Tree biomass and soil carbon in 17- and 22-year-old stands of teak (Tectona grandis L.f.) in northern Thailand

Abstract

We estimated the trunk volume, aboveground and belowground biomasses, and carbon stock in the soil of 17- and 22-year-old teak (Tectona grandis L.f.) stands in northern Thailand. Allometric equations for estimating the trunk volume and biomass of each organ, based on five sample trees in each stand, gave high accuracy (r2 = 0.881 to 1.000). The trunk volumes of the two stands were 116.9 and 139.6 m3 ha-1, respectively. The total aboveground and belowground biomasses of the trees were 89.3 and 98.8 Mg ha-1, respectively. The ratio of below- to above-ground biomass was 25.6 % in the 17-year-old stand and 20.0 % in the 22-year-old stand. The mean annual increment (MAI) of the trunk volume and the total biomass of the trees were 6.9 and 6.3 m3 ha-1 yr-1, and 5.3 and 4.5 Mg ha-1 yr-1, respectively. The average carbon stock in the soil was 211.4 MgC ha-1 (range: 153.2 to 251.8 MgC ha-1) in the 17-year-old stand and 137.2 MgC ha-1 (range: 122.7 to 157.9 MgC ha-1) in the 22-year-old stand. These values are about three times larger than the carbon stock of the trees themselves (44.6 and 49.4 MgC ha-1; assuming 50 % carbon content of tree biomass). These results highlight the importance of estimating the belowground carbon pool.