Alien Invaders
Along the Grand
By
Larry Lamb
A lot of money has been spent to acquire natural habitats, including many in the
Grand River watershed. These areas
perform vital ecological functions related to hydrology, erosion control, air
purification, climate tempering, and are habitats for plants and animals. They are also valuable for passive recreational use including
aesthetic appreciation. A key
criterion for determining a high quality natural ecosystem is its degree of
ecological integrity. Is it
representative and intact as an ecosystem?
The less disturbed a habitat is, the better it will serve as a benchmark
or example of a component of our globally unique, bioregional identity.
Unfortunately,
it is rare to find pristine habitats anywhere where long-term human occupation
has occurred. Since day one of
human visitation in the watershed, non-indigenous organisms were introduced.
"Nonindigenous" implies that a species may be
native, i.e. of a particular country but is not a natural component of a smaller
politically-defined unit or habitat of the nation.
For example, Douglas Fir is a native Canadian tree but is not
indigenous to Ontario or for that matter parts of B.C. where it would not occur
naturally (without the intervention of humans).
Over the past two to three centuries of Caucasian settlement,
hundreds of alien animals and plants have been added to our ecosystems.
"Alien" implies that a species is not a natural component of a
particular nation, (i.e. Norway maple is from Norway and other European
nations). Fortunately, most of the
introduced alien species did not succeed or are relatively benign.
Why
should we be worried about alien species? Alien
species can be disease agents that kill or weaken native species, physically
overwhelm desirable species, or simply occupy space that a native component
could. A good number of alien plant
species are not useful to our native animal populations, which can be adversely
affected when familiar, useful native plants are displaced.
Most
of us are well aware of how alien fungi are killing our sweet chestnut, elms,
butternut and flowering dogwood; how European starling, house finch and rock
dove have disrupted native bird populations; how the zebra mussel has changed
our Great Lakes and how purple loosestrife has disrupted our wetlands.
Very few realize the extent and seriousness of the damage alien species
have done to our natural habitats. Few
are aware of the tremendous costs in dollars, time and energy needed to restore
degraded habitats. There are
literally hundreds of different alien species in the Grand River watershed, all
of them damaging to some extent. On
average, 50 to 80% of the vegetation seen from a car window, while passing
through southern Ontario countryside or urban areas, is non-indigenous!
It is safe to say that not even a square metre of any habitat type in the
watershed is pristine. Even our
earthworms are alien!
Although
all habitats in the watershed have been severely impacted by competition from
alien species, one in particular has been disrupted more so than others.
This is our floodplain or riparian forest system.
This habitat has always been prone to disturbances, naturally from ice
scouring during floods, and unnaturally from early settlement needs at the
water's edge, related to navigation, drinking water supply for humans and
livestock, waste discharge, crop irrigation, fire-fighting, milling and
recreation.
Many
alien species originated from Europe or Asia where agriculture has been
practiced for millennia. These
plants and animals adapted to the disturbances inherent in annual crop
production, and thrive in disturbed areas.
They evolved to mature quickly and set seed prolifically, or developed
root systems that could survive the annual cycle of disturbances from ploughing,
seeding and harvesting. Seed of
many of these species is viable for decades.
Aside from disturbance, floodplains are also vulnerable to invasion by alien
species due to their fertility from silt deposition during floods.
The floods bring seed from plants upstream, often from undesirable,
aggressive (weedy) material that has been dumped along the watercourse.
Watercourses are also corridors for the efficient movement of
animal life which is an important agent for dispersing plant material upstream
and downstream. Because early
settlement tended to occur along rivers there is a long history of agriculture
and domestic gardening, resulting in a super diverse concentration of plant
material that could escape downstream. Grain
and other seed mills are notorious among botanists for the many alien species
growing around them.
The
practice of grazing livestock is particularly common in floodplain forests due
to the convenient supply of drinking water and shade for the animals.
The farm animals often graze indiscriminately, eating many native
wildflowers. They also bring in
seed on their bodies and in their faeces from fields, and from their forage,
which often contain alien species. These
undesirable, introduced seeds can readily germinate in the hoof-trampled,
disturbed, forest soils. Prior to all the cultural disturbances, our floodplain
forests were enchanting communities.
The main tree species throughout the Grand River watershed
were Peach-leaved and Black Willows, Bur Oak, Black, Silver and Sugar Maples,
White, Red and Rock Elms, Basswood, Bitternut Hickory, Red and White Ashes,
Hawthorns and White Cedar.
In
the southern reaches of the watershed, within the Carolinian zone, special
species were also dominant, such as Black Walnut, Cottonwood and Sycamore.
Characteristic floodplain shrubs included raspberries, running strawberry
bush, currants, and the southern watershed specialties, Bladdernut and Burning
Bush.
The
herbaceous or ground layer was the richest in diversity and the most vulnerable
to disruption and displacement by alien species.
Many of the characteristic herbaceous species of the surrounding upland
forest are also common on the floodplain. There
are, however, a dozen or so species more-or-less restricted to floodplains.
These Grand River floodplain indicator species include White Trout-lily,
Twinleaf, Harbinger of Spring, Green Dragon, Golden Alexanders, Lizard's Tail,
False Mermaid, Wild Garlic, Gromwell, Nodding Trillium, Marbleseed, and Great
Angelica.
All
of the floodplain herbs listed above are at risk in one jurisdiction or another
throughout the watershed, and most are either rare or threatened in Ontario and
Canada.
The main reasons for their imperiled status are: livestock
grazing, logging, reservoir construction and, most importantly, competition from
aggressive alien plants. Today,
except for rare examples, the floodplain forests are missing trees such as the
Elms, especially Rock Elm, which seems to be the most susceptible to Dutch elm
disease, and Sycamore, which is severely disfigured by anthracnose.
Very
few of our native floodplain species can compete with the alien plants that now
predominate.
Among the most serious alien tree and shrub competitors are
Norway Maple, Crack Willow, Buckthorns, European Barberry, Tartarian
Honeysuckle, Bittersweet Nightshade and Dog-strangling vine.
Most damage to our floodplain flora has been in the herbaceous layer by
species such as Bedstraws, Burdocks, Periwinkle, Garlic Mustard, Yellow Rocket,
Gill-over-the-ground, Moneywort, Goutweed, Watercress, and a particularly
vexatious showy mustard, Dames Rocket, the popularly misnamed "wild
phlox", which carpets too much of our floodplains in white, pink and mauve
in June.
In
spite of this daunting picture, we can all help to stem the tide of alien
species invasion in the Grand River watershed.
We can remove and safely dispose of any of the previously mentioned,
undesirable species from our properties and, with permission, from wild areas.
With hard work, sore fingers and backs, progress is being
made against some of the invaders at some sites.
Workshops are being held by the Nature Conservancy to root out invaders
like buckthorn and Garlic Mustard. Community
groups are pitching in with trowels and shovels to restore local wild areas to
their natural beauty and integrity.
If
we live close to a floodplain, or other sensitive area, we can avoid planting
invasive ground-covers such as goutweed or periwinkle, and use native species
for our landscaping where possible. We
can educate ourselves from a variety of publications available through agencies
like the Nature Conservancy of Canada, the Federation of Ontario Naturalists,
the Region of Waterloo, and the GRCA.
Our
yard trash should be completely composted to kill alien seeds and not tossed
over the fence into a natural area or on a stream bank.
We can avoid using seed mixes that contain invasive alien plant seed, and
educate local nurseries about alien plants including the undesirable ingredients
in some seed mixes. We can inform
our friends and neighbours of the severity of this issue and lobby for effective
weed control legislation. We may
not win all the battle but together we can preserve some of our natural heritage
for the future.
Larry
Lamb is the Manager of the Environmental Studies Ecology Laboratory at the
University of Waterloo (Ontario,
Canada) and an Adjunct Lecturer. He is well-known as a vocal and passionate advocate for
native plants.
Larry Lamb has written other articles on plants
which appear on this website. See the Naturalization and
Alien Plants sections.
Copyright © Larry Lamb, reproduced with
permission.
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