Alien Invaders: Invasive Species and Wetlands

Welcome to the first issue in our third volume of Wetland Sights & Sounds. During March and April, you will receive one newsletter each week leading up to our celebration of American Wetlands Month in May. This year, the Izaak Walton League’s Protect Our Wetlands Program is highlighting the threat of invasive species with a special theme for American Wetlands Month 2007: “Alien Invaders: Invasive Species and Wetlands.” You will receive eight issues of Wetland Sights & Sounds, each one filled with valuable information that will help you protect and conserve wetland habitat in your community. You can also access archived copies of Wetlands Sights & Sounds by clicking on this link.

Wetlands all over the country are under attack, and we are not talking about bulldozers and backhoes. There is another kind of threat to wetlands that may not always be so obvious. What appears to be a beautiful display of purple flowers, or a thriving population of tiny snails, could in fact be signs that a wetland is in grave danger. Species like purple loosestrife and the New Zealand mud snail, which aren't native to North America, wreak havoc on the plants and animals that are native to our wetlands. Every year, thousands more of these invasive species are introduced into our waterways, costing us billions of dollars in economic losses and causing irreversible damage to some of our most beautiful and valuable landscapes.

In this issue, we will give you some background information about invasive species, and explain why they are such a threat to our nation’s wetlands and waterways. Each of the next seven issues will feature the worst invasives in the various regions of the United States. You will also find out what you can do to protect your local wetlands from these invaders.

What is an Invasive Species?

Invasive species are called by many names – including "introduced," "exotic," "non-native," and "alien." What these names all point out is that these species are foreign invaders within an otherwise “natural” landscape. But using these names interchangeably can be misleading. Although all invasive species are foreign to the landscape that they have been introduced to, not all non-native species become invasive. An invasive species is defined as any species introduced by humans to an ecosystem where it is not native and which ends up causing economic or environmental harm, or harm to human health.

Since the arrival of the first Europeans in North America, about 50,000 alien plants and animals have been introduced to our native ecosystems. Yet, not all of these species are considered to be invasive. Most of them are non-threatening, or even beneficial. Some of them, in fact, have become so important to our economy that they are considered icons of the North American landscape. Familiar staples such as wheat and barley did not exist on this continent before the arrival of European settlers.

Only a small fraction of these introduced species are considered to be invasive, but these are causing the most damage to our natural landscapes. A 2004 Cornell University study pointed out that the economic damages due to invasive species and the costs of controlling them add up to more than $120 billion a year.

Of all the planet's ecosystems, wetlands are the most vulnerable to invasive species. Wetlands may only cover 6 percent of the Earth's land mass, but they are host to 25 percent of all invasive species. This is because some of the characteristics of wetlands that make them so unique and valuable to us, can also make it easier for invasive species to spread quickly and take over.

The Threat to Wetlands

Imagine taking a stroll through different types of wetlands. Some places you step into might not seem so wet at all. But if you take a closer look, you would see skunk cabbage, black willow, buttonbush, and other plants that give you clues that you are standing in a wetland. In other places, the ground might be so wet that your boots would make a sucking sound as you walk. You might see tall cattails swaying in the breeze, and hear red-winged blackbirds calling from their reed-perches. There are still other types of wetlands where you may not be able to walk at all. These watery landscapes would be full of all kinds of aquatic plants, and you would see tiny fish and tadpoles darting around their submerged leaves and shoots.

Wetlands provide an astounding variety of habitat types. This is why you can find so many different kinds of plants and animals living in them. But this habitat diversity, which makes wetlands so unique and valuable, also makes them a vulnerable target to a greater number of non-native invasive species.

Wetlands also face a high risk of being invaded because they are often located at lower elevations and along the floodplains of rivers. Lots of debris, sediment, organic material, and toxins get washed into our waterways from the surrounding land, sewage pipes, and storm drains. Though wetlands are excellent at filtering out these harmful substances before they reach open water, some of these pollutants can build up in the tissues of wetland plants and animals and make them less able to compete with non-native invaders. Also, some kinds of invasive plants can easily spread from one place to another by seeds and small pieces of vegetation that get washed downstream and deposited into wetland soil.

Many native wetland plants and animals can easily adapt to different water levels, soil conditions, and other habitat changes that often occur in wetland ecosystems. But invasive species are a different story. They can cause sudden, drastic changes that native species are unable to keep up with. Alien species also tend to be aggressive feeders and fast breeders, and they usually face few natural predators. All of these characteristics make invasive species one of the most serious threats facing wetlands across the country.

Now that you know more about the danger of invasive species, its time to identify the problem species in your region and learn about what you can to prevent their spread. The next seven issues of Wetland Sights & Sounds will tell you how, so stay tuned.

America's Least Wanted:
Purple Loosestrife

A vast field of waving purple flowers might seem like a beautiful landscape to many folks. But if you are standing in a wetland, those flowers could be purple loosestrife--a highly invasive European import that was accidentally transported across the Atlantic in the ballast water of ships, and also deliberately brought to beautify backyard gardens. This species was first introduced to New York in the early 1800's and since then, it has spread to almost every state and province in North America, including Alaska.

What makes purple loosestrife such a nuisance? Like many invasive species, it reproduces quickly. Purple loosestrife can sprout from seeds and from broken pieces of stem or root. Once it is established, purple loosestrife can outgrow native cattails, sedges, rushes, and other aquatic plants that local wildlife depend on for food, shelter, and breeding sites. Its roots form a thick impenetrable mass, which clogs up the water channels that fish use to spawn and chokes out all other types of vegetation. A wetland community infested with purple loosestrife is quickly reduced to one dominant plant species instead of a healthy variety of species. And because purple loosestrife doesn't provide the food and shelter that wetland wildlife need to survive, the local animal diversity is also reduced. Eventually, purple loosestrife can alter the entire structure and character of a wetland landscape.

What is being done to save wetlands from this alien menace? In some areas of the country, volunteers are hand-pulling these weeds before they seed. Others are repeatedly cutting down the dense stands to give native vegetation a chance to grow and compete more effectively. One more recent technique for removing purple loosestrife is called biological control. After years of careful research, scientists have isolated a species of European beetle that only eats the leaves and buds of purple loosestrife. The finicky Galerucella beetle is now being introduced to infested wetlands across the country as a way to control purple loosestrife and allow native species to regain a foothold. As a result of nation-wide Galerucella campaigns, wetland enthusiasts in New York, Colorado, Washington, and Maine are celebrating significant diebacks of purple loosestrife stands.

You, too, can help stop the spread of invasives like purple loosestrife by reporting any infestations that you see to your local or state natural resource agency. You can also join or start an invasive species removal project in a wetland near you. Check with your local Izaak Walton League chapter or natural resource agency to see if there are any projects already underway in your area. Also, remember to always make sure that the plants you buy at your local nursery are not invasive varieties. Purple loosestrife is still being sold in certain areas of the country, sometimes under different names. So do your research before buying ornamentals for your backyard, and help protect your wetlands from alien invaders.

Click here to find out how to properly identify purple loosestrife, and learn more about how to control the spread of this species.

VOLUME THREE
Issue No. 1