Battling Invasive Species

The thumbnail-sized zebra mussel, an aquatic invasive species, forms such large populations that they clog pipes and drains and have been responsible for shutting down hydro-electric power plants. (Photo by Michael Massimi, Barataria-Terrebonne National Estuary Program, Bugwood.org.)

Article by TAMRA BOLTON

Since the 1500s when the Conquistadors brought us the feral hog, invasive species have been trying to take Texas. Others such as the Chinese tallow tree, which was imported by colonists in the 1700s as an ornamental, and salt cedar, (which arrived in 1823 as potential erosion control) have escaped their original boundaries and spread like wildfire over the Texas landscape. The good intentions of man sometimes have a way of backfiring, especially when it comes to introducing non-native species.

Texas now has more than 800 documented invasive species, and that list is growing every year. While the economic impact of the damage caused by these hundreds of invasive species is anyone’s guess, some estimates are “many billions of dollars,” said Jerry L. Cook, Ph.D., Sam Houston State University.

Cook cited a study completed over a decade ago at Texas A&M University which attempted to calculate the cost of just one species, the red imported fire ant. The study estimated the ants cost Texans over $100 million annually. Many in the science community think this figure is too small, and the cost has certainly grown over the last 10 years.

As landowners in Texas, we can help in the ongoing battle against many of these harmful intruders and hopefully reduce the massive economic losses forecast for the future and save our state’s incredible biodiversity.

WHAT IS AN INVASIVE SPECIES?

Many people call any plant that is fast-growing and a nuisance “invasive,” but according to Cook, invasives have to meet two

criteria: (1) they are introduced into an area where they do not occur naturally, and (2) they usually have a harmful effect on other species and the ecology of their introduced region.

The list of invasive species includes animals, insects, plants, aquatic invertebrates and even pathogens.

“They have invaded essentially all of the ecosystems of Texas,” said Dr. Jim Armacost, Director of Environmental Science at Lamar University.

These intruders pose a threat to our native wildlife, waterways, forests, agriculture and even our health.

WHAT TO LOOK FOR

All the experts I contacted agree that some of the worst offenders are the feral hog, red imported fire ant, Chinese tallow tree, salt cedar, emerald ash borer, zebra mussel, hydrilla and giant salvinia. These eight species alone are responsible for billions of dollars in damage within the state of Texas.

The feral hog can be found in almost every county in Texas and is the most recognizable invasive we have, next to the red imported fire ant. On-going research will hopefully find new ways to battle these two invasives, but effective methods still depend on individuals doing their part to help control the species.

In most areas, trapping or hunting feral hogs has a minimal impact on the overall population because the hogs breed faster

Photo by Tamra Bolton

than they can be hunted or caught. Many ranchers and farmers are resorting to “hog-proofing” their pastures and cropland with special fencing and other barriers to prevent further damage, but this alternative is expensive and cost prohibitive for many landowners. Several types of poison bait have been tried, but nothing has managed to make a dent in the ever-growing feral hog population in Texas.

Dr. Christopher Ritzi, Professor of Biology at Sul Ross University, summed up the damage: “The feral hogs have truly left their stamp on the landscape. They range across the entire state, and unlike other threats like fire ants and some of the noxious invasive weeds, these animals have been ecosystem engineers, completely changing the environment from what it was before.”

The battle against the red imported fire ant has had somewhat better success, but the ant still occupies most of the territory it previously invaded and is controlled only through constant monitoring and regular treatment.

Ashley Morgan-Olvera, Director of Research and Education with the Texas Invasive Species Institute, Sam Houston State University, paints a bleak picture of what we are up against.

“Many invasives are well-established before they are documented or recognized as invasive, making management a steep uphill battle,” she said. “But what encourages us to

Feral hogs can cause thousands of dollars in damage in just one night. Landowners have a constant battle to keep these intruders out of their pastures and forests.

Photo by Tamra Bolton

The Chinese tallow tree forms dense clumps and can eradicate native vegetation along creek and river banks, forever changing the biodiversity of an infested area. The embedded image is a Chinese tallow tree fruit and a visible white seed.

Photo by Jessica Spencer, Bugwood.org

Salt cedar grows along waterways such as river floodplains and can consume large quantities of water and reduce water availability. Saltcedar displaces native plants and degrades habitat for wildlife. continue in this battle is the significant contribution that engaged and mindful citizens provide in the control of invasive species. These helpful citizens provide more ‘boots on the ground’ in our attempts to curb these invasives.”

According to the experts, the Chinese tallow tree is so resilient and prolific that herbicides or controlled burns are not completely effective. These trees can create vast stands that eradicate native species and create monocultures that deplete soil nutrients, lower the water table and destroy the biodiversity of the land or waterway they occupy.

“Often a mixture of diesel fuel and herbicides must be applied multiple times for the treatment [of the Chinese tallow tree] to be effective,” said Morgan-Olvera. “Persistence through multiple treatments and regular maintenance of the species on your property are the keys to successful management.”

Armacost agreed, “Although it is labor intensive, local stands of tallow trees can be controlled by cutting the trees and through application of herbicides.”

Another plant that creates a monoculture is the salt cedar. This invasive has spread along the majority of waterways in the southeastern United States and has replaced native plants wherever it grows causing a reduction in the number of insects and birds, among other species.

“Salt cedar actively deposits salt in the ground to impede the growth of competing plants, making it difficult to mitigate and heal the land after the invasion has taken place,” Ritzi explained. “Like the feral hog, the salt cedar can forever alter the biodiversity of the region it invades.”

As far as control measures go, Ritzi recommends a number of tools.

“Herbicides can usually knock salt cedar back, but due to the hardiness of the plants and their root system, they tend to bounce back and regrow,” he said. “Mechanical removal will also reduce above ground biomass, but if [roots] left in place and not followed by chemical treatments, it can result in spreading the plant rather than controlling it.”

The salt cedar is so resilient that even after a hot fire regrowth will appear in two to three months. Ritzi is currently monitoring the salt cedar beetle which feeds on the plant, but not agricultural crops or other plants. He is hopeful that this beetle will help control and slow the spread of this invasive cedar.

The emerald ash borer has only been in Texas since the 1990s, but this Asian native beetle has already spread to six northeastern counties. The brilliant metallic green borer can devastate not only the ash tree population, but also attacks the white fringe tree.

It is the only borer with a bright coppery-red abdomen which may be visible only if the elytra, the hard outside covering on back, and wings are raised. Our native species of borers have either blue, green, or black (dorsal surface) abdomens.

Humans have unwittingly spread this insect invader in firewood, nursery stock, green lumber, branches, logs and chips. Infested trees are hard to treat and usually the only way to effectively eradicate the beetle in an area is to remove and properly dispose of all infected trees.

First found in Lake St. Clair on the Michigan and Ontario, Canada border in 1988, the tiny zebra mussel has since wreaked havoc up and down the Mississippi Waterway. Native to Russia, this thumbnail size aquatic invasive “forms such large populations that they clog pipes, drains and have been responsible for shutting down hydro-electric power plants” according to Morgan-Olvera.

These mussels are so hard to combat because the larvae are invisible to the naked eye and can live for days in water trapped in a boat or equipment. That is why it is so important to follow the “Clean, Drain and Dry” campaign the Texas Parks and Wildlife Department and others are using to educate the public on this and other aquatic invasives.

An aquatic plant that has troubled Texas waters since the 1950s is hydrilla. A native of the Indian subcontinent, this invasive was introduced to the United States by the aquarium trade. Hydrilla creates dense mats on the surfaces of infested bodies of water. The clarity of water produced by the relatively recent presence of zebra mussels now allows the hydrilla to grow at an even greater depth, creating a much more devastating threat than before.

Difficult to treat, hydrilla can choke intakes to power plants and impede water flow to agriculture operations. It creates monospecific stands, often replacing our native submerged vegetation, which creates an almost irreversible change in the biodiversity of the bodies of water it infests.

Popular as an aquarium and water garden plant, the giant salvinia was found in Texas in 1997. This aquatic plant invader is one of the most insidious threats to our lakes, ponds, rivers and other waterways because of its astounding ability to spread. Giant salvinia can double in size every two weeks and can cover a quarter acre pond in as little as six weeks.

Like the hydrilla, the giant salvinia shades out or replaces native species, causing a radical change in the biodiversity wherever it is present. Giant salvinia also affects the quality of water in our waterways and hinders recreational boating, fishing and duck hunting.

WHAT CAN YOU DO?

If you’ve ever encountered an invasive species, you know it can be a frustrating, expensive and an even downright alarming experience. Public education is the starting point in effectively dealing with these interlopers. Individual action combined with knowledge is vital in slowing or stopping the encroachment and subsequent establishment of these harmful intruders.

The Texas Parks and Wildlife Department has a great resource for education about invasive species: identifying them, reporting and properly treating them. Through their partnership with TexasInvasives.org, the TPWD joins nine other agencies in providing support to concerned citizens and landowners. The TexasInvasives.org site has a fitting slogan, “Hello Invasive Species. Goodbye Texas.”

To emphasize the seriousness of the invasive problem, Cook said, “The initial stage of introduction is really the only time that it is possible to eradicate invasive species. Once they become

Photo by Eric R. Day, Virginia Polytechnic Institute and State University, Bugwood.org

The emerald ash borer is a brilliant metallic green beetle that can devastate not only the ash tree population, but also attack the white fringe tree.

Image source: TAMU Aquaplant https://aquaplant.tamu.edu/

Hydrilla creates monospecific stands, often replacing our native submerged vegetation, which creates an almost irreversible change in the biodiversity of the bodies of water it infests.

In addition to its ability to replace native species, causing a radical change in the biodiversity wherever it is present, giant salvinia also affects the quality of water in our waterways and hinders recreational boating, fishing and duck hunting.

established, it is almost impossible. Then, it becomes a process of managing the invasive species, essentially forever.”

“But,” he adds, “landowners should not think that they have to take on this process alone. The TPWD and Texas Department of Agriculture, among others, have expertise that can help identify and fight invasive species.”

Ritzi advises landowners to “know your land, know what plants and animals are usually present and keep an eye out for pests or species that look out of place. If you discover an invasive has started to encroach onto your land, talk with experts and learn how to best control that particular species. Also, a healthy landscape can protect itself better from invasion and attack just like a healthy body can better handle a disease. By managing your land responsibly and making sure it has the resources to keep the native plants and animals alive and well, such as water, food and shelter, the land should be more resilient to attack from invasive threats.”

As Ritzi said, good management can not only protect the land, but keep it healthy for wildlife. If invasives destroy the native vegetation or diminish water supplies, wildlife suffers. This creates a domino effect of destruction in the area which is difficult or even impossible to reverse.

Although there is no simple way to mitigate the effects of these unwelcome intruders, Texans must continue to educate themselves and understand the immense losses we face from these pests.

Ritzi reminds us that “invasives create a huge loss in biodiversity across the state…invasives are replacing and changing the face of Texas.”

Through education and awareness, landowners across the state can help slow the spread of damaging species.

“By far the best way to deal with invasive species is early detection followed by a rapid response to eliminate or at least control the spread of the invasive species,” Cook agreed.

There are also proactive measures citizens can take to help with the invasive problem.

“By not releasing non-native animals into the wild and by landscaping with native plants instead of non-native ornamentals, we can provide better habitat for our native wildlife and help stop the spread of invasive species,” Armacost said.

There are good alternatives to non-native ornamentals, but MorganOlvera warns that there are some invasive plant species that are not federally regulated and can still be bought at garden supply stores. She recommends avoiding these ornamentals: Bamboo species, Brazilian peppertree, Chinese privet, Giant Reed, Kudzu, Japanese honeysuckle and Tree-of-Heaven.

Opt for native plants instead. Researching the best plants for your region and sticking with native plants for your landscape will go a long way in helping the fight against invasives.

Awareness and active engagement in the fight to keep our ecosystems healthy and strong is in the hands of all Texans. Saving our native flora and fauna is an on-going challenge, that will in large part, be decided by future generations and how they work to prevent further invasions of non-native species and how they respond to threats as they arise.

As a landowner, you are on the front lines of the battle against invasives in Texas. The outcome of this battle depends largely on raising your own awareness of invasives and employing all the weapons at your disposal to eradicate or control species on your property. These measures can make the difference between victory or defeat.

Texas landowners and wildlife managers have an especially big stake in maintaining the biodiversity across all ecological regions. Our immensely diverse landscapes and the wildlife that inhabit them are some of the features that make Texas such a great place to live, work and play… let’s not let invasives destroy the very things that makes this state so special.

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