Invasive Exotics Narrative

Inside and outside of Waterton-Glacier International Peace Park (W-GIPP), a threat is exploding in slow motion. Imagine litter that reproduces itself and grows exponentially when it is thrown next to a trail. It is happening, because the “litter” is biological. Exotic plants become invasive, or noxious “weeds” when they are poisonous or unpalatable to wildlife, and they out-compete native plants for space to a point where native plants are displaced from that habitat. Spotted knapweed, for example, was introduced into Missoula county about 50 years ago and now infests over 5 million acres in Montana and an unknown amount of land in Alberta.

Spotted knapweed spreads quickly because each plant produces 18,000 seeds every year and it chemically prevents native plants from growing near it. A new invader, tansy ragwort produces 150,000 seeds per plant and each seed can lie dormant for 15 years waiting for the right growing conditions! Leafy spurge infests over a million acres in the W-GIPP area. It is deep-rooted, the roots spread 25 feet vertically and 15 feet horizontally, and it typically reduces native species by 90% or more where it grows. Its sap is poisonous to the taste and to the skin of wildlife, so they avoid any area with leafy spurge.

Weeds have been called “growing pains,” “silent invaders,” “botanical barbarians” and many other non-complimentary names by government agencies – for good reason. They infest 100 million acres in North America, 3 million more each year. They have claimed more than 7 million acres of National Park land, and infest 10 square miles of public and Crown land every day!

Succession patterns of native plants are relatively slow and predictable. Not so with invaders. Spotted knapweed is often succeeded by sulfur cinquefoil, and then leafy spurge and dalmatian toadflax. Each of the succeeding plants is harder to kill.

So what, you say. Isn’t it just survival of the fittest, nature’s way? Not exactly. Waterton-Glacier is one of the world’s best places for biodiversity. Many plants and animals from very different places converge here. The Pacific, Atlantic and Arctic watersheds converge here, bringing a fantastic array of species into one place. It is a major reason why the Peace Park has International Biosphere Reserve and World Heritage Site status.

Weeds could easily change that. Every ecological study ever done on noxious exotic plants shows that they reduce biodiversity drastically – they simplify the ecosystem and make it more vulnerable to disease, further infestations and extinctions. Insects disappear, then birds, then small mammals and their larger predators. Weeds are indeed a threat to W-GIPP, and to most areas outside the park as well.

Besides destroying wildlife habitat and biological diversity, weeds can have severe impacts on grazing land, increase erosion, reduce crop production, reduce land value, and are expensive to control once infestations become large.

Here is a list of noxious weeds in our area:

  • Spotted knapweed
  • Purple loosestrife
  • Russian knapweed
  • Common crupina
  • Diffuse knapweed
  • Rush skeletonweed
  • Dalmatian toadflax
  • Tansy ragwort
  • St. Johnswort
  • Oxeye daisy
  • Canada thistle
  • Orange hawkweed
  • Sulfur cinquefoil
  • Meadow hawkweed
  • Field bindweed
  • Houndstongue
  • Leafy spurge
  • Absinthe wormwood
  • Whitetop
  • Tamarisk (saltcedar)
  • Common tansy
  • Tall buttercup
  • Dyer’s woad
  • Mullien
  • Yellow starthistle
  • Burdock

Weeds will never be eliminated. The best that can be hoped for is aggressive control measures will keep them in check. The options for control are hand removal, repeated mowing, grazing (goats seem to work best because they will eat plants other animals won’t), chemical herbicides and biological control with insects specific to the weed plant. Some of these methods work with some plants and some don’t. Each plant has a preferred method or combination which works best. It is rarely a one-time process. Total eradication often takes repeated control processes – sometimes it takes years.

Prevention is surprisingly effective. Our outdoor activities, such as ATV trail riding, horseback riding, hiking and hunting, snowmobiling and fishing, often accelerate the spread of weeds because we can inadvertently transport seeds from one area, into others.

An integrated exotic plant management plan, using combinations of all of the above methods, is the best hope we have of stopping an “explosion” from leveling the health of our plant and animal diversity. Anything we can do as individuals will help.


Non-Natives in Glacier
Native species have taken millions of years to develop complex interactions with other species in shared habitats and exploit a tremendous variety of niches in both terrestrial and aquatic ecosystems. Whenever non-natives are introduced the consequences are always unpredictable, frequently unexpected, and more often than not detrimental to the natural equilibrium that previously existed. Glacier Park is no exception to these principles.

At least 127 non-native species of plants have either invaded or been deliberately introduced into the Park. Currently, over 800 sites of nuisance plant infestations impacting more than 2500 acres have been discovered. Routine monitoring by park biologists regularly reveals new infestations. Eighteen species of exotics plants are of sufficient concern to be targeted for control measures. The North Fork prairies are threatened by leafy spurge and yellow toadflax. Without the natural limitations of their original environment, exotic plants often tend to be highly prolific and develop a monoculture that is difficult or impossible to displace. Leafy spurge, for example, has a deep root system which is difficult to kill with even the most powerful chemicals.

Spotted knapweed and ox-eye daisy have invaded disturbed areas throughout the Park. Common timothy and other exotic grasses were introduced intentionally for horse grazing and unauthorized grazing of other stock within the park has spread nonnative weeds as well. Control measures have been only partially successful in slowing the spread of these infestations. Biodiversity among native plants is seriously threatened and only a major sustained effort will restore some of these systems.

Glacier Park's aquatic systems have been tinkered with for nearly a century, primarily through game fish introductions for recreational angling. This practice was was scaled back Lake trout, native to a few lakes in the Hudson Bay drainge of the park, have been introduced to several west-side lakes. The highly predacious foraging behavior of lake trout has had a catastrophic effect on native fish including the Federally listed bull trout. Further complicating the situation, introduced brook trout can hybridize with bull trout and produce sterile offspring. Introduced kokanee salmon and Lake Superior whitefish compete for food with native westslope cutthroat trout. Introduced rainbow trout also hybridize with the native cutthroat trout and corrupt their gene pool.

Full restoration of the native fishery in Glacier Park is impossible at this stage, but limited rehabilitation of native fish populations in some waters may be feasible. Partial recovery of native fisheries in the Park will come about only through further study, increased funding and aggressive management in cooperation with neighboring agencies.

Last updated: November 6, 2017

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West Glacier, MT 59936


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