Realistic potential increases in carbon storage via timber rotation extensions: an analysis of the Pacific Northwest

Abstract

Extensions of harvest rotation length are a commonly proposed method to increase carbon sequestration in forests that are managed for timber. However, several limitations constrain realistic storage potential in intensively managed forests. We present an analysis of the realistic potential for additional carbon sequestration via rotation extension across the Pacific Northwest of the United States, an important timber-producing region, taking into account specific limitations. We first assess the limitations on rotation length imposed by the stand age at which wood production would decline over the long term, and then incorporate the age at which trunk diameter surpasses a reasonable threshold for logging. Using publicly available forest survey data, we empirically model growth parameters across this region for use in this analysis. Despite uncertainties, we find some opportunities for rotation length extension in western Washington with variation by sub-region and timber species, emphasizing the importance of geography- and species-specific growth parameters for forest carbon management even within a general region. However, the total realistic potential for sequestration under this improved forest management scenario is small relative to gross emissions: the estimated cumulative additional sequestration in aboveground live biomass would offset one year of gross emissions in the case of Washington state, while a decadal-scale rotation extension implemented gradually over the landscape to avoid a total pause on commercial timber production would take on the scale of a century to achieve. Overall, practical considerations greatly limit the realistic potential of this carbon sequestration strategy.