Canopy Soils of Sitka Spruce and Bigleaf Maple in the Queets River Watershed, Washington

Canopy or arboreal soils develop from the accumulation and decomposition of epiphytes on branches and in bifurcations of trees in tropical and temperate rainforests. Canopy soils are important because they provide habitat and water, and accumulate allochthonous nutrients for epiphytes and their associated biota. This study characterized the chemical and physical characteristics of canopy soils developed on Sitka spruce [Picea sitchensis (Bong.) Carriere] and bigleaf maple (Acer macrophyllum Pursh) in an old-growth forest at the Queets River watershed, Washington. Bigleaf maple canopy soils were dominated by hemic horizons, had higher pH, N content, cation exchange capacity, and extractable N levels relative to Sitka spruce canopy soils, which had higher bulk density and C/N ratios. Compared with the forest floor, canopy soils had lower total C, total N, and C/N ratio. The bigleaf maple canopy soil was classified as a Typic Haplohemist, whereas the Sitka spruce canopy soil was classified as a Typic Haplosaprist. The main differences between these canopy soils are due to different inputs of host tree litter and decomposition states of the two species. Canopy soils in this ecosystem are enhancing the pool of C and N by 20 and 25%, respectively, relative to the C and N pools of the forest floor.