In this issue:
Has Your Relationship
Gone Sour?
by Karen Jensen Miles, Botanist
Alice Ferguson Foundation
Have you ever known someone who was beautiful in an exotic way and fun to
be around initially, only to find out that your relationship was "poisonous"
and squelched your way of life? Well, the same may be said for hundreds
of plants and animals that have been introduced to our area because of their
great beauty. If they only behaved themselves, the natives and aliens could
have lived in harmony!
While the beauty of a plant is not the only reason for plants being bought in from places afar, the lovely ones are those I want to emphasize here. When I bring up the subject of oriental bittersweet (Celastrus orbiculatus) or lesser celandine (Ranunculus ficaria) or Japanese stilt grass (Microstegium vimineum) to the uninitiated, their reply is almost always "But they are so pretty. Who cares if we have a whole lot of something so beautiful?" On the surface, that seems logical. But, we humans are not the only creatures to inhabit the earth and a sharp shift in the biota of an area knocks nearly everything else out of kilter.
The worst of the alien invaders out-compete nearly everything that previously lived there. Out of their own native environment, they lack natural predators that keep them in check. They are quite efficient at seed production or asexual replication and few native plants can survive in their wake. The biodiversity of an area decreases sharply. Where there might have been 50 or 60 species, only a dozen or so remain and most of those struggle to survive. Many animals rely on the leaves and flowers of these native plants for food sources, nesting places or hiding spots to elude predators. When their numbers are depleted, the animals attempt to use the new monoculture species, but most often their needs are not met.
Jil Swearingen of the National Park Service has compiled a list of some of the negative effects that alien invasives have on the environment. Examples follow:
Garlic mustard, (Alliaria petiolata) (it's prettier than it sounds):
- Reduces and eliminates host plants for native insects and other wildlife. For example, it replaces native toothworts (Cardamine spp.) (also prettier than they sound) that serve as host plants for the West Virginia Whitebutterfly. Its leaves are toxic to the eggs and larvae of the butterfly, which unknowingly uses garlic mustard as a substitute host.
- Competes with and encroaches upon the limited habitat of several endangered plants. Garlic Mustard threatens two state endangered plants, goldenseal and white trout lily at Antietam Park.
- Large numbers of seeds produced and lack of natural predators allow it to quickly take over the native ground cover species
Oriental bittersweet (Celastrus orbiculatus):
- Reduces forest stream buffers by toppling trees. The vines climb to the forest canopy by twining around the trunks and branches of trees, making them highly susceptible to toppling during high winds and from the heaviness of the vines themselves.
- Increases the incidence of plant disease and stress in forested areas due to reduced air flow through forests. This occurs due to the increased density of exotic vegetation. Dense tangles of oriental bittersweet reduce the flow of air through forests, increasing temperatures and humidity levels that can lead to increased fungal diseases.
- Serves as a host for plant pathogens and other organisms that can infect and damage native plants.
- Prevents seedling establishment of native trees and shrubs by covering the ground with a dense covering, so much so that most plants cannot germinate and push through the bittersweet vegetation.
Lesser celandine (Ranunculus ficaria):
- Out-competes native spring flowering plants by forming a solid vegetative mass on the forest floor.
- Eradicates native plant communities, disrupting associated animal populations.
Japanese stilt grass (Microstegium vimineum):
- Out-competes native flora populations in disturbed areas. It can go unnoticed until all of the native plant species are replaced by it.
- Deer don't eat it, so it takes hold in over-browsed areas.
- It grows equally well in deep shade and full sunlight.
In some areas, our forests, roadsides and fields are being overtaken by these exotic plants. There are some things we can do to stem the tide. Volunteer eradication groups can be assembled to target the worst species. Interested individuals meet in a couple of parks in Charles County on the first Saturday of each month to hand pull and spray alien invasives and they are seeing good results after revisiting sites several times. Probably the best thing that most of us can do to help is to NOT PLANT ANY OF THE PLANTS KNOWN TO BE INVASIVE on our property. There are well-behaved similar alternatives to all of the bad actors. For example, we have a native bittersweet that won't overtake the world. Plant that if you want bittersweet. Marsh marigiold is the native "version" of lesser celandine. The Maryland Native Plant Society has done extensive work on the subject of alien invasive plants and it is worthwhile to visit their web site, www.mdflora.org. There you can find articles on some species NOT to plant, native plant nurseries and a native species planting list.
Remember, we aren't the only ones out there. Let's not be greedy or thoughtless about the other inhabitants on earth, our island home. These exotic travelers may be pretty, but "beauty is only skin deep," as we all know!
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