Digging Deeper into Invasive Species

Invasive species have a bad reputation.

According to the Canadian Council of Invasive Species, these are plants “introduced to an area beyond their native range.” Their proliferation “can have a severe and irreversible impact on the ecosystems they inhabit.” Prevention and eradication is the traditional approach to this threat. We are the destroyers and they the destroyed.

Is destruction the only option? There are calls for a more nuanced approach to understanding the harms and benefits of invasive organisms. Ken Thompson, ecologist and author of Where Do Camels Belong? The Story and Science of Invasive Species, suggests that efforts to get rid of such plants may do more harm than the actual plant every could. It’s not so much that invasive organisms are supplanting native populations; they are responding to opportunities in compromised environments created by human activity.

Illustration by Mabel Ray Richens

So, who’s invasive now?

Purple Loosestrife (Lythrum salicaria), the pop star of invasive plants in North America, grows in threatened wetlands, where degradation and pollution have already taken their tolls. Mr. Thompson states that studies of Loosestrife show, contrary to popular belief, that its impact on biodiversity is actually little. Rather than harming an ecosystem, the plant cleans the water ways by soaking up phosphorous and nitrogen from agricultural fertilizer run off. It grows in polluted soils where other plants cannot. And it’s a good pollinator.

The very term “invasive,” in fact, is becoming a moving target during this time of accelerated climate change. Climate change pushes all species to adapt, to move into new habitats. Efforts to deal with these outsiders are being re-examined; eradicating species in increasingly stressed ecosystems could hurt, not help, the environment they have become an integral part of.

Consider their medicinal value. In his book Healing Lyme, American herbalist Stephen Harrod Buhner notes a correlation between the spread of Lyme disease and the invader Japanese knotweed (Polygonum cuspidatum) in North America. Knotweed is a remedy for Lyme. Unsurprisingly, there are profound connections between plants, humans and our shared ecosystem.

The old vegetable patch adage “plants that go together grow together” extends beyond excellent partners like tomatoes and basil. The poison ivy growing in my backyard also grows happily with an abundance of jewelweed (Impatiens capensis) —a remedy for poison ivy.

When it comes to “invasive” and/or aggressive plants I fluctuate between an eradication and cultivation mindset. When my youngest daughter started to take my cues and vilify these plants it made me reconsider my approach. Garlic mustard (Alliaria petiolata), common here in Prince Edward County, is considered invasive, and it’s very aggressive, but it’s also edible and medicinal. It is a good poultice for bug bites, among other uses.

Unbeknownst to us, some of these invasive species may soon become welcome ones.

Catherine Richens is a professional gardener living in Prince Edward County. [email protected]