Title: Threat of Invasive Exotic Species
The world as we know it is getting smaller. Distant countries, once thought inaccessible, can now be reached in a day. Products and natural resources unique to different parts of the world are now traded globally at an amazing rate. Despite the benefits this provides, increased globalization comes with a hidden danger: the introduction and spread of new pests that severely damage our native ecosystems, residential landscapes, agricultural crops, and possibly human health. Invasive exotic species, which include non-native animals, insects, plants, and disease-causing pathogens – like fungi and bacteria – are recognized as one of the top critical threats to our nation’s ecosystems. Their consequences are estimated to cost the American public over 130 billion dollars annually.
In every ecosystem, native plants, animals – even tiny organisms -- provide unique functions that other creatures depend upon for survival. Populations are kept in check and a delicate balance is maintained. But that balance can be severely disrupted with the introduction of just one exotic pest species. Even when it is not a pest in its native environment, a species can become an invasive exotic pest when it is suddenly transported to a new ecosystem without its usual natural enemies. Facing little or no resistance, these alien invaders are too often able to out-compete native organisms for habitat and resources, or easily damage or kill vulnerable native plants. Left unchecked, these invasive exotic pests can have devastating economic, aesthetic, and ecological impacts in their new environments. And nowhere is this more evident than in our nation’s forests.
The American chestnut was one of the most economically valuable and ecologically important trees in the eastern United States. In the early twentieth century, an aggressive fungus was accidentally introduced into America’s eastern forests. Arriving on infected chestnut material from Asia, this non-native pathogen swept across the country killing nearly four billion chestnut trees. Within a span of just 50 years, the majestic tree was practically eliminated by the chestnut blight, crippling wildlife communities and local economies dependent upon the chestnut. Today, a number of other native trees, including American elms, beeches, butternuts, and dogwoods, are being killed at alarming rates by non-native, disease-causing pathogens.
Our nation’s forests are also under siege by exotic insects. Since its discovery in 2002, the emerald ash borer has killed more than 20 million ash trees in Michigan and surrounding states, and is poised to eliminate this prized timber and shade tree from American forests. This exotic beetle is only one of a large number of foreign insects creating unimaginable damage from our nation’s woodlands to our tree-lined communities.
Like insects and pathogens, alien plants can become pests as well. Almost one-third of Florida’s 4100 plant species are not native to the state. About 130 of these exotic species are invasive pests. Many of these exotic plants were introduced for ornamental or management purposes but have escaped into the natural environment with unintended consequences.
When a natural habitat is overwhelmed by a single exotic invasive plant species … when almost all native vegetation, and the wildlife dependent on it is forced out … a monoculture is created. Certain exotic vines, like kudzu…old world climbing fern…Japanese climbing fern…and air potato…form nearly impenetrable mats that completely smother surrounding vegetation. Other invasive plants, like Cogongrass (CO-gon-grass), form dense monocultures that can become flammable fuel for potentially damaging wildfires.
One of the most damaging exotic plants in Florida is the melaleuca tree. Native to Australia, melaleuca was introduced into southern Florida in the early 1800s for landscaping and "swamp drying." Unfortunately melaleuca is a very aggressive invader, and in a single year, one melaleuca tree can produce a dense island hammock nearly 600 feet in diameter. Since the early 1900s, it has taken over hundreds of thousands of acres of the unique Florida Everglades ecosystem. Native plant communities such as sawgrass marshes, wet prairies, and aquatic sloughs have been converted into melaleuca monocultures and thickets. The result is a habitat completely foreign to the native plant and animal communities, posing an extreme threat to the existence of this world-renowned ecological treasure.
Throughout history, fire has been an integral part of Florida ecosystems. Fast-burning fires would control the growth of native vegetation and spur the growth of new plants. But the spread of melaleuca has altered the way fire behaves in south Florida in dangerous ways. The papery bark of melaleuca quickly carries fire into the canopy, which burns with intense heat and smoke due to natural oils in the leaves, and poses a threat to life and property.
“These melaleuca stands are against homes … And the intense heat that melaleuca puts off -- sometimes its radiant heat will set homes on fire, will set property on fire.”
Fire also helps perpetuate the spread of melaleuca. Filling the branches of a mature melaleuca are tens of thousands of small capsules, each containing hundreds of tiny seeds. When under stress, these capsules open, scattering up to fifty million grain-sized seeds per tree.
Efforts to control melaleuca have involved multiple agencies and a variety of integrated tactics, including mechanical, chemical, and biological control. Because melaleuca will quickly resprout from cut stumps or roots, herbicide applications, applied either aerially or on the ground, have been necessary to eradicate melaleuca in places where it is heavily established. Through years of repeated applications, some areas, like portions of the Big Cypress National Preserve, have been restored from melaleuca monocultures to diverse native Florida habitat.
“We have a responsibility to address habitats for threatened and endangered species such as, Florida panthers, Red Cockaded Woodpeckers, tree snails, things like that. So when we have exotics that invade these areas, they tend to dominate areas. And when they dominate areas, native species just don’t have the ability to compete effectively and they become very scarce … And so we want to maintain the diversity and native character of areas to maintain these species.”
Unfortunately, vast areas of melaleuca remain untreated, and the expansion of new infestations on private lands may nearly offset the amount removed in control efforts to date. The most promising tactic for long-term control of this invasive plant is biological control. In its native Australia, the species is kept in check by a number of natural enemies. Researchers in Florida have imported some of these enemies – including a leaf-feeding weevil and a sap-feeding psyllid – to help fight the spread of melaleuca.
“To be able to introduce a biological control agent we have to go through, a very rigorous and long research process screening these agents to make sure that not only do they do the damage we want them to do but that they will only do it on the target pest, the target plant.”
“Our studies are conducted for two or three years in the quarantined environment. Our work is scrutinized by outside scientists - both federal and state by the time we get ready to recommend release, the insect has a very narrow range of plant preference and we’re confident that it will not go over onto other plants.”
Since 1997, biological control agents have been released against melaleuca in Florida and have reduced the plant's ability to reproduce. Researchers are confident that the build-up and establishment of these beneficial insects will help minimize the development of new melaleuca infestations.
While dense melaleuca thickets pose their own threat to the environment, they also serve as a breeding ground for one of the most recent and potentially devastating insects to reach Florida: the lobate lac scale. Each no larger than the head of a pin, the hardshelled lobate lac scales attach themselves in large numbers to small branches of woody plants. Sucking the sap of their victim, the insect kills the branches and often the plant itself. It also secretes a sugary substance that becomes covered by a sooty mold fungus, giving infested plants an unattractive, blackened appearance.
Native to India and Sri Lanka, the lobate lac scale was first found in Broward County in 1999. Within four years the insect had spread north to Lake Worth, south to Homestead and west into the Everglades. Concern exists that this insect will also spread to northern Florida as well as islands in the Caribbean.
One of the most troubling aspects of the lobate lac scale is the number of woody plant species it can attack. It has already infested over 300 species of plants in Florida, including many landscape trees, ornamental shrubs, and fruit trees. Commercially important trees like mango, lychee and star-fruit are particularly vulnerable. One of the most susceptible tree species is the berry-producing, wax myrtle.
“Wax myrtles are a very common native tree in natural areas. And they’re an important source of food for birds, especially migratory birds. So what we’re concerned about is that by eliminating a lot of wax myrtles, the Lobate Lac Scale could have an impact on populations of wild birds.”
An international team of researchers at the University of Florida is working to evaluate the impacts of lobate lac scale and to develop methods of controlling it. Due to its wide distribution, ease of spread, inconspicuous size and long list of host plants, biological control is believed to be the most promising means of reducing the impact of this pest. Until these natural enemies are discovered, researched, approved, and established, however, lobate lac scale will continue to cause major problems for land managers, landscapers, commercial plant dealers, and fruit growers.
Florida’s exotic pest problems are not limited to South Florida. On Fort George Island in the Timucuan Ecological and Historic Preserve just northeast of Jacksonville, park managers began noticing the unusual death of some redbay trees in late 2004. By 2005, dead redbay trees were appearing further and further inland, and by the following summer 80% of the preserve’s monitored redbay trees were dead.
The trees are killed by a non-native fungus that spreads through the wood, plugging the flow of water, causing the trees to wilt. This fungus is carried into the tree by the redbay ambrosia beetle. A native of Asia, this beetle is believed to have arrived in the US in untreated wood shipping material.
“Native ambrosia beetles typically attack only dead and dying trees, and they’re a natural part of replacing those weaker trees in the forest. In contrast, this new redbay ambrosia beetle and its associated fungus are not a natural part of our forests, and it appears that even healthy redbay trees are vulnerable to them. So, in areas where this new beetle is becoming established, it seams that all the mature redbays are being wiped out.”
While it was first detected in an insect survey trap at a port near Savannah, Georgia in 2002, its connection with extensive redbay deaths was not realized until years later. By that time, it had already become widely established in coastal Georgia and South Carolina and was working its way to Florida.
“Red bays belong here. They’ve been here for, for eons. They’re part of this system. When you take that red bay out of the system, we see some potential other problems and we’re not even sure what they are. Birds eat the berries. Will those birds leave? Butterflies need that tree to, to have their, their young larval stages. Will other species drop out without the red bay here? So we, we’re seeing some real changes in what Florida forests should look like and aren’t going to anymore.”
Beyond the ecological damage to Florida’s forests, redbay mortality will also bring economic damage to local communities. Homeowners, neighborhoods and parks that rely on redbays for shade, will face costly tree removal bills for trees killed by the redbay ambrosia beetle and its associated fungus.
“Depending on the size and location of the tree, tree removals in urban and residential landscapes can cost hundreds if not more than a thousand dollars per tree. So, in neighborhoods where redbay makes up an important component of the shade tree canopy, homeowners are facing not only the loss of valuable shade, but big economic costs as well to have those trees removed.”
Concern exists that the redbay ambrosia beetle will not limit its onslaught to redbay trees. The beetle has already spread to the sassafras, a tree closely related to the redbay. In laboratory studies, disease specialists have shown that artificial inoculation with the associated fungus results in the death of seedlings of several other tree species in the same family, including some endangered species. If the beetle is also attracted to avocado, a close relative of the redbay, it could become a major problem for the multi-million dollar south Florida avocado industry.
Florida’s beautiful diversity of natural forest communities make our state unique and contribute to our quality of life. Forests contribute over $7 billion annually to Florida’s economy, sustain an estimated 30,000 jobs, and provide numerous recreational, aesthetic, and environmental benefits. Exotic pests are currently the most serious threat to the forests of eastern North America and the benefits they provide, as well as to our agricultural crops and livestock. With this much at stake, it is vital to prevent the introduction and establishment of new exotic pests in our nation.
The first line of defense against invasive exotic pests is to stop them from crossing over the borders. Because many of these pests are imported unintentionally, it is increasingly important that travelers not bring wood, plants, fruits, vegetables, or illegal animals home from foreign countries. At US ports of entry, government agencies must inspect travelers, and enforce regulations to ensure that cargo is pest-free before it is shipped.
On the home front, local landscaping should consist primarily of native plants. Nurseries that sell non-native plants should stock only those species that are not identified as invasive by state or local experts, and they should be certain that plants imported from – or exported to -- other areas of the country are pest-free. Every community needs to know and recognize which invasive species in their area are pests, and should cooperate when government officials conduct detection surveys for exotic pests around warehouses, ports, natural areas, or neighborhoods.
Even after exotic pests become established, the damage they cause can be minimized by preventing or slowing their spread to new areas. Invasive pests can spread by means of clothing, muddy shoes, vehicles, boat hulls, excavators, and other equipment. These items should be cleaned before moving to a new area, especially if they have been someplace where exotic pests are established.
Campers should avoid transporting firewood over long distances. Tree-killing exotic insects at various stages of growth can remain undetected inside cut firewood, only to emerge later in a new location and infest new trees.
The resources that we use, and enjoy and depend on for day-to-day life come from our forests and our natural ecosystems. So if we don’t seriously prevent and address exotics pests introductions we’re really damaging the ecosystems that support us and, in a sense, biting the hand that feeds us.
Invasive exotic species are recognized as one of the top critical threats to our nation’s environment for good reasons. These invasive pests can destroy the health of our forest ecosystems, dismantle residential landscapes, and ruin agricultural crops. Every effort should be made to eradicate and manage these invasive pests. While the destruction caused by invasive exotic species is estimated to cost billions of dollars annually, what the American public really loses is priceless.