By Sarah Reed
In an effort to spread awareness this Invasive Species Awareness week, we're dedicating this blog post to the most common invasive plant species in The Land Between. What is an invasive plant species, you might ask?
The term invasive plants refers to foreign trees, shrubs, and aquatics that have been introduced to non-native areas, primarily through human activity and have proliferated to the extent that they out-compete species that naturally occur in the area. They can overtake habitats and suppress native plants because they typically lack any native predators. Associated negative consequences extend not just to native vegetation but to wildlife in the area and the ecosystem as a whole.
The Land Between has the highest percentage of shoreline to area than anywhere in the province – it’s called lake country for a reason! – and while the wealth of connected waterbodies provides habitat for wildlife and a multitude of critical ecosystem services, it also enables the spread of riparian and aquatic invasive species. Four of the 5 most common invasives in The Land Between fall into this category, endangering the health of our lakes and wetlands and the wildlife that depends on them.
Phragmites
Map of Phragmites distribution
In 2005, Agriculture and Agri-food Canada named phragmites Canada’s worst invasive plant. Phragmites is a reed native to Eurasia whose spread across Ontario has increased by almost 30% between 2010 and 2017, with ecosystems in nearly every region of Ontario now negatively impacted. Distinguished from the native species by their tan stems and large fluffy seed heads, Phragmites is fast-growing and aggressive: not only does it form thick stands that out-shade and out-compete native plants, it also releases chemicals through its roots designed to kill or impede the growth of other species.
Phragmites is not an adequate source of habitat nor food for native wildlife, so these dense monocultures have dangerous implications for lake and shoreland biodiversity. Moreover, because this species grows so quickly – stems reach 1.6”/day, and rhizomes up to 16”/year – when phragmites establishes in lakes or wetlands, it lowers water levels and reduces the amount of open water.
Phragmites has disastrous impacts on wildlife and lake quality, but tackling this invasive plant can be intimidating – not least because stands can reach 15 feet high. The Land Between offers training for Phragmites removal, and has created a Phrag Fighters volunteer program for inspired individuals.
Photo: Phragmites can grow to heights of 15ft. Via J. Gilbert.
Eurasian watermilfoil
Map of Eurasian watermilfoil distribution
Eurasian watermilfoil is a perennial aquatic that grows underwater, with thin stems reaching over 8ft tall. Growing into large dense mats, Eurasian watermilfoil displaces native plant species, degrades fish habitat, and hinders human activities like boating or fishing. Moreover, when these masses of watermilfoil die each fall, their decay reduces dissolved oxygen, altering water conditions which can be fatal for fish and other aquatic organisms.
With a wide tolerance range for ecosystem characteristics including acidic and alkaline water, cold and warm temperatures, and all levels of nutrient availability, Eurasian watermilfoil has become one of the world’s most widely spread invasive plants: besides its native range, it has been introduced on all continents except Antarctica. Since new plants can sprout from any small piece, boat propellers that disturb Eurasian watermilfoil masses will merely support its spread.
Eurasian watermilfoil has a native look-alike, though these two plants can be distinguished from each other using the rules in the diagram below. For more history, identification tips, and instructions on how to combat the proliferation of this invasive through The Land Between’s waterways, check our website.
Japanese knotweed
Map of Japanese knotweed distribution
Japanese knotweed is, as evidenced by the name, native to East Asia. It was introduced to North America in the 1800s as an ornamental garden plant, and more deliberately, to aid with erosion control. Ironically, Japanese knotweed lacks fine surface roots, so these plants can increase erosion; since their preferred habitat is riparian and wetland areas, this has particular consequences for increased erosion, water turbidity, and flooding.
At at early age, Japanese knotweed resembles asparagus. Stems grow rapidly, however, over 3”/day, reaching full height up to 10ft. Dense thickets of these invasives can reduce sunlight penetration by 90%, altering the ecosystem for all low-lying native species. Japanese knotweed has dramatic impacts on human infrastructure as well: this plant can grow through septic beds, building foundations, and even driveways and sidewalks.
There are many ways to tackle this invasive plant, though which method depends on the size and location of the established site. Consider these options, and don’t give up!
Photo: Flowers and foliage of Japanese knotweed. Via Kateej.
Starry stonewort
Map of Starry Stonewort distribution
Starry stonewort is actually a macroalgae, not a plant! It was introduced to North America in the 1970s through ballast water dumped in the St. Lawrence River; it has since spread throughout the Great Lakes basin. Individual plants can reach a height of 6ft, but collectively Starry stonewort forms large, thick stands that impede fish movement, human recreation, and the growth of more desirable native species. Masses of SSW may also alter the water chemistry, impacting the ability of native plants to uptake necessary nutrients.
Starry stonewort may show different physical characteristics depending on the attributes of the environment they are growing in; this makes them difficult to identify and has led to misidentifications. While SSW has not been successfully eradicated from any of the lakes in which it has been found, the Starry stonewort Collective is a program devoted to research, outreach, and best management practices within the Great Lakes Basin to target this widespread invasive.
Within its foreign distribution, SSW is more likely to occur in waterbodies with more human activity; therefore increased human awareness can impact its spread.
Photo: The white ‘starry’ bulbils (seed-like structures) that give SSW its name. Via Department of Environmental Conservation.
Dog strangling vine
As the name indicates, Dog-strangling Vine is a fast-growing and highly competitive plant that twines around other plants or itself to form dense mats, suppressing all other species. While pets may become entangled in the vines, the real victim of this invasive’s strangling are the young saplings in forest understories: by choking out new growth, DSK effectively prevents forest regeneration.
As a member of the milkweed family, DSV has specific consequences for Monarch butterflies (a Species of Special Concern in Ontario): Monarchs may mistakenly lay eggs on Dog-strangling Vine instead of their native milkweed hosts, leading to starvation of the caterpillars and further population declines.
For small or young establishments of DSV, digging up the plants, or mowing or clipping may be effective ways to eradicate this invasive. It is imperative that the roots be removed, however, otherwise the plants may return with vigour.
Photo: DSV climbing the branches and trunk of a tree. Via D. Gordon E. Robertson.
How to spot and avoid spreading invasive plants
Studies have shown that investing in spread prevention is 100 times more economically effective than spending on long-term management and control after an invasive species has already become established in an area.
- Clean shoes and bicycle tires, and brush pet fur when moving from areas with established invasive populations. Invasive plants are often spread accidentally from seeds catching in treads, on clothing or fur.
- Invasive aquatic plants can spread from fragments transported between bodies of water. It is critically important to clean, drain and dry boats and aquatic equipment (nets, waders, etc).
- Never buy or plant invasive plants. Be wary of ornamental non-native plants that are described as “fast-spreaders”, or “enthusiastic growers.”
- Plant native species in your garden! There are many beautiful native species that attract native pollinators, birds and wildlife, helping to maintain local biodiversity.
However, once invasive plants are established, there are still ways to reduce their spread, and mitigate their impact on the native species of these ecosystems.
- Learn how to identify these species, and report sightings of invasive plants on iNaturalist. Finding these established populations early, and alerting others to their presence is a key to eradicating them.
- Do not attempt to compost invasive plants, and dispose of yard waste properly. Any seeds, rhizomes, or even the fragments of some invasive plants are enough to support their growth and establishment elsewhere.
- Carefully put all plant material in black plastic bags, seal the bags tightly and leave them to “cook” in direct sunlight for 1-3 weeks, depending on the temperature and amount of sunlight.
- For large amounts of plant material, contact your local municipality to determine if plant material can be disposed of in the landfill or brought to their composting facility.
Check out our website for more tips and tricks about how manage invasive species in The Land Between.
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