By Bill Ward
Published in The Boerne Star on June 17, 2005
In many places ecological restoration requires removal, not addition. Restoration of some habitats can be accomplished by eliminating exotic species without reintroduction of native plants and animals.
For example, this spring we saw the results of last year’s removal of many large ligustrums that were crowding out native plants along Cibolo Creek on Cibolo Nature Center property. Several native wildflowers and bushes that were dwindling to obliteration in the dense ligustrum shade have begun to flourish again.
Ligustrums are just one of many introduced plants that have escaped into the countryside to replace native vegetation. And these invasive exotic plants come at a high price, both figuratively and literally.
There is widespread agreement that maintenance of biodiversity is of utmost importance in maintaining a healthy human existence on Earth. Ecologists and biologists have evidence that the spread of invasive exotic species is a major cause of the current rapid loss of biodiversity in many places.
Some ecologists estimate that it will cost $104.2 million to control exotic mustards that are threatening to displace native plants from the California desert. Three species of exotic mustard (family Brassicaceae) are spreading over much of the Southwest and maybe northern Mexico. They’re calling it a “mustard tsunami” that is wrecking ecological havoc. It’ll be very expensive to control.
Texas has an exotic-mustard problem, too. The turnip weed or giant yellow mustard (Rapistrum rugosum), a native of the Mediterranean, is increasingly displacing native wildflowers along roadsides in Central Texas. For example, it is so thick along the highways in Austin near the Wildflower Center that is has replaced many Texas bluebonnets.
For the last couple of years, I’ve seen the yellow blooms of the turnip weed along local roads. Where did it come from? Probably from cattle feeds or perhaps from wildflower seed mixes that contain exotic seed. Let’s hope it doesn’t get a strong hold along our local roads, but the outlook is not encouraging.
The turnip weed is just one of many invasive exotics that are threatening to displace plants indigenous to Texas. About 18 percent of Central Texas flora is nonnative and much of the exotic vegetation is invasive, spreading rapidly to replace native plants.
The Lady Bird Johnson Wildflower Center now supports a Web site that educates about the invasive-plant problems in Texas: www.texasinvasives.org. Check it out!
The 2005 Texas Invasive Plant Conference will be held Nov. 17 and 18 at the wildflower center in Austin. This will be the first statewide conference in Texas on non-native invasive plants, and it is hosted by the Pulling Together Initiative of the North American Weed Management Association. To learn more: www.texasinvasives.org.
Certain exotic plants are able to escape into the wild and upset ecological balance by displacing the native vegetation on which many other organisms depend.
I’ve heard some people say that there is no real need to worry about that, because all our plants were introduced some time in the past, and those exotics eventually will become part of our “native” vegetation. I doubt that is true.
It seems more likely that plants native to our area were never introduced by man. Most natives originated where they exist, some over large areas and some only in limited areas. They are the products of thousands of years of evolving specific characteristics that allow them to fit into certain ecosystems.
Whole ecosystems have evolved so that every element is an integral part of the systems.
Eliminating a native plant from its native habitat affects all sorts of soil organisms, as well as the insects, birds, mammals and other plants that depend directly or indirectly on that native species. Invasive exotic plants upset the whole balance.
