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Impacts of Invasive Plant Species - aka Noxious Weeds

“Invasive plants are ecological tumors that won’t stay in your yard.”
– Dr Doug Tallamy

Noxious Weeds...

  • Are invasive plant species that are able to establish easily, grow quickly, and spread to the point of disrupting biological communities or ecosystems. 

  • Are known as "habitat transformers" because they change the physical structure and forage availability in habitats, eventually pushing out resident wildlife.

  • Are a biodiversity threat, as they are capable of causing extinctions of native plants and animals, reducing biodiversity, competing with native organisms for limited resources, and altering habitats. This can result in fundamental disruptions of local ecosystems.



Noxious Weeds...


  • Reduce forage - spotted knapweed has reduced available winter forage for elk by 50-90% 

  • Alter thermal and escape cover

  • Change water flow and availability to wildlife

  • May reduce territorial space necessary for wildlife survival

  • Disrupt seasonal distribution patterns

Water & Fish

Noxious Weeds...


  • Increase soil erosion, thus decreasing water holding capacity and storage

  • Alter hydrologic cycles in riparian areas, lower the water table, and affect flooding cycles

  • Increase sedimentation of streams, impacting spawning grounds and food sources

In areas dominated by spotted knapweed, runoff is 1.5 times higher and sediment yield was found to be 3 times higher (Lacey, et all. 1989)

Rainbow Trout, Gallatin River, Montana.jpg
Bitterroot Crop

Native Plants

Noxious Weeds...


  • Reduce biodiversity

  • Replace complex communities with simple communities

  • Displace rare plant species

  • Serve as reservoirs of plant pathogens

  • Compete for pollinators


Noxious Weeds...


  • Reduce the value of land

  • Require resources (time and money) to manage

  • Impact neighborly relations, as inaction by one landowner negatively affects others

  • Degrade aesthetic values


Recreation & Hunting

Noxious Weeds...


  • Reduce recreation & hunting access on private lands

  • Alter habitat for game animals and fish

  • Decrease success of hunters and anglers

  • Increase cost to manage trail systems


Noxious Weeds...


  • Alter fire intensity and frequency

  • Modify successional pathways

  • Act as alternate hosts for insects and diseases

  • Initiates a process that many scientists believe is the beginning of desertification

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