Ecologists Name Troublesome Invasive Plants

Exotic invasive pest plants:  chances are you host them in your yard and so do I.

I asked ecologist Belinda Esham to name a few of the most troublesome plants considered a severe threat in Tennessee.  Her personal worst of the worst list included at least two plants in my yard:  privet and Japanese honeysuckle.  She also named multiflora rose, tree of heaven, Japanese stiltgrass and Japanese knotweed.  Esham volunteers on the board of directors for the Tennessee Exotic Pest Plant Council, while her professional work for the USDA is also in natural resources.

I could see that the extensive TNEPPC list included several plants available for purchase at local garden stores. So I asked Esham why these so-called pests would be offered for sale.  She explained that plants now considered invasive often are hardy, easy to grow, and easy for nurseries to propagate.  These plants that ecologists consider troublesome are often accepted as popular landscaping elements.  Privet grew quickly to create hedges, and now birds help replant it all over our yards.  Remember when every new housing development had streets lined with bradford pear trees?  Tennessee ecologists now have that tree listed with an alert status indicating their concern.  Tennessee has the distinction of being the first known US location where Japanese stiltgrass was introduced, probably being unintentionally imported as packing material.  Now it competes with native grasses.

It's easy for homeowners and landscapers to feel a bit defensive about ecologists listing some of our lush greenscapes as threats to the ecosystem.  Isn't any green good in our yards?  Esham says allowing invasive plants to thrive and choke out native plants "alters the ecosystem."  It's about the plants, tiny creatures that rely on those plants, and everything else in the food web.  Esham says we all should strive for a balance in our backyards, "Manage the ecosystem for overall health and vigor so that native species have a better chance to compete with the exotics."

The TNEPPC provides public information at its website about which native plants can be desirable alternatives to various invasive plants. It also offers Wildland Weeds printed magazine.  The group uses a rating system to identify plants that need to be watched closely and to set apart the plants considered the most severe threat to the state's biodiversity.  Some exotic plants seem to be more easily tolerated than others if they don't have the worst invasive tendencies.  

One of the most striking examples of how popular do-it-yourself landscaping has gone awry is with our efforts to attract butterflies.  While many of us have heard of the butterfly bush and seen it for sale in garden centers, it turns out that this plant so attractive to butterflies cannot serve them throughout their life cycle.  TNEPPC board member Pat Parr says the native milkweed or butterfly weed is what monarch butterflies need in order to lay eggs and let their young survive.  Butterfly bush is on the TNEPPC watch list of exotic plants.

Sometimes, although not always, invasive plants can be eradicated manually or with herbicides.  Other times, ecologists strive for the perfect balance by introducing more native plants and simply letting them reclaim an area little by little.