Invasive Exotic Species Ranking Southern Ontario

This page comes from the URBAN FOREST ASSOCIATES INC. and I think it is a must read for anyone who gardens or tends a plot of land and wants to know about what could be on your property. Thanks, Amy
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Invasive Exotic Species Ranking for Southern Ontario
© Urban Forest Associates Inc.
January 2002
This is a listing of the invasive exotic species found in natural habitats in southern Ontario according to the observations of restorationists and nursery owners we have consulted over the past 10 years and available written documents (see references).
Most exotic species that are found in natural areas do not appear to be a problem for
restoration or protection of native biodiversity. They co-exist with indigenous (native) species and can increase local biodiversity without dominating the site. There is sometimes an argument made that since good quality natural habitats are so rare, the exotic species are taking up space that could potentially be occupied by indigenous plants, some of which are uncommon or rare. However this is not a practical approach in most areas since these areas are and will continue to be highly impacted by human activities. A goal of 100% indigenous species, although desirable, is not possible on most sites.
Some species, while highly invasive in early-successional situations, are eventually outcompeted by native shade-tolerant species. The choice to control or not will depend on the objectives of a project.
Any exotic species can become invasive if provided with optimum soil, moisture, and
disturbance conditions. We have tried to limit this list to those species that are most problematic in Ontario.
Four categories have been used here. Some species may belong in more than one category, but they are listed here where they have the greatest negative effect. This list does not attempt to prioritize these species for ease of control, since control options can vary and new research may provide new options. We have placed species in each category based on reports and observed effects. The level of negative effect for each species is somewhat subjective in the absence of a formal survey.
“Invades” as used here means that an exotic species becomes a significant component of the plant community. “Dominates” means that the species excludes most other species. “Native” as used here means indigenous, and is used for simplicity.
Plants marked with an asterisk (*) may be indigenous to parts of Ontario, but have aggressive behaviour that threatens natural biodiversity (and there seems little doubt that the range expansion was aided by human activities). They are considered invasive exotic plants outside their natural range.
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Invasive Exotic Species Ranking for Southern Ontario - January 2002 © Urban Forest Associates Inc.
Category 1
Aggressive invasive exotic species that can dominate a site to exclude all other species and remain dominant on the site indefinitely. These are a threat to natural areas wherever they occur because they can reproduce by means that allow them to move long distances. Many of these are dispersed by birds, wind, water, or vegetative reproduction.
These are the top priority for control, but control may be difficult. Eradication may be the only option for long-term success.

Scientific Name Common Name Effect on Natural Area
Acer negundo* Manitoba maple takes place of native early-successional forest,
aggressively invades all habitat types
Aegopodium podagraria Goutweed dominates forest understorey
Alliaria petiolata Garlic mustard dominates forest herb layer
Alnus glutinosa Black alder dominates wetlands, causes changes by shading
Betula pendula European birch dominates open wetlands, causes changes by shading
Butomus umbellatus Flowering rush dominates open marshes
Cirsium arvense Canada thistle dominates meadows, prairies, forest edges
Coronilla varia Crown vetch dominates disturbed meadows
Cynanchum nigrum Black swallow-wort dominates meadows & forest understorey
Cynanchum rossicum Pale swallow-wort dominates meadows & forest understorey
Elaeagnus umbellata Autumn olive dominates forest edges
Glyceria maxima Rough manna grass dominates wet meadows
Hesperis matronalis Dames rocket dominates open forest understorey & meadows
Hydrocharis morsus-ranae European frog-bit dominates open water habitats
Impatiens glandulifera Himalayan balsam dominates forests & wet meadows
Lonicera japonica Japanese honeysuckle dominates forest understorey in northern U.S.
Lonicera maackii Amur honeysuckle invades meadows & forest edges
Lonicera morrowi Morrow’s honeysuckle invades meadows & forest edges
Lonicera tatarica Tartarian honeysuckle invades meadows & forest edges
Lonicera xylosteum Eur. fly honeysuckle invades meadows & forest edges
Lythrum salicaria Purple loosestrife dominates wetlands
Morus alba White mulberry hybridizes with rare M. rubra
Myriophyllum spicatum Eurasian water milfoil dominates open water habitats
Nymphoides peltatum Floating heart dominates open water habitats
Phragmites australis* Common reed dominates wetlands & wet meadows
Potamogeton crispus Curly pondweed dominates open water habitats in SW Ontario
Rhamnus cathartica Common buckthorn dominates forest understorey, meadows & prairies
Rhamnus frangula Glossy buckthorn dominates wetlands
Rosa multiflora Multiflora rose dominates forest edges

Invasive Exotic Species Ranking for Southern Ontario - January 2002 © Urban Forest Associates Inc.
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Category 2
Exotic species that are highly invasive but tend to only dominate certain niches or do not spread rapidly from major concentrations. Many of these spread vegetatively or by seeds that drop close to the parent plant. They may have been deliberately planted and persist in dense populations for long periods. Control where necessary and limit their spread to other areas.

Scientific Name Common Name Effect on Natural Area
Acer platanoides Norway maple dominates forest canopy
Acer pseudoplatanus Sycamore maple dominates forest canopy
Ailanthus altissima Tree of Heaven replaces native early-successional forest
Celastrus orbiculatus Oriental bittersweet dominates forests and forest edges, has become more common than native C. scandens.
Galium mollugo White bedstraw invades meadows
Lotus corniculatus Bird-foot trefoil dominates meadows & prairies
Lysimachia nummularia Moneywort dominates wet forest understorey
Melilotus alba White sweet clover dominates meadows & prairies
Melilotus officinalis Yellow sweet-clover dominates meadows & prairies
Pinus sylvestris Scots pine invades meadows
Poa pratensis Kentucky bluegrass dominates prairies
Polygonum cuspidatum Japanese knotweed dominates wet meadows & moist forests
Populus alba White poplar invades meadows
Robinia pseudo-acacia Black locust invades meadows
Scilla siberica Scilla dominates spring ephemerals in forest understorey
Sedum acre Mossy stonecrop invades alvars
Syringa vulgaris Lilac dominates shallow limestone areas, persists for decades
Ulmus pumila Siberian elm invades prairies, causes changes by shading
Vicia cracca Cow vetch dominates meadows & prairies
Vinca minor Periwinkle dominates forest understorey
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Invasive Exotic Species Ranking for Southern Ontario - January 2002 © Urban Forest Associates Inc.
Category 3
Exotic species that are moderately invasive but can become locally dominant when the proper conditions exist. Control where necessary and limit their spread to other areas.
Scientific Name Common Name Effect on Natural Area
Abutilon theophrasti Velvet-leaf invades meadows
Acinos arvensis Mother-of-thyme invades alvar habitats
Aesculus hippocastanum Horse-chestnut reproduces moderately, creates dense shade
Artemisia absinthum Absinth sage invades disturbed meadows
Barbarea vulgaris Yellow rocket invades meadows
Berberis vulgaris Common barberry invades forests
Berberis thunbergii Japanese barberry invades forests
Berteroa incana Hoary-alyssum invades prairies
Carduus nutans Nodding thistle invades meadows & prairies
Centaurea maculosa Spotted knapweed invades meadows and prairies
Convallaria majalis Lily-of-the-valley a frequent garden escape in forests
Convolvulus arvensis Field bindweed dominates meadows, slows natural succession
Crataegus monogyna Singleseed hawthorn dominates shrub communities, meadows & prairies
Dactylis glomerata Orchard grass invades meadows & prairies
Dipsacus sylvestris Teasel dominates meadows & prairies
Elaeagnus angustifolia Russian olive invades meadows & shrub communities
Elymus repens Quack grass dominates meadows and prairies
Euonymus alata Winged euonymus invades forest understorey shrub layer
Euonymus europaeus Spindle-tree invades forest understorey & edges, similar to rare
E. atropurpurea
Euphorbia cyparissias Cypress spurge invades meadows
Festuca arundinacea Tall fescue dominates moist meadows & prairies
Galium verum Yellow bedstraw invades meadows & prairies
Hedera helix English ivy invades forest understorey
Hieracium aurantiacum Orange hawkweed invades meadows
Hieracium caespitosum Yellow hawkweed invades meadows
Hieracium vulgatum Common hawkweed invades meadows
Hieracium x floribundum Pale hawkweed invades meadows
Humulus japonicus Japanese hop invades wet meadows
Kochia scoparia Summer cypress invades meadows
Lycopus europaeus Bugleweed invades wetlands, displaces native Lycopus sp.
Miscanthus sinensis Eulalia dominates wet meadows
Pastinaca sativa Wild parsnip invades meadows
Ranunculus repens Creeping buttercup invades meadows
Rorippa amphibia Marsh cress invades wetlands in SE Ontario
Salix alba White willow invades wetlands, displaces native Salix spp.
Salix fragilis Crack willow invades wetlands, displaces native Salix spp.
Salix x rubens Hybrid willow invades wetlands, displaces native Salix spp.
Saponaria officinalis Bouncing bet invades meadows
Solanum dulcamara Bittersweet nightshade invades forests & wetlands
Sorbaria sorbifolia False spiraea invades meadows & forest understorey
Tanacetum vulgare Tansy invades disturbed meadows
Thymus praecox Creeping thyme invades meadows
Urtica dioica ssp. dioica European stinging nettle dominates forest understorey
Vicia sativa Common vetch invades meadows
Vicia tetrasperma Slender vetch invades meadows
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Invasive Exotic Species Ranking for Southern Ontario - January 2002 © Urban Forest Associates Inc.
Category 4
Exotic species that do not pose a serious threat to natural areas unless they are competing directly with more desirable vegetation. These can often be tolerated in restoration projects if they are already present. They may eventually be replaced through natural succession or management. Control where necessary and limit their spread to other areas.
Some of these exotic species are substituted in restoration projects for indigenous species but may not reproduce aggressively once established. They do occupy space that desirable indigenous species require and do not achieve project objectives when used.
Scientific Name Common Name Effect on Natural Area
Acer ginnala Amur maple frequently planted
Ajuga reptans Creeping bugleweed persists in forest understorey & edges
Bromus inermis Smooth brome resists conversion to native meadow & prairie
Campanula rapunculoides Creeping bellflower invades forest edges & meadows
Euphorbia esula Leafy spurge can dominate prairies (mostly in western provinces)
Glechoma hederacea Ground ivy competes with meadow & prairie species
Hemerocallis fulva Orange Day lily dominates meadows
Hypericum perforatum St. John’s-wort can dominate meadows
Inula helenium Elecampane invades meadows
Iris pseudacorus Yellow flag invades wetlands
Ligustrum vulgare Privet invades forest edges
Linaria vulgaris Butter-and-eggs invades meadows
Lolium perenne Perennial rye grass competes with meadow & prairie species
Malva moschata Musk mallow invades meadows
Medicago lupulina Black medick invades meadows
Medicago sativa Alfalfa invades meadows & prairies
Myosotis scorpioides True forget-me-not dominates shaded seepage areas
Mentha x piperita Peppermint invades meadows
Nepeta cataria Catnip invades meadows
Origanum vulgare Wild marjoram invades disturbed meadows
Pachysandra terminalis Japanese spurge persists in forest understorey & edges
Populus x canadensis Carolina poplar often misidentified as P. deltoides by nurseries
Rumex acetosella Sheep sorrel invades meadows
Salix caprea Goat willow frequently substituted for S. discolor
Salix purpurea Purple willow invades wetlands, displaces native Salix spp.
Senecio jacobaea Tansy groundsel invades meadows
Setaria sp. Foxtail grasses invade meadows, resist invasion by natives
Sorbus aucuparia European Mountain-ash invades forests
Symphoricarpus albus var Western snowberry frequently substituted for S. albus var albus
laevigatus
Trifolium arvense Rabbit-foot clover invades meadows
Trifolium pratense Red clover invades meadows
Trifolium repens White clover invades meadows
Tussilago farfara Sweet coltsfoot invades wet meadows & riverbanks
Ulmus glabra Scotch elm invades disturbed forests
Viburnum opulus ssp. opulus Guelder rose frequently substituted for V. opulus ssp. trilobum; has
replaced V. trilobum across most of southern Ontario
Invasive Exotic Species Ranking for Southern Ontario - January 2002 © Urban Forest Associates Inc.
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Potentially Invasive Exotic Species to Monitor
Some of these species have the potential to become invasive exotics in Ontario. They can reproduce aggressively on occasion but have not been shown to be a serious threat to natural areas in Ontario. Some are very similar to indigenous species and could simply have been overlooked.
Scientific Name Common Name Risk to Natural Areas
Alnus incana ssp. incana European white alder similar to Speckled alder A. incana ssp. rugosa, nursery
trade is using European name to describe A. rugosa as
well, creating the possibility of misidentification.
Ampelopsis brevipedunculata Porcelain-berry invasive in northeast U.S.
Artemisia vulgaris Common mugwort highly invasive in New York City natural areas
Cabomba caroliniana Fanwort invasive in New England lakes
Cornus sericea Red osier dogwood ambiguous species name being used in the nursery trade
to describe C. stolonifera, creating possibility of
misidentification with similar Eurasian red dogwoods.
Daphne mezereum Mezer’s Daphne has invaded moist forests in S. Ontario
Egeria densa Waterweed known to be invasive in Massachusetts wetlands
Fraxinus excelsior European ash sometimes misidentified as F. nigra, can reproduce in
shade
Isatis tinctoria Dyer’s woad a new invader to the Bruce Peninsula
Lapsana communis Nipplewort
Najas minor Minor naiad invasive in New York and New England waterways
Humulus lupulus Common hop locally invasive in Ontario
Hydrilla verticillata Hydrilla known to be invasive in mid-Atlantic states of U.S.
Phalaris arundinacea* Reed canary grass hypothesized that a European strain dominates wet
meadows, or native species may be responding to high
nutrient availability, to be determined.
Populus tremula European aspen very similar to P. tremuloides
Prunus avium Bird cherry reproduces but does not seem to dominate natural areas
Prunus mahaleb Perfumed cherry
Sambucus racemosa European red elder may be misidentified as S. pubens
Tilia cordata European linden reproduces but does not seem to dominate natural areas
Trapa natans Water-chestnut invasive in New York and New England waterways
Typha sp. Exotic cattail species being sold in nursery trade in northeast U.S.
Viola odorata Sweet violet very aggressive garden plant, many Viola sp. are difficult
to identify accurately, leading to misidentification.
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Invasive Exotic Species Ranking for Southern Ontario - January 2002 © Urban Forest Associates Inc.
References
Anon. 1990. Vegetation Management Guidelines for Illinois Nature Preserves. Illinois Nature Preserves
Commission.
Anon. 1991. Invasive Exotics. Andropogon Associates, Inc. factsheet reprinted by Maryland Native Plant Society.
4 pp.
Anon. 1992. Compendium on Exotic Species. Natural Areas Association, Mukwonago, Wisconsin.
Association for Biodiversity Conservation. 1999. The Real Alien Invasion. Have they invaded your land?
Association for Biodiversity Conservation, Toronto, Ontario. 12 pp.
Christensen, T., and S. Strobl. 1999. Preliminary Survey of Dog-strangling Vine (Cynanchum/Vincetoxicum spp.)
in the East Don River Corridor in Toronto, Ontario. Forestry Division, Parks and Recreation, City of Toronto.
Crow, G. E., and C. B. Hellquist. 2000. Nuisance Aquatic Plants of the Northeast. In Aquatic and Wetland Plants
of Northeastern North America. University of Wisconsin Press, Madison, Wisconsin. pp. xv-xviii.
Gavine, Kim. 1996. Natural Invaders: Invasive Plants in Ontario. Federation of Ontario Naturalists, Toronto,
Ontario. 15 pp.
Klick, K., O’Brien S., and L. Lobik-Klick. 1989. Exotic Plants of Indiana Dunes National Lakeshore. A
Management Review of their Extent and Implications. United States National Park Service. 135 pp.
Overlease, W. R. 1987. 150 Years of Vegetation Change in Chester County, Pennsylvania. Bartonia No. 53;
pp. 1-12.
Proceedings of the Eastern Native Plant Alliance 1993 annual meeting. St. Louis, Missouri. September 24-26
1993.
Randall, J.M. and J. Marinelli (eds). 1996. Invasive Plants: Weeds of the Global Garden. New York, Brooklyn
Botanic Garden, Inc. Handbook # 149.
Urban Forest Associates Inc. 1996. Invasive Alien Plants in Ontario. Urban Forest Associates Inc, Toronto,
Ontario. 2 pp.
White, D.J., E. Haber and C. Keddy. 1993. Invasive Plants of Natural Habitats in Canada. Habitat Conservation
Branch, Canadian Wildlife Service, Ottawa. Publication No. CW-66-127/1993E.
Wyckoff, P.H. and S. L. Webb. 1996. Understory influence of the invasive Norway maple (Acer platanoides).
Bulletin of the Torrey Botanical Club, 123(3). pp. 197-205.