North Central Washington

Risky Business: Invasive species management on National Forests - A review and summary of needed changes in current plans, policies and programs

Chapter 5 - Prevention

Report Published by Kettle Range Conservation Group (
February, 2001
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Prevention of new invasions and the prevention of the spread of existing infestations should be the top priority of Forest Service invasive species programs. To date, this is not occurring. Pacific Northwest Forests that have been using herbicides during the 1990s are still not in compliance with the stipulation in the Mediated Agreement (1989), to “detect and ameliorate the conditions that cause or favor the presence of competing or unwanted vegetation,” i.e., to use prevention.

Agency weed management plans and publications typically emphasize weed control and eradication using herbicides rather than prevention (Sheley et al., 1988; Sheley, 1994; BLM, 1996; Santa Fe NF, 2000; Deschutes NF, 1988; Okanogan NF, 1997, 1999; Colville NF, 1998). A large number of prevention measures are available for managers (see Appendix A), but these often go unheeded.

As an example, weed management plans such as the Integrated Weed Management Environmental Assessments (EAs) produced by the Okanogan NF (1997), called for herbicide spraying on approximately half of 10,000 infested acres as the main treatment method for noxious weeds. Although the EA stated that prevention is the most important method to stop the spread of noxious weeds, it gave little attention on how prevention would take place or what changes would have had to occur for prevention to work.

The Integrated Noxious Weed Treatment EA for the Colville NF (1998, p. II-13), states that “(p)revention is incorporated into the alternatives discussed in this document only to the extent that treatment activities would reduce or prevent the need for treatments in the future”. Essentially, the agency is only willing to consider the concept of prevention within the scope of the current treatment plan, while ignoring the great majority of infestations spreading through other activities such as logging, road-construction, and livestock grazing.

These plans focus on the concepts of reduction, mitigation and continual treatment of infestations as their way of preventing further infestations; however, this fails to consider the underlying factors that cause invasive species to spread into new areas and fails to prevent further infestations. The treatment plans are merely symptomatic, and they lack prevention measures that could be a viable means to control the threat of plant invasions.

Section A. Preventive measures must receive high priority.

Prevention implies an impediment, hindrance, or preclusion. Compared to reduction, which implies a lessening or decline, or mitigation, which implies relief or alleviation; prevention calls for a barrier to the spread of invasive species, not a band-aid.

The Forest Service places a low priority on incorporating prevention measures into ongoing activities, including logging, livestock grazing and road maintenance and use. Little consideration is given to limiting or modifying the activities that cause weed invasions on public lands. This lack of responsibility must change if the agency is going to take their role in prevention seriously.

When the Forest Service conveys an intention to use prevention measures, it is usually given as a rationalization for a management action, e.g., thinning a forest to prevent stand-replacing fires, which are assumed to bring in more weeds. Rarely is the action itself examined for its role in the actual causes of weed spread and suitable prevention measures, e.g., reduction of soil disturbance.

As another example of this piecemeal approach to prevention, the Forest Service frequently acknowledges the presence of weeds along heavily traveled roads, while failing to connect that with the logical cause—motorized vehicles, ORVs and livestock, which all transport the seeds of damaging exotic species.

The willingness to allow and even encourage activities that spread weeds without tracking the consequences is the real culprit in the process of alien plant invasions. While it might be true that vehicles, logging equipment, or livestock actually transport weed seeds, it is the agency’s refusal to act on this promotion of plant invasions that degrades public lands.


Section B. Plans need comprehensive prevention strategies.

In order to reverse the invasion of public lands by aggressive and exotic species, plans and programs should incorporate comprehensive prevention strategies. A large number of prevention measures are given in Appendix A.

In addition to the specific requirement made in the Mediated Agreement (1989) that the Region 6 Forest Service use a prevention strategy prior to using herbicides, scientists and agencies widely agree that prevention is the least expensive and most effective way to manage plant invasions:

Early detection and treatment of invasions before explosive spread occurs will prevent many future problems—Hobbs and Humphries (1995).

Prevention and early detection are the best means of limiting weed problems—Youtie (1997).

Effective prevention and control of biotic invasions require a long-term, large-scale strategy rather than a tactical approach focused on battling individual invaders—Mack et al. (2000).

Goal 4 - Prevention and detection: develop a prevention and early detection program—Bureau of Land Management (1996).

The Invasive Species Council’s Risk Analysis and Prevention Working Group (2000) explored issues related to developing a comprehensive, systematic strategy to prevent the introduction and spread of invasive species into United States ecosystems. The Working Group recognized that invasive species threaten our environment, agriculture, human health, economy, and quality of life, then outlined a prevention strategy:

A successful prevention strategy assesses and mitigates risk of entry, establishment, and spread of invasive species by considering pathways for movement of invasive species, characteristics of individual invasive species organisms regardless of pathways, and inherent vulnerability of ecosystems.

The components of a successful prevention strategy that the Working Group came up with include:

1) Risk assessments of known pathways for intentional and unintentional introductions of invasive species;

2) Organism level risk assessments of known invasive species independent of pathways;

3) Ecosystem level risk assessments to rank ecosystem vulnerability;

4) Assessment of gaps in the safety net protecting U.S. ecosystems by arraying results of pathway, organism, and ecosystem risk analyses;

5) Evaluation and application of measures to close gaps in the safety net

6) Identification of research needs in the area of prevention of invasive species;

7) Recognition of the tendency for many introduced species to exhibit a long (> decades) lag phase between introduction, establishment and expansion and that this lag phase may offer “windows of opportunities” for risk management.

The first three of these components are concerned with prioritizing the likelihood of plant invasions through an analysis of the pathways (processes) that lead to invasion; the characteristics of species involved in an invasion; and the characteristics of the invaded ecosystem (site-specificity), respectively. The fourth and fifth components are concerned with developing legal and procedural measures that will minimize these risks. The sixth component seeks to insure that prevention measures remain up-to-date. The seventh component is a reminder that an understanding of the processes of invasion may lead to innovative measures to prevent future epidemics.

While these components offer some broad guidelines that may guide policy, they do not give enough specific details to be used in formulating prevention strategies. At the end of this section, some more specific directions are given for incorporating prevention measures into plans, however these are still general enough to allow a range of flexibility in designing Forest Service programs. While considering the full range of possible prevention measures for inclusion into invasive species programs, an Integrated Pest Management procedure was used to develop a list of all available prevention tools, and these procedures were then summarized into generalized strategies. A list of these prevention alternatives considered is given in Appendix A.

Prevention measures cannot be applied in a blind fashion. Prevention measures, like other treatments, require monitoring to insure they are effective. It is possible that weed inventories may fail to observe dormant seeds, and then incorrectly manage an area as weed-free when it is actually contaminated. This warning includes the case where restoration grasses may be used to revegetate a disturbed site without a follow-up survey. It is possible that weeds will subsequently re-emerge at the site, possibly through the use of contaminated seed mixes, or seed banks containing dormant weeds, or reintroduction by animals or vehicles. In these cases, prevention measures should be considered as ineffective.

Case example: Tansy ragwort along the Salmon River

At a March 29th, 2000, weed management meeting with the Forest Service in Bend, Oregon, Caroline Cox of the Northwest Coalition for Alternatives to Pesticides (NCAP) related some details about her study in a Research Natural Area in an old pasture along the Salmon River estuary north of Lincoln City, Oregon.

When I first visited the site in 1980 the ragwort was literally a jungle. It was taller than I was, virtually a monoculture ...

...The combination of the ragwort flea beetle, the cinnabar moth, and the ragwort seed fly had a dramatic impact on my study site. By 1984 there was practically no live ragwort on the site—a density of zero.

What are the important concepts that this story of mine illustrates? First, the ragwort decline occurred because the Forest Service addressed the causes of the ragwort “jungle” ... prevention was the strategy used to deal with the ragwort problem ... on my site, competing grasses had been removed by the cattle that grazed on the site when it was being used as a pasture, allowing the ragwort to become a monoculture. That cause was addressed by ending the grazing. The other important cause of ragwort’s success on this site was that ragwort had been introduced to the area without its natural enemies, and by introducing them this balance had been restored and ragwort could no longer predominate the way it had.

It’s also important to look at what would probably have happened had prevention not been the strategy of choice at this site and herbicide treatments used instead. During the 1980s the herbicide used would probably have been 2,4-D. The huge ragwort populations left a legacy of ragwort seeds in the soil—literally thousands of them per square meter, so it is unlikely that a single herbicide treatment would have been successful—more than likely repeated treatments would have been necessary. There would have been other consequences, too. The site as I mentioned is adjacent to the Salmon River estuary. Given that 2,4-D has been detected in 10 - 13% of the river and stream samples tested in the US Geological Survey’s nationwide water monitoring program, there is at least a good chance that some of this 2,4-D would have ended up in the estuary. Concentrations of less than 1 ppm are toxic to a variety of aquatic organisms that serve as food for fish and other animals.

One of the most interesting plants to reappear on the site following the ragwort decline was a Sidalcea—not an endangered species, but a pretty rare native species. Had 2,4-D been used on this site to deal with the ragwort, the Sidalcea would have been killed as well, and not had a chance to reappear.