Borders Don't Mean Much To a Plant (Or a Possum)
- Karina Lapierre McIntosh
- Jul 17
- 3 min read
Updated: Jul 18
Here's a question worth asking: if a plant that's a 'near-native' - meaning it occurs naturally just south or west of Ontario - shows up here because people have planted it, or on its own because it was carried by a warming climate, is that actually detrimental to local ecosystems? Or could the fixed native/non-native line, drawn from historical botanical surveys, be less meaningful than we treat it as? Animals and plants do, in fact, cross borders.
I think of my friend, a farmer who's lived here his entire life. Not long after I'd moved out to Stirling (which is almost two decades ago - how time flies!) and started a hobby farm, something got into my chicken coop and killed a small hen. As usual, I consulted the predator identification guide in my well-worn Encyclopedia of Country Living by Carla Emery to pinpoint the culprit - which by all accounts pointed to a possum as the culprit. I mentioned this finding to my farmer friend who just laughed and told me to toss the book into the fire - he'd never seen a possum here in his life, and neither had his father nor his grandfather before him.
Within a few years, I started seeing possum roadkills on the sides of the road. Now they seem to be everywhere. I brought the story up to him recently - "remember when?" - but interestingly, he didn't recall telling me possums don't live around here.
Opossum populations have been expanding northward for a few decades now, possibly because of warmer winters with less snow cover, sure, but perhaps also because of development - now they can more easily find food and shelter where humans live, on farmland and in suburbs.
Plants are doing the same thing: their natural ranges are shifting due to climate change, and ecologists have a real term for deliberately helping them along - assisted migration ("human-assisted movement of plants or animals to more climatically suitable habitats") - because for slower-moving species, climate change is outpacing their ability to shift on their own. The harms or benefits are debated, and for good reason: it's believed that introducing a species into a new area may carry risk, particularly where it might cross with or crowd out a closely related plant that's already part of an intact, wild population.
I think this distinction matters for what I actually do as a landscape designer. Most of what I plant goes into yards, disturbed soil, spaces that have very little established within them for wildlife to begin with (think lawn, old hay field, new suburban landscape). In that context, the goal is to build function into a space where that currently lacks, and a near-native migrating in is almost always doing more for the insects here than an ornamental from another continent would. Plants native to areas just south or west of Ontario share a lot more co-evolutionary history with our regional insects than an ornamental or highly cultivated plant does, because plant-pollinator relationships are often built at the genus or family level, not hyper-locally. So a "near-native" migrating in, with human assistance or naturally, is going to do more for local wildlife than a Korean or European cultivar bred for a garden centre.
That said, I do have the privilege and the responsibility of working in a region with real conservation areas nearby, and that's exactly the context where I still choose caution over the broader argument. Biodiversity, not a line on an old map, is the actual goal. But knowing which situation you're dealing with and the effects of our plantings on the surrounding ecosystems still matters.
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