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Long-Term Effects of Weed Control With Picloram Along a Gradient of Spotted Knapweed Invasion
Issue Date
2011-01-01Keywords
broadleaf herbicideCentaurea maculosa
cheatgrass
exotic plants
grassland restoration
native plant functional groups
Metadata
Show full item recordCitation
Ortega, Y. K., & Pearson, D. E. (2011). Long-term effects of weed control with picloram along a gradient of spotted knapweed invasion. Rangeland Ecology & Management, 64(1), 67-77.Publisher
Society for Range ManagementJournal
Rangeland Ecology & ManagementAdditional Links
https://rangelands.org/Abstract
Broadleaf herbicides are commonly used in rangelands to suppress exotic weeds and release native communities from negative impacts of invasion. However, few studies have comprehensively evaluated treatment effects on differing community components across a gradient of initial invasion levels. We conducted a 6-yr experiment within grasslands of western Montana to measure local- scale effects of a broadcast application of picloram on 1) cover of the target invader, spotted knapweed (Centaurea stoebe L.), 2) prevalence of native functional groups, and 3) the secondary invader cheatgrass (Bromus tectorum L.) at differing initial levels of knapweed invasion. Treatment effectively suppressed knapweed, with cover in treated vs. control plots reduced by > 60% in the sixth posttreatment year. Treatment also appeared to alleviate knapweed’s impacts on native perennial grasses, but only at the highest initial level of invasion, where cover of this group increased by > 30% in treated vs. control plots to equal levels associated with noninvaded plots. In some cases, treatment appeared to exacerbate knapweed’s impacts on native forbs. At the no-invasion level, perennial forb cover declined by > 20% in treated vs. control plots to match values associated with moderate or high levels of invasion, but these treatment effects were minimal at the latter invasion levels. Across initial invasion levels, species richness of perennial and/or annual forbs declined by > 20% in treated vs. control plots. Treatment also promoted increases in cheatgrass cover, although differences between treated and control plots were relatively small by the sixth posttreatment year. Overall, effects of picloram application depended on initial levels of knapweed invasion, largely due to the varying strength of release effects. Selective treatment of invaded patches vs. broadcast applications would reduce side effects of broadleaf herbicide application and increase compatibility with other management measures designed to improve rangeland conditions and restore grassland communities.Type
textArticle
Language
enISSN
0022-409Xae974a485f413a2113503eed53cd6c53
10.2111/REM-D-10-00034.1