Carbon Storage in Young Growth Coast Redwood Stands

Carbon sequestration is an emerging forest management objective within California and around the world. With the passage of the California’s Global Warming Solutions Act (AB32) our need to understand the dynamics of carbon sequestration and to accurately measure carbon storage is essential to insure successful implementation of carbon credit projects throughout the State. As the leader in forest carbon credit projects within the U.S., California's forest carbon protocols are being looked to as templates for successful carbon credit accounting. Coast redwood (Sequoia sempervirens) stands have the largest measured biomass per acre making the argument for use of the species in long-term carbon sequestration projects self evident. To date no direct measurement of both carbon fraction and wood density of coast redwood has been undertaken. With this study we tested the applicability of the current forest carbon project protocols set out by the Climate Action Reserve for forest carbon credit projects within California. Specifically we tested the applicability of a carbon fraction of 0.5 and a greenwood density of 0.34 g/cm for coast redwood trees. Our main findings were that: 1) a species-average of 0.34 g/cm significantly underestimated the wood density of the measured trees, 2) wood density varied predictably with tree height and wood type, 3) carbon fraction was significantly higher than the default 0.5, and 4) carbon fraction varied predictably in relation to wood type. Our results indicate that a simple approach to estimating carbon storage utilizing a carbon fraction of 0.5 and a species-average wood density underestimates carbon budgets in young growth redwood stands. Given the regional nature of carbon credit projects our results indicate that forest project protocols should be adjusted to allow for calculations that incorporate directly measured wood density and carbon fraction values within the forest carbon project area.