Three-Year Effects of Crown Removal by Clipping or Burning on Beargrass (Xerophyllum tenax) Size and Biomass

Abstract

Beargrass (Xerophyllum tenax), an evergreen perennial herb of the northern Rocky Mountains, Pacific Northwest, and northern California, is used in Native American basketry and commercial floral greens. We studied beargrass size and biomass responses to crown removal by clipping or burning over three years in a coast Douglas-fir (Pseudotsuga menziesii var. menziesii) woodland with variable shrub cover in the southeastern Olympic Peninsula of Washington State. Clipping forested plants resulted in 28% mortality, mostly from smaller plants growing under 26% more total cover than the surviving plants; however, only 3% of completely crown-scorched open-grown plants died. Three years after treatment, crown width of surviving plants was only 61% of the pre-treatment size for clipped plants, compared to 88% for completely crown-scorched plants. Regression analyses indicated that the percentage of crown scorch accounted for only 16% and 27% of crown width and foliar height variation, respectively, one year post-burn, decreasing to 10% and 19% at three years post-burn. During the three years after burning, percentage flowering increased linearly to 64% of plants. Three years post-burn, foliar browse was higher on crown-scorched than on non-crown-scorched plants. Although shade tolerant, long-term survival of lowland beargrass is likely limited by combined competition from shrubs and trees. Stand density management is needed to maintain healthy, reproducing populations in the lowlands of western Washington.