Invasive Plant Species Threaten the Health of Your Forest

Forests are a wonderful place to relax, enjoy nature, hunt, and engage in other fun activities, but our enjoyment of our forests is threatened by numerous invasive plant species. These plants can outcompete – and sometimes, even replace – native plant species, which significantly impacts the long-term health of our forests.

Garlic mustard found on a Shiawassee County forest edge.

One of the most obvious problems created by invasive plants is their ability to crowd-out native plant species. Garlic mustard (Alliaria petiolata) – a herbaceous biennial native to Eurasia and Africa – is an example of one such species; since it is shade-tolerant and each plant can produce up to 3,000 seeds, it can spread to cover an entire forest floor. This prevents other native herbaceous plants – and even tree seedlings – from growing.

Many invasive plants, including garlic mustard, are also unappetizing as food sources to wildlife. The shrub Japanese barberry (Berberis thunbergii), for example, has spines that make deer avoid it. Since Japanese barberry takes up space that would otherwise be used by native tree species, like sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis), the deer have less of their preferred food available. This is a double-whammy for the native trees, as their future is then jeopardized not only by a lack of space, but also by higher-intensity deer browsing. Long-term forest planning can be ruined by invasive species!

Black locust (Robinia pseudoacacia) foliage. Photo by Paul Wray, Iowa State University,

Some invasive species can even change the chemistry of the soil, potentially altering what species can grow there for years to come. While native to North America, black locust trees (Robinia pseudoacacia) are not native to Michigan, and can quickly form large areas of nothing but black locust. Since black locusts are legumes, like soy beans, they fix nitrogen into the soil, which can alter the natural nutrient cycling of a forest. And since black locusts are very fast-growing and shade-tolerant, they can prevent anything else from growing where they become established.

While invasive plants do indeed pose a serious threat to your forest, there is a lot you can do. Regularly monitoring for invasive plants in your own forest is very important; the best way to prevent a major problem is to catch it early! The Shiawassee Conservation District can also provide you with information on ways to fight invasive plants, and programs that can help you to protect your forest. You can contact the office at (989) 723-8263 ext. 3, or stop by the office at 1900 S. Morrice Road in Owosso.

Photo above: Large patch of flowering garlic mustard (Alliaria petiolate). Photo by Steven Katovich, USDA Forest Service,