FWS and UT botanists team up to revitalize rare grass populations in Texas

In 2014, U.S. Fish and Wildlife Service botanist Chris Best visited Big Bend National Park to collect data on a rare grass – Guadalupe fescue – that was petitioned for an Endangered Species Act listing in 2007. The plant had been monitored at the park for several decades, but each year botanists were finding its population continuing to decline. Now Best and colleagues are partnering with researchers at the University of Texas at Austin to improve population estimates for rare grasses and to better understand what they will need to shed their endangered status.

Best's visit came on the heels of a historic, years-long drought that resulted in billions of dollars of loss to agricultural producers across Texas. Some feared the impacts to imperiled plant species could be bad. If cotton, hay and commercial timber were having trouble surviving the historic drought, how would the state’s most vulnerable plant populations fare in one of the hottest, driest corners of Texas?

Best, along with long-time park botanist Joe Sirotnak, climbed into the Chisos Mountains to visit six permanent plots established for the grass and found the impacts of the drought and other threats over the years were about as bad as they’d feared. The last known population of Guadalupe fescue remaining in the United States was down to just 47 individual plants.

In 2017, the rare grass was listed as endangered under the Endangered Species Act.

Botanists speculate that Guadalupe fescue may be a unique living artifact from previous Ice Ages, when the Trans-Pecos region was less like a desert and more like a woodland. It may have thrived in pinon-juniper-oak woodlands at lower elevations of the Trans-Pecos, then retreated higher up into the “sky islands” of the Chisos Mountains as the climate warmed. Today, it has settled into isolated pockets where it is found in the relatively cool, damp climate above 6,000 feet.

In the early 1990’s, botanists established permanent plots around all of the remaining individual plants found at the park. But although the permanent plots gave biologists a lot of good information about the plants – like how long they live, when they flower and how they reproduce – Best said it wasn’t the best way to collect unbiased and statistically valid data on the entire population size.

“The problem with setting up a plot only where you find a colony of rare plants is it’s not a representative sample; in fact, what you’re doing is highly unrepresentative and totally biased because you’re picking the one part of the landscape that has an extremely dense population of the species,” Best said. “If you draw a circle around it and collect data, it’s almost certain that over time that dense group of plants will decline. But what is the whole population size? That is what they were never measuring.”

After Sirotnak mentioned he might have seen the plant in other areas outside of the plots, the duo agreed they needed researchers to come out to the park to do statistically valid sampling to get a better idea of population size for these plants. They also realized that the same biased sampling problem had skewed population estimates of three other listed plants at the park: Chisos hedgehog cactus, Lloyd’s mariposa cactus, and bunched cory cactus. That’s where Dr. Norma Fowler, Professor in the Department of Integrative Biology at the University of Texas, came in.

“That the kind of thing she does, and she’s really good at it,” Best said.

Fowler’s lab is made up of plant population and community ecologists and plant conservation biologists who do research projects in plant demography, plant community structure and dynamics, fire ecology, rare and endangered plants, and non-native invasive plants. In other words, they are the ones to call when you need to know “where do plants live, and why do they live there?”

“Most of [the students] want to do a project that is useful to the world and has an applied component,” Fowler said. “Pretty much all of our projects can be thought of as dual projects where they are addressing basic scientific questions, but they are also producing results that are going to be useful to land managers.”

To secure funding for the research, the team applied for a grant through Section 6 of the Endangered Species Act, administered by the Texas Parks and Wildlife Department under an agreement with the Service’s Cooperative Endangered Species Conservation Fund. Carolyn Whiting, a PhD student with Fowler’s lab, took the lead role on the project and traveled to the park in spring 2019 to start counting the population sizes of Guadalupe fescue as well as Chisos hedgehog cactus, bunched cory cactus, and Lloyd’s mariposa cactus.

“It’s exciting to get to work with species that have a very narrow endemism because it feels very special,” Whiting said. “Like, ‘this is it, this is the only place in the world this grows and I am here, I am looking at it.”

Instead of using the permanent plot sampling style, which involved revisiting the same plants year after year, Whiting’s team is counting the Guadalupe fescue plants found in a larger number of circular plots evenly distributed throughout the species’ potential habitat. For the other species, they used evenly distributed linear transects.

“You only have so much time in the field, you can’t count everything and you can’t look at everything, and this design balances field resources and time with statistical rigor,” Whiting said.

Best said after one year of data, it is clear that populations “are larger, in fact considerably larger, than we previously understood.”

“One thing we’re finding is a lot of plants where they previously weren’t known to be, like new plants that people hadn’t known about, and it is helping us refine the definitions or how we would define the habitat,” Whiting said. “Before, you would ask, ‘is there no plant here because it’s not the right habitat, or is there no plant here because no one has ever looked?’ In some cases, like the [Guadalupe fescue], we’ve ended up finding our estimates were higher than what had been previously thought. It’s now under 2,000 individuals when before they were saying 100 individuals.”

For all of the species, Fowler said the problem with the permanent plots established decades ago was that they didn’t take into account that over time plants move around “playing musical chairs around the site.”

“What people did is they went up where they thought the plants were, they found them, and then they put down plots where the plants were on the day that they found them,” Fowler said. “But the problem – or one of the problems – is that over time, plant populations tend to move around. They die here, they grow there, the plants move. It’s a dynamic world.”

Best said the findings reinforce the point that no matter how well researchers understand what the habitat requirements are of rare plants, typically they occupy a very small fraction of potential habitat.

“One of the take home messages to this realization is that you can’t just put a fence around that one acre place where you found those rare plants,” Best said. “They need large areas and they need all that habitat, because over the next 100 years they may die out where they are now and their continued existence depends on being able to continually recolonize new areas.”

Whiting’s preliminary data is included in a draft recovery plan for the Guadalupe fescue published in May 2021 The plan incorporates and details the strategy and objectives by which scientists could accomplish the species recovery goal: to ensure the conservation and long-term viability of Guadalupe fescue in the wild such that it no longer requires protections under the Endangered Species Act.

Although the discovery of the new individuals is some much-needed good news, they still have to overcome many obstacles before coming off the Endangered Species Act list. In addition to threats from changes in wildfire frequency, livestock grazing, erosion and trampling by visitors hiking off the trail, they are still threatened by the small number and sizes of populations and remain susceptible to drought and climate change.

“I’m really concerned about climate change for these species because they are growing in such harsh conditions anyway with very little rain,” Whiting said. “I don’t think it takes much to push them into a perilous situation. A bad drought could knock out a lot of them.”

Though the future is uncertain for the plants, Whiting said she is grateful for the diverse group of botanists and researchers who have come together to aid her in the study. After Sirotnak left the Park in October 2016, volunteer Deb Manley has contributed her considerable botanical expertise on all the field surveys. Other partners on the project include undergraduate and graduate students from the University of Texas, state and federal biologists and botanists, park staff and local conservation organizations.

“One great thing about this project is we’ve been able to wrangle up all sorts of people to come out into the field,” Whiting said. “I really love bringing other people out to the field because everyone gets excited when we’re walking along and there’s this hedgehog cactus with a big pink flower on top, and we’re all really excited and I look at the map and say ‘this is a new one guys’ and everyone goes ‘yay!’ It keeps the morale up when we have good days like that.”

Read more: https://www.fws.gov/southwest/stories/2021/guadelupefescue.html