National Invasive Species Awareness Week

By Sarah Wolpow – owner and operator of SweetFern Garden Design, specializing in design and install of ecological gardens and also works on, and teaches about, invasive plant removal.

My daughters recently sent me this short video: A young man is happily walking through a field of gorgeous yellow flowers.  He comments on how lovely it is. Then his friend pipes in from behind, “uh… actually, those are really invasive.” The look on the first fellow’s face is a look I know well, having received it ever so many times from family members, clients, strangers, and basically anyone who will listen.

What is an invasive species anyhow? Many people think it’s simply a plant or animal (or insect, bird, fungus, etc.) that grows or multiplies very aggressively. While that is generally the case, it’s also a requirement that the species not be native to a given area. The reason this is so important is because species that have evolved together are part of an inter-connected web of dependency in which critters help each other and also keep each other in check.

Owls keep mice from over-populating; milkweed plants provide food for monarch butterfly caterpillars; some plants are only pollinated by ants and others only by bats. These types of very specific relationships turn out to be the norm rather than the exception.

Some species, like squirrels and blue jays, are “generalists,” and can adapt to huge variations in food and habitat types; which is why there are lots of squirrels and blue jays. But many, if not most other species, like monarch butterflies and songbirds, have much more specific requirements.

The problem with invasive species is that they often have no natural “predators,” and can therefore quickly take over natural areas and completely out-compete native species.

One particularly compelling example of this problem concerns our beloved chickadee. While chickadees normally eat a wide variety of foods, including seeds and berries, they primarily feed their babies caterpillars. A pair of chickadees must collect over 6,000 caterpillars to raise one nest of chicks. Because our native caterpillars didn’t evolve to eat the leaves of non-native plants, a forest or suburb filled with invasive plants can’t generate enough food for nesting chickadees.

Studies have shown that chickadee nesting success is directly correlated with the percentage of native plants in suburbs—you know, those green, leafy, tree-lined neighborhoods filled with nice houses and “beautiful,” but invasive, Norway maples, burning bushes, barberries, and Japanese shrub honeysuckles.

Note that one of the selling features for ornamental non-native plants is that they are “pest-free.” Of course, that’s partly because our native insects can’t eat them, which, as you can now see, also means our native birds have no food for their babies.

When I tell people all of this, they often say, “but my (invasive) burning bushes are always filled with birds.” It’s true that native songbirds do eat the berries of some invasive plants, but they can’t feed those berries to their chicks, and research has demonstrated that the berries of invasive plants are generally not as healthy for birds as the berries of the native plants that were displaced.

Folks also wonder what the point is trying to mitigate invasive plants given how prevalent they are in our landscapes. Aren’t we just spitting in the wind? But the goal is not to get rid of all invasive plants. The goal is to maintain areas where our native species can continue to thrive.  More often than not, if we clear invasive species from a natural area, the dormant seeds of native plants are just waiting to return, and there are enough native insects left to repopulate.  Every native tree planted and every acre of land cleared of invasives is a place where a chickadee or a woodpecker may build a nest, a toad may move in down below, and native bees may come to pollinate.

Two years ago I helped my niece install a tiny native plant garden on the 2’ x 10’ strip land in front of her apartment building in the middle of Boston. Asian cherry trees lined the street, along with some languishing burning bush, yew, and privet (all non-native). She also put up a small structure to attract native bees. The very first summer she could see perfect circles cut out of the edges of the leaves of her blueberry bushes and those same leaf circles stuffed into an empty hole of the bee next box – a sure sign of native leaf-cutter bees. She found monarch butterfly eggs on her milkweed. Great gold digger wasps visited the goldenrod. She’d never seen any of them before on her street – and she’d been looking (she’s a biologist).

The moral of these stories is that we should learn to identify and remove as many invasive plants as we can before they become problematic. Every single time I learn to ID a new invasive, I start seeing it and am able to stop infestations when they are as small as the first sprig of black swallowwort on a several acre property.

We should also try to avoid planting anything in our gardens that are known as invasive plants (the state only restricts the worst of the worst, leaving many problematic plants still easily available).

And of course, we should incorporate more natives into our gardens. Once that’s all done, we can sit back and watch the birds and butterflies show up.

Resources & Event Reminders:

My favorite plant app is PictureThis (small annual fee). You should always confirm the apps’ suggested ID by checking with another source or field guide. Two important caveats: 1) PictureThis will give you a lot of other info about the plant which is very spotty in quality, and I recommend ignoring it entirely. Check other more reputable sources for info about the plant. 2) When using PictureThis ONLY pay attention to the Latin name of the ID. The app will often offer a common name for a native plant that is identical to the common name we typically give an invasive plant. It can be extremely confusing. Note that this means you will need to know the Latin names of the invasive plants.

The state of Maine publishes an excellent field guide to invasive plants (Maine Invasive Plants Field Guide, approx. $25). It gives you good ID features, notes about what plants are easiest to confuse with your plant and how to tell them apart, and it goes over various treatment options. This guide is fabulous bedtime reading. No kidding.

Sign up for BTLT’s events enewsletter to find out when Sarah will be running invasives removal workshops starting mid-summer AND keep an eye out for BTLT’s spring plant sale (Saturday, May 30th), which will feature native pollinator-friendly plants!