Carbon pools and biomass stores in the forests of Coastal Alaska: Uncertainty of estimates and impact of disturbance

Forests provide significant long-term carbon (C) storage, but have the potential to increase future C emissions with a changing climate. Aboveground biomass, C stores, and the effect of disturbance were examined using forest inventory data collected across all ownerships on 6.2 million ha in Coastal Alaska. We modelled six C pools using empirical data, estimated two others using the literature, and quantified estimate uncertainty. The average (+/- SE) aboveground live (218.9 +/- 4.6 Mg/ha) and log (28.1 +/- 1.8 Mg/ha) biomass in the Alaskan Temperate ecoregion were among the lowest in the Pacific Northwest, whereas snag biomass (30.5 +/- 1.0 Mg/ha) was among the highest. In the Alaskan Boreal ecoregion, on the Kenai Peninsula, coarse woody debris (CWD) biomass comprised almost 50% of the regional average of aboveground woody biomass (76.7 +/- 3.8 Mg/ha) with bark beetle damaged stands containing 82% of the total CWD biomass. In contrast, in the Temperate ecoregion, CWD comprised 20% of the regional aboveground woody average (277.5 +/- 5.4 Mg/ha) with 76% of total CWD biomass in undisturbed stands. Total C stores estimates in Coastal Alaska forests ranged between 1523.6 and 1892.8 Tg with the highest contribution from soils. The largest potential reductions in uncertainty are related to the tree and soils C pools. Disturbance determined total biomass amounts in the system and controlled the ratio between live and dead biomass pools and thus has the ability to shift forest stands into a C source to the atmosphere.