Caring for and Healing the Earth

Alien Plants

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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