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Allen Press ˇ DTPro System GALLEY 248 File # 53TQ
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Weed Technology. 2004. Volume :000000
Management of Plant Invasions: The Conflict of Perspective1
?2 JAMES O. LUKEN and TIMOTHY R. SEASTEDT2
Abstract: During the past decade, as the issue of plant invasion gained recognition in the public
domain, both ecologists and weed scientists voluntarily or by mandate moved to provide their ex-
?1 pertise to the management of invasive plants on public lands. Diverse views of nature carried to the
table by ecologists and weed scientists have resulted in different priorities and opinions on manage-
ment strategies. However, both groups share the goal of protecting natural resources for the public
good. Efforts to achieve consensus among ecologists and weed scientists should acknowledge and
resolve how and why the two groups come to different views of nature. Then, areas of mutual
strength need to be identified so that improved management or restoration plans can be developed.
Additional index words: Ecosystem management, restoration.
INTRODUCTION grams in ecology and weed science suggests that artifi-
cial academic boundaries delineating colleges and de-
Plant invasion of public lands has emerged as a cross-
partments may be high and thick, although both disci-
disciplinary issue regularly involving ecology and weed
plines are characterized by moves toward greater levels
science (Luken 1997). Historically, few resource man-
of interdisciplinary research. Academic programs in
agement issues simultaneously invoked these two disci-
ecology are heavy in theory but require almost no
plines because ecologists focused their attention on sys-
coursework in economics or management of commodity
tems managed for biodiversity (e.g., nature preserves,
production systems. Academic programs in weed science
national forests, national parks), whereas weed scientists
are heavy in management but require almost no course-
focused their attention on systems managed for com-
work in plant or theoretical ecology. Conservation bi-
modities (e.g., turf, agricultural fields, tree plantations).
ology is rarely required in either discipline. There is,
During the past decade, as the issue of plant invasion
however, some evidence that both groups have borrowed
gained recognition in the public domain, both ecologists
and modified ideas and concepts from one another. For
and weed scientists voluntarily or by mandate moved to
example, almost all weed science programs require a
provide their expertise. The diverse views of nature car-
course in weed ecology where students learn about weed
ried to the table by ecologists and weed scientists often
interactions with crops as well as spatial variation of
lead to different priorities and opinions on management
weed populations in fields. Ecologists, on the other hand,
strategies. However, both groups share the goal of pro-
have borrowed the weed concept to make the case that
tecting natural resources for the public good. Successful
plant invasions are indeed a critical problem on public
management of plant invasions in the future will likely
lands and thus are deserving of more ecological research
require multidisciplinary approaches where weed scien-
or management efforts.
tists and ecologists work side by side. The purpose of
Ecologists appreciate long-term system trends as mod-
this article is to demonstrate that both weed scientists
ified by natural rather than human disturbances and their
and ecologists can provide valuable expertise within the
management goals often focus on structure, function,
context of ecosystem restoration.
and biodiversity of ecosystems. Weed scientists appre-
The Lasting Influence of Training. Concepts of nature ciate short-term population trends as modified by human
and the perceived role of humans in shaping nature are disturbances and their management goals focus on tan-
likely forged during undergraduate and graduate train- gible production. A similar dichotomy in goals was not-
ing. A quick survey of undergraduate and graduate pro- ed by McNaughton (1993) when he assessed the inter-
action between ecologists studying natural grazing sys-
1
Received for publication February 6, 2004, and in revised form September tems and range scientists studying agricultural grazing
4, 2004. systems.
2
Department of Biology, Coastal Carolina University, P.O. Box 261954,
Conway, SC 29528; Ecol. Evol, Biol., University of ColoradoBoulder, Boul-
In the arena of plant invasion, there is indeed oppor-
der, CO 80303. Corresponding author's E-mail: joluken@coastal.edu. tunity for both groups to make valuable contributions to
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WEED TECHNOLOGY
management plans. However, each group will need to Aerial application of herbicides was again proposed in
modify somewhat their learned paradigm because of the 1997, without providing an analysis of 1996 results or
fact that most public lands now experiencing plant in- without providing nontarget effects on plant species in
vasions support multiple-use ecological systems (Kessler the Boulder area. Local ecologists expressed concern
et al. 1992). These systems have long histories of human about the absence of monitoring of nontarget effects, an
modification; human modification will continue in the essential activity when one needs to know how the sys-
future. These systems do not fit the ecologist's version tem is responding to management activity (Christensen
of unbridled nature; neither do these systems fit the weed et al. 1996; Noss 1999). Although the literature indicated
scientist's version of bridled nature. For example, ecol- that herbicide treatment would provide reductions in the
ogists would do well to recognize that many public lands densities of the target species, the widespread presence
are mandated to function as commodity production sys- of the plant and its ability to recolonize herbicide-treated
tems. Although the commodities may be difficult to val- areas from either tumbleweed or seed bank sources sug-
ue (e.g., recreation, aesthetics), management for these gested that herbicides as a one-time activity was not go-
commodities may not contribute to biodiversity goals ing to achieve control (Beck 1995; B. F. Roche and C.
and may also create disturbances that contribute to in- T. Roche 1999). ?5
vasions (Mack et al. 2000). Weed scientists, on the other By the end of 1998, limited monitoring of diffuse
hand, would do well to recognize that any management knapweed indicated that the plant was not a short-term
of natural vegetation (e.g., successional communities threat to native biodiversity. It was argued that research
with relatively high richness) is likely to change the on system trends and alternative control methods should
long-term trend of the system (Walters and Holling be conducted before once again spending large sums on
1990). Short-term successes in management may not broadcast spraying of established knapweed populations.
emerge as long-term successes. In summary, ecologists However, this argument was challenged by weed scien-
could better appreciate the influence of economics on tists: herbicides killed plants and therefore herbicides
natural systems, weed scientists could better appreciate represented proven technologies. Ecologists argued that
the unpredictability of system trends over the long term. temporary reduction of plant densities was not a long-
The following case study suggests that management of term solution.
plant invasions on public lands is indeed a complex so- At the request of County Commissioners, after a hear-
cial activity and that ecologists and weed scientists are ing in April 1997, an ecosystem management approach
still far from achieving synergy.
to examine control of diffuse knapweed populations us-
Management of Diffuse Knapweed Along the Colo- ing both bottom-up (plant competition and resource ma-
rado Front Range. Local governments are responsible nipulations) and top-down (classical biological control)
for managing over 50,000 ha of public lands in and approaches was initiated. The testing of biocontrol in-
around the Boulder area of the Colorado Front Range. sects in particular had not been performed in the Colo-
These lands provide open space and are used for various rado Front Range. Previous research on biocontrol of
combinations of passive recreation, biological conser- diffuse knapweed in other areas gave negligible effects
vation, and agriculture. Some of these lands are now (Carpenter and Murray 1999; Smith 2004); however,
managed for the control of invasive plants, including such studies did not include the suite of biocontrols ap-
species with large regional distributions such as diffuse proved for use on diffuse knapweed because of limited
?3 knapweed (Centaurea diffusa Lam. #3 CENDI). Woodall availability of the insects. Biocontrol insects were re-
et al. (2000) documented the social dilemmas faced leased although ecologists are, in general, concerned
when conducting relatively controversial management about nontarget effects of nonindigenous insect species
activities such as large-scale herbicide treatment of pub- (Louda et al. 2003; Simberloff and Stiling 1996) and
lic lands. As mentioned in the report of Woodall et al. although weed scientists do not generally appreciate
(2000), aerial spraying for diffuse knapweed was initi- these insects because of their apparent lack of damage
ated by public land managers in Boulder County, CO, in to target species (DeLoach 1997). Unique chemistry of
?4 1996. A lawsuit, eventually dismissed, by citizens op- Centaurea species provided the expectation of few or no
posed to aerial spraying was brought against the County. nontarget effects (i.e., the insects were specialists), and
a few hundred each of several species of biocontrol in-
3
Letters following this symbol are a WSSA-approved computer code from
Composite List of Weeds, Revised 1989. Available only on computer disk
sects were released at the study site in 1997. Somewhat
from WSSA, 810 East 10th Street, Lawrence, KS 66044-8897. surprisingly, by 2001, insects had reduced densities of
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LUKEN AND SEASTEDT: PLANT INVASION PERSPECTIVES
knapweed below those suggested as acceptable target 1996; Ludwig et al. 1993; Noss 1999; Wilson and Lantz
levels. This research program eventually led to the pub- 2000).
lication of a management approach that at least equaled Initial general questions about the invaded system are
the efficacy of herbicide treatment, that had zero cost to as follows: (1) Who are the stakeholders associated with
the County, and had no known nontarget effects (Seas- the public lands? (2) What are the critical natural re-
tedt et al. 2003; Suding et al. 2005). In summer 2001, sources that need to be protected? (3) Where are the
site tours were given to land managers, and the local critical resources? (4) What are the relative threats to the
papers carried these findings. The reduction of knapweed critical resources? (5) Considering the stakeholders, what
increased at the demonstration site in 2002 and 2003, are the resource-use goals for the vegetation? (6) What
and continued presentations and reports to managers are the long-term trends in the system?
were made. In early 2004, broadcast spraying in Boulder Initial specific questions about invasion ecology are as
and in Colorado remained the standard and accepted follows: (1) What are the major disturbances in the sys-
management approach for diffuse knapweed. Yet, pas- tem? (2) What are the historical trends for species loss
tures treated with herbicides in 1996 and 1997 had re- (extirpation) and addition (introduction)? (3) What sys-
turned to their pretreatment densities of knapweed by tem characteristics are modified by human activities? (4)
2001. How are invasive species working against management
goals? (5) How are invasive species contributing to man-
The Case Study in Retrospect. This case study dealing agement goals? (6) What are the true invaders and where
with diffuse knapweed reflects many of the complex is- are they located?
sues associated with managing public lands for sustain- Initial specific questions about managing invasions are
able use (Ludwig et al. 1993). On the surface it appears as follows: (1) What are the management options? (2)
as a relatively simple problem: weeds are present, elim- How will management affect long-term trends in the sys-
inate the weeds. However, in reality, the situation de- tem? (3) Will management contribute to restoration of
veloped into a battle of opinion over the most appropri- the system? (4) Will management have nontarget or off-
ate management approach. Notice that the weed scien- site effects? (5) Has the public been adequately informed
tists were managing, that is what they are trained to do. about planned management? (6) Are management re-
Notice that the ecologists were studying long-term sys- sources being allocated based on prioritized threats?
tem trends, that is what they are trained to do. On the The sheer number of questions, usually unanswered,
one hand, ecologists viewed herbicide spraying as a associated with managing invasions of public lands is
short-term fix with many potential nontarget effects and typically sufficient to discourage many ecologists and
no proven long-term benefits. On the other hand, weed weed scientists from participating in the process of pro-
scientists viewed monitoring, the biocontrol release, and tecting public resources (Walters and Holling 1990).
soil and plant competition manipulations of ecologists as Those that become involved in the process quickly gain
having little immediate or widespread effect on the prob- an appreciation for how difficult it is to answer these
lem at hand. questions especially when monetary resources are lim-
ited. It should not then be surprising to find that many
Elements of the knapweed case study are not unique.
resource managers, regardless of educational back-
Indeed, most prominent plant invaders of public lands
ground, make assumptions and then act based on what
are subject to a variety of control methods, and there is
can be easily done and based on what has been done in
a growing volume of published literature documenting
the past with observable results. In the case of invasive
success or lack of success (Anderson et al. 1996; Luken
plants, the assumption is commonly that the plants
1997; Mack et al. 2000). However, when these control
should be killed or removed. Furthermore, spraying of
methods are moved to the operational phase, it quickly herbicide to kill plants is encouraged by a large array of
becomes clear that the success or failure of a manage- relatively cheap products, product support, application
ment method to control plants represents one small part technology, and readily observable results. This ap-
of protecting natural resources for the public good (Wag- proach is personally and professionally satisfying be-
ner 1996). Indeed, many questions should be raised and cause the results of herbicide application are usually ap-
answered before any management is undertaken on pub- parent even to the general public.
lic lands. In this study, we present a list of those ques-
tions, but such lists have been iterated a number of times Reconciliation Through Restoration. There are now
in the past decade (Byers et al. 2002; Christensen et al. numerous examples suggesting that direct management
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WEED TECHNOLOGY
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