Monday, June 27, 2022

How do we decide what is an invasive species?

Here's an interesting discussion on just how we should define and categorize invasive species, a topic that has always been a little fraught, but is coming under increasing scrutiny as climate change affects the nature around us. As with so many other discussions, there are purists and pragmatists, and it is hard to definitively agree or disagree with either side.

The context of the article is little Small's Creek ravine, a cute but diminutive natural ravine and wetland, right here in our own neighbourhood, that has come under development pressure from a new rail line that (it is argued) Toronto desperately needs. In order to make way for a new retaining wall for the expanded GO Transit Lakeshore East line, Metrolinx has recently cut down hundreds of mature trees, an act that many local people and environmentalists have loudly criticized.

As part of their justification, Metrolinx claims that, "268 trees were identified for removal, and of those, 206 were invasive species", mainly Norway maples and Manitoba maples. Most people applaud efforts to get rid of invasive plants like garlic mustard, dog-strangling vine, European phragmites, giant hogweed, etc, that are rapidly taking over our parks and even our wilder areas, even though these efforts seem doomed to failure in the long term. But when it comes to trees, the issue seems less clear-cut (sic!)

No-one denies that non-native species represent a threat to local native species, whicb may not be able to compete. But such is life: survival of the fittest, and all that. If we applied the same kind of purity test to human migration, we would be accused of xenophobia and racism, even eugenics. Is it justifiable to apply the same lens to our natural environment?

And just because Manitoba maples are native to Manitoba not Ontario, does that make them totally unwelcome here? As global warming (heating) takes hold and our climate changes, some species that are historically native are finding it increasingly hard to survive in their ancestral homelands. Other species, which may be more resilient or more used to warmer/wetter/drier conditions, may be better adapted to thrive in a particular area. Is it so wrong to allow them to? Many species - from deer to lobsters to armadillos to maple trees - are on the move ("range-shifting" or "climate-tracking") as climate change accelerates and habitats change. Do we have to protect EVERY last native species, even when the climate writing is quite clearly on the wall? 

And what constitutes "native" anyway? Our natural environment has always been in a state of flux, and species come and go with alarming regularity over longer time periods. Should "native" mean species that were around in the 1800s? At the time of European settlement? A thousand years ago? Ten thousand? Should we only protect those species that are at risk specifically from human development? What about those that are only locally at risk, but are thriving elsewhere in Canada (or in the world)? Is the ecosystem that results from invasive species necessarily inferior to the old one, or just different? Who are we to say? These are knotty problems, with no single, definitive answer.

As the article (and other similar articles, like this one in Vox) points out, many biologists and Indigenous land stewards are starting to question the conventional wisdom on native and invasive species. Many scientists see habitat shift as a good and necessary thing, and not all non-native species become problematic (some may even be beneficial). There is also a recognition among some that Norway maples and Manitoba maples and invasive plants like buckthorn still provide shade, clean air and soil protection, and help out cities deal with climate change and carbon concentrations. And if they grow better than historically local plants, then maybe that is how it is meant to be. And we do, after all, need railway lines (and even new housing).

The idea of "invasion" and "invasiveness" has been a defining paradigm in environmental management and policy for decades now, and is ingrained in the consciousness of the general public, as well as many scientists. But that, like the climate, may be changing.

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