With Trees As My Witness: The Use of Historical Survey Records in Understanding Contact-Era Forest Structure in the Upper Middle Fork Willamette River Watershed
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Date
2023
Authors
Petraglia, Grace
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
This research examined the use and limitations of United States General Land Office surveys for reconstructing historical landscape patterns. We reconstructed forest structure for three townships surveyed in 1869 and 1902 in the Upper Middle Fork Willamette watershed. Survey of the area was preceded by early Euro-American explorers, construction of the Oregon Central Military Wagon Road, and timber and grazing activity. We used historical survey notes to conduct an iterative fuzzy classification of section lines that assigned each line degree of membership to closed canopy forest. The final fuzzy classification relied on a composite index comprised of the number of witness and bearing trees recorded along each line and the average distance of each tree recorded from the line. This approach minimized research bias and mitigated the inherent limitations of historical data. Fuzzy membership was then compared with other variables derived from survey notes as well as a previously published reconstruction that uses discrete vegetation classes. Our findings show a positive relationship between survey line membership to degree of closed canopy forest and elevation. We conclude that fuzzy set theory is an appropriate method to work with GLO survey records. However, our investigation suggests that on their own, GLO survey data is insufficient in quality and reliability to confidently reconstruct historical forest structure at a spatial grain needed to inform management plans.
Description
60 pages
Keywords
Land surveys, fuzzy classification, reconstruction, forestry