Fall Out of Love With Invasives

Fall marks the season of change, the days become shorter and most of our greenery begins to disappear. While a lot of our favourite plants begin to wilt, some species are just beginning the hard work to ensure their survival in the next year. Unfortunately for Ontario’s biodiversity, many of these plants are dreaded unwanted invasives.

What’s the big deal?

Invasive plants compete with our native species, often creating dense monocultures. Varying plant species that have co-existed in a certain area for often hundreds of years are now pushed out by these competitive, generalist, fast reproducing plants with little to no native enemies.

This is the problem.

Many species of plant set seed towards the end of the growing season, invasive species are no different. In this post we’re going to cover some of the lesser talked about invasive species to watch for this fall.

Norway Maple (Acer platanoides)

(Photo source: Credit Valley Conservation)
(Photo Source: Haliburton Master Gardener)

Our first species is Norway Maple, often rightly nicknamed the “tree killer.” This tree is often planted as an ornamental as it’s foliage typically stays on much longer, often late into the fall, much longer than that of our native maples.  The colour can range along the spectrum from green to yellow. This species is extremely invasive in North America. The Norway Maple grows in dense stands, which shades out our native sapling trees and wildflowers and competes for resources. As if that wasn’t enough to deter one from planting this invasive, it also releases toxins that alter the fungi and microbes in the soil. A few extra weeks of fall colours definitely do not out weight the negative of this species, always opt for native maple species in Ontario, and don’t plant the infamous Norway Maple.


Oriental bittersweet vine (Celastrus orbiculatus)

(Photo Source: BYGL, Ohio State University)
(Photo Source: University of Maryland Extension)

This lesser known perennial invasive vine is native to Eastern Asia, and can be found across several parts of Ontario. This vine forms a dense monoculture and pushes out native biodiversity and chokes out trees. Make sure not to confuse this vine with the native American bittersweet. A quick way to tell the difference between the two: on the invasive Oriental Bittersweet the berries grow along the vine with a yellow capsules, whereas the native variety has berries at the tip of the vine and orange capsules. These yellow capsules will burst open in the fall, making them a key ID factor this time of year. Oriental bittersweet has a competitive advantage against its native rival, it’s colour throughout the seasons is more attractive to birds, as well its berries tend to be more appealing. Not to mention the invasive variety, like most invasive species, is just generally better at reproducing.


Himalayan Balsam (Impatiens glandulifera)

Himalayan Balsam is not one of the lesser known species, unfortunately. This prolific invasive herb is extremely common and extremely invasive in Ontario. Native to the western Himalayas, some of the tallest reported sightings of this invasive species in Ontario have been found in Northern Ontario (over 8 ft!). This species made our fall list because of its unique method of seed dispersal, which occurs late in the growing season, towards the beginning of fall. This plant is accurately nicknamed the “Touch Me Not” plant, as the mature seeds will explode when disturbed, spreading as far as 5 meters away from the host. Because of this, humans often inadvertently help this plant spread further by brushing up against it, or tracking the seeds further along trails, back to their homes, etc. When developing a management plan, always avoid executing control efforts at the end of the growing season to avoid further spread.


Common Buckthorn (Rhamnus cathartica)

Common buckthorn, also known as European buckthorn is an invasive shrub, native to Eurasia. Often planted as an ornamental as it is usually the first to leaf out in the spring, and the last to lose its leaves in the fall. Under the Ontario Weed Control Act this plant is classified as a noxious weed, as it can alter the nitrogen levels in the soil to favour its own preferences. This can impede agricultural crop growth, thus leading to its classification as a noxious weed. If that wasn’t enough of an advantage, it is also able to germinate quickly and disperse its seeds over extremely long distances, allowing it to completely invade the under story of a forest. It is also often the overwinter host of a specific type of aphid that can destroy soybean crops. So how do you identify it in the fall? It produces clusters of berry-like black seeds in the fall. Avoid planting this species, and always opt for the native variety (Alder-leaved buckthorn).


So what now?

Invasive plants are often hardier than our native species, appearing earlier in the spring and lasting well into the fall. This is likely where the appeal to plant as an ornamental comes from, prettier for longer, and more bang for your buck. But buyer beware, these species will do a lot more harm than good in the long run.

Understanding the lifecycle of an invasive plant that spreads by seed is an integral part of any management plan. Planning a removal when the seed has set can lead to more harm than good. Always avoid planning a removal strategy around the plants seed dispersal timeframe, or plan to take extra precautions. Each plant will be different.

Seeds of invasive plants are also notorious for hitch-hiking on hikers and pets. To avoid being a vector for spread yourself use a boot brush and wipe away any visible mud and dirt from your clothing, pets and equipment.

If you think you’ve spotted an invasive species report it to eddmaps.org/Ontario or download the app on Android or iPhone. EDDMapS Ontario (Early Detection and Distribution Mapping System) is a real-time reporting application to track invasive species distribution in Ontario.