Published in thespec.com. March 22, 2019.
Spring is just around the corner and of course, with the warmer weather comes an explosion of growing things, evidence of lovely nature. Except, there’s the issue of invasive species getting the upper hand, proliferating in our natural areas, our trails and forests, our lakes, our rivers, and at home, our yards.
Invasive species are plants, animals, aquatic life and micro-organisms that are introduced outside of their natural environment and threaten local biodiversity (variety of life). They harm what are delicately balanced eco-systems, already under great stress from other factors like sprawl and pollution. They outcompete native species. They are pervasive, they move aggressively, they are hard to get rid of once they establish themselves. Invasive species are now considered only second to habitat loss as the highest threat to biodiversity.
But what about the natural evolution argument? Survival of the fittest? To find answers, I turn to Lesley McDonell, ecologist with the Hamilton Conservation Authority (HCA) to get an understanding of exactly why letting invasives become our biodiversity is deadly.
Lesley describes a scenario, where at the grocery store, there are only five different things that are available for purchase, maybe one or two are available in the spring, one or two in the summer and one or two in the fall. Now put this in the context of a natural area where we get our ecosystem services. If invasives are natural evolution, they tend to dominate the landscape, reducing biodiversity and resiliency: “So a fall forest turns yellow all at the same time and thanks to invasives. No more mosaic of colours.”
It’s worse for the animal or insect consumer. “It goes to the forest to get pollen or food in the spring after hibernating or migrating, but that forest has lost the plant that it used to eat or use,” Lesley continues.
Now Lesley asks us to imagine what would happen if we only had three of four tree species and an invasive insect came that could kill three of them, further reducing our biodiversity. Think about what we stand to lose when a part of the web of life disappears: “I think sometimes, things are too interconnected for us to realize and plan for,” Lesley muses.
How did they get here?
Invasives are either brought to a city intentionally or by accident, like when seeds hitch a ride on clothing when people travel. Lesley points to the nursery industry as a major culprit of how invasives are arriving in Hamilton: “There are many invasive plant species sold by the horticultural industry that the public can purchase,” she says, giving examples such as Giant Hogweed, which was originally sold in nurseries for its beauty, that is, its large leaves and flower head and Japanese Knotweed, “also sold because it has pretty flowers and looks like bamboo.” Japanese Barberry and burning bush are two invasive species still sold in nurseries today. These species escape into natural areas and wreak havoc. According to Lesley, our shipping ports are another pathway of entry. “Zebra mussels came in the ships ballast water whereas Emerald Ash Borer likely arrived in shipping pallets from overseas,” she says. “Others, such as Common Buckthorn, have been here for a long time, promoted in the past as a hedgerow for farmers and Garlic Mustard was a pioneering food plant because it is edible so early in the spring.”
What can we do to curb them or stop them?
Lesley advices that the public familiarizes itself with these harmful species; learn the common ones. In Hamilton, these include Garlic Mustard, Dog-strangling vine, Common Buckthorn, Purple Loosestrife, Multiflora Rose, Periwinkle, Black Locust, and Norway Maple, to name some of the top offenders. When gardening, do not throw unwanted plant material and cuttings into your local parks, woodlot, forest or in a natural area.
“Usually, your unwanted plants contain invasive species and these lower the biodiversity of the forest or natural area,” Lesley says.
Neither should they go in the green bin or brown compost bags. Rather, Lesley recommends putting unwanted plants, if you know they are invasive, in garbage bags and leaving the bags in the sun to dry for up a week to two weeks before throwing them out. If you want to remove invasives from your property, she suggests contacting your local Conservation Authority or a professional company, because, “sometimes just cutting them down can make the problem worse, or it does not kill the plant completely.”
In removing invasive species, consider the plant. For example, Lesley says early spring is the best time to pull Garlic Mustard, before it flowers or seeds, whereas this would not be the ideal time to tackle Phragmites: “It does make it hard for control because it is so variable, but targeting the species at the best time can save money and ensure you are successful.”
When buying plants for your garden, try and buy native plant species where you can. Encourage the City to use native tree species in our parks and as street trees.
While Ontario has an Invasive Species Strategy, the City of Hamilton has yet to develop one.