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Title: LONG TERM EFFECTS OF TEBUTHIURON ON BROMUS TECTORUM

Author
item Blumenthal, Dana
item NORTON, URSZULA - PAST POST-DOC
item Derner, Justin
item Reeder, S

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2006
Publication Date: 12/8/2006
Citation: Blumenthal, D.M., Norton, U., Derner, J.D., Reeder, S.J. 2006. Long term effects of tebuthiuron on bromus tectorum. Western North American Naturalist. 66:420-425.

Interpretive Summary: The use of herbicides to thin dense stands of Artemisia spp. (sagebrush) can free up resources for herbaceous plants and increase forage production, but may also facilitate weed invasion. We revisited a sagebrush thinning experiment in a North-central Wyoming big sagebrush-grassland 11 years after application of the herbicide tebuthiuron. Our objectives were to determine the long-term responses of shrubs, available soil resources and Bromus tectorum L. (downy brome) to the herbicide application. We found that after 11 years, hercide treated plots still contained less than half the shrub cover of untreated plots. Downy bome cover increased four-fold in response to herbicide treatment. We also found that shrub death resulted in increased availability of nitrate, a key soil resource for downy brome, but did not find differences in soil water content. The relatively recent expansion of downy brome populations at this site, together with the high nitrate levels observed under dead shrubs suggest that conditions facilitating downy brome invasion may persist for many years following sagebrush thinning. These results demonstrate that sagebrush thinning can cause long-term increases in downy brome populations, and suggest that caution should be used when considering thinning sagebrush if downy brome is present, even if intial populations are small.

Technical Abstract: The use of herbicides to thin dense stands of Artemisia spp. (sagebrush) can free up resources for herbaceous plants and increase forage production, but may also facilitate weed invasion. We revisited a sagebrush thinning experiment in a North-central Wyoming big sagebrush-grassland 11 years after application of tebuthiuron to determine the long-term responses of shrubs, available soil resources and Bromus tectorum L. (downy brome). Treated plots contained 48% of the live shrub cover (p=0.002) and 3.9 times the downy brome cover (p=0.02) of untreated plots, but differences were not found in cover of perennial grasses or bare ground. In comparisons of resource availability among microsites available NO3 was higher under dead shrubs than under live shrubs (p=0.03). No significant differences in soil water content were detected. The relatively recent expansion of downy brome populations at this site, together with the high NO3 levels observed under dead shrubs suggest that conditions facilitating downy brome invasion may persist for many years following sagebrush thinning. These results demonstrate that sagebrush thinning can cause long-term increases in downy brome populations, and suggest that caution should be used when considering thinning sagebrush if downy brome is present, even if intial populations are small.