, Volume 33, Issue 3, pp 409–420 | Cite as

Exotic Plant Colonization and Occupancy Within Riparian Areas of the Interior Columbia River and Upper Missouri River Basins, USA

  • Robert Al-ChokhachyEmail author
  • Andrew M. Ray
  • Brett B. Roper
  • Eric Archer


Exotic plant invasions into riparia often result in shifts in vegetative composition, altered stream function, and cascading effects to biota at multiple scales. Characterizing the distribution patterns of exotic plants is an important step in directing targeted research to identify mechanisms of invasion and potential management strategies. In this study, we employed occupancy models to examine the associations of landscape, climate, and disturbance attributes with the colonization and occupancy patterns for spotted knapweed (Centaurea stoebe L.), Canada thistle (Cirsium arvense L., Scop.), and cheatgrass (Bromus tectorum L.) in the riparia of headwater streams (n = 1,091) in the Interior Columbia River and Upper Missouri River Basins. We found relatively low occupancy rates for cheatgrass (0.06, SE = 0.02) and spotted knapweed (0.04, SE = 0.01), but moderate occupancy of Canada thistle (0.28, SE = 0.05); colonization rates were low across all species (<0.01). We found the distributions of spotted knapweed, Canada thistle, and cheatgrass to exhibit significant associations with both ambient climate conditions and anthropogenic and natural disturbances. We attribute the low to moderate occupancy and colonization rates to the relatively remote locations of our sample sites within headwater streams and urge consideration of means to prevent further invasions.


Exotic plants Occupancy model Riparia Headwaters 



Funding for R. Al-Chokhachy was in part through the U.S. Geological Survey Mendenhall Fellowship Program. We would like to thank the extensive list of summer field technicians who collected the data for these analyses and A. Sepulveda (U.S. Geological Survey) for reviewing and contributing to earlier drafts of this manuscript. The U.S. Forest Service regions 1, 4, and 6 and BLM offices in Oregon–Washington and Idaho provided funding for this project. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.


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Copyright information

© US Government 2013

Authors and Affiliations

  • Robert Al-Chokhachy
    • 1
    Email author
  • Andrew M. Ray
    • 2
  • Brett B. Roper
    • 3
  • Eric Archer
    • 3
  1. 1.U.S. Geological SurveyNorthern Rocky Mountain Science CenterBozemanUSA
  2. 2.Greater Yellowstone Network, National Park ServiceBozemanUSA
  3. 3.U.S. Department of Agriculture, Forest ServiceLoganUSA

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