When approaching a thicket of the “mean and thorny” plants that make up Tamaulipan thornscrub habitat, it’s easy to initially question how anyone could comfortably live in or with it. Even early explorers in South Texas’ Lower Rio Grande Valley wondered what to make of it.
“Could all this thorny jungle and chaparral have been created in vain?” asked Rio Grande Valley ethnographer Capt. John. G. Bourke in 1895. “No… the more we examine into the great scheme of nature, the more do we see that nothing has been made without some purpose.”
Though Bourke posed the question as part of a quest to find out how the local vegetation could “make men wiser and happier,” today we know that this ecologically and economically valuable habitat provides an array of important ecosystem functions for wildlife and the local community.
This essential habitat hosts more than 1,200 plant species, 519 bird species, and 316 butterfly species, including 45 federal and state threatened or endangered species, in one of the most biologically diverse regions in North America.
Peer within this dense foliage and you could find many unique and rare birds, including ferruginous pygmy-owls, buff-bellied hummingbirds, green jays and blue buntings. Look even lower, and you (or more likely a well-placed trail camera) could even spot one of the United States’ only endangered ocelots in the wild.
“It’s the dense understory that makes it really beneficial for ocelots,” said Mitch Sternberg, South Texas Gulf Coast Zone Biologist for the U.S. Fish and Wildlife Service. “Thornscrub is really kind of a safe haven for them.”
The benefits to the region go beyond supporting native wildlife populations. Thornscrub helps provide carbon sequestration, erosion control, economic gains in ecotourism, recreational opportunities, and pollinator services for the local community.
“All of these plants are doing wonderful things – converting carbon dioxide to oxygen, supporting pollinators to help the agriculture industry, hosting birds that draw in bird watchers,” Sternberg said. “And beyond that, the whole outdoor economy for this area, including hunting and fishing on the coast here, is a huge industry when you look at hotel stays and boats and ammunition.”
For those who have never encountered it, thornscrub can be recognized by short, spiky shrubs and trees that fill the landscape at 3,000 to 8,000 plants per acre. The Texas Department of Agriculture once described it as “luxuriant, often forming veritable jungles” in the Lower Rio Grande Valley.
“The mesquite, which here reaches the dignity of a tree, sometimes being as much as two feet in diameter, predominates with guajillo, ebony, retama, tornillo, huisache, cactus, and many other varieties of semitropical trees and brush in abundance,” they said.
“It’s extremely dense – to the point where if you didn’t have a trail system in the mature stuff you’re probably not going to get through it,” said Jon Dale, American Forests’ Director for forest restoration in the Lower Rio Grande Valley and chair of the Thornforest Conservation Partnership.
If the name didn’t already tip you off, it also has a lot of thorns. In fact, the name “huisache,” a common tree found in this habitat, can be translated to "many thorns" in the Nahuatl language.
Because this impenetrable habitat isn’t exactly easy for people or livestock to live in, over the last hundred years much of South Texas’ native thornscrub has been cleared in favor of friendlier vegetation. Today, only 10 percent or less of native thornscrub habitat remains in a natural state, having been lost primarily to agriculture, industrialization and urbanization.
But efforts to reforest and restore this habitat are underway.
Since the 1980s, the U.S. Fish and Wildlife Service, American Forests and other conservation partners have restored more than 14,000 acres of thornscrub, with an additional 100-300 acres being planted every year.
Due to the depletion of native seed banks and the aggressive spread of invasive grass species, thornscrub restoration isn’t as simple as letting a field go wild and hoping the native plant species will re-establish on their own. To take a cleared field to a fully restored thornscrub forest takes a lot of time, manpower, and most important of all, seedlings.
“There's a lot of moving parts…planning, seedling production, planting and success monitoring,” Dale said. “Everything has its place, season and time.”
In order to increase genetic diversity in restored habitats, all seedlings utilized by the Service for thornscrub restoration in South Texas must be grown from locally sourced seeds. This is a challenge, because in the past the supply of native thornscrub plant seedlings could not meet demand largely due to shortages of native plant seeds.
“Everything begins with a seed,” Dale said. “We can't talk about doing massive restoration of thornscrub if we don't have that source of seeds in place.”
To help meet this need, permitted seed hunters with American Forests and other local groups search state and federally owned lands, along with some private lands with the consent of landowners, for 30 types of flowering trees and shrubs. Year-round, these seed hunters traverse Cameron, Hidalgo, Starr and Willacy counties searching and collecting from populations of the different species to build genetic diversity in the restoration program.
The individual species chosen for restoration are drought tolerant, promote quick establishment of diverse species within the restored areas, provide benefits and food sources to wildlife like birds and pollinators, and provide improved canopy shade and moisture retention to ward off invasive grasses and help new generations grow.
After collecting the seeds, seed hunters transport them to the Service’s Marinoff Nursery in Alamo, Texas, where they can be processed and stored at the right temperature and moisture conditions in preparation for the busy planting season.
Over the last 40 years, restoration staff have continued to refine the process of taking the wild-collected seeds and turning them into thriving thornscrub habitat. Once the planting season hits early in the year, Sternberg says the program becomes “a big, busy, complicated machine.”
“But a very interesting and rewarding one for sure,” he added.
Before any seedlings touch the ground each spring, staff at the nursery get busy collecting the young plants from contracted growers, caring for them at the nursery, tallying the total number for the year and working with cooperators for supplies. Additionally, seedlings at the nursery are separated by size and species and recombined so that individual crates of plants have specific mixtures of targeted species.
In late February and early March, staff engage in a month of “chaos” as they continuously trailer the plants and supplies to the professional contracted tree-planters who install the seedlings by hand at the restoration sites.
“We have to ensure that the seedlings going to the ground are installed well,” Sternberg said. “Really the best way that we found to do that is hiring professional crews to put them in the ground.”
At the restoration sites, the professional crews walk in a line and bury the young trees or shrubs in the ground about every 6-8 feet. In total, the crews aim to plant about 1,000 seedlings per acre.
But the work doesn’t stop there. Placing tree tubes around the newly planted seedlings is an essential part of ensuring the growth and survival of the plants. In addition to containing soil moisture and promoting quicker establishment, the tubes protect the young plants from hungry wildlife and help stave off advances from invasive grasses for about a year, before they are removed and used again in future projects.
The tree tubes work so well that the Service has found they improve seedling survivorship by more than 80% compared to standard ‘open’ planting methods.
After the seedlings are planted, staff work throughout the year to monitor survivorship, check on the progress of previous year’s plantings, and conduct treatments in restoration areas to prevent the invasion of buffelgrass and other exotic grasses.
While restoration is a slow and ongoing process, biologists are seeing wildlife dispersing into and populating the areas that are being restored.
“It's really rewarding to get to go back and see it through time,” Sternberg said. “I did a bird, small mammal, and reptile survey in replanted areas and we compared them to the mature areas and found real good similarities. They're kind of telling you, wildlife community wise, that this is on the right trajectory.”
The Lower Rio Grande Valley is unique in that it has hundreds of thousands of acres of protected public lands spread among state parks, wildlife management areas, and National Wildlife Refuges owned by the state and federal government. Much of the thornscrub restoration accomplished so far has been done on this public land, particularly on the three national wildlife refuges that make up the South Texas Refuge Complex: Santa Ana, Lower Rio Grande Valley, and Laguna Atascosa.
But with much of the remaining landscape in private ownership and working lands rapidly becoming developed for housing and other urban infrastructure, working with private landowners is becoming increasingly important in the effort to expand connectivity of thornscrub habitat.
This year, the Service expanded its restoration efforts to include planting on a 47-acre portion of a Service-managed at the privately-owned Yturria Ranch in Willacy County. In addition to providing habitat for one of the largest ocelot populations in the U.S., the historic ranch hosts a diversity of native wildlife that support ecotourism opportunities like bird watching, wildlife viewing, hunting and fishing.
“This is a major new milestone for the Service to work with a private landowner to conduct thornscrub restoration on their lands,” Sternberg said.
“One of the things that motivates me, and I hope motivates other people, is that we want people’s ranching lifestyles to be sustainable,” Sternberg said. “Because ultimately, we don't want to see the land fragmented or put in some kind of development, and it doesn't have to be if they can still make money from it and keep it in their ownership. We can help them diversify or improve on the landscape in such a way that it can also benefit and be an economic generator for them.”
Outside of the Service’s restoration efforts on public lands, a coalition of state and federal agencies, universities, nonprofits and community organizations called the Thornforest Conservation Partnership have formed to help guide thornscrub conservation across all land ownerships in the region.
“We're all working towards this common goal of trying to put parts of this ecosystem back together, Dale said. “With all of the development and as every day passes there's less time to do that.”
In 2020, the partnership launched a Thornforest Conservation Plan to expand restoration opportunities and link thornscrub habitat throughout the Lower Rio Grande Valley. According to the plan, there are more than 80,000 acres of potential restoration sites for thornscrub restoration in the area. Of these, only 30% are public. Dale said working with private landowners in the future is going to be essential to conserve and expand the region’s thornscrub ecosystem.
“The conservation plan is setting the table for what we envision moving forward and what we're already moving towards,” Dale said. “The first order has always been to catalyze and expand that habitat to provide connectivity in this fragmented landscape. If the connectivity isn’t there, there isn’t going to be much of a future for those isolated core areas of thornscrub.”
Partners and contractors assisting with thornscrub restoration in the Lower Rio Grande Valley include American Forests, Land Life Company, The Nature Conservancy in Texas, University of Texas Rio Grande Valley, Conservation Service, Inc., Friends of the Wildlife Corridor, and The Student Conservation Association.