Invasive Exotic Weeds

One of the many perplexing challenges land managers face is the threat that invasive exotic plants (sometimes also called exotics or exotic weeds) present. This is a particularly difficult problem for National Parks because our mission is to retain naturally functioning ecosystems. Invasive exotic weeds can upset natural processes and often use that "strategy" to spread. Exotic weeds are not native to the area they are invading. As a result, they frequently have few effective predators, competitors, parasites, or diseases. They can spread across a landscape quickly and replace native species that have important functions in the ecosystem.

Exotic weeds upset natural processes in a variety of ways. Some are poison if consumed by wildlife. Some release compounds into the soil to prevent the seeds of other plants from germinating. Some produce such thick aggregations of plants, they shade out native plants. In a study conducted in Rocky Mountain National Park, researcher Sara Simonson found that exotic thistles attracted pollinators away from native plants. It is likely that the native plants could not produce as many seeds as a result. This not only disrupts native plants, but also the butterflies themselves. Butterfly caterpillars often feed on only one or two types of host plants. With fewer native plants, the adult butterflies may not be able to find the necessary host plants on which to lay their eggs in future years. Thus the natural ecosystem processes are even more disrupted.

Currently the park is using a variety iof different strategies to control exoctic weeds. One of the largest and most labor intensive is to hand pull weeds. While this takes a lot of time, and involves a great deal of effort from both park staff and volunteers, it is an effective strategy for some species. Other mechanical controls can involve digging, mowing, cutting off seed heads before they can release their seeds, or scalding plants with steam to kill them. After careful evaluation, the park sometimes uses biological controls - insects that target the weed, and have been shown not to harm native species.

Noxious weeds are a subset of invasive exotic weeds that land owners are required by law or regulation to control. If you are interested in learning more about exotic or noxious weeds in and around Rocky Mountain National Park, there are noxious weed lists available for Larimer County, Boulder County, and Grand County, the three counties in which parts of the park are located. Also, check out the park's list of exotic plants.

Last updated: March 31, 2012

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