While Winter Storm Uri was an unusual Texas wild ride, our state is generally characterized by wildly beautiful, even breathtaking, extremes. Texans tend to mimic their landscape, being more inclined to roll with what comes at them. However, in the face of climate change, this may result in hazardous levels of what scientist Jared Diamond refers to as “creeping normality,” the tendency humans have to grow accustomed to changes around them. While some of the changes are sure to be benign, others will jar ecological and cultural norms.
The introduction and subsequent invasion of Mediterranean annual grasses is just one example. These grasses, such as annual ryegrass and wild oats, are often used for revegetation as quick soil stabilizers. Like other grasses, they have fibrous root systems but, unlike our robust perennial grasses, they are small, short-lived, and have low forage value. It is therefore surprising that they are sometimes recommended as turf and for the development of pasture. Furthermore, these annuals complete their cycle of reproduction and go to seed early in the season leaving soils bare and baked, more vulnerable to rapid drying, erosion, and loss of nutrients and organic matter. In addition, the practice of revegetation using fast-establishing annual grasses reduces native biodiversity through homogenization and soil alteration and threatens our native food webs, including wildlife.
I was born and raised in Texas but trained as an ecologist and botanist in California. When I returned for my first real job in my home state, I discovered that someone had really messed with Texas biodiversity. Perennial grasslands and our roadsides had been homogenized by purposely introduced, non-indigenous, invasive species, in particular perennial Old World Bluestems, like KR and Kleberg, and buffelgrass. Like all invasive exotics, these species tend to outcompete and displace native species, reducing the amount of food and habitat for native animals all the way up the food chain. Indeed, we now know that homogenization of grasslands has resulted in, for example, reduced food for insects, birds, mammals and degraded habitat for ground-nesting birds.
Nonetheless, coming from California where vast perennial grasslands were replaced by exotic, invasive, annual grasses from the Mediterranean, I was comforted by the fact that our grasslands were still dominated by perennial, warm-season grasses, even if much of it came from the invasive sorts. This was part of my own “creeping normality” when I began to see Mediterranean annual grasses persist in disturbed places like heavily grazed ranches, roadsides, and San Antonio lawns.
Mediterranean annual grasses have been used in Texas for soil stabilization for decades. For a time, they would germinate and grow with only limited flowering or fruiting. But now, climate change and our generally wetter winters, which Mediterranean annuals love, permit these grasses to complete their cycle of reproduction and persist in the soil seed bank across seasons.
These species now germinate and persist alongside our native cool-season grasses, such as Texas wintergrass, as well as highly competitive, warm-season, exotic, invasive species, such as Bermuda grass and the Old World Bluestems. Further fueling this concern, and likely attributed to the same ecological phenomenon, is the introduction and spread of bastard cabbage and Malta and yellow starthistle, other Mediterranean annuals recently introduced to Central Texas. These species also impact the food web through homogenization and reduce the amount of biomass that stays in place as cover for animals and soil protection.
The solution to this problem is to use Texas native perennial grasses that also quickly cover disturbed soils. We are only just beginning to better understand the mechanisms driving this trend but exotic species are often introduced without their pathogen and herbivore enemies, which would normally reduce their growth rates. In addition, many of the introduced exotic species that become invasive grow quickly under disturbed and high nutrient conditions, which humans are very good at creating, through activities such as earthmoving, fertilizer addition, and atmospheric nitrogen deposition from cars and industrial processes. In short, what conservation ecologists refer to as “the precautionary principle” is in order when choosing between native and exotic species for revegetation or restoration.
In my research, I have found a number of native grasses that establish and persist among the perennial exotic invasives. While we love the higher forage value, deeply rooted native grasses such as Indiangrass, Texas cupgrass, and big and little bluestem, their establishment may require that we first seed or plug fast-growing natives, such as sideoats grama, Texas grama, hairy grama, and green sprangletop.
Unfortunately, these native species lack research and development funding and remain more expensive. Some organizations, such as the Kika de la Garza Plant Materials Center, working in collaboration with the Caesar Kleberg Wildlife Research Institute and the South Texas Natives Project, have been leaders in this arena. However, due to their lack of widespread use, the natives are more expensive than the exotic, invasives.
Public entities such as the Texas Legislature, Texas Department of Transportation, Texas Commission on Environmental Quality, and Texas A&M AgriLife can make firm commitments to regulating, recommending, and utilizing only native perennial species for large-scale public (e.g., highways) and private (oil and gas) revegetation and rangeland restoration projects. This would both create demand and bolster research and development for supply.
Though Texans often reject all things California, our grasslands are beginning to look more and more alike. With a stronger commitment to the legacy of Texas rangelands and Lady Bird Johnson’s call for the protection of our biodiversity, we can keep Texas looking like Texas.