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Emily K Heyerdahl, USDA Forest Service
Ken Lertzman, Simon Fraser University
Dave Schaepe, Stó:lo Nation
Bob Mierendorf, North Cascades National Park Service Complex
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Abstract
The recent encroachment of woody species threatening many western North American meadows has been attributed to diverse factors. We used a suite of methods in Chittenden Meadow, southwestern British Columbia, Canada, to identify the human, ecological, and physical factors responsible for its historical dynamics and current encroachment by woody vegetation. We evaluated three hypotheses about the origin and processes maintaining the meadow: the meadow is (1) of recent human origin; (2) of ancient human origin, maintained by aboriginal burning; and (3) of ancient non-human origin, not maintained by aboriginal burning.Our data supported the idea that the meadow had ancient non-human origins and its recent history and current status have resulted from complex interactions among landform, climate, and fire. Soil properties (both horizonation and charcoal content) indicate that the meadow is of ancient, non-human origin. Tree ages in the meadow and surrounding forest indicate that encroachment is recent, not related to a variety of recent human activities, and is probably a result of increasing spring temperature and decreasing spring snow depth. Although ethnographic surveys and historical documents revealed indigenous use of the general area over millennia, including the use of fire as a management tool, we found little direct evidence of indigenous use of the meadow. However, there was no proxy record of fire frequency in the meadow that we could have used to determine the role of fire in maintaining the meadow in the past, or the role of humans in igniting those fires. Thus, the historical role of humans in the maintenance of the meadow by prescribed fire remains indeterminate. Based on these conclusions, we combined hypotheses (2) and (3) into an a posteriori hypothesis that reflects changing interactions among people, fire, and climate over time. Without management intervention, we expect that tree encroachment will continue.
Several general lessons emerge from our study of Chittenden Meadow. A single modern ecosystem condition may result from diverse antecedents, but ecosystems may not carry a memory of all the processes driving their historical dynamics. The historical role of indigenous reource management activities may be one such process: despite millennia of human occupation and resource use in the region, local First Nations left only a light footprint on Chittenden Meadow. Finally, there is value and challenge in integrating data and perspectives from different disciplines.
Key words
anthropogenic influence, archaeology, British Columbia, Cascade Range, Chittenden Meadow, climate change, dendrochronology, fire suppression, historical dynamics, meadows, ponderosa pine, tree encroachment