Vegetation Conversion to Desirable Species Along Caltrans Rights-of-Ways

摘要

This study evaluates several establishment sequences to determine effective ways to convert existing annual non-native vegetation to native perennial species. Sustained weed control for several years is shown to be required for vegetation conversion. No single treatment was sufficient, but each provided different weed control characteristics. Burning provides control of non-native seeds and plants and stimulates native perennial plant growth. Tillage prepares the seed bed, stimulates germination of weed seed and provides soil volumes for root penetration. Ecotypic plant species are thought to be adapted to different topographic zones away from the road edge. Herbicide use was important to selectively reduce non-native annual plant species. Chemical treatments to control weeds included 1) postemergence, non-selective (glyphosate), 2) postemergence, broadleaf selective (clopyralid) and 3) preemergence, non-selective (chlorsulfuron). After vegetation conversion, herbicide use is shown to be reduced or eliminated except for occasional weed control. After three years of cultural and chemical management, we found native perennial grasses most abundant in sites that had been burned once and sprayed at least twice. In established roadside stands of native perennial grasses, a combination of spraying, mowing and/or burning for two consecutive years is required to reduce or eliminate non-native, invasive species, such as yellow starthistle. Once established, native perennial grass stands can persist for more than a decade and remain relatively weed resistant.