Assessment of invasive Bromus inermis (smooth brome) in Castilleja christii (Christs paintbrush) habitat, Mount Harrison, Idaho

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Castilleja christii (Christ’s paintbrush) has been a Candidate for Threatened and Endangered listing since 1980. This perennial forb with showy yellow to yellow-orange bracts is known from a single population near the summit of Mount Harrison, in Cassia County, Idaho. The population extends over ~81 ha (200 ac) of Sawtooth National Forest land. It is threatened by the recent invasion of non-native species, particularly Bromus inermis (smooth brome)—a rhizomatous, perennial grass that competes with and displaces native vegetation. In 2003, the US Forest Service and US Fish and Wildlife Service began funding B. inermis treatment using hand-pulling; in 2004, hand-wicking with the herbicide ‘Roundup’ was initiated with careful efforts to avoid C. christii; in 2005 and 2006, herbicide was applied earlier in the year, followed by hand-removal of the seed heads; in 2007, 2008, and 2009, herbicide applications were increased to three times during the growing season, and seed heads removal and hand-pulling of plants increased to two times. In July 2006, US Fish and Wildlife Service funded initiation of a study to compare C. christii, other native species, and B. inermis in areas with and without B. inermis invasion and treatment. While this study cannot evaluate the effects of treatment per se, because treatment began in 2003, and no invaded areas were left as untreated controls, it does provide comparisons between sites that were invaded and treated and those that were neither invaded nor treated. It also documents baseline levels of B. inermis, C. christii, and other species for comparisons in future years and provides a means of detecting other invasive species. In Jul 2007 and 2008, my colleagues and I returned to the established transects and collected data following the protocol developed in 2006. These data included photo points and canopy and ground cover estimates within 20 x 50-cm frames along 20-m transects. We also initiated counts of C. christii individuals within 1 x 1-m frames along the transects and collected data on other non-native species within the study area. Our analysis across all transects showed that in comparison to sites that were neither invaded nor treated, the invaded and treated transects had higher mean canopy cover and frequency of B. inermis and lower cover of most native species, including C. christii, Festuca idahoensis (Idaho fescue), Lupinus argenteus (silver lupine), Penstemon rydbergii (meadow beardtongue), and Cymopterus davisii (Davis’ wavewing), which is also a rare species. Exceptions to this pattern were the native species Artemisia tridentata spp. vaseyana (mountain big sagebrush) and Solidago multiradiata (Rocky Mountain goldenrod), which had higher mean cover and frequency on invaded/treated transects. Mean ground cover was higher for litter, and lower for bare ground, rock/gravel, and basal vegetation on invaded/treated transects than on non-invaded/non-treated transects. Mean density of C. christii individuals in all categories on invaded/treated transects was only half that of non-invaded/non-treated transects (e.g., 2.5 vs. 5.6 plants/m2 and 2.3 vs. 5.2 flowering stems/ m2 in 2007; 2.0 vs. 4.7 plants/m2 and 3.3 vs. 7.7 flowering stems/ m2 in 2008). Due to the study design (starting three years after treatment began and having no controls), the differences found cannot be attributed to invasion, treatment, a combination of the two, or other factors (e.g., soil disturbance) that existed before invasion. But the differences found seem most likely to be caused by invasion alone. From 2006 to 2008, mean canopy cover of B. inermis decreased on the invaded transects (5.9, 4.1, and 0.83% over the three years), and remained very small (<0.02) on the non-invaded transects. Mean frequency of B. inermis also decreased on the invaded transects (62.8, 58.3, and 36.1% over the three years), and remained small (<1.2%) on the non-invaded transects. These declines appear to be due to treatment, rather than some other factor (e.g., disease). As B. inermis declines and native vegetation recovers, the differences between the invaded and non-invaded transects are expected to disappear.

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Reference Code: U11KIN02IDUS <br>

Full Citation: C. Lynn Kinter. 2011. Assessment of invasive Bromus inermis (smooth brome) in Castilleja christii (Christ’s paintbrush) habitat, Mount Harrison, Idaho. Idaho Natural Heritage Program, Idaho Department of Fish and Game, Boise, Idaho. 34 pp. plus appendices <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES {Castilleja christii}