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Effectiveness of Invasive Weed Management in National Parks

by Wyoming Livestock Roundup

The goals of weed management programs vary among types of properties and individual properties, depending on the desired land use. We often discuss weed management benefits in terms of increasing forage for livestock, reducing crop yield losses, etc., but other goals, like increasing species diversity or improving aesthetics, may also be important. 

Land management groups may have different perspectives on how active humans should be in the conservation or preservation of natural resources. Establishing protected areas with reduced consumptive, human-directed land use may protect those areas from development, mismanaged logging or grazing or other potential negative impacts, but removing active management of invasive weeds may negatively impact the reasons those lands were set aside for preservation in the first place. The “leave it alone” approach is insufficient for maintaining species diversity and habitat quality in areas impacted by invasive weeds.

U.S. National Parks were established to preserve significant cultural and natural features unimpaired for future generations, and some of the parks face impairment of natural features by invasive weeds. About 4,000 exotic plant species are estimated to be established in parks across the U.S. A recent review published in the journal Invasive Plant Science and Management (Effectiveness of Exotic Plant Treatments on National Park Service Lands in the United States, S.R. Abella, 2014) reveals some interesting trends regarding invasive weed control efforts within the National Park System. 

Much of the published literature on weed control in National Parks comes from Florida or Hawaii – perhaps the most “invaded” states in the country. Park weed managers are having some success with weed control because the majority, more than 80 percent, of treatments in studies reduced the target weed species. Approximately half of the reviewed studies indicated an increase in native species when weed control was implemented. A minor pattern revealed, yet a legitimate concern for many land managers, is the replacement of one invasive weed species with another weed species following control efforts. 

Weed managers in the National Park system face similar challenges as other land managers. Current understanding of distribution and severity of weed infestations within and among parks is limited. Remote locations, vast acreages and challenging terrain make comprehensive weed mapping difficult for many parks. Reliable data supporting control recommendations for thousands of target weed species is hard to come by, and the logistics of providing site-specific research for so many species is nearly impossible. The research that exists is primarily of a short-term nature and often limited to only one treatment, with no follow-ups. 

This summer, as every other summer, tourists will flock to National Parks around the country. They will take in the iconic scenery, view wildlife in their natural habitats and create memories for years to come. Will they understand the ongoing efforts of Park personnel to actively reduce the expansion and potential impacts of non-native species in those areas? Will future generations be able to have the same quality of experience? 

Brian A. Mealor is an assistant professor and Weed Extension Specialist at the University of Wyoming and can be reached at More information about ongoing weed science research at the University of Wyoming can be found at

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