EDITED:

REGIONAL BIODIVERSITY SERIES:
North Carolina Botanical Garden—Working to Safeguard Biodiversity
Mary Stauble

Do no harm to plant diversity.
Do no harm to natural areas.

Recently hundreds of people gathered in Greenville, SC to discuss the growing problem of invasive plants at a two-day conference titled "Terrestrial Plant Invasions in the Temperate South."  Representatives from federal and state governments spoke of programs they are implementing to deal with "green pollution," which is all the more insidious because most people do not see it.  The average person mistakenly assumes green is good.  In addition to presentations by foresters, chemists and ecologists, Dr. Peter White, Director of the North Carolina Botanical Garden (NCBG), spoke about what their garden is doing to halt the spread of invasive plants. 

The primary mission of the NCBG is to "participate in and promote the conservation of biodiversity."  They recognize the threat invasive exotic plants pose to natural areas is second only to habitat destruction.  Of the 285 woody plants that invade natural areas of the U.S., 85% were imported for ornamental and landscape use (Reichard and Campbell 1996). 

Many of the same traits that make a plant a desirable ornamental, such as rapid growth, prolific flowering and seeding or cold or heat tolerance may also make them ideal weeds.  Every new plant introduction is an experiment with an unknown outcome.  Thankfully, only a small percentage of exotic introductions are invasive in our natural areas.  However, the damage these problem plants cause can be extensive, costing millions of dollars.  In 1994 their impacts upon the U.S. economy were estimated at or above 13 billion dollars (Westbrooks, 1998).

Invasiveness is a relative term occurring on a continuum, rather than with clear-cut distinction.  There is frequent disagreement as to what is truly invasive.  It is also complicated by the fact that plants behave differently in different habitats.  What is a problem in one region is benign in another.  Research has shown that a number of plants may appear fine for fifty to a hundred years (known as a lag phase) and then suddenly become an invasive.  In trees the lag phase may be 150 years.  Biologists are most concerned about invasive plants that spread into undisturbed natural areas and reduce or eliminate native species or actually change ecosystem function, reducing whole suites of native species. 

In 1999 the NCGB took a visible stand on this issue posting a thesis and challenge to botanical gardens, arboreta and the plant industry.  It begins with the statement "Do no harm to plant diversity, do no harm to natural areas" and is followed by eight principles or codes of conduct.  In a symbolic gesture they nailed this thesis to a Princesstree, Paulownia tomentosa—an invasive exotic.  The NCBG is implementing these protocols, which are designed to minimize the spread of invasive plants.  The principles are highlighted below, followed by activities the NCBG is undertaking to support this work. 

1. Perform risk assessment for introductions.  Prevention is the first line of defense in controlling invasive exotics, so the easiest, most cost effective approach is to stop introducing invasive plants into the landscape.  All new plant introductions to the botanical garden undergo a risk assessment based upon a species' life history traits that are used as a screening device.  They do not introduce plants with a high potential to be invasive.  They believe risk assessment should be done on a regional basis.

2. Remove invasives from plant collections.  The NCBG is evaluating plant material currently in their collections and taking steps to remove known invasives.  A large oriental Wisteria arbor that was spectacular in bloom was removed and replaced with our native vines such as Wisteria frutescens, and a native Honeysuckle, Lonicera sempervirens.  It took years for this project to become realized, yet it is now equally as stunning as its invasive counterpart. 

3. Control invasives in natural areas.  In many cases prevention is no longer an option.  We must pursue the second line of defense—implementing active control measures.  The NCBG has produced a pamphlet entitled Controlling invasive exotics in your yard which helps educate and inform residents of the North Carolina Piedmont about some of the more common terrestrial invasive exotic plants and the means to control them. 

4. Develop non-invasive and native plant alternatives and certify non-invasiveness for the trade.  The NCBG uses native plants wherever possible and strives to promote native plant cultivars and select varieties.  In addition to making available lists of problem plants for our region, they are developing "clean lists" in an effort to offer positive alternatives to invasive exotics.  Promoting the use of good plants in the first place is a way to prevent problems at the source. 

5. Do not distribute seeds/plants that will be invasive elsewhere.  For many years the NCBG has promoted a "Conservation through Propagation" program, which highlights a wildflower of the year for which people can purchase a variety of native seeds.  Now mindful that our native seed distributed outside a certain region may pose unintended risks, the NCBG has revised its seed distribution policy and no longer sell it outside a defined region of the southeastern U.S. 

6. Educate the public.  All of the above activities help educate the public about the issue of invasive plants.  The NCBG is taking a leadership role and is learning as they go.  In 2001, Dr. Peter White was part of an organizing committee for a conference "Linking Ecology and Horticulture to Prevent Plant Invasions."  It was hosted by the Missouri Botanical Garden and the Royal Botanical Garden, Kew (England).  In this meeting they developed "Voluntary Codes of Conduct" for government agencies, nursery professionals, the gardening public, landscape architects and botanic gardens and arboreta. 

7. Become partners with conservation organizations.  The NCBG was the first garden in North America to establish an exotic pest plant policy (1998) and helped organize a North Carolina chapter of the Southeast Exotic Pest Plant Council (1999).  Working with other conservation organizations such as the Nature Conservancy and the National Park Service, the NCBG provides Web links to various resources on their Web site.  They are creating an invasive plant database based on the risk assessment scheme used as a screening device.  This database will be made available to others. 

8. Obey import rules and enact strong procedures to minimize the risk of introducing disease and pest organisms.  The NCBG understands that our current global economy has accelerated the spread of invasive plants and animals all around the world.  A careless action or a small violation can have devastating environmental consequences.  The NCBG obeys import rules, wanting to minimize any potential risks. 

Many botanical gardens and arboreta continue to be a source of potentially invasive exotic plants and inadvertently create a demand for these problem plants.  The NCBG is an exception to this, demonstrating to the public that spectacular non-invasive native landscape material is available.  They are making an important contribution protecting and helping others appreciate the biodiversity of our region. 

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Sources:  Much of the information was taken from a lecture by Dr. Peter White titled "8 Elements of the Conservation Garden," given June 4, 2003 at the "Terrestrial Plant Invasions in the Temperate South" Conference in Greenville, SC.  Other references include the North Carolina Botanical Garden Web site, www.unc.edu/depts/ncbg, the pamphlet Controlling invasive exotics in your yard, published by the NCBG, and the Invasive Plant Fact Book, Understanding the Problem developed by Dr. Randy Westbrooks and the Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW).