WORSE THAN WEEDS

By Ella Tyler

A free pocket guide to the twenty most dangerous invasive plant species in the Galveston Bay Area has just been published by Galveston Bay Estuary Program and the Houston Advanced Research Center. The guide has color pictures of the listed plants and includes information about their local distribution, preferred habitat, reproduction, and growth patterns.

The guide also describes the ecological, economic, or social impact of each plant, which is useful in encouraging plant suppression. Ordinary gardeners are unlikely to be willing to kill a vine named “balloon vine” or “love in a puff,” particularly after they see the pretty white flower. However, killing a vine that will smother native vegetation, pose a particular threat to riparian trees and shrubs, or be a destructive weed in soybean fields is a noble occupation.

Tallow trees, known to many for hard seeds that children love to stomp on and for colorful fall foliage, came to the US as seeds sent by Ben Franklin from Paris to Georgia. The US government brought them to the Gulf Coast in about 1900 with hopes of using the wax-covered seeds as an agricultural crop. However, tallow trees are now on the Texas Department of Agriculture’s noxious plant list and may not be sold, distributed, or imported into the state in any live form without a permit. What has happened?

The trees escaped cultivation and have transformed native habitats into mono-species tallow forests.

In 2002, Rice University ecologist Evan Siemann reported, “The incredible diversity of native plants in the coastal prairies is gone within 30 years after the Chinese tallow tree invades the area.” According to Siemann, “Once Chinese tallow trees replace bluestem grasses, sunflowers, blazing stars, and other plants found in the prairies, those species and their associated animal fauna will not come back.”

Some researchers, such as Sandy Mathieu, a speaker at the Peak Oil Conference in Houston last week, believe that tallow tree seed has excellent potential as a biofuel. There are plenty of seeds in the area to experiment with. Tallows are the most abundant tree in the Houston-Galveston region; in the southwest quadrant of the region more than 70% of the trees are tallows.

Lisa Gonzalez, a research scientist with HARC, said that she hopes gardeners, land managers, and landscape architects will carry the guide with them to identify plants that can be harmful to local habitats before the plants have spread out of control.

Invasive plant removal is an ongoing need at such places as Memorial Park, along Buffalo Bayou, and on the Katy Prairie.

“Early identification helped us prevent the spread of Brazilian peppertree, which is a serious problem in Florida,” she said. “As soon as it was identified in Galveston County, Department of Agriculture staff worked with the landowners where it was found to eradicate it.”

These plants are a threat to native habitats even when grown in urban gardens, Gonzales says. The same factors that make them attractive to gardeners make them a problem when they escape cultivation. She says tallow seeds, for example, can float into bayous and streams. Many noxious weeds spread by underground rhizomes and are very difficult to control.

The booklet also suggests ways to control the twenty unwelcome plants. For many of them, the suggested method of control is to cut the plant down and then apply an herbicide, which Gonzales says is unavoidable once the plants attain any size.

“We had to weigh the harm that we know herbicides cause against the damage that invasive plants cause, and unfortunately herbicides are the only way to control regrowth,” she said.

The other banned plants described in the guide are deep-rooted sedge, water hyacinth, alligator weed, giant reed or cane, Japanese dodder, deep-rooted sedge, hydrilla, purple loosestrife, melaleuca, Eurasian water milfoil, water lettuce, kudzu, salvinia, and tropical soda apple. Kudzu has been found in lower Galveston County and in Liberty County. Plants that aren’t banned but are of concern are Chinese and Japanese privet, elephant ear, and Vasey grass.

The guide, plus photos and information about another twenty plant species that threaten native plants, can be found on the web at www.galvbayinvasives.org.

To request a free hard copy of the guide, contact Jeff DallaRosa at jdallaro@tceq.state.tx.us or Lisa Gonzalez at (281) 486-1242 or at lgonzalez@harc.edu or (281) 364-6044.