Descriptions of plant communities at the proposed reference repository location and implications for reclamation of disturbed ground

This report presents an ecological description of the natural vegetation in the Cold Creek Valley located in the west central portion of the US Department of Energy's (DOE) Hanford Site in southeastern Washington state. The description includes plant species composition, canopy cover, and shrub density obtained from 10 study plots distributed in three habitat-types: sagebrush/Sandberg's bluegrass, spiny hopsage/Sandberg's bluegrass, and sagebrush/needle-and-thread grass. Of the relatively few species of shrubs and herbs in the Cold Creek Valley, the most abundant were sagebrush and spiny hopsage. The most abundant herbs were cheatgrass, Sandberg's bluegrass, and needle-and-thread grass. The amount of canopy cover provided by shrubs ranged between 7.4 and 33% in seven plots without a history of recent burning. Herbaceous plants in these same plots provided canopy cover that ranged between 18 and 41%. The three plots placed in areas with a recent history of burning had more herbaceous cover than did adjacent plots without a recent burn history. This was attributed to absence of living shrubs and freedom from competition for soil water and nutrients. There was less living herb cover in 1987 than in 1986 which is likely due to the lesser amount of growing season precipitation in 1987 (i.e. 10.3 cm vs 17.1 cm). Even with the absence of livestock grazing for 44 years, cheatgrass, an exotic annual generally provided more canopy cover than native perennial grasses. However, in the few places with good stands of Sandberg's bluegrass, cheatgrass was less abundant. 12 refs., 6 figs., 6 tabs