Master’s Thesis Abstract by Carolyn Sanscrainte (2000)

Quantification of carbon (C) pools in subalpine systems is an important first step to understanding the potential responsiveness of terrestrial C dynamics to climatic change in temperate mountainous regions. We compared vegetation and pedology between tree islands and adjacent meadows at three sites (Thornton Lakes, Heather Pass and Harts Pass) in the North Cascade Range to determine how the presence of tree islands affects soil C storage in the subalpine landscape. Mean C concentrations in the mineral soil (E and B horizons) range from 17.2 to 154.8 g kg-1 with no consistent relationship between vegetation type (tree island vs. meadow) and C concentrations. Mineral soils in tree islands store approximately 8.6 kg C m-2, while mineral soils in meadows store 10.0 kg C m-2. Patterns of mineral soil C storage vary between tree island interiors and meadows. Harts Pass is the only site where total mineral soil C storage differs significantly between tree islands and meadows, with meadows storing more C than tree islands (14.1 vs. 2.7 kg m-2). Spatial variation of O-horizon C is a function of the distinctness of the transition between trees and dominant meadow species. Ecosystem C storage is higher in tree islands (35.1 to 98.5 kg m2) than meadows (7.4 to 18.0 kg m-2), primarily due to large amounts of C in the aboveground biomass of trees. Consequently, the effects of future climatic variability on C storage in subalpine ecosystems will largely depend on the degree to which conditions that limit tree island expansion (winter snowpack, summer drought) are affected.