Retreating Glaciers, Incipient Soils, Emerging Forests: 100 Years of Landscape Change on Mount Baker, Washington, USA

Glacial forelands are harsh environments where incipient pedogenesis provides the basis for vegetation establishment and succession. The Easton Glacier foreland on Mount Baker, Washington, has till deposited during five time intervals over the last 100 years as determined from historic ground and air photos. A soil chronosequence was established on the different age surfaces to assess rates of pedogenesis. As hypothesized, all soil variables, except pH, showed increasing values on progressively older surfaces, with several orders of magnitude increase between the active till and the 100-year surface. Till on ice showed no vegetation cover, low organic matter (0.4 percent), little to no nitrogen content (maximum 0.001 percent), minimal carbon (maximum 0.0083 percent), and a carbon/nitrogen (C/N) ratio of 5.9. The 100-year-old surface has continuous vegetation cover, high organic matter (12.6 percent), 0.67 percent nitrogen, and 9.47 percent carbon, and the C/N ratio was at its highest (22.6). Organic matter content started higher than expected in fresh till and gradually increased before vegetation became established, suggesting aeolian deposition of detritus built soil fertility. We estimate that after about sixty years of exposure, till surfaces became fully covered with vegetation and soil organic matter increased by almost 2,800 percent (0.4–12.6 percent). This rapid rate of soil development, given a short growing season, is hypothesized to be related to several edaphic conditions (topographic setting relative to established vegetation, aspect, and andesitic parent material), rather than a normal condition for the Cascades Range as a whole, demonstrating that ongoing climate change is affecting many environmental processes.