Ghosts of the forest: Mapping pedomemory to guide forest restoration

Abstract

Soil morphology can provide insight into how ecosystems change following periods of extensive disturbance. Soils properties can often be linked to historic environmental influences (e.g., vegetation or climate) to provide a record of pedomemory. Identification and mapping of soil pedomemory properties show promise in providing context for ecological restoration. We have developed a novel use of digital soil mapping of spodic morphology to estimate historical forest composition in the high-elevation forests of the Central Appalachians. This region was extensively disturbed by clear-cut harvests and related fires during the 1880s–1930s. Hardwood forest species recovered much better than local conifers and generally encroached into historic populations of red spruce (Picea rubens) and eastern hemlock (Tsuga canadensis). Spodic soil morphology, which is often associated with subalpine and boreal conifer forests, was mapped using a random forest probability model and showed correspondence to red spruce — eastern hemlock distribution, as derived from local historic property deed witness tree records from 1752 to 1899. These data and resulting models indicate a greater spatial extent of spodic soil properties than documented in previous soil maps, which is more consistent with general theories of much more extensive historic spruce populations. The resulting maps and models provide guidance for field scale restoration planning for historically disturbed spruce–hemlock forests. Our results suggest that historic Euro-American disturbance probably induced conifer-to-hardwood state transitions at mid to high elevation coniferous ecological sites within the Appalachians. Where transitions have occurred, there appears to have been dramatic losses in forest floor thickness (O-horizons) and associated soil organic carbon stocks into atmospheric carbon pools. Spatial modeling of similar pedomemory properties and other soil-ecology linkages is likely to be a powerful tool to guide restoration in other regions as well.