Carbon fraction of Pinus radiata biomass components within New Zealand

Abstract

Background: Carbon fractions are applied to dry matter estimates to calculate carbon stocks in forest stands. A default carbon fraction has been applied to planted forest species in New Zealand; however, various studies have shown that the carbon fraction can differ among species and between tree components. New Zealand-specific carbon fractions were, therefore, developed to improve the accuracy of carbon stock estimates for international reporting purposes. Methods: Carbon fractions were analysed using subsamples of tree components from 684 stems, 1125 crowns and 70 root systems from 14 sites distributed throughout New Zealand. The carbon fractions for needles, branches, cones, stem wood, stem bark and roots reported by the laboratory at a drying temperature of 104 °C were corrected using published procedures to the moisture content attained after drying subsamples to constant weight at 70 °C, the drying temperature used in New Zealand biomass studies. Results: Carbon fraction averaged 0.514 g C g−1dm in needles, 0.507 g C g−1dm in branches, 0.519 g C g−1dm in cones, 0.498 g C g−1dm in stem wood, 0.501 g C g−1dm in roots, and 0.539 g C g−1dm in stem bark of radiata pine. The stem bark carbon fraction increased asymptotically with stand age. Conclusions: The default carbon fraction (0.50 g C g−1dm) used previously in the FCP model underestimates carbon stocks in New Zealand’s planted forest estate. Applying carbon fractions derived from New Zealand biomass studies will increase carbon stock estimates for the planted forest land by approximately 1% and also increase estimates of removals during harvesting operations. Information on in-forest debarking activities will further improve estimates of removals associated with harvesting.