Oregon Statewide Historical Vegetation
As part of the Oregon Gap Analysis Program, ORBIC worked with the Defenders of Wildlife and Jim Strittholt to develop the first statewide map depicting historical vegetation. Scale varies throughout the coverage, depending on the source data, but the overall scale is 1:100,000. The map was first compiled in 1999 and is updated as needed. It integrates several sources of historical spatial data:
- The Andrews and Cowlin timber maps for Oregon and Washington (1936-1937, digitized by USFS 1994-1996, scale = 1:253,440),
- GLO-based coverage where available (compiled 1994-present by ORBIC and partners, scale = 1:24,000),
- NRCS SSURGO data (scale = 1:24,000), and
- Current land cover mapping from the USDI Bureau of Land Management (BLM).
The Andrews and Cowlin layer forms the background into which more detailed coverages were incorporated. It was mapped to forest type, with a secondary classification for young forests. Because the layer lacked detail for non-forest vegetation, ORBIC supplemented the data with more detailed information contained in the sources cited above. Because SSURGO data present potential vegetation based on soil types, they were used to replace post-settlement land cover types such as agriculture or urban occurring on well-defined riparian and floodplain soils. Where SSURGO data were not available, these types were replaced with potential pre-settlement vegetation based on the composition of adjacent polygons, and the presence of rivers and streams for riparian areas and bottomlands. Recent burns and regenerating young forests were reverted to forest.