Invasive Plants: Why Should We Care?

By Priscilla Seimer

Asiatic Bittersweet (yellow leaves) in the Fall

When members of the Harpswell Invasive Plant Partnership are removing invasives in the area, people often stop to ask what we’re doing.  Sometimes folks ask us what an invasive plant is, or what plants in our area are invasive.  And sometimes someone asks why we bother.

The answer to  “why we bother” is biodiversity.  Biodiversity, simply put, is the astonishing variety of life on earth.  The more biodiversity we have, the healthier the planet.  Think of it this way.  If we only had one grain crop, say corn, and a disease wiped out that crop we’d be in trouble.  Remember the Irish Potato Famine?  If we have multiple types of grain, and multiple types of corn, that disease won’t have such a damaging effect.  Invasives – whether plant or animal – limit biodiversity.

They do this in several ways:

  1. Invasives outcompete native species.  Next time you drive down Routes 24 or 123 notice the often huge stands of Japanese knotweed (Fallopia japonica).  Nothing else is growing there.  This knotweed (like most invasives) loves disturbed areas, and spreads very rapidly.
  2. Invasives can alter habitat by reducing light, moisture, available nutrients, and space.  Notice how high and thick Asiatic bittersweet (Celastrus orbiculatus) grows, overtopping trees and shrubs, fully shading them out, completely taking over an area.
  3. Invasives’ growth reduces natural habitats for native insects, birds, and other wildlife, and so reduces the available food potential.  Purple loosestrife (Lythrum salicaria) takes over ponds and marshes, displacing cattails and other native plants wildlife use for food, as well as reducing habitat for spawning fish and waterfowl in some areas.
  4. Invasive growth patterns can change soil chemistry.  Garlic mustard (Alliaria petiolata) has roots that exude a chemical that inhibits the growth of important soil fungi, altering its immediate habitat to help prevent competition at the expense of a more diverse ecosystem.

In each of these cases the invader limits biodiversity.  So even if bees love Japanese knotweed, or migrating birds devour the berries of autumn olive (Elaeagnus umbellata), the end result is still a greater loss of biodiversity.

In comments echoed by other sources, the Encyclopedia of Life (eol.org) states, “Invasive species rank second only to habitat destruction, such as deforestation, as a threat to biodiversity.” Minimizing the loss of biodiversity to the best of our ability is why HIPP keeps at it.  You’re welcome to join our efforts.