The aim of this study was to establish an allometric relationship to estimate the above-ground (stem wood, stem bark, branches, and foliage) and belowground (roots) biomass using an easily measured value, such as the diameter at breast height (DBH), diameter at the stem base (DSB) and tree height (H). Forty-six mahogany saplings (0 cm ≤ DBH ≤ 10 cm), with different ages in the second compartment of this forest station, were used to establish the allometric functions of DBH and biomass, and functions of DSB and biomass. A significance test of the correlation was used to test the relationship between DBH and biomass in different sections, including foliage, branches, stems, above-ground, below-ground, and the entire tree. The DSB was also tested. The results showed that the power regression function was superior to other functions. The correlation between DBH and biomass was higher than the correlation between DSB and biomass. The allometric functions for the entire tree biomass, above-ground biomass, and below-ground biomass were W = 175.67×DBH^2.29 (R^2 = 0.9692), Wabove = 112.21×DBH^2.34 (R^2 = 0.9621), and Wbelow = 61.65×DBH^2.19 (R^2 = 0.9610), respectively. The carbon content of each part of mahogany trees was as follows: stem wood (45.83±0.92%), roots (45.09±0.89%), foliage (44.95±1.21%), branches (43.74±1.09%), and stem bark (42.64±1.01%). Managers can estimate the biomass, carbon content ratio, and carbon storage of mahogany without destroying trees.