The objective of this project, covering the Puget Lowland and Willamette Valley ecoregions within Washington state, was to create a unified digital map of: (1) untilled grasslands now existing in landscapes that formerly supported native dry grasslands, and (2) oak dominated or co-dominated canopies. The map’s scale and level of detail are designed to be appropriate for both regional-level conservation planning and county-level planning and development screening.

Native grasslands and oak woodlands are some of the most imperiled ecosystems in western Washington (Dunn and Ewing 1997). For example, native grasslands in the south Puget Sound area have declined to less than 3% of their pre-settlement areal extent (Crawford and Hall 1997). Factors contributing to the decline and degradation of these ecosystems include fire suppression and associated conifer tree invasion, invasion of non-native species, grazing, and urban and agricultural conversion (Giles 1970, Agee 1993, Clampitt 1993, Crawford and Hall 1997).

Many species of flora and fauna associated with these unique habitats are of conservation concern due to declines in population, local extirpation, or close associations with the declining habitat. These include the western gray squirrel (Sciurus griseus), Mazama pocket gopher (Thomomys mazama), Lewis’ woodpecker (Melanerpes lewisii), white-breasted nuthatch (Sitta carolinensis aculeata), streaked horned lark (Eremophila alpestris strigata), western meadowlark (Stunella neglecta), Oregon vesper sparrow (Pooecetes gramineus affinis), western bluebird (Sialia mexicana), racer (Coluber constrictor), mardon skipper (Polites mardon), Puget blue (Plebejus icaroides blackmorei), whulge checkerspot (Euphydryas editha taylori), zerene fritillary (Speyeria zerene bremnerii), white-topped aster (Aster curtus), golden paintbrush (Castilleja levisecta), common bluecup (Githopsis specularioides), and rose checkermallow (Sidalcea malviflora spp. virgata) (Dunn and Ewing 1997).

Native grasslands and oak woodlands in the Puget Lowland and Willamette Valley ecoregions (Omernik 1987) are found in dry environments formerly strongly influenced by frequent fires, many if not most of which were ignited by Native Americans (Norton 1979). Oak woodlands may be dominated by Oregon white oak (Quercus garryana), or co-dominated by that species and Douglas-fir (Pseudotsuga menziesii), Oregon ash (Fraxinus latifolia), bigleaf maple (Acer macrophyllum), or Pacific madrone (Arbutus menziesii). They range from open savannas of scattered trees to dense-canopied forests, with a range of herbaceous or shrubby understory types (Agee 1993, Chappell and Crawford 1997). They occur on relatively dry sites or moist riparian environments within prairie, or formerly prairie, landscapes.

Native grasslands are dominated primarily by Roemer’s fescue (Festuca idahoensis var. roemeri), red fescue (Festuca rubra), or California oatgrass (Danthonia californica), but also harbor a wide variety of forbs that sometimes co-dominate with the grasses (Chappell and Crawford 1997). Three broad categories of grasslands can be distinguished based on the type of environment in which they grow. “Prairies” are located on flat to rolling or mounded plains that formed from deep soil deposits, most often consisting of coarse glacial outwash. They can be extensive in area. Most prairies are now located in the southern Puget Sound area. “Balds” are located on shallow-soiled moderate to steep slopes that most often face south or west. Rock outcrops are typically present within or adjacent to balds. Balds are typically naturally smaller in extent than prairies and surrounded by forest. Most balds are located in the northern Puget Lowland. Grasslands can also be located on coastal bluffs of the northern Puget Lowland, where soils are derived from sandy glacial deposits. Many formerly native grasslands are now dominated or co-dominated by non-native grasses, or have been invaded by shrubs, especially Scot’s broom (Cytisus scoparius), Nootka rose (Rosa nutkana), and common snowberry (Symphoricarpos albus). A now-rare fourth major type of native grassland, “wet prairies”, was not mapped as part of this project.

Prior to this project, digital maps of oak woodlands or grasslands existed for specific geographic areas of western Washington, including Fort Lewis, McChord Air Force Base, and Thurston County (Kessler 1990, Macklin and Thompson 1992, Crawford et al. 1995, Rolph and Houck 1996). A map of oak woodlands in the remainder of Pierce County was completed in 1999. In addition, the Washington Natural Heritage Program has been compiling locations of high-quality native grasslands and oak woodlands for many years. A single ecoregion-wide digital cover of oak woodlands and grasslands was envisioned by multiple cooperating partners as a valuable tool for biological conservation and resource planning. The first iteration of such a comprehensive digital cover was completed in 1999 and summarized by Chappell et al. (2001). The product described herein is an updated version of the 1999 cover.

The objective of this project, covering the Puget Lowland and Willamette Valley ecoregions within Washington state, was to create a unified digital map of: (1) untilled grasslands now existing in landscapes that formerly supported native dry grasslands, and (2) oak dominated or co-dominated canopies. The map’s scale and level of detail are designed to be appropriate for both regional-level conservation planning and county-level planning and development screening.

Native grasslands and oak woodlands are some of the most imperiled ecosystems in western Washington (Dunn and Ewing 1997). For example, native grasslands in the south Puget Sound area have declined to less than 3% of their pre-settlement areal extent (Crawford and Hall 1997). Factors contributing to the decline and degradation of these ecosystems include fire suppression and associated conifer tree invasion, invasion of non-native species, grazing, and urban and agricultural conversion (Giles 1970, Agee 1993, Clampitt 1993, Crawford and Hall 1997).

Many species of flora and fauna associated with these unique habitats are of conservation concern due to declines in population, local extirpation, or close associations with the declining habitat. These include the western gray squirrel (Sciurus griseus), Mazama pocket gopher (Thomomys mazama), Lewis’ woodpecker (Melanerpes lewisii), white-breasted nuthatch (Sitta carolinensis aculeata), streaked horned lark (Eremophila alpestris strigata), western meadowlark (Stunella neglecta), Oregon vesper sparrow (Pooecetes gramineus affinis), western bluebird (Sialia mexicana), racer (Coluber constrictor), mardon skipper (Polites mardon), Puget blue (Plebejus icaroides blackmorei), whulge checkerspot (Euphydryas editha taylori), zerene fritillary (Speyeria zerene bremnerii), white-topped aster (Aster curtus), golden paintbrush (Castilleja levisecta), common bluecup (Githopsis specularioides), and rose checkermallow (Sidalcea malviflora spp. virgata) (Dunn and Ewing 1997).

Native grasslands and oak woodlands in the Puget Lowland and Willamette Valley ecoregions (Omernik 1987) are found in dry environments formerly strongly influenced by frequent fires, many if not most of which were ignited by Native Americans (Norton 1979). Oak woodlands may be dominated by Oregon white oak (Quercus garryana), or co-dominated by that species and Douglas-fir (Pseudotsuga menziesii), Oregon ash (Fraxinus latifolia), bigleaf maple (Acer macrophyllum), or Pacific madrone (Arbutus menziesii). They range from open savannas of scattered trees to dense-canopied forests, with a range of herbaceous or shrubby understory types (Agee 1993, Chappell and Crawford 1997). They occur on relatively dry sites or moist riparian environments within prairie, or formerly prairie, landscapes.

Native grasslands are dominated primarily by Roemer’s fescue (Festuca idahoensis var. roemeri), red fescue (Festuca rubra), or California oatgrass (Danthonia californica), but also harbor a wide variety of forbs that sometimes co-dominate with the grasses (Chappell and Crawford 1997). Three broad categories of grasslands can be distinguished based on the type of environment in which they grow. “Prairies” are located on flat to rolling or mounded plains that formed from deep soil deposits, most often consisting of coarse glacial outwash. They can be extensive in area. Most prairies are now located in the southern Puget Sound area. “Balds” are located on shallow-soiled moderate to steep slopes that most often face south or west. Rock outcrops are typically present within or adjacent to balds. Balds are typically naturally smaller in extent than prairies and surrounded by forest. Most balds are located in the northern Puget Lowland. Grasslands can also be located on coastal bluffs of the northern Puget Lowland, where soils are derived from sandy glacial deposits. Many formerly native grasslands are now dominated or co-dominated by non-native grasses, or have been invaded by shrubs, especially Scot’s broom (Cytisus scoparius), Nootka rose (Rosa nutkana), and common snowberry (Symphoricarpos albus). A now-rare fourth major type of native grassland, “wet prairies”, was not mapped as part of this project.

Prior to this project, digital maps of oak woodlands or grasslands existed for specific geographic areas of western Washington, including Fort Lewis, McChord Air Force Base, and Thurston County (Kessler 1990, Macklin and Thompson 1992, Crawford et al. 1995, Rolph and Houck 1996). A map of oak woodlands in the remainder of Pierce County was completed in 1999. In addition, the Washington Natural Heritage Program has been compiling locations of high-quality native grasslands and oak woodlands for many years. A single ecoregion-wide digital cover of oak woodlands and grasslands was envisioned by multiple cooperating partners as a valuable tool for biological conservation and resource planning. The first iteration of such a comprehensive digital cover was completed in 1999 and summarized by Chappell et al. (2001). The product described herein is an updated version of the 1999 cover.