AUTHORS: Gavin McNicol*, University of Alaska Southeast; Brian Buma, University of Alaska Southeast; Ian Giesbrecht, Hakai Institute; Santiago Gonzalez Arriola, Hakai Institute; Allison Bidlack, Alaska Coastal Rainforest Center
ABSTRACT: Temperate rainforests exhibit some of the highest ecosystem carbon (C) stocks globally and have been studied much less than their tropical counterparts. The perhumid zone of the North American temperate rainforest blankets over 100,000 km2 of remote fjords and lowland islands in southeast Alaska and coastal British Columbia. These wet, cool ecosystems provide ideal conditions for large soil organic carbon (SOC) accumulations, particularly in forests (Spodosols) and deep peatbogs (Histosols). Quantifying SOC stocks across the perhumid coastal temperate rainforest (PCTR) is important to understand the landscape distribution of sequestered C and the lateral terrestrial-to-aquatic fluxes of organic C.We built a Random Forest (RF) model from pedon data and 10 environmental covariate datasets to predict SOC stocks across the North American PCTR. Pedons and associated SOC stocks were compiled from Natural Resources Conservation Service (NRCS) data and a recent Canadian Forest Service pedon database. Model evaluation included comparisons with FAO and SoilGrids SOC and validation with USFS Forest Inventory and Analysis pedon data. Preliminary results suggest the PCTR contains significant SOC stocks with a median pedon SOC stock to 1 m of 480 Mg ha-1, compared to stocks of 93 Mg ha-1 and 186 Mg ha-1 in boreal and evergreen tropical forest soils, respectively. The strongest environmental predictors include MAP, slope, and aspect, along with latitudinal effects resulting in increasing stocks moving north from Vancouver Island, and south from Juneau, to a maximum across the southern extent of the Alexander Archipelago. Aboveground C is also compared to belowground C to determine overall spatial partitioning of C resources in the PCTR which is important to questions of sensitivity to change, C export to marine systems, and management.
