Monitoring smooth brome (Bromus inermis) within the Christ’s paintbrush (Castilleja christii) population at Mount Harrison, Idaho

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Christ’s paintbrush (Castilleja christii ) is a perennial herbaceous plant known from a single population near the summit of Mount Harrison, at the northern end of the Albion Mountains, in south-central Idaho. Christ’s paintbrush is a former U.S. Fish and Wildlife Service Candidate for listing under the Endangered Species Act, and also a Sensitive plant species for the Sawtooth National Forest, on whose land the entire population occurs. The major conservation concern for the species in recent years has been the establishment and spread of smooth brome (Bromus inermis), an introduced and invasive grass species, within portions of the Christ’s paintbrush population. Efforts to control smooth brome began in 2003, with herbicide application and/or other treatments taking place each year since then. A program to monitor the efficacy of smooth brome control efforts and possible impacts to Christ’s paintbrush was initiated in 2006. Monitoring also occurred in 2007 and 2008. Sampling takes place in a series of nine paired plots (total of 18 plots), three pairs in each of the three community types supporting Christ’s paintbrush – snowbed, graminoid, and mountain big sagebrush. For each pair, one plot occurs in an area invaded by smooth brome, the other in a nearby area lacking smooth brome. After a lapse of four years, all plots were resampled in 2012. This report reviews the monitoring protocols, summarizes 2012 monitoring results, analyzes comparisons to the earlier datasets, and discusses results in context of the monitoring program objectives. <br>

In 2012, mean canopy cover was 0.7% and mean frequency 31% for smooth brome on invaded transects, values significantly less compared to 2006 and 2007, but not 2008. The decrease in smooth brome is very likely a direct result to the control program, although the lack of untreated control plots precludes an unequivocal cause and effect determination. Nearly all of the decrease in smooth brome abundance occurred between 2006 and 2008, the period coinciding with the most aggressive, multi-treatment control applications. Although smooth brome abundance has declined, monitoring results suggest a once-a-year herbicide treatment program as applied since 2010 may be insufficient to make further gains in reducing smooth brome abundance within the Christ’s paintbrush population. Mean canopy cover and frequency values for Christ’s paintbrush on invaded transects have remained approximately the same since 2006. In addition, tallies for Christ’s paintbrush were higher or approximately the same in 2012 compared to previous years on most invaded transects. Christ’s paintbrush has maintained its level of abundance concurrent with the large decline in smooth brome abundance on invaded transects. This indicates smooth brome removal has not been detrimental to Christ’s paintbrush. The most puzzling monitoring results from 2012 involves Christ’s paintbrush abundance on non invaded transects. Both mean canopy cover and frequency were significantly less compared to 2006, 2007, and 2008 values. In addition, 2012 counts for Christ’s paintbrush were less compared to previous years on most non-invaded transects. There appears to be no ready explanation for this result, but perhaps is related to the inherent variability in abundance past monitoring has documented for Christ’s paintbrush. At the plant community scale, smooth brome control treatments have not eradicated any native plant species, nor altered native species composition to a notable degree within Christ’s paintbrush habitat. The dramatic decline in smooth brome abundance highlights the success of conservation actions taken on behalf of Christ’s paintbrush. Monitoring will continue to be an important conservation tool for Christ’s paintbrush by providing land managers relevant and timely information for continued proactive conservation actions.

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Reference Code: U13MAN03IDUS <br>

Full Citation: Mancuso, Michael. 2013. Monitoring smooth brome (Bromus inermis) within the Christ’s paintbrush (Castilleja christii) population at Mount Harrison, Idaho. Report prepared by Mancuso Botanical Services for U.S. Fish and Wildlife Service, Idaho Fish and Wildlife Office, Boise, ID. 39 pp, plus appendices <br>

Location: ELECTRONIC FILE - BOTANY: PLANT SPECIES: Castilleja christii <br>

Keywords: Bromus inermis, Castilleja christii, Cymopterus davisii, monitoring, Mount Harrison, Idaho <br>