Wednesday, March 9, 2011

New controversary about invasive species?

I was wondering why I was seeing so many articles about exotic and invasive species recently and then I discovered that last week was National Invasive Species Awareness Week.

The articles that I have seen floating around on local blogs and garden discussion groups seem to be slanted towards the opinion that exotic species might not be quite as bad as they were once thought.

A contributor to the WashingtonGardener Yahoo group mentioned Mark A. Davis's new book, Invasion Biology, in which he states that invasive species might actually be getting a bad rap.

Davis certainly doesn't say that ALL invasive species are okay. But he does say that if an exotic species is “not causing significant harm,” then “altering one’s perspective is certainly much less costly than any other sort of management program. ”

In my mind, Davis's highly controversial opinion does make sense. There seems to be a tendency to assume that all exotic, non-native species are bad and that all native species are better.

Much of this is, of course, a matter of semantics. Many people seem to interchange the words exotic and invasive and, of course, all exotic species are NOT invasive and some are even considered beneficial by many (did you know that many species of honeybees are non-native?)

According to the USDA National Invasive Species Information Center, an invasive species is defined as:

1) non-native (or alien) to the ecosystem under consideration and 

2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

By this definition, the fact that a plant or animal is alien (exotic) does not, by itself, make the organism invasive.

According to another website, over 85% of exotic species are NOT invasive.

Continuing the discussion on the Yahoo group, trumpet vine was mentioned as being both Native and Invasive. Again, this is a matter of semantics.

The NC State University website states that:

Native plants are never invasive. The term invasive applies only to exotic plants and not to native plants; invasive implies a negative effect on native plants and animals. On the other hand, native plants that establish quickly in your garden and spread readily are more appropriately termed “aggressive”.

The same website goes on to provide this statement:

There are many exotic plants that do not become invasive, and many can safely be planted in your landscape. However, it takes scientists many years or even decades to fully understand an exotic plant's potential invasiveness. New information is being gathered, and you should check with your local nature center, botanical garden, or Cooperative Extension agent to find out about a plant's invasiveness before introducing it to your property. 

We can easilly heed that advice by referring to these local lists of problematic invasive species in Maryland and Virginia.

Invasive Species of Concern in Maryland

Invasive Alien Plant Species of Virginia (pdf file)

Another term to add to the discussion is the word "noxious", which I found on a National Park Service website. 

Noxious Weeds.  The term noxious is a legal designation used specifically for plant species that have been determined to be major pests of agricultural ecosystems and are subject, by law, to certain restrictions. The U.S. Department of Agriculture regulates noxious weeds. Plants can also be designated as "noxious weeds" by states and counties, usually through "noxious weed boards". Many noxious weeds are designated for their impacts to agriculture also threaten natural areas.

You can refer to this USDA page to find plants listed as Noxious Weeds in your state: State Noxious Weed Lists

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