Biotic Homogenization - What The Heck Is That?

November 21st, 2017

It seemed like a harmless idea in 1852. The attractive ornamental shrub that had been cultivated in China for hundreds of years might just work here in the southeastern US as well. So, a nurseryman imported it and set about propagation. In the early 1860’s, the famous Berkman’s Nursery in Augusta, Georgia began producing and selling Chinese privet in large numbers for the horticultural trade, and you can still see remaining hedgerows of it at their old site today. In 1890, the federal government planted Chinese privet in the Chickamauga and Chattanooga National Military Park. And then there was a delay, a lag time, if you will, before Chinese privet started to pop up in the surrounding environment, and it isn’t until about 1920 that we start seeing it show up in county records as a plant found in the wild.  

It had escaped.

Sometime in the 1950’s, the population exploded, and Chinese privet began spreading like wildfire. Today, Chinese privet forms dense thickets on roadsides, forest margins, and in forest understories from southern New Jersey, down to Florida, and west to Texas. It fills abandoned fields and crowds the floodplains along streams and rivers. It is arguably the most ubiquitous invasive exotic plant in the Southeast. The Tennessee Invasive Plant Council ranks it as a “Severe Threat” in Tennessee, and it has similar designations in states throughout the southeastern US.  

Most organisms don’t become a problem. Unfortunately, the few that do can have catastrophic effects on biodiversity across huge scales.

So, who cares? It’s an ornamental shrub, right? And it’s done well in its new home, right? Shouldn’t we just accept and admire it as a real winner? Well, “winner” is exactly the term Mike McKinney at the University of Tennessee uses to describe Chinese privet and other species like it, but not in a good way. In 1999 Mike McKinney and Julie Lockwood coined the phrase “biotic homogenization” for a process in which most species on the planet are in a state of decline as a result of human activities (losers) and are being replaced by a much smaller number of species that thrive as a result of human activity (winners). These winners are typically a subgroup of human-introduced exotic species that have the ability to invade an ecosystem and displace the existing native species to the point of exclusion. The net result is a loss of biological diversity and a homogenization of the biota in the landscape.

But it doesn’t stop there. Not only does this homogenization occur within local landscapes; it occurs between local landscapes, making them all look like each other. It also occurs at the regional scale too. You should be able to go into a forest in Maryland and recognize it as different from the forests you see in Tennessee, with plant communities distinctive of each locale. Instead, you see a forest understory dominated by Chinese privet, Japanese honeysuckle, and Japanese stiltgrass in both 
locations. You see them in Maryland and in Georgia, on the Coastal Plain of North Carolina and on the Cumberland Plateau of Tennessee, in southern Louisiana and in central Kentucky. These regions have lost their botanical identity.

This phenomenon isn’t restricted to plants. There are invasive “winners” among birds, reptiles, mammals, fish, insects, and every other form of life. For all classes of organisms the result is a net loss of biodiversity because many species are being replaced by few. The kicker is that it’s very difficult to tell which organisms are going to behave like this beforehand. It’s not even that high of a percentage. It is estimated that approximately 2% of bird species become invasive, while only 1% of mammals become a problem in new regions. For plants, the estimate is 2%. These low numbers lead decision makers into a false sense of security because most organisms don’t become a problem. Unfortunately, the few that do can have catastrophic effects on biodiversity across huge scales.

So What can you do?

On a personal level, you can become more aware and make good individual decisions, especially if you are a property owner. Most of us aren’t importing exotic birds or reptiles and letting them loose in the wild, but many of us buy plants and shrubs for gardening and landscaping. Learn what to plant and what not to plant. Choose plants native to your area whenever possible. By doing so you can, in a small way, create habitat for those species that are in decline due to human activity and 
the invasive species associated with it. Additionally, learn which species are either known invaders or have demonstrated the traits that make them potential invaders. Chinese privet is far from the only culprit. The Tennessee Invasive Plant Council publishes a list of invasive, or potentially invasive, plants and ranks them according to threat level. If you are a large-scale land owner, learn sound land management practices that reduce unnecessary disturbance and the associated risk of creating conditions conducive to exotic plant invasion.

You can also contribute to sound public policy by making your voice heard to legislators and other policy makers at the local, state, and federal level. Many state and federal agencies that are charged with environmental protection are losing both their authority and their funding. Agencies such as the Environmental Protection Agency and US Department of Agriculture are directly responsible for protecting our national borders against the import of invasive species. They are also responsible for identifying their presence once they get here, and managing them when they find them, but they are grossly understaffed and underfunded. When support for such regulatory agencies comes into question, tell your leaders you support their work to preserve biodiversity.

Posted by John Evans  | Category: Gardening
1 Comment(s):
Great article, John!
Thank you for drawing more attention to this important issue.
I'm so glad Reflection Riding Arboretum and Nature Center is here as a teaching resource for Chattanooga.

Lyn Rutherford - November 27th, 2017 at 11:16 am

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