By:Michele S. Byers
As I hiked along the Delaware River with a group of friends last weekend, one of them asked me to identify the tall, purple flowers growing along the river’s banks.
"Purple loosestrife" I told them, "they’re an invasive exotic."
"They’re a what?" my friend asked, looking puzzled.
Suddenly, I realized that I had hit on a topic for another "Ecology College" lesson from Emile DeVito, Ph.D. As you may recall, Emile is director of conservation biology for New Jersey Conservation Foundation and a trustee of the New Jersey State Natural Lands Trust.
"According to Webster, exotic is also a noun meaning ‘something foreign or imported,’" Dr. DeVito stated. "Now add the adjective invasive, meaning ‘attacking, harmful or troublesome,’ and we have described a set of plants that don’t belong in North America.
"In New Jersey alone, over two dozen invasive exotics, including purple loosestrife, are wreaking havoc with our natural communities! Yet, ironically, although they choke our native habitats, many varieties are major items in nursery catalogs and therein lies the problem; invasive exotics have been introduced – intentionally and accidentally – by humans.
"While many of us think that butterflies, warblers, orchids and old-growth forests are worth saving simply because they are beautiful, regardless of their utilitarian value, only recently have we begun to realize the importance of the genetic potential of biological diversity.
"Disturbingly, while our concern for natural areas has increased, so has the problem of the dreaded invasive exotics!
"These plants consume natural habitats from the forest floor to the forest canopy. They outcompete native species for germination sites, nutrients and light, resulting in the local elimination of native species and a corresponding loss of species diversity. Just compare these two scenes:
"During an autumn stroll through a pristine forest in the New Jersey Highlands, your eyes delight in the brilliant hues of scarlet black gum, orange sugar maple and lemon yellow birch leaves drifting through towering spires of dark green hemlock.
"At eye level, migrating gray-cheeked thrushes feed on bright red spicebush fruits, sunbeams cascade across yellow witch-hazel flowers set against a green curtain of mountain laurel, and on the forest floor, a quilted rainbow of leaves is draped across summer’s ferns.
"Unseen beneath this insulating blanket, tubers of dozens of species of wildflowers wait patiently for the return of spring, their network of roots firmly grasping soil, water and nutrients.
"In our second scene, a forest on the outskirts of a sprawling suburban area, a stroll takes you across a paved parking lot, through a soccer field, and onto a forest path. At the sunny edge of the woods, ailanthus trees rocket skyward, and a thorny thicket of barberry occupies the forest understory, supplanting native wildflowers. Where a giant red oak has died from a combination of old age and gypsy moths (another foreign invader), Japanese stiltgrass suffocates the forest floor, preventing native black cherries, viburnums and dogwood from germinating in the sunlit gap.
"Nowhere in this forest can one find a seedling or sapling of a native tree; the native species don’t stand a chance when competing with invasive exotic species that have no local predators.
"In places, the trail is completely surrounded by invasive shrubs such as tartarian honeysuckle, Norway maple and winged euonymus. While some of these shrubs possess tiny fruits, eaten as a last resort by birds staying the winter, they are of no nutritive benefit to the migratory thrushes, catbirds, waxwings and sparrows, which require fruits high in sugar and fat. The native spicebush, magnolias and dogwood are what the birds need.
"Forests like the one in the second scenario have been transformed into collections of invasive exotics from Europe and Asia, and they don’t give humans all the utilitarian functions of a biologically diverse habitat. Research on the biological control of invasive exotics needs to be expanded if we hope to have forests rich in species at the end of this century.
"At first glance, you might say the woods look well," Dr. DeVito concluded. "But look a little closer – you may be surprised at how little you see."
Michele S. Byers is executive director of the New Jersey Conservation Foundation based in Far Hills.
