Fire effects on spiny hopsage in south central Washington

Grayia spinosa (spiny hopsage) is a dioecious, short~statured, multi~stemmed, summer decidu~ ous shrub erratically distributed across the lowelevation Columbia River plain on the 1400~ lan2 US. Department of Energy's Hanford Site in south central Washington. The Columbia River plain differs from other rangeland habitats in Washington because it has not been grazed by livestock since 1943 and has served as a refugium for native plants and ani~ mals in a surrounding matrix of land devoted to cultivation agriculture and urbanization (Rickard and Rogers 1983, Gray and :Rickard 1989). Daubenmire (1970) studied steppe commu~ nities throughout eastern Washington and observed that burning was not a threat to hop~ sage because it readily sprouted. Rickard and McShane (1984), however, reported that hop~ sage growing with Sarcobatus vermiculatus (greasewood) did not resprout after burning. It is important for rangeland managers to be able to predict the response ofsteppe shrubs to wildfires. Spiny hopsage is a browse species palat~ able to livestock, and hopsage plantings could be useful in rangeland restoration, especially if hopsage sprouts after burning. Managers of conservation areas may need to consider fire protection for hopsage communities as a way to sustain a measure of landscape biodiversity and wildlife habitat, especially when hopsage is easily killed by fire. Small, peripheral populations of otherwise widely distributed species such as hopsage can be reserves of genetic variability and are worthy of protection (Jones et al. 2001). Six botanical study plots were established in 1986 and 1981 on the Columbia River plain adjacent to the Arid Lands Ecology (ALE) Reserve in south central Washington. This location had been selected as a pOSSible location for a deep underground repository for highly radioactive waste (Rickard and Schuler 1989). Each plot was 50 x 50 m with the perimeter marked with steel posts at 5-m"intervals. Shrub density was determined by counting all shrubs greater than 0.2 m tall in each plot. Shrub canopy cover was measured by line intercept, " and herb cover by species was ocularly estimated along three 40-m transects systemati~ cally spaced in each plot using the canopy coverage method of vegetational analysis proposed by Daubentnire (1959). The repository project was abandoned in 1988, but all plots remained undisturbed until a massive wildfire burned through the repository location and allof the adjacent 30,000-ha ALE Reserve on or about 1 July 2000. Each plot was resurveyed during spring and summer 2001 and spring 2002 with particular atten~ tion to sprouting of spiny hopsage. Five of the 6 study plots supported hopsage shrubs in 1987 (Table 1). According to Rickard and Schuler (1989), the sparse herbaceous understory was dominated by Bromus tectorum (cheatgrass) and Poa secunda (Sandberg's bluegrass). Most of the combustible fuel in all study plots was wood. Hopsage was the only shrub species on 1 plot and it was subordinate to Artemisia tridentata (Wyoming big sage~ brush) on the other plots. All hopsage shrubs on the study plots and surrounding areas were burned in July 2000 (Fig. 1). Only 1 hopsage shrub on plot 2H sprouted after the 2000 wildfire (Fig. 2). None of the hopsage shrubs on the other plots sprouted. One Purshia tridentata (bitterbrush) shrub escaped burning on plot 6S along with a few Ericameria nauseosa