Southwestern Washington Prairies: Using GIS to find rare plant habitat in historic prairies

More than 99% of the grasslands of southwestern Washington (Clark, Lewis, and Cowlitz Counties) have been converted to agriculture and other uses. Remnant grasslands of southwestern Washington support, or did support, four federally listed species and two federal Species of Concern: Nelson’s checker-mallow (Sidalcea nelsoniana), Bradshaw’s lomatium (Lomatium bradshawii), Kincaid’s lupine (Lupinus sulphureus ssp. kincaidii), golden paintbrush (Castilleja levisecta), pale larkspur (Delphinium leucophaeum), and thin-leaved peavine (Lathyrus holochlorus). These grassland areas (“prairies”) also support 12 other species of plants that are considered rare in Washington State.

GIS analysis for inventory and possible re-introduction sites was done using available GIS data layers: soils data derived from the Private Forest Land Grading system (PFLG), USGS GNIS names containing “prairie” or “plain”, the oak/grasslands layer developed by Chris Chappell of WNHP, elevation (below 1500 feet), georeferenced General Land Office (GLO) TIFF files of historical survey cadastral surveys, and digitized delineated prairie areas from the cadastral survey maps. The identified prairie areas were used as a basis for reconnaissance fieldwork in the summer of 2004. We performed an initial reconnaissance in thirty-two separate prairie areas in Lewis, Cowlitz, and Clark counties. Bicycle surveys were used in portions of the area. Nine prairies supported no visible native prairie vegetation. Twenty-three prairies had at least some remnant prairie species, generally along the roadsides. Ten populations of five rare species were found in the course of the survey, including two new populations of Kincaid’s lupine. Most of the populations were found on roadsides or along fencerows.

In addition, the maps produced through GIS analysis were used to identify potential habitat for rare grassland butterflies (results not included in this report), and will be used in 2005 and 2006 as a basis for further rare plant inventory.