Soil Organic Carbon Stocks in the Forests of Mount Rainier National Park, Washington

Soil organic C represents a substantial component of the total ecosystem C in temperate and boreal forests. We used an isocluster‐driven process of principal components (based on elevation, precipitation, temperature, etc.) to stratify Mount Rainier National Park, a 957‐km 2 federal reserve in the state of Washington, for estimating total soil organic C stocks. Eight stratification‐based forest sites for groups of soil pits and vegetation plots were located throughout the park. Average organic C in the park's forest soils (primarily Andisols, Spodosols, and Inceptisols) was 163 Mg C ha −1 (95% confidence interval [CI] = 138–188), and 205.0 Mg C ha −1 (95% CI = 177.9–232.1) with the litter layer included. The low‐elevation Andisols and Spodosols held the greatest per‐hectare stocks. Total ecosystem C stocks, strongly influenced by the live overstory C pool, varied by almost an order of magnitude across plots, ranging from 168 to 1583 Mg C ha −1 . Temperature variables, rather than precipitation, were correlated with soil C pools. Site membership accounted for a significant proportion of variance in C stocks, and beta regression indicated that the proportion of total C stored in the soil varied across sites. Additional sampling in the highly variable top 35 cm of the soil significantly improved the precision of estimates for soil C to that depth. The C stocks determined in this study provide baseline data for Mount Rainier National Park and aided in developing a systematic method for resampling to determine flux with time and establishing a basis for a future comparison with adjacent managed forest landscapes.