Try to visualize the unique ecosystem in south Florida known as the Everglades. Picture its vast expanses of native saw grass, its beautiful tree-island forests, its slow, wide southern sheet flow of water and its rare and endangered wildlife – the snail kite, Florida panther and American crocodile. Imagine the millions of birds that call this ecosystem home. Try to understand the importance of this ecosystem to the fish and wildlife and, especially, to the citizens of southern Florida, who depend on it for water. Then consider the economic value of this unique place, not only as a natural resource but as a prime tourist destination.
With this picture firmly in mind, imagine a battalion of giant bulldozers slowly crawling across the gladelands. As they move, they remove everything in their paths. The wetlands are filled in. The waters are drained. Plant diversity vanishes. Birds and animals are driven out, and their wildlife food sources are lost forever. This scenario is the equivalent of what’s happening in the Everglades today because of the invasion of the exotic, or nonindigenous, Australian melaleuca trees.
The thirsty melaleuca was originally brought in early in this century to turn the ““wastelands’’ of the Everglades into valuable timber forests. Its natural ability to fill in wetlands with leaf litter, its fire-resilient qualities during the dry fall and winter, and its prolific seed production made the melaleuca seem like an ideal choice. When the timber industry discovered that the tough wood was too difficult to harvest, the tall trees were sold by nurseries for landscaping. Today, more than 450,000 acres of the Everglades and the tropical wetlands of south Florida have been taken over by the melaleuca. Scientists estimate that forests of the Australian native are expanding their range by 50 acres a day.
In the United States, the tropical melaleuca has no natural enemies. Like many other imported plants, it came into this country ““clean’’ – without its natural insect controls. Melaleuca forests without insects become forests devoid of insect-feeding reptiles, birds and other predators. This sets up a domino effect that ends in biological impoverishment. A melaleuca can be killed by herbicides, but six months later thousands of seedlings will sprout in its place from the dead tree’s capsule-protected seeds, making it difficult to control.
The agriculture, aquarium, landscape-design and pet industries have brought in hundreds of other invaders. Brazilian pepper, a bushlike member of the poison-ivy family, is another imported ornamental infesting the Everglades. This foreigner is now fighting for space with existing species in the wetlands and forests. Nonindigenous amphibians, reptiles and mammals in Florida are displacing native species – reducing the food supply for natural predators. Urban sprawl and farming have created loss of habitat. With all this combined, we have a prescription for mass extinction of our native species.
As a biologist working in Florida for the past 13 years, I have watched public lands be overtaken by exotic plant species. It is depressing to see ecosystems that took thousands of years to evolve destroyed almost overnight. I walk regularly through the once highly diverse plant communities now overrun with dense stands of melaleucas or pepper shrubs. These areas have been deserted by their native wildlife and usurped by invaders.
Exotic species invasions are not confined to Florida. Large parts of our national and state parks, wildlife refuges and wilderness areas have been invaded by purposely introduced species. The rapid-growing kudzu vine – the plant that ate the South – was imported from Asia in 1876 and later used as cattle feed.
Other kinds of invaders arrived accidentally. The zebra mussel, for example, was released into the Great Lakes from the ballast water of a tanker arriving from Europe. This mollusk clogs water lines that support cities and factories throughout the Midwest. It also gobbles up plankton and algae that feed the rest of the aquatic food chain.
Despite warnings from scientists, little attention is being paid to the problem of foreign invaders. No state legislatures or environmental organizations have tackled the issue with the urgency given to clean water, clean air and hazardous waste. Yet our biological heritage is steadily being displaced. Of course, wildlife doesn’t vote. Tree and shrub invasions don’t satisfy the public’s demand for action on the TV news. They aren’t sexy enough to warrant front-page coverage in newspapers.
Scientists have many weapons in their arsenal to combat these biological invaders. A number of areas have been restored where sufficient funding was available. The floating water hyacinth is no longer a threat to Florida’s waterways. Eliminating melaleuca trees from the Everglades is a labor-intensive project. In Australia, the tree is no threat to anyone. It has more than 400 known insect species keeping it in check. But the search for an insect species that targets only the melaleuca is expensive and timeconsuming.
Prevention is the key. Florida, despite it own efforts, cannot totally prevent the intentional introduction of environmentally harmful species. Existing federal laws do not prohibit the sale of known invaders across state lines. And federal agencies aren’t required to screen imported plants for their potential as deadly takeover artists.
I’m not saying that all foreign plants and animals are bad. A great many are beneficial. Nonindigenous crops and livestock, such as soybeans and cattle, form the foundation of U.S. agriculture and help feed the world. Exotic fish and animals make cherished pets in our homes. The trouble comes when the foreign flora and fauna escape human control and cause serious and, in some cases, permanent ecological damage.
Billions of governmental dollars have been spent to buy environmentally sensitive lands. In many of these land purchases, we want to save the biological characteristics of the landscape for future generations. Yet nothing is being done on any significant scale to preserve this heritage from harmful exotic invaders. It just doesn’t make a whole lot of environmental or economic sense.
