Are all invasive aliens bad?

Years ago I had to commute along the Juniata River.  There were a few ramshackle cottages between road and river.  One of them sported a sign saying ‘bittersweet for sale’.  I thought bittersweet was pretty with its bright orange berries in the winter, but I never stopped to buy some.

Since then bittersweet began growing on the property across the road from where I live and recently it has traveled across that road to populate a hedgerow and the edge of the woods as well.  I still think  its berries are pretty, but now I know it’s considered an invasive alien.

Oriental bittersweet (celastrus orbiculatus) arrived in this country in the mid-19th century, imported as a decorative garden plant.  It is a vine which can grow 40 feet by wrapping itself around a tree trunk.  All parts of it are poisonous to humans, but that doesn’t seem to affect birds and animals who eat the bright orange berries. Their excrement is generally the way oriental bittersweet travels to new homes.

Our natural environment is not static; it changes all the time.  Alien plants and animals take up residence next to native plants and animals.  While some alien plants are polite, some are indeed invasive.  Conservationists would say they are crowding out the natives. Many conservationists would like to manage nature to get rid of alien, invasive plants and animals. But how do you decide what is native or a polite alien and stays and what is an invasive alien?

Fred Pearce writes in The New Wild that invasive species might be nature’s salvation.  Flora and fauna do die.  Although some conservationists have proclaimed that the disappearance of some natives is due to invasive species crowding them out, there are many examples of those native species dying due to a change in food, temperature, or other habitat essentials and not due to the invasive itself. Those aliens simply took advantage of spaces that were less populated due to weakness or death of natives.

While the author admits that some species truly are invasive in a negative sense, he cites a number of examples where alien species have adapted to new habitats. And some aliens such as the honeybee, originating in Europe, actually fulfill a need in North America.

Pearce writes that often aliens take up residence where other plants and animals are weak or diseased, filling in the environment.  When my parents bought their small farm in the early 1950’s, there were remnants of three fields already returning to nature.  Red cedars seemed to be the pioneer then.  And three fields were still in cultivation, rented by a nearby farmer.  As a result of soil washing down the hillside, they asked the farmer to implement soil conservation procedures.  When he didn’t, they removed the fields on the slope from cultivation.  That area returned to nature.  Black birch, tulip trees, and ash trees began to grow there.  The site has also been invaded by alien autumn olive, not a preferred food for the growing number of deer.

The deer themselves, although native, were scarce more than 50 years ago but have now multiplied 5-10 times since then and negatively impact the landscape, eating planted gardens and trees and hosting black-legged ticks which carry the bacteria causing Lyme disease.  Like changes in fauna such as deer and ticks, the forest that grew up in old fields is once again changing. The ash trees are dying and falling over due to an infestation of the alien emerald ash borer.  This leaves wide open spaces in the woods.  What will grow there now to take the place of the fallen ash trees?

The author of The New Wild argues that ecology keeps changing and invasive aliens may be the salvation of our environment.  They will fill in where weaker native species cannot compete or are dying.  If we were successful in keeping aliens out of our environment, eventually it would become less diverse and could fail.

Pearce’s observations are worthwhile considering.  What role do you think aliens, invasive and non-invasive should play in our ecosystem?