As I mused last year on one of my other blogs, it’s often bugged me that, in the classic tearjerker E.T.: The Extra-Terrestrial, little Gertie offers a geranium plant to a hapless member of an alien race. Although her intentions are pure, the unfortunate fact is that the introduction of even the smallest rodent, fish, plant, insect, microbe, or other exotic organism into a foreign ecosystem can have devastating consequences for native inhabitants—even extraterrestrial beings. Just consider how tiny Formosan termites, which accidentally arrived via American ships returning from the Pacific during World War II, have caused millions of dollars in damage, repairs, and pest control throughout the historic French Quarter of New Orleans. Like such ferocious super-termites, many unwanted animals, insects, plants, and other pests have spread from region to region by wind, water, birds, vessels, and vehicles, but many others are transferred by humans, either by accident (as with many recreationists and travelers) or by design (as with consumers of exotic pets and horticulture), without understanding the potentially harmful effects of their behavior.
To better comprehend this alien “bioinvasion,” it’s helpful to know the key terminology involved. A native species is one that occurs in a particular habitat, ecosystem, or region without direct or indirect human actions. Every organism on the planet—whether plant, animal, insect, fungi, or bacteria—is native to some locale, where it’s probably existed for thousands of years due to natural forces like climate, storms, moisture, fire, soil, and species interactions. In North America, native species are considered those that occurred prior to European settlement. Approximately 18,000 plants are native to this continent, serving as the foundation for a variety of landscapes as well as providing sources of food, fiber, and other necessities.
Nonnative species, meanwhile, are organisms that occur artificially in locales beyond their natural ranges. Also known as exotic, foreign, introduced, nonindigenous, and alien species, such nonnatives can do irreparable damage to fragile ecosystems in the United States, whether they’re accidentally or intentionally transported between continents or from one part of the country to the other. In America, nonnative invaders and habitat destruction have led to the extinction of roughly 200 native plant species since the 1800s. That’s because, without natural enemies in their new habitats, these aliens quickly proliferate by preying on or hybridizing with native populations, polluting food supplies, degrading native habitats, and introducing fatal pathogens.
Of course, not all nonnative species are dangerous. Without such exotics as honeybees, kiwi fruit, soybeans, and tulips, American consumers would still be limited to the several dozen crops that existed prior to 1492. Still, no matter the advantages of certain nonnatives, all such aliens can affect the present balance of nature, often in negative ways. Just consider anglers who have accidentally transferred parasites from shoreline mud to healthy waters via infected boots and equipment, families who have released unwanted and potentially diseased goldfish and cats into the wilderness, homeowners who have used smothering water hyacinths and English ivy to decorate their gardens, and wealthy landowners who imported Indian peacocks, prized for their ornamental feathers, during the late 1800s, only to have them overrun countless zoos and sanctuaries, subsequently uprooting or smothering fledgling plants.
Many national parks have been adversely affected by such alien invaders. In Hawaii Volcanoes National Park, for instance, feral cats and pigs have spread deadly mosquitoes, cleared pathways for exotic plants, and preyed upon fragile orchids, ferns, and other native species, while grizzly bears and other animals in Yellowstone National Park have suffered a loss of sustenance due to the illegal introduction of deep-water lake trout, which devour other native fish. While researching southern Florida for my upcoming travel guide Moon Florida Keys, I discovered that several invasive plant species are currently threatening native plant populations in Everglades National Park (40001 S.R. 9336, Homestead, 305/242-7700), which can, in turn, affect other native inhabitants, such as alligators. Such alien invaders include:
Australian pine: (Casuarina equisetifolia) Native to Australia, Malaysia, and southern Asia, this tall, fast-growing pine tree was introduced to Florida in the late 1800s for the purposes of ditch and canal stabilization, shade, and lumber. Today, dense thickets have displaced native dune and beach vegetation; radically altered the light, temperature, and soil chemistry of beach habitats; inhibited the growth of native plants, upon which native insects and other wildlife depend; and increased beach and dune erosion, which has affected the nesting activities of sea turtles and American crocodiles.
Brazilian pepper: (Schinus terebinthifolius) As the name indicates, this bushy, spreading evergreen tree hails from Brazil, Argentina, and Paraguay. Given its aromatic leaves, white flowers, and red berries, it’s no wonder that the Brazilian pepper was imported as an ornamental in the 1840s. Since then, however, the seeds of this fire-resistant, salt-tolerant plant have spread, resulting in the formation of dense monocultures in farmlands, pinelands, hardwood hammocks, and mangrove forests. As an unfortunate bonus, chemicals in the lovely leaves, flowers, and berries can irritate human skin and respiratory passages.
Latherleaf: (Columbrina asiatica) Found along coastal areas of eastern Africa, India, Southeast Asia, Australia, and the Pacific Islands, this sprawling bush was brought from Asia to Jamaica by immigrants in the 1850s. From there, the seeds, which can be dispersed by tides and storms, probably floated to southern Florida on ocean currents. Nowadays, latherleaf has invaded coastal beaches and dunes, pine and hardwood forests, and mangrove estuaries, smothering native vegetation and threatening to form a monoculture if left uncontrolled.
Melaleuca: (Melaleuca quinquenervia) Originally from Australia, New Guinea, and the Solomon Islands, this subtropical tree was introduced to southern Florida in the early 1900s for landscaping and “swamp drying” purposes. Today, the fast-spreading melaleuca is the greatest threat to the Everglades ecosystem, which faces extreme and perhaps irreversible alteration because of the tree’s ability to convert native plant communities like sawgrass marshes and wet prairies into impenetrable thickets.
Old World climbing fern: (Lygodium microphyllum) Native to Australia, Africa, and tropical Asia, this intertwining vine was introduced to Florida in the 1960s as a landscape ornamental. Since then, the climbing fern, which has a dense root system, has blanketed pine forests, cypress swamps, and other Floridian habitats; altered the water flow through streams and wetlands; and provided fuel for fires that would not normally spread through a wetland area.
Seaside mahoe: (Thespesia populnea) Indigenous to the tropical seashores of Africa and India, this tall, flowering tree was brought to Florida as an ornamental for coastal landscapes in the 1920s. Since then, the seaside mahoe has invaded shoreline habitats, where its dense shade has smothered its competitors. Unfortunately, its seeds float in seawater, which means it can also ride the ocean currents to colonize other unsuspecting shores.
Management methods vary from plant to plant, and some are definitely more effective than others. Over the years, biologists have struggled to fight the melaleuca, for example, with herbicides, managed fires, and melaleuca snout beetles. Unfortunately, they’ve discovered that trees can become resistant to herbicides, fires can actually spread the seeds, and released insects can attack non-target organisms. Because nonnative species don’t recognize regional borders, the key to limiting the harmful impacts of invasives is to prevent them from becoming established in the first place. Since most exotic species don’t pose a threat until years after they’ve been introduced, it’s crucial for humans to pursue activities that guard America’s distinct lands, waters, and national parks from such alien critters. To prevent the introduction or spread of all invasive plants, you can take the following actions:
- Avoid disturbance to natural areas, such as clearing native vegetation, planting nonnatives, and dumping yard wastes
- Refrain from the use of exotic species in your landscaping, land restoration, or erosion control projects
- Use ornamentals that are native to your local region
- Consult a local university, arboretum, nature center, native plant society, or Department of Agriculture office if you have any concerns about a plant that you intend to grow
- Use techniques such as cutting, mowing, pruning, or herbicide to remove or manage any invasive exotics
- Ask local nurseries and garden shops not to sell invasive exotic plants
- Notify land managers about invasive exotic plant occurrences
- Assist in exotic plant removal projects
- Work with your local government to encourage the use of native plants in urban and suburban landscapes
- Be careful not to transport exotic animals, plants, and microbes (even on camping equipment, fishing supplies, and the soles of your shoes)
Such precautions—however tedious they might seem—will go a long way in helping to preserve the natural state of our national parks and other precious regions for decades (and, hopefully, centuries) to come—as long as they’re not permanently damaged, that is, by major oil spills and the like.