Restoration of Native Plant Communities
Infested by Invasive Weeds—Sawmill Creek
Research Natural Area
Peter Rice
Abstract—Invasive alien weeds established themselves on the
Sawmill Creek Research Natural Area, harming elk feeding grounds
and threatening the integrity of the native pant community. Management enacted herbicide control over several growing seasons,
resulting in greater elk winter forage on study plots. Monitoring the
long-term effects of herbicide as a restoration tool continues.
Sawmill Creek was designated a Research Natural Area
(RNA) in 1992 to provide superior examples of fescue grassland and open canopy forest habitat types. However, a
number of invasive alien plants had become established in
the RNA. A 1994 weed mapping effort confirmed that spotted knapweed (Centaurea maculosa) had spread throughout
almost the entire 160 acres of montane grasslands within
the RNA. Small colonies of the noxious weeds leafy spurge
(Euphorbia esula), dalmatian toadflax (Linaria dalmatica),
Saint Johnswort (Hypericum perforatum), and sulfur cinquefoil (Potentilla recta) were scattered throughout the grassland and forest habitat types. The continued expansion of
these exotics threatened the integrity of native plant communities and the value of the site as elk (Cervus elaphus)
winter range. Working in conjunction, personnel from the
Bitterroot National Forest and the University of Montana
have written an integrated vegetation management plan.
The management goals of the plan were to restore the native
plant communities and enhance the value of the site for elk
winter range. Herbicides, biocontrol insects, changes in
access and use patterns, limited hand digging, and finally
reintroduction of fire are being employed to control the
weeds and revitalize native species. The control objective for
spotted knapweed was to suppress its abundance within the
RNA. The other noxious weed species, which still had infestations of limited size, were targeted for eradication or
containment. An extensive plant community monitoring
system, with replicated plots and transects, was installed on
the RNA. The purpose of the monitoring is to provide
scientific documentation of the results of these weed control
and grassland restoration techniques being implemented at
an operational scale.
Earlier small plot work using herbicides to suppress
spotted knapweed in bunchgrass and open canopy forest
habitat types had suggested that significant conservation
benefits could be realized by appropriate use of herbicides.
In: Smith, Helen Y., ed. 2000. The Bitterroot Ecosystem Management
Research Project: What we have learned—symposium proceedings; 1999 May
18-20; Missoula, MT. Proceedings RMRS-P-17. Ogden, UT: U.S. Department
of Agriculture, Forest Service, Rocky Mountain Research Station.
Peter Rice is a Research Associate, Division of Biological Sciences, University of Montana, Missoula, MT 59812.
USDA Forest Service Proceedings RMRS-P-17. 2000
Tordon (picloram), Transline (clopyralid), and Curtail
(clopyralid plus 2,4-D) had been applied to replicated experimental plots at four sites in western Montana. Plant community response was measured for an eight-year period. By the
third year after spraying, herbicide plots averaged 47 percent greater elk winter forage than the no-spray check plots
(Rice and others 1997a). By three growing seasons postspray, all herbicide treated plots had plant community
diversity as high or higher than no-spray check plots (Rice
and others 1997b). A second round of herbicide treatments
to control recently emerged knapweed was made following
the third year post-spray measurements. Plant community
diversity was still maintained after eight years even with
the second herbicide application. A detailed comparison of
the community composition of the sprayed plots with the
original Mueggler and Stewart (1980) data sets that define
these specific bunchgrass habitat types revealed that the
sprayed plots were more similar to the potential natural
communities than the no-spray checks (Rice and Toney
1998).
Test plots on the RNA sprayed with Tordon herbicide in
the fall of 1996 confirmed that the Sawmill native bunchgrass communities, including the native wild flowers, would
also respond favorably to release from the constant competition with spotted knapweed. One hundred and sixty acres
of spotted knapweed infested grasslands were broadcast
sprayed by ATV, truck, and backpack sprayers in the fall of
1998. Tordon was used in the open grasslands and Transline
in the ecotones with the forest habitat types. Starting in
1996, moths (Agapeta zoegana) and weevils (Cyphocleonus
achates) whose larvae bore out the roots of spotted knapweed
were released on adjoining private land and portions of the
RNA that were not suitable for ground based herbicide
applications. It is intended that these insects will provide
long-term biological suppression of knapweed.
An environmental impact statement (EIS) is currently
required for aircraft application of herbicides on Forest
Service lands, while a ground based treatment can be implemented following an environmental assessment (EA). Most
of the Sawmill site was treated using a spray boom mounted
on an ATV. Some areas adjacent to the roads were treated by
hose reel and handgun from a truck, and a backpack sprayer
was used on a few spots inaccessible to the ATV. Although an
EA can be completed at lower cost than an EIS, as was the
case with the Sawmill project, there are significant cost
savings in helicopter application. Spraying cost in this
rugged steep terrain was $110 per acre for ground application. A helicopter application would have cost only $20 to $30
per acre.
Helicopter spraying has important conservation and environmental advantages over ground based application in
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addition to lower per acre treatment costs. Aircraft operator
exposure to herbicide residues is lower than for ground
vehicle and backpack sprayer crews. Large blocks can be
sprayed very quickly when weather conditions and plant
growth stages are optimal for spraying. A narrow window of
opportunity with the most favorable conditions can be used
to reduce drift, maximize efficacy on target weeds, and
minimize herbicide injury to desirable plants. Normal use of
the site by wildlife and recreationists is disrupted less by
compressing the duration of treatment activities. Sawmill
could have been helicopter sprayed in less than half a day.
The ground-based work took 36 days.
Elk are quickly attracted to the enhanced grazing conditions in the herbicide sprayed areas of knapweed degraded
winter ranges. The elk exhibit a strong early spring selection
preference for these newly vigorous bunchgrasses. If too
small an area is sprayed, the concentration of elk may negate
some of the benefit of treatment and slow recovery of the
native plants. Cost effective treatment of larger blocks
should help disperse grazing elk during the initial years of
recovery of the bunchgrass communities from competition
with knapweed.
The Sawmill RNA Project demonstrates that appropriate use of herbicides can provide clear benefits in the
restoration of native plant communities and the enhancement of the wildlife value of montane grasslands. The
Ravalli County Weed District, adjacent private land owners, Rocky Mountain Elk Foundation, Stewart Spraying,
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Western Agricultural Research Center, University of Montana, Rocky Mountain Research Station, and the Bitterroot
National Forest cooperated in the design, funding, and
implementation of this restoration project. Now that the
weeds are suppressed it is possible to reintroduce fire to both
the grassland and forested areas of the site without increasing the weed problem. Response monitoring will continue
beyond the year 2000. Experience gained on this project can
serve as a model for the restoration of other high conservation value sites that are being degraded by invasive weeds.
References _____________________
Rice, P.M.; Toney, J.C. 1998. Exotic weed control treatments for
conservation of fescue grassland in Montana. Biological Conservation. 85: 83-95.
Rice, P.M.; Toney, J.C.; Bedunah, D.J; Carlson, C.E. 1997a. Elk
winter forage enhancement by herbicide control of spotted knapweed. Wildlife Society Bulletin. 25(3): 627-633.
Rice, P.M.; Toney, J.C.; Bedunah, D.J.; Carlson, C.E. 1997b. Plant
community diversity and growth form responses to herbicide
applications for the control of Centaurea maculosa. Journal of
Applied Ecology. 34: 1397-1412.
Rice, P.M.; Toney, J.C. 1996. Plant population response to broadcast
herbicide applications for spotted knapweed control. Down To
Earth. 51(2): 14-19.
Rice, P.M.; Bedunah, D.J.; Carlson, C.E. 1992. Plant community
diversity after herbicide control of spotted knapweed. Res. Pap.
INT-460. Ogden, UT: U.S. Department of Agriculture, Forest
Service, Intermountain Research Station. 7 p.
USDA Forest Service Proceedings RMRS-P-17. 2000