VEG1851_V5

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Title: VEG1851_V5

Abstract:

This polygon coverage depicts "presettlement" vegetation in Oregon as described by surveyors for the General Land Office between 1851 and 1909, when surveying township and section lines. Most low-elevation sites with arable land were surveyed between 1851 and 1865, while most foothill and mountainous areas were surveyed between 1865 and 1895. Coverage currently includes the entire Willamette Valley and surrounding foothills, most of the tributary valleys of the McKenzie, Tualatin, and Yamhill rivers. The project, initiated in 1993, has to date been funded by the Oregon Division of State Lands, the Bureau of Land Management, the Environmental Protection Agency, the Army Corps of Engineers, the Bonneville Power Administration, the Oregon Community Foundation, The Nature Conservancy, and the City of Portland. The Principal Investigator is John A. Christy (Oregon Natural Heritage Program, The Nature Conservancy of Oregon), with GIS management by Linda Ashkenas, Paula Minear, and Doug Oetter (Oregon State University).

Supplemental_Information:

Coverage was created at 1:24,000 using databased transcriptions of survey notes for township and section lines, with standard USGS 7.5 topographic maps as a base. When resurveys offered more than one data set for a given line, data from the earliest survey were used whenever possible. Survey data for meander lines deviating from section lines, and for Donation Land Claim boundaries, were not used in this study.

Vegetation types were defined by descriptors used in the survey notes, supplemented when needed by distances to witness trees as recorded in the notes. Coverage was delineated using distances recorded as points along the survey lines. Vegetation in the interiors of sections was delineated using features depicted on the surveyor's township plat maps, historic air photos, modern soil maps, and best professional judgement based on topographic features.

Mylars were digitized by hand early in the project, and later scanned directly into ArcInfo using the ArcScan module. Once in ArcInfo the polygon coverage was built or cleaned with a fuzzy tolerance of 1 meter and polygons were attributed with the veg abbreviation. Edgematching and elimination of sliver polygons was done by hand to avoid losing tiny polygons that were necessary to the coverage (gravel bars, etc.).

Department of Corrections, Division of State Lands, and Oregon State University (Department of Fisheries and Wildlife) have all assisted with digitizing of these topo quads.

The final editing was