Hurricane Invasion
Hurricane Invasion
Invasive plants may take root in Harvey’s wake
Cliff Tyllick stands by a dead tree, looking up at its bare branches with an expression that is part pity, part indignation.
“See this oak?” He motions to the gnarled trunk, placing a hand on its peeling bark. “This died of thirst because of that ligustrum.”
We turn our faces skyward to see a dark canopy of leaves shining smugly overhead: this is the offending ligustrum. The sight of the tall, shady plant, also known as the glossy privet tree, seems to almost cause Tyllick physical pain. As if this tree were growing not on the hard-packed soil of Austin's Walnut Creek Metropolitan Park, but under Tyllick’s own skin.
Tyllick, an IT coordinator turned invasive plant vigilante, spends many of his weekends and holidays out here at the park. Either alone or with others, he wages a silent war on the glossy privet, which was brought into the U.S. from Asia as a garden shrub. Since its introduction, the privet has grown out of control, and is now classified as invasive in Texas.
According to Tyllick, even a few ligustrums can usurp entire groves by shading out the shorter plants and sucking up enough water to mortally dehydrate the tallest trees.
A HIKE WITH CLIFF TYLLICK
The Citizen team went out in the field with Tyllick, a citizen scientist who dedicates his free time to fighting invasive plants in Austin's Walnut Creek Metropolitan Park.
In·va·sive Spe·cies
/'in-ˈvā-siv 'spē-shēz/
n. non-native species that cause harm to either the economy, the environment or human health.
Foreign plants such as the glossy privet or the prolific, water-dwelling giant salvinia thrive in Texas ecosystems. They crowd out existing species and leach the nutrients that native plants depend on to survive. And though many of them grow quickly on their own, studies have shown that the spread of some invasive species can be greatly increased by the winds and flooding associated with hurricanes -- a trend that could affect Texas in the coming months as the state recovers from the widespread destruction of Hurricane Harvey.
According to Hans Landel, the invasive species program coordinator at the University of Texas Lady Bird Johnson Wildflower Center, Texas’ natural areas may be in for a wild ride within the next year as invasive species take hold in places made vulnerable by Harvey.
Landel said hurricanes can facilitate the spread of invasive species in a number of ways: first, the hurricane winds can carry seeds or spores farther than they would travel usually, leading to growth of invasive plants in an extended range. Additionally, storms can knock down trees and uproot native plants, creating sunny open areas that invasive species can seize on and take over.
Finally, the intense flooding due to hurricane rains can bridge the gaps between ponds, lakes and rivers, allowing water-dwelling plants to spread. In four days, Hurricane Harvey dumped an average of 27 inches across Harris County, Texas, alone, and some areas saw over 35 inches. The historic floods, which deluged Texas with more rain than the rest of the U.S. has seen in months according to the Washington Post, may have created the perfect conditions for invasive water plants to spread.
“The aquatic organisms would be the ones to look out for (in the aftermath of Harvey,)” Landel said. “Those are the things like the floating hearts, giant salvinia, and hydrilla. Those aquatic species would have had a great opportunity to move around because of the flooding, and so new places may become infested because of that.”
The United States Geological Survey recently created a map of Texas that uses rain and flood data to predict the spread of invasive aquatic species. Giant salvinia, for instance, shows a risk of spreading in nearly every affected county.
John Pascarella, dean of the college of science and engineering technology at Sam Houston State University, said the spread of aquatic invasive plants due to Harvey may become evident in the coming months.
“Plants and other organisms might have been spread around the landscape, so there is going to be a reshuffling, a resorting of the landscape here in Texas,” he said.
Pascarella, who has done extensive research on the regrowth of plants after hurricanes, first saw this type of reshuffling after Hurricane Andrew hit Florida in 1992.
“We identified that after that hurricane a number of invasive species kind of surged,” he said. “They had a big growth in terms of their population … And one of the big things hurricanes do is move stuff around, so you may find an area where you didn’t have a lot of invasives before, but suddenly all these invasives are there afterwards.”
Many of Texas’ invasives are relatively new on an ecological scale. Giant salvinia, for example, was likely introduced to the U.S. around 1980, according to researchers at Mississippi State University. Historically though, hurricane-induced spread of invasive plants is nothing new.
An example borders ponds and lakes across the U.S., its elegant stalks and tassels blowing gently in the wind: the common reed, or Phragmatis australis. According to the National Park Service, the reeds, which are native to Europe, were most likely introduced to America in the late 1700s or early 1800s via ballast, or rocks or gravel used to weigh down ships. Since then, the reeds have taken over the banks of ponds and lakes across the eastern part of the country and are still spreading.
A study conducted by researchers at Louisiana State University used geographic images going back 27 years to see the geographic spread of the reed, and how its growth correlated with hurricane activity. The results were conclusive: hurricanes explained 81 percent of the variation in spread of common reeds throughout the regions studied.
“In light of the many climatic models that predict an increase in the frequency and intensity of hurricanes over the next century, these results suggest a strong link between climate change and species invasion and a challenging future ahead for the management of invasive species,” wrote Ganesh Bhattarai, the lead author of the study.
Although the U.S. is not likely to get a respite from hurricanes in the future, there are ways that people can take action to help document and prevent the spread of invasive plants in the wake of intense storms.
“People can use (the Wildflower Center’s) app to start reporting locations of invasive plants that they see,” Landel said. “They can report those new areas of plants coming in, especially if they put a note in there saying they haven’t seen this before, or it seems like maybe it came in right after or because of the hurricane.”
Landel, who works to limit the spread of the Brazilian peppertree with the Texas Gulf Region Cooperative Weed Management Areas invasive species team in Port Aransas, said they are readying themselves to deal with the potential surge in invasive plant growth caused by Hurricane Harvey.
"It won't be clear for some months as to the effects the hurricane had on the Brazilian peppertrees, but it is clear that disturbances in the prairie landscape will make it easier for invasives such as guinea grass to spread," he said. "We are trying to figure out what the next steps are.”