Management of Invasive Plant Species in Natural Areas:
Can we preserve native biotic diversity and minimize pesticide use?
T.R. Seastedt
Department of EPO Biology, and
Institute of Arctic and Alpine Research
University of Colorado
Boulder, CO 80309-0450
Introduction
Weed control with pesticides is a very contentious issue. This issue has the potential to polarize the community into two camps: those that see pesticides as a needed tool to protect private or public resources, and those that see pesticides as a threat to human health and ecological sustainability. Emotions can run high: big bucks and human health is at stake. David Pimentel (see web for article) points out that there are about 110,000 accidental non-fatal poisonings from pesticides each year. He estimates that pesticide effects on public health and the environment cost the United States $9 billion per year! Of course, the chemical companies have generated a multi-billion dollar business selling pesticides, so it's safe to state that pesticides have brought riches and misery--the question here is whether or not they function as a useful, routine tool to preserve biotic diversity.
The scientist's job is to review the facts and weigh the evidence for each argument. Objectivity in this exercise is important. Since the spring of 1997 I've tried to understand management practices used on diffuse knapweed, and I remain unable to understand the logic behind current management protocols that involve wide-area application of pesticides in natural areas. As a scientist, I recognize this area is open to debate, and I do listen to logical arguments!
As you know scientists are often a boring bunch. We focus on detail to the point where the public loses interest. However, I don't want what I say to be overly generalized into half-truths...So...to solve that problem...but hopefully stick to some very important and simple facts...I'm supplementing my talk with both a hand-out and a web-page address. Thus, I'm mollified that the requisite amount of detail required for a scientific presentation is available to those that want the facts behind my summary statements.
The polar opposites:
THE CHEMOPHOBE HYPOTHEIS:
Pesticides are a major threat to human health and a threat to non-target species. Pesticide use does not address restoration issues on native ecosystems. Pesticide represents a form of disturbance that may prevent natural successional processes from assisting in restoration efforts.
THE NOZZLE-HEAD HYPOTHESIS:
Pesticides kill weeds that are harming native ecosystems. Following treatment, desirable species recover (and these species then maintain their dominance over future invasions).
REGARDLESS OF YOUR STAND ON CHEMICALS, MONITORING OF PLANT RESPONSES IS ESSENTIAL TO ESTABLISH THE VALIDITY OF YOUR ARGUMENT!
1. Both cases demand careful studies and monitoring to establish the validity of the arguments.
2. Both cases have correct examples. Tonight, however, the focus is on finding alternatives to the aerial or wide-area spraying of knapweed usiing the particularly toxic pesticide, picloram (Tordon). .
First, why the need for minimal chemical use in general, and why the need to not use large-area treatments with chemicals such as picloram (Tordon).
A. Chemical use in natural areas "is like hitting a nail with an anvil." (Robert Devine 1998).
Effects on non-target species must be monitored.
B. Picloram (Tordon), the chemical of choice used to spray large acreage of pastures, is not a safe chemical.
EPA's Ecological Effects Branch and Environmental Fates and Groundwater Branch recommended against the re-registration (use) of picloram because its use would pose unreasonable adverse effects to the environment.
Specifically, picloram is particularly dangerous because of
Its persistence and mobility lead EPA to state that "no practical use restriction can prevent it from contaminating the environment surrounding the target site."
(these documents posted on web site referenced above)
While I'm not a toxicologist, I accept the opinions of those who are, especially when they do not have vested interests in the registration process. Until additional data from reputable sources are produced, repeated, wide-scale use of this chemical should be considered an unacceptable risk in Boulder County.
While picloram is remarkably toxic to knapweed at low doses, we still do not know what other species in the Colorado Front Range share that response. Without those data, the use of this chemical for that reason, alone, is sufficient reason to restrict the use of this pesticide to "last resort" status.
We have essentially no data on non-target effects of most chemicals used in natural areas. We don't know what's being killed, and we don't know what's being genetically modified.
"The large scientific gaps in knowledge (of biocontrols) does not warrant a moratorium on use of other proven technologies (chemicals)…"
Letter to the editor of the Boulder Planet
There's the disconnect. Chemical users see the killing of weeds with pesticides as a "proven technology" for protecting natural areas? At best this is unproven, at worst, the activity exacerbates the problem by creating a chronic disturbance activity that perpetuates the conditions for weedy species.
Is diffuse knapweed a threat to the native biological diversity of the Front Range grasslands?
While the weed certainly affects species abundance, existing data suggest that this forb will not achieve monoculture status in prairies around Boulder. HOWEVER, the weed may achieve monoculture status in and along disturbed sites such as trails, roads, gravel pits, right-of-ways, etc. Once these areas achieve these kind of weed densities, the subsequent effects on grasslands are unknown.
Thus, there's substantial argument for finding ways to control this weed, but there's little evidence to suggest that large-area spraying of grasslands is an appropriate activity, at least, not when we continue to grow the stuff in great quantities along every trail and fence row.
"Diffuse and spotted knapweed... are readily controlled with herbicides. However, the weed will reinvade unless (additional) techniques are used."
George Beck CSU Extension Document 3.110
In a letter to the Boulder Planet, Dr. K. Lair stated:
"Considerable scientific literature...indicates in no way that herbicides should be used as a last resort if true control of the weed is a paramount goal."
Exactly my point!!! Aerial or wide-area coverage without concurrent proactive treatment WILL FAIL to control knapweed. I'm glad Dr. Lair is in complete agreement with my findings!!!
Hence, the method, alone, won't work. Knapweed is so common that eradication is not feasible. Chemically treated lands on Open Space were re-inoculated with knapweed as a result of the 1999 windstorms. Thus, down the road, the sites will again contain knapweed...and using existing management logic, require chemical treatment. This is the chemical treadmill. I refuse to buy into the argument that, after we've sprayed 10,000 acres once, we won't have to again because weed densities will be sufficiently reduced. No, unless we address the causal factors for the presence of the weed, the weed will not decline in abundance.
Weed managers are well aware of the non-chemical methods required to reduce the densities of knapweed. Mowing, grazing, the use of biocontrols, and the planting of competitive species are what it takes. Dr. George Beck from CSU, the same individual who explained why "spray only" doesn't work, is an excellent information source on these techniques and I'm not going to detail these here.
However, the key to controlling (not just periodically killing) knapweed is to create an ecosystem type that doesn't allow the species to dominate. Our native grasses did not allow forbs such as knapweed to be common components of the prairie. There's good reason to believe that if the conditions that favored the dominance of the prairie grasses are restored, then this weed can be controlled without chemical use.
"Many exotic plants can be controlled in prairies and savannas be restoring natural processes such as fire and the natural hydrological regime. Attempts to control problem species without restoring such natural processes may offer merely short-term relief."
M.K. Solecki, 1997
"Much of the plant invasion problem is caused by socioeconomic rather than ecological factors. Attempts to treat the problem will fail unless the underlying causes are identified."
"Some weed problems may be untreatable under current land uses. In these cases, successful treatment requires radical changes in land use."
"A framework for establishing management goals and priorities needs to be established based upon the relative ecological or economic values of different areas. Weed problems are too ubiquitous to allow for ad hoc management decisions."
Hobbs and Humphries 1995
III. What makes natural areas vulnerable to invasion?
d) Inadvertent nitrogen fertilization from multiple sources favors different plant species.
Solutions, whether to restore Open Space to a truly native state, or to manage these areas as they are now (synthetic, anthropogenic or anthropic ecosystems) is a site-specific exercise. Given current budget constraints, triage is necessary. I see non-chemical control of knapweed a much easier exercise than maintaining our Front Range ecosystems in any sort of near-natural state.
TAKE-HOME MESSAGES:
Invasive plant species are a component of global change. To focus on killing of a subset of these species (the noxious weeds) and not placing equal emphasis on restoration or addressing the causal mechanisms for change is not sound management.
If you want to see less chemical use on public lands, you're going to have to also advocate larger management budgets with funds specifically allocated for site rehabilitation efforts. The use of a suite of non-chemical controls is warranted and cost-effective over the long-term. We should manage public lands to cure the disease, not just treat the symptoms (which is what large-scale aerial spraying involves).
Knapweed in Boulder grasslands may not be a threat to native plant diversity, and may be less serious than are other species (currently not on noxious weed list) and/or other management activities. We desperately need to identify the villains.
Non-chemical management demands more personal, hands-on approaches. That's ok...we should encourage a large "adopt a prairie" program for open space.
Aerial spraying for knapweed on grasslands of Open Space is not justified based on the argument of preserving natural biotic diversity. Sustainable controls of knapweed include grazers and insect parasites. These are believed to be much less of a threat to our environment than the continued use of chemicals such as picloram.
Procedures for the development of a weed management program within the context of ecosystem management are offered in my handout and on my website. If pesticide use was limited to individual species treatments (wicking), or only allowed if concurrent activities involving biological, mechanical, and cultural controls, we would have a much stronger weed management program.
Outline and References
I. Are invasive weed species a threat to native plant diversity?
"We suggest that biological invasions…have become so widespread as to constitute a significant component of global environmental change." (Peter M. Vitousek et al., 1996)
Alien species is second only to habitat destruction as a threat to native biotic diversity.
(David S. Wilcove et al. 1998)
Boulder Open Space is heavily infested with non-indigenous plant species:
(Craig et al., in press)
Percent of vegetation cover that is non-indigenous plant species:
Shortgrass: 44.3%
Mixed grass: 29.2%
Tallgrass: 44.7%
Hayfields: 84.9%
II. Which invasive species are an actual threat to native biological diversity?
Non-indigenous species will replace native species IF
1. Both have identical requirements and the non-native has some competitive edge (such as no predators, parasites, or diseases on the site)
2. The non-indigenous species is capable of modifying the environment to give itself (or other non-indigenous species) the competitive edge.
3. The ecosystem has been transformed by other factors associated with global change such that the native, dominant species no longer have a competitive advantage.
III. What makes natural areas vulnerable to invasion?
Fire suppression and inadequate fire return intervals have changed the microclimate of the prairie to favor different species.
Flood control has prevented riparian scouring. Certain species (e.g., cottonwoods) cannot survive as seedlings.
Stream channel modification, irrigation ditches, roads, and trails have greatly altered the hydrology.
Inadvertent nitrogen fertilization from multiple sources favors different plant species.
IV. What management strategies maximize the protection of natural areas and minimize pesticide use?
First, why the need for minimal chemical use in general, and why the need to not use large-area treatments with chemicals such as picloram (Tordon).
A. Chemical use in natural areas "is like hitting a nail with an anvil." (Robert Devine 1998).
Effects on non-target species may be deleterious and must be monitored.
B. Picloram (Tordon), the chemical of choice used to spray large acreages of pastures, is not safe.
EPA's Ecological Effects Branch and Environmental Fates and Groundwater Branches recommended against the re-registration (use) of picloram because its use would pose unreasonable adverse effects to the environment.
Specifically, picloram is particularly dangerous because of
Its persistence and mobility lead EPA to state that "no practical use restriction can prevent it from contaminating the environment surrounding the target site."
(these documents posted on web site referenced above)
While I'm not a toxicologist, I accept the opinions of those who are, especially when they do not have vested interests in the registration process.
In any event, chemicals, hand-pulling, or even nuclear weapons only kill weeds (and maybe some non-weeds…). That's only part of the equation. What's the rest?
How do you fix the ecosystem without chemicals?
First, it's critical to have the data that says it needs fixing. I think we have that for many Open Space areas.
"Many exotic plants can be controlled in prairies and savannas be restoring natural processes such as fire and the natural hydrological regime. Attempts to control problem species without restoring such natural processes may offer merely short-term relief."
M.K. Solecki, 1997
"Much of the plant invasion problem is caused by socioeconomic rather than ecological factors. Attempts to treat the problem will fail unless the underlying causes are identified."
"Some weed problems may be untreatable under current land uses. In these cases, successful treatment requires radical changes in land use."
"A framework for establishing management goals and priorities needs to be established based upon the relative ecological or economic values of different areas. Weed problems are too ubiquitous to allow for ad hoc management decisions."
Hobbs and Humphries 1995
Solutions, whether to restore Open Space to a truly native state, or to manage these areas as they are now (synthetic, anthropogenic or anthropic ecosystems) is a site-specific exercise. Given current budget constraints, triage is very likely necessary.
How to decide whether or not to control weeds in natural areas: http://www.aqd.nps.gov/pubs/ranking/index.html (by Ron Hiebert and James Stubbendieck)
How to conduct ecosystem management within the framework of ecosystem management: (these lists taken from: http://www.methow.com/~gwooten/ecology/weedmgt.htm (by George Wooten)
PRINCIPLES FOR CONDUCTING WEED MANAGEMENT PROJECTS (Wooten 1995)
I. Social and Cultural Objectives
Goals of proposed projects will be realistic and objectives will be measurable.
Proposed projects will provide clear and concise definitions and terms.
Public involvement will be open and welcome during the planning, preparation, and implementation of weed management projects. Education will be an integral part of weed management projects.
Weed management projects will be designed in the interests of the general public, without favor to special interests. (For example, weed management's goal on public lands is not to generate cattle forage, unless that's what the public has approved.)
Proposed projects will include integration of cultural values with resources (e.g., commitment to ranching.)
Proposed projects involving the use of pesticides or herbicides will include risk analyses for public health and safety, and thresholds for health and safety tolerance will be publicly available
Proposed projects will describe and analyze the economics of control methods, and projects will describe and analyze costs/benefit ratios.
Monitoring will be incorporated in all weed management programs.
II. Integration with Ecosystem Management
Managers will describe weed control measures within an ecosystem management framework involving an understanding of the biology, demographics and etiology of weed spread.
Managers will describe weed control measures within an ecosystem management framework involving an understanding of the different functional attributes of invading species vs those present in the current or desired system.
Damage thresholds will be established for invading species that activate a process of strategic weed management.
Areas in which eradication of certain species may not be feasible will be identified, and goals will be directed toward control strategies rather than eradication in these areas.
Areas in which control or containment may not be feasible will be identified, and management will not use funds in these situations until control mechanisms have been established.
Use of native species for recovery will be encouraged. The use of introduced forage grasses will be discouraged.
Monitoring will be incorporated in all weed management programs.
Based on ecological risk assessment, the use of herbicides will, in most cases, be a LAST resort.
III. Preferred Alternatives
Preferred alternatives will have clearly stated goals
Preferred alternatives will substantially involve the public.
Preferred alternatives will be long-term solutions.
Preferred alternatives will be economically cost-effective and have clearly stated costs.
Preferred alternatives will be specific about dates and times.
Preferred alternatives will be site-specific.
Preferred alternatives will be species-specific, and will use scientific nomenclature for plant names.
Preferred alternatives will incorporate effectiveness monitoring.
IV. Management Criteria for Projects Using Herbicides
Decision documents will provide analyses of health and safety risks associated with pesticides, and will do so openly and without bias. Descriptions of potential hazards will be available to the public, and will include discussion and analysis of potential effects on sensitive individuals and children.
Decision documents will describe the affects of proposed treatments on the environment, and will include discussion and analysis of potential, but unknown effects of herbicides including above- and below-ground transport, breakdown factors, food-web incorporation, nature of targets, synergistic effects, and aquatic effects. If the balance of such effects is completely unknown, herbicide use will be restricted to emergency cases in which eradication is imminently attainable, and for which other documentation has been completed.
Decision documents will include worst-case scenarios including a discussion of potential effects resulting from chemical spills, herbicide drift, off-target contamination, and accidental over- application.
Permits for use on public lands will be rejected for chemicals containing so-called "inert ingredients". Manufactured products containing trade secrets for ingredients have no place on public lands.
All areas treated with herbicides will be posted for the duration of pesticide residuals on the site.
Monitoring will involve studies of cumulative effects, including the potential for development of herbicide tolerance, chemical buildup, and selective changes in vegetation structure resulting in loss of resources.
References and additional readings
Craig, D.P., C.E. Bock, B.C. Bennett and J. C. Bock. In press. Habitat relationships among grasshoppers (Orthoptera: Acrididae) at the western limit of the Great Plains in Colorado. American Midland Naturalist.
D'Antonio, C.M. and P.M. Vitousek. 1992. Biological invasions by exotic grasses, the grass-fire cycle, and global change. Annual Review of Edcology and Systematics 23: 63-87.
Devine, R. 1998. Alien Invasion: America's battle with non-native animals and plants. National Geographic Society, Washington D.C.
Hobbs, R.J., and S.E. Humphries. 1995. An integrated approach to the ecology and management of plant invasions. Conservation Biology 761-770.
Huenneke, L.F. 1997. Outlook for plant invasions: Interactions with other agents of global change. Pages 95-103 IN: Luken, J.O. and J.W. Thieret (eds). Assessment and management of plant invasions. Springeg-Verlag, New York.
Knight, D.H. 1994. Mountains and Plains. Yale University Press, New Haven, CT. 338 pp.
Solecki, M.C. 1997. Controlling invasive plants. Pages 251-278 in: S. Packard and C.F. Mutel, editors. The Tallgrass Restoration Handbook. Island Press, Washington D.C.
Vitousek, P.M., C.M. D'Antonio, L.L. Loope and R. Westbrooks. 1996. Biological invasions as global environmental change. American Scientist 84: 468-478.
Walker, L.R. and S.D. Smith. 1997. Impacts of invasive plants on community and ecosystem properties. Pages 69-86 IN: Luken, J.O. and J.W. Thieret (eds). Assessment and management of plant invasions. Springeg-Verlag, New York.
Wilcove, D.S., D. Rothstein, J. Dubow, A. Phillips and E. Losos. 1998. Quantifying threats to imperiled species in the United States. BioScience 48: 607-615.