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Invasive Species
Invasive plants and animals are the second
greatest threat to biodiversity after habitat loss.
The economics of controlling invasive species
damage can be considerable. In 2004-05, the
British Columbia government spent $8 million
to protect valuable forest and range land from
the effects of non-native plants and weeds.
In the Yukon, we are not aware of any species of introduced mammals or birds, and only two species of introduced fish. In contrast, there are 140 species of introduced plants. Forty-four are persistent and widespread; 59 are persistent but not widespread; and most of the remaining 37 are casual introductions that may not persist.
Many of these plants are responsible for
habitat damage, loss of subsistence resources,
and economic loss in other North American jurisdictions. Yukoners are in the enviable
position of preventing plant infestations before
they become so widespread that control is
costly and eradication impossible.
Everyone can help reduce the spread of those already established. Keeping invasive species from becoming established in the territory should be everyone’s responsibility.
The following are the eight worst
invaders.
White Sweetclover (Melilotus alba)
Sweetclover is a biennial, occasionally annual plant in the pea family that can attain a height of 2 m but is usually less than 1 m. It rapidly colonizes gravelly well-drained soils such as roadsides, waste areas and river banks and bars.
A single plant can produce 300,000 seeds and
the seeds remain viable in the soil for many
years (80% survival after 30 years). This is likely
Yukon’s most invasive and problematic species.
Range in Yukon:
Widespread throughout
the southern Yukon.
It is known along much
of the Alaska, Robert
Campbell, Top-of-the-
World highways and
20 km up the Dempster
Highway. It has proved
to be highly invasive
along the LaBiche River.
The only site so far
reported on the Yukon
River in Yukon is in
Whitehorse; although it
is a serious problem on
Alaskan waterways
including tributaries of
the Yukon River.
Perennial Sow-thistle (Sonchus arvensis)
Despite the name, sow-thistles more closely
resemble giant dandelions than true thistles.
Sow thistle is considered a noxious weed
throughout most of its range. This is a highly
invasive species able to spread long distances
by wind-blown seed. It is perennial with
rhizomes that grow
up to 3 m deep
are very difficult
to remove by hand.
It is particularly
a problem
for agricultural
producers.
Range in Yukon:
primarily in the
Whitehorse area as
far north as Carmacks
but has been reported
from Destruction Bay,
Johnson’s Crossing
and the Kotaneelee
gas plant; found
commonly along
highway corridors.
Canada Thistle (Cirsium arvense)
Though named Canada thistle, this species is native to Europe, Asia and Africa where it is called Creeping Thistle. It is one of the most invasive species in North America and is a noxious weed in most jurisdictions throughout Canada and the USA including Alaska. The seeds of thistle and knapweed continue to mature after pulling. You may put plants into black garbage bags and then leave them in the sun to kill off the plants and roast the seeds. Herbicide control may be required.
Range in Yukon:
known from just south of Haines Junction and observed in the LaBiche River Valley.
Spotted Knapweed (Centaurea biebersteinii)
Knapweeds resemble thistles but differ in their
lack of spiny leaves. They are biennial or shortlived
perennials. This species reproduces entirely
by seed. Large plants can produce over 20,000
seeds. It has not been known to be a problem in
the north, but to date it has not had a chance to
get established. Alaska has an active program of
eradication.
Range in Yukon:
It is presently not known in
the Yukon but was removed from Haines
Junction after several years of effort. It can be
found in Atlin, BC.
Greater Butter-and-eggs (Linaria vulgaris)
This very attractive plant resembles a yellow perennial snap-dragon. It is widely found in gardens and invading roadsides in Whitehorse. It is usually less than 50 cm tall. The plant is mildly toxic, persistent, and is known to alter local pollination ecology. It is a restricted noxious weed in Alaska.
Range in Yukon:
Greater butter-and-eggs has been found throughout the Whitehorse area, South Canol Road in the Quiet Lake area, Watson Lake and Haines Junction. It is mainly spread through yard waste.
Foxtail Barley (Hordeum jubatum)
Foxtail barley is a perennial tufted plant that is
native to North America including Yukon. It has
feathery looking awns that many find attractive
but are barbed and can work their way into the
eyes, nose, gums and throats of animals, both
domestic and wild. It is potentially invasive
especially in the dry alkaline soil of the southern
Yukon where it is problematic to agricultural
producers.
Range in Yukon:
known throughout the
territory south of and including the Porcupine
and Peel river drainages.
Common Tansy (Tanacetum vulgare)
Common Tansy is a robust perennial plant that grows in clusters and forms flat-topped heads of bright yellow, button-like flowers. The plant emits a strong pungent smell when crushed. It is mildly toxic. It likes growing in full sun usually in disturbed sites such as roadsides, riverbanks and beaches. It is considered as a noxious weed in some areas of BC and Washington.
Range in Yukon:
presently known from
Whitehorse, Marsh Lake, Kathleen Lake and the
Alaska and Robert Campbell highways. It is
beginning to be used as a hardy garden plant.
Altai Wild Rye
(Leymus angustus)
Altai wild rye is an Asian dune grass found
throughout Mongolia, Siberia and China. In
Canada it was previously only known to occur
out of cultivation in Saskatchewan. This is a tall
(1 m) coarse grass that reproduces mainly by
seed and forms dense tussocks from short
rhizomes. This is a dune stabilizing grass that
could be a threat to the Carcross Dunes and
the animals
and plants that
depend on
the ecosystem.
It may have
already entered
the Yukon River
system.
Range in Yukon:
known only from Carcross where it was first reported in 1998.
You can help by:
Careful gardening – many of the plants are
attractive and are used to beautify homes and offices. Care must be taken when selecting which
plants to grow and how to handle yard waste.
Keeping it clean – invasive species can be
transported on vehicles, heavy equipment,
footwear and clothing. All of these should be
inspected and/or cleaned before entering or
being used in the territory. Vehicle wheel-wells
and CAT tracks are especially likely to hide
invasive species and should be cleaned
thoroughly.
Requesting and using only weed-free soil, hay,
straw, mulch and certified seed.
Becoming aware – learn about invasive species
that may be found in your area and report
new findings. Learn about new ways to reclaim
disturbed land. Seeding may not always be
necessary.
Picking and carefully disposing of small
infestations encountered, and reporting larger ones.
Spreading the word – Yukon is in a unique position to remain pristine, but the spread of invasive species and the costs and damages associated can only be prevented through vigilance and cooperation.