Drainage New Weeds Risk Assessment
Species Selection and Assessment of
The geographic region treated in this analysis
was the 11-county area approximately centered on the Blackfoot River drainage
(Missoula + Powell and their 9 surrounding counties Mineral, Sanders,
Lake, Flathead, Lewis and Clark, Jefferson, Deerlodge, Granite, and Ravalli).
A list of plant species exotic to North America that have been recorded
in the 11-county "infiltration area" (Wilson and Lee 1989) was generated
from the INVADERS Database Release 6.4 (Rice 1997). Distribution
records were available for 411 exotics in the project infiltration
area. This initial list was reduced by first excluding well-known
widespread weeds (e.g., spotted knapweed, leafy spurge, Dalmatian toadflax,
cheatgrass) and other common exotic plants known to be non-invasive or
only minor ruderal weeds (e.g., Draba verna, Myosotis micrantha).
The reduced list contained 308 species. For these species the following
information was examined:
1. Presence on noxious weed lists:
2. Presence on other lists of pest/invasive
Northwest states (MT, ID, WY, OR, WA) in which
the species is legally designated as a noxious weed (any category).
Other western states and provinces where the
plant is designated legally as noxious. The other western states/provinces
examined are AZ, CA, CO, KS, ND, NE, NM, NV, SD, UT, BC, SK, AB, and MB.
The Federal Noxious Weed list.
Weed status in Australia: Noxious Weeds
of Australia (Parsons and Cuthbertson, 1992). The Australian noxious
weed list was examined because of the climatic similarity between southern
Australian and the western United States. A number of species known
to be important weeds in Australia have also invaded in Montana such as
rush skeletonweed (Chondrilla juncea), tansy ragwort (Senecio
jacobea) and yellow starthistle (Centaurea solstitialis).
3. Overall rate of spread in the five-state
northwest region (WA, OR, ID, MT, WY), expressed as the average number
of counties with records per decade (first year of record to 1996, derived
from the INVADERS Database)
Other western states and provinces where the
plant has been recognized as a problem weed but is not legally listed
as noxious. This includes ecological problem plants, county-designated
noxious weeds, agricultural weeds etc. The other western states/provinces
examined are AZ, CA, CO, KS, ND, NE, NM, NV, SD, UT, BC, SK, AB, MB, CPR
(Canadian Prairie Region).
Countries in which the plant is considered
an agricultural weed, as described by Holm et al. (1979) A Geographic
Atlas of World Weeds.
The Brooklyn Botanic Garden list in Invasive
Plants: Weeds of the Global Garden (Randall and Marinelli 1996).
The National Association of Exotic Pest Plant
Council's "Worst" Invasive Plant Species in Continental United States.
(Sept. 1997 update provided by Faith Campbell)
The Pacific Northwest Exotic Pest Plant Council
list, Non-Native Pest Plants
of Greatest Concern in Oregon and Washington as of August 1997. The
focus of this list is on non-native plants with potential to impact wildlands,
including natural areas; national, state and community parks; wildlife
areas; and all other public lands that have not been highly disrupted by
human activities. Plant species which are solely confined to croplands
or highly disturbed habitats have not been included in this list.
4. Number of occurrence records and number
of counties within the 11-county infiltration area (INVADERS Database).
We looked for species with the following
characteristics, but that were not presently listed as noxious weeds in
Montana: 1) Reported frequently as a noxious weed or problem plant elsewhere,
and 2) Spreading rapidly in the northwest region, yet recently introduced
into North America, recently invading in Montana or otherwise not well
known in comparison with species already declared noxious in Montana.
Thirty-two species were selected to comprise an Alert List for the Blackfoot
River drainage. Spring annuals, weeds which complete their life cycle in
a single growing season, are seldom declared noxious. Most species
which are designated noxious are perennials, while a limited number are
biennials or winter annuals. However, we have included seven species on
the Alert List that are primarily annuals because of their potential to
alter the species composition of native grassland communities or impact
For each of the 32 species on the Alert
List, ratings of weed potential, which generally should be considered
preliminary, were assigned for six broad environmental types. The small
proportion of total land area comprising riparian and wetland environments
in Montana increases the resource and ecological value of these types
far above the actual acreage. These environments are particularly
important to the Blackfoot area..
These risk ratings were determined by examination
of the specimen comments field for INVADERS distribution records (i.e.
associated vegetation, environmental factors, land use, extent/severity
of weed infestations, etc.), available scientific literature, and previous
work on cover/habitat type susceptibility (Rice and Rider 1995, Rice 1997)
and climatic correlations (Rice et al. 1997) of weeds in the northwestern
Hobbs, R. J. and S. E. Humphries.
1995. An integrated approach to the ecology and management of plant
invasions. Conserv. Biol. 9:761-770.
Holm, L., J. V. Pancho, J. P. Herberger,
and D. L. Plucknett. 1979. A Geographical Atlas of World Weeds. John
Wiley, New York.
Parsons, W. T. and E. G. Cuthbertson.
1992. Noxious Weeds of Australia. Inkata Press, Melbourne.
J. M. and J. Marinelli (eds). 1996. Invasive Plants.
Weeds of the Global Garden. Brooklyn Botanic Garden, Brooklyn, New
Rice, P. M. 1997. INVADERS
Database Release 6.4. Division of Biological Sciences, The University
of Montana, Missoula. http://invader.dbs.umt.edu.
Rice, P.M and C. Toney. 1997. Susceptibility
of Northern Region Habitat Types to Invasion by Five Noxious Weed Species
- First Approximations. http://invader.dbs.umt.edu/htrate.
P. M., J. C. Toney, R. Sacco and D. Cooksey. 1997.
Climatic correlations and predicted potential ranges of species in the
Montana Weed Seed Free Forage Program: first approximations. Final
Report, Coop. Agric. Pest Survey, Dept. Plant & Soil Sci., Montana
State Univ., Bozeman. 156 pp.
P.M. and J. Rider. 1995. Landscape Ecology: Noxious weed invasion analysis.
Interior Columbia Basin Ecosystem Management Project. Contract Order Number
43-0E00-5-5264. Contract Officer Jim Olivarez, USFS Northern Regional Office,
Missoula, MT. (susceptibility matrix available for download on the
Databases page - reference the "Noxious Weeds Database")
Whitson, T. D. (ed.), L. C. Burrill, S.
A. Dewey, D. W. Cudney, B. E. Nelson, R. D. Lee, and R. Parker. 1991.
Weeds of the West. The Western Society of Weed Science in cooperation
with the Western United States Land Grant Universities Cooperative Extension
Services (printer: Pioneer of Jackson Hole), Jackson, Wyoming.
Wilson, J.B. and W.G. Lee. 1989.
Infiltration invasion. Functional Ecology 3:379-382.
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