Primary Succession and Soil Development in a Deglaciating Valley, Mt. Baker, WA

Authors: Andrew Bach*, Western Washington University
Topics: Physical Geography, Mountain Environments, Geomorphology
Keywords: succession, soil development, climate change impacts, Pacific Northwest, glacier
Session Type: Poster
Day: 4/11/2018
Start / End Time: 8:00 AM / 9:40 AM
Room: Napoleon Foyer/Common St. Corridor, Sheraton, 3rd Floor
Presentation File: No File Uploaded

Over the last hundred years climate conditions have caused glaciers in the Pacific Northwest (PNW) to retreat up valley, progressively exposing new land. For the first few decades following exposure the land remains a barren rocky landscape, with active erosional processes. Microorganisms begin to colonize surfaces, and organic detritus is blown from vegetated slopes above the valley floor. After two to three decades, the organic matter has built up enough (~1%) that geminating seedlings have sufficient nutrients to survive. For the next few decades plant cover remains low, and plant mortality is high due to the low fertility, ~9 months of deep snow cover, and dry summer conditions on the south-facing aspect. Pioneering species are typical PNW early-successional alpine species such as lupine (Lupinus polyphyllus) and Partridge Foot (Luetkea pectinate), while many of the surviving individuals are Mountain Hemlock trees (Tsuga mertensiana), typically a late-successional species. Once established, vegetation further colonizes in clusters around the original plants due to organic inputs (~2.5%) and increased soil moisture retention. By about sixty years of exposure, the landscape is completely covered with vegetation, and especially the mountain hemlock trees begin to grow into a vertical structure, rather than in a krumholtz form. Plant richness and diversity rise with surface age, but after 100 years only 15 species are present. Under the continuous vegetation cover, organic matter has increase to ~12.6%. This rapid rate of soil development, given a short growing season, is hypothesized to be related to several edaphic conditions.

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