Dear Readers, as promised I wanted to have a little chat about the invasive species of Toronto (and Canada generally), as it’s something of an object lesson in how a plant that might be perfectly controllable in its own habitat becomes something much worse when it travels abroad. First up is this lovely blue flower, Siberian squill, which has taken to places like the Toronto Ravine system with gusto. Trouble is that it shades out other earlier flowering plants, such as the trillium and the Canadian windflower which make up the understorey in places like the trails around the Royal Botanical Gardens at Burlington.
I spotted one or two patches of trout lilies, but these too would be overpowered by the squill.
In fact, even the innocent-looking lesser celandine are not native, and in Burlington are actually being sprayed so that they don’t overpower the other plants (they’d tried weeding them out, but these plants spread by tiny bulbules so it’s almost impossible). If we aren’t careful what we’ll end up with is completely generic habitat zones, with few differences between the woodlands of North America and those of Western Europe.
The Ravines also have our old friend Japanese Knotweed, and something that we don’t have (yet) – dog-strangling vine (Vincetoxicum rossicum). This last seems to be particularly pernicious, with no way of preventing its spread. It seems to impact on milkweed, which is one of the main foodplants of the migratory Monarch butterfly. I’m surprised that I didn’t notice it in the Ravine, but there were some tangled masses of stems that I now think might have been the plant.
Another major problem, both in the ravines and in Tommy Thompson Park, is the Phragmites reed. Often grown for bioremediation (it’s good at filtering out toxic chemicals in run-off along streams) it can quickly take over and destroy riverside habitats.
Purple loosestrife, such a useful and pretty plant in its native Europe, is also a major problem in North American bogs and seeps.
And then there’s garlic mustard. In the UK it’s the foodplant of brimstone and orange-tip butterflies, but in North America it’s not so popular with invertebrates, and therefore also not so popular with naturalists.
So, it’s clear that it’s not only the UK that has a problem with plants arriving from other countries and then jumping over the garden wall and wreaking havoc with the native flora and fauna. And we certainly shouldn’t be feeling complacent. Since Brexit, although Europe has been inspecting plants brought to the continent from the UK for pests, we have not been inspecting plants from Europe in return. At the end of April, we’ll start inspecting any floral imports, and in response garden centres have been bulk-buying trees, shrubs and perennials because they fear that the inspection process will take too long for many plants to survive in good condition. With climate change it’s very likely that plants and animals that wouldn’t otherwise have survived will survive our winters (such as the Asian Hornet, which it’s feared is now established in parts of Kent), but many creatures, plants and fungi are imported with our pot plants (ash dieback is thought to have arrived with some imported ash trees) and sometimes our food. Let’s hope that we can improve our biosecurity, as so many problems are much easier to deal with if they’re picked up early and nipped in the bud. And let’s hope that the urban forests and wetlands of Toronto can thrive, with the help of all the local people who obviously love them.