By Bill Ward
Published in The Boerne Star on August 11, 2006
Biologists who study ecologic changes have long agreed that the leading reason for the decreasing biodiversity in the world is destruction of habitat. In the last several years there has been a growing consensus that the second leading cause of decrease in biodiversity is the invasion of exotic species of animals and plants.
Ever since man came to North America during the last Ice Age, non-native plant species have been continuously introduced to this continent.
By now many thousands of exotic plants grow here, and almost none of them do any major harm to natural habitats. A small percentage of these exotic plants, however, have invaded the countryside like bioterrorists, doing major damage to natural ecosystems.
Plants are the fundamental elements of an ecosystem. Plants directly or indirectly influence every other organism in an ecosystem, and they affect climate, rates of weathering and erosion, and quality and quantity of surface and subsurface water.
Changes in native-plant populations can bring changes to every level of the biosphere from the soil zone upward. Removal of native vegetation may even bring long-term changes in regional climates, such as the desertification of parts of northeastern Mexico that were stripped of native foresis.
The widespread invasion of alien plants costs a lot of money and time. One recent estimate of the cost of invasive exotic plants to the US economy is $37 billion a year. I heard that the botanist at Big Bend National Park has to spend most of his time on controlling exotic species.
In response to the damage done by invasive exotic plants in this state, the Texas Department of Agriculture has identified nearly three dozen “noxious weeds.” State statutes prohibit commercial trade in these plants.
Many of the noxious weeds are aquatic plants that have clogged Texas waterways and replaced the native aquatic vegetation. Also included on the blacklist are several species of Tamarix (“salt cedar”), invasive shrubs and small trees which have done major damaged to riparian and coastal habitats.
One tree on the list of noxious weeds is the Chines tallow (Triadica sebifera), which probably still is planted in some home landscapes, even though commercial trafficking in Chinese tallow is against the law.
Chinese tallow is fast growing and rapidly crowds out native saplings. This native of the Orient seems to suffer few diseases or predators, making it a tough competitor for native bushes and trees.
The Chinese tallow tree has been turning Gulf Coast grasslands into single-species forests. Chinese tallow also is a threat to riparian habitats in the Boerne area. There are hundreds of Chinese tallow along Cibolo Creek downstream from Boerne.
We have removed many Chinese tallows of various sizes at Cibolo Nature Center, but there are many tens more to cut down. Chinese tallow can be controlled by cutting down and then painting the stumps with an approved systemic herbicide. Cutting alone without treating with herbicide will allow re-sprouting of multiple trunks.
Even though we have had only a few re-sprouts from treated stumps, new plants are continually coming up, because Chinese tallow are prolific seed producers.
As long as there are Chinese tallow in the area, the seeds will be brought downstream by floodwaters and birds.
Chinese tallow tree is on the official list of Texas noxious weeds, but there are several other invasive exotic plants that are of equal concern in the Hill Country.
Next time I’ll discuss some of the other dreaded invasives and tell about a citizen-science surveillance program that is monitoring these bioterrorists in Texas.
