Association of State Wetland Managers - Protecting the Nation's Wetlands.

The Compleat Wetlander: Alien Invaders – The Problem Keeps Growing

Such strange beasts and fish
Are also bred
             That no man can give name to—
                          –The Compleat Angler

An invasive species is “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” There are 50,000 invasive species in the U.S. and they cost Americans over $150 billion a year in clean-up costs, depressed property values, lost recreation opportunities and environmental harm.  (Argentine Rodent Devastating Wetlands

They get here in various ways.  Some species, such as the zebra mussel, arrived as hitchhikers on ocean-going vessels.   Others like the sea lamprey took advantage of a new canal system in the Great Lakes.  Still others like nutria and purple loosestrife were brought into the country on purpose.  Nutria were introduced on a fur farm in Chesapeake Bay in the 1930s and purple loosestrife was brought into New England as an ornamental plant in the early 1800s.

Invasive species threaten upland and aquatic habitats.  In Maine for example the Norway maple is crowding out the sugar maples in the forests threatening the future of the maple syrup industry.  Eurasian milfoil, which forms dense mats in waterways, has only been identified in a 2-3 Maine lakes in the last couple years.  To try to keep the plant out, there is a state boat sticker program and some public boat landings even have volunteers inspecting boats to make sure they aren’t milfoil and other aquatic plants aren’t introduced into Maine lakes.

Invasive species are an issue of concern that have received increasing attention from the U.S. government particularly in the last 10-15 years.  In February of 1999 Executive Order 13112 – Invasive Species was signed and a federal task force was established and new efforts are undertaken every year to avert the spread of harmful invasives. 

It’s not an easy issue.  For example not all non-native species are considered harmful.  The ring-necked pheasant, the state bird of South Dakota, was introduced from China in 1892.  They are very important game birds in the Midwest.  Honey bees and earthworms are also alien species and nowadays we consider both of these critical to ecosystem and agriculture health.  A thoughtful guidance paper by the National Invasive Species Council provides a good analysis of what is and is not an invasive species.

It’s worth noting that North America has supplied invasive species to other parts of the world.  In Europe for example Canada geese and brook trout are considered invasive species. 

Then there is climate change which brings new challenges.  As animals native to North America change their range in response to changes in temperature and precipitation, there will be further disruptions in natural ecosystems.  What are the criteria for ceasing to manage for plants and animals that can no longer be sustained in their native range as a result of changes in climate?  What criteria should wildlife managers use to determine when it is correct to welcome migrating plants and animals not native to their state?   How do we incorporate these changes in species distribution and diversity into other contexts such as wetland mitigation standards?

There are many websites and new articles that provide useful information on invasive species:

Underwater Fight is Waged for Health in San Francisco Bay

One Hundred of the World’s Most Invasive Species

United States Federal Aquatic Nuisance Species Task Force

IUCN Invasive Species Task Group (ISSG)

ISSG Clickable Map of the World (includes summaries by continent)

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