Appreciating Native Grasslands
Photo: Art Arizpe
Appreciating Native Grasslands
Habitat Enhancing Land Management
Part 2 — Learning to Manage Them
“There can be no purpose more inspiring than to begin the age of restoration, reweaving the wondrous diversity of life that still surrounds us.”—E.O.Wilson
Christine Middleton
Dating back to the earliest paleoecological and archeological evidence, the Edwards Plateau has been an ever-changing mosaic of woodland and grasslands, and humans have actively contributed to shaping the ecology of the landscape. Drought and the nature of the soil influenced what thrived here. Generally, grasses grew in open areas, primarily those characterized by deeper soils, often in valleys. Woodlands formed in places with shallower soils and dominated rocky slopes. Back then, grassland areas were largely maintained by lightning-caused fires that occurred mostly in summer and by grazing herbivores (bison and now extinct megafauna—wooly mammoths, mastodons, giant sloths…). That means our native grasses evolved along with a dependency on periodic disturbance. But fires generally only happened every few years, and the buffalo kept moving on in search of new undisturbed grazing grounds. Thus, there were also long periods between disturbances sufficient for grasslands to recover and build root mass.
Here in Hays County and across the rest of the Hill Country, we are rapidly losing our natural grasslands. So it has become even more incumbent on land stewards to protect and restore the ones they have. In Appreciating Native Grasslands - Part 1 - Getting to Know Them, we suggested landowners begin by simply learning to identify the myriad of grasses growing on their property. To aid in that effort, Part 1 discussed the parts of grass you can see and how to use that knowledge as an aid to identification. As we now seek to understand the best ways to manage our grassy areas, understanding what is happening underground can be just as important!
What’s out of sight matters
As a grass seed begins germinating, the plant extends both upward and downward. The very first downward shoots become primary roots. Their job is to feed the first few blades (leaves) as the grass plant begins to sprout. The primary roots only stay active for a few weeks. Then secondary roots begin to develop. As the primary roots die, the young grass seedling enters a critical period in its life. If the secondary roots haven’t developed sufficiently to feed the growing grass shoots and if moisture in the top few inches of soil is limited, the grass seedling is unlikely to make it to maturity.
Roots serve the grass plant by absorbing water and nutrients needed for photosynthesis. This is accomplished through very small hair roots growing on the outer layer of the larger roots. These almost microscopic roots enable intimate contact with soil and water. Fungi in the soil increase the surface area of the roots. Moisture and nutrients taken up by the fungi are shared with the grass plant. As grass blades begin producing sugars, a portion of that food is transported back to the roots. Some of the carbohydrates are used to facilitate root growth. Some are shared with the fungi. The rest are simply stored for future seasonal regrowth. The secondary roots of perennial grasses generally live for one year before they are replaced by new roots. This cyclical pattern of growing, aging, dying, and decaying is key to building healthy soil.
Secondary roots also serve to anchor the grass plant. And herein lies the difference between non-native lawn grasses and more robust native species. The roots of lawn grasses such as Bermuda, St. Augustine, and Zoysia extend only a few inches into the soil. Those of the big four prairie grasses—Big bluestem (Andropogon gerardii), Little bluestem (Schizachyrium scoparium), Indiangrass (Sorghastrum nutans), and Switchgrass (Panicum virgatum)—can extend as much as six to ten feet.
Remember that those secondary roots die back and must replace themselves every year. So what happens when too much blade growth is removed too frequently—by overgrazing or frequent mowing? Photosynthesis is what feeds growth, including the roots, so with fewer leaf blades to soak up light, less food is produced, and root growth slows. If the plant is not permitted sufficient time to regrow leaf blades, the supply of energy stored in the roots dwindles. Eventually root growth stops. As older roots die, they aren’t replaced. With fewer roots to absorb water and nutrients, the leaf blades produce less sugar. Thus a downward spiral begins, ultimately resulting in the loss of our grass cover. Goes a long way to explaining how overgrazing got us to where we are today!
However, if top growth removal is done with sensitivity to natural processes, grazing, burning, or mowing can actually stimulate growth. Removal of the growth point (where the stem sends up new leaf blades) forces the plant to send up new shoots, effectively starting over as if the growing season had just begun. Done right, these management tools increase plant vigor and enhance seed production. But it’s actually a bit more complex. Timing can favor some grass species over others and also influences the proliferation of wildflowers growing among the grass blades. Also keep in mind that native and invasive grasses often mature on different schedules. So bad timing can assist invasive species in outcompeting more desirable native ones. Yes, it’s complicated enough for a separate article, but read more here.
200 years - big changes!
Understanding what has happened to our ecosystems across the last two centuries is also important. While Native Americans definitely learned to use fire in managing the prairies to the east and north of the Hill Country, it is up for debate as to how much those techniques were employed here in Hays County. Even if they were, Native American fire practices closely mirrored natural processes already at work.
The big changes started in 1820, when European settlers arrived and built fences to contain their livestock (primarily sheep, goats, and cattle). The settlers looked upon the tall grasses they found as a vast, inexhaustible resource. They didn’t understand the dynamics of Hill Country grasslands, especially that our native grasses don’t respond well to continuous grazing. Lacking that extended period of rest for root regrowth, native grasses found it hard to thrive.
Remember how the bisons’ habit had always been to graze lightly and move on? Well, starting in 1840, settlers began killing them off by the millions, and by 1880 the Hill Country’s bison were gone. And by the second half of the 19th century, sheep overstocked on unrotated pastures were degrading grasslands and contributing to woody encroachment. The settlers also brought practices intended to limit fire frequency and spread—another factor that threw off the natural balance in favor of woodlands.
As cattle ranching replaced sheep, the search for grasses that would provide better forage and control erosion began. Grasses thought to be even more drought tolerant and better adapted to heavy grazing (grazing resistant) than our native species were imported from Asia and Africa. Fast spreading non-native varieties were also employed to help stem erosion and provide lush lawns.
Introduced warm-season grasses you are likely to encounter today include Bermudagrass, Dallisgrass, Johnsongrass, Kleingrass, and King Ranch (KR) bluestem. This last one, KR bluestem, was first shipped to the United States from China in 1914. Three years later KR had made its way to Texas. By 1949 KR seeds were sold commercially. Other more recent migrants to our area, many of which were introduced into south Texas in the 1950s, include Silky Bluestem (Dichanthium sericeum), Buffelgrass (Cenchrus ciliaris), and Guinea grass (Megathyrsus maximus). Ironically, the very reasons many of these imported species were initially greeted enthusiastically—they resist drought, spread quickly, and withstand heavy grazing—make them invasive: capable of crowding out many of our native plant species.
Silky Bluestem found at the Lady Bird Johnson Wildflower Center
Overgrazing, fire exclusion, bison extinction, and the introduction of non-natives significantly changed the composition of our grasslands. Species that were favored by livestock were replaced by less palatable ones. Introduced non-natives outcompeted native grasses. Grazing with too little time for grass recovery resulted in more bare ground. This led to decreased rainfall infiltration and more runoff. More runoff meant more erosion. Much rich soil, built over centuries, was lost forever. Without fires, the percentage of land that was oak/juniper forest increased. And within the remaining natural grasslands, the distribution of species was significantly modified. Tall and mid-sized grasses were replaced by shorter ones; favorites were replaced by grasses that livestock only nibbled in desperation. And, especially during periods of extended drought, non-native species proliferated.
Fast forward to the 21st century. Developers love plots with flat ground and few trees to clear away. Today’s greatest threat to Hays County grasslands is our rapid growth. The problem is not only the building and paving, but the park-like aesthetic that often accompanies it: carefully manicured, well-watered lawns. Mowed areas around structures is fire wise, and families need short grass areas for recreation. But that doesn’t need to lead to a huge expanse of non-native monoculture. Doug Tallamy, author of Nature’s Best Hope: A New Approach to Conservation that Starts in Your Yard, suggests that if every landowner in the United States converted half their lawn to productive native plant communities, we would have a Homegrown National Park (https://www.homegrownnationalpark.org/). He goes on to ask, “How big would that be? It’s bigger than the combined areas of the Everglades, Yellowstone, Yosemite, Grand Tetons, Canyonlands, Mount Rainer, Northern Cascades, Badlands, Olympic, Sequoia, Denali, and the Great Smoky Mountains.”
Many here in Hays County are working hard to preserve our most sensitive areas by creating parks, encouraging large landowners to adopt conservation easements, setting aside lands for water quality protection, and the like. But that’s just not enough. We need landowners to join us in restoring some of the ecosystem richness we have lost. For owners of postage stamp lots this might simply mean converting a portion of their lawn into a pollinator garden. Those with slightly larger lots might consider giving over a portion of their property to a “pocket prairie” (https://www.wildflower.org/magazine/native-plants/make-pocket-prairie). And those with more acreage can take the necessary steps to restore a significant portion of their acreage to its natural state.
The science of managing grasslands
Grasslands are complex ecosystems. Simple logic and solutions can lead to unanticipated outcomes. Burning, grazing, and mowing are all techniques used to manage grasslands with varying results. As already discussed, the timing of these activities can have a significant impact. There are also other variables beyond control of the landowner, such as extended drought. Much of the research on grasslands has focused on Midwestern prairie ecosystems. Many are also more focused toward either producing nutritional forage or restoring the ecosystem that existed prior to European influence. Nonetheless, it is instructional to explore basic findings that span many such studies.
Clearly, both fire and grazing remove plant biomass and return nutrients to the soil, though in very different ways. Fire doesn’t choose, as does a cow, what plants it consumes, but roots remain. So many species of native grasses recover rapidly after low intensity fires. (Fire can, however, reduce populations of certain species, primarily annuals whose seeds are destroyed by the flames.) On the other hand, grazing results in the loss only of certain “grazer preferred” plants. Thus, the removal of biomass by grazing is more selective than by fire. Both fire and grazing have a positive impact on plant vigor in that they increase soil temperature and allow more light to reach the soil surface. Mowing shares many of these characteristics with fire and grazing. But fire and grazing more closely mimic natural ecological processes. So mowing’s impact may not be as significant.
There is ongoing research at a place where you can visit and observe the results. Since 2001, the Lady Bird Johnson Wildflower Center has been studying the impact of fire and mowing in managing Hill Country landscapes. Seventy-four acres at the center have been divided into 54 plots of 1-2 acres. Each of these plots is being used to test nine different treatment regimes. Burn sites are paired with mow and control sites, based on treatment frequency and timing (summer, fall, winter). Parallel sites are burned or mowed within a week of each other. Go there and walk the Hill Country Trails (https://www.wildflower.org/visit/hill-country-trails) to see the results of this long term study. As you walk the trail, compare sites that were burned or mowed on varying schedules with control sites that were simply left alone.
View of two plots at the Wildflower Center with differing treatment regimes
Not surprising, the Wildflower Center research clearly demonstrates that burning produces the most ecologically balanced results. Fire removes the thatch layer from the soil surface, helping forbs and other native plants germinate. Summer burns increased the diversity of spring wildflowers such as black-eyed Susan (Rudbeckia hirta) and Indian paintbrush (Castilleja indivisa). However, fall burns result in more wildflower diversity overall. And winter burns lead to higher abundances of non-native grasses and the general absence of native species like Little Bluestem (Schizachyrium scoparium) and Curly Mesquite (Hilaria belangeri).
The findings with respect to invasive species are also informative. Summer burns proved to be the best way to control some invasive species, including KR bluestem. However, winter burns tended to promote the growth of KR. Fires also killed tree seedlings as does mowing. Not surprisingly, the unburned control sites had the most encroachment by trees, shrubs and vines. Overall, the experimental sites remained compositionally and functionally distinct from our natural old-growth grasslands. Thus the conclusion that any treatment should be supplemented by seeding or planting of low density or missing species.
To mow or not to mow?
For most Hays County landowners, burning is not an option. And fewer and fewer want to take on the management of grazing livestock. So most of us have just one choice: to mow or not to mow. If you decide to mow, be aware that when and how can make a huge difference in the results. After the 2015 Blanco River flood, the Wildflower Center and Texas Parks and Wildlife collaborated on a guide for landowners living along the Blanco. That publication was subsequently revised and is now available as the Hill Country Design Guidelines. On page 59 is a discussion of mowing that was clearly influenced by the decades of research at the Wildflower Center.
The Wildflower Center provided landscape guidance after the May 2015 flood.
The Guidelines distinguish between tallgrass and shortgrass. Tallgrass areas are what they sound like: fields dominated by grass species that grow tall, most likely lots of Little Bluestem. Generally, such areas do not require regular mowing. While annual mowing can be tolerated, the preferable approach is to maintain such areas with less frequent mowing—perhaps once every three to five years and no lower than 6 inches. Not mowing at all is also an option. And, if you do mow, the recommended timing is after the grass seeds have ripened in December and no later than just before the grasses begin to green up (late February).
Shortgrass prairies are characterized by species growing closer to the ground. Examples are grasses found mixed in Habiturf® (https://www.wildflower.org/project/habiturf). Developed by the Wildflower Center, this turf grass replacement is a blend of buffalograss (Bouteloua dactyloides), blue grama (Bouteloua gracilis), and curly mesquite (Hilaria belangeri). Shortgrass areas can be mowed up to three times a year to a height of 3-4 inches. A late winter mow (January-February), after warm season grass seeds have ripened and before the spring growing season, helps remove standing dead material. After spring wildflowers have dropped their seeds, a one-time summer mow (June-July) helps promote next year’s batch. Another one-time mow in early fall (September-October) can help maintain the grass height at 3 inches.
While these are suggested guidelines, every situation is a bit different. For some properties not mowing at all may be the best approach, particularly in early years as the land seeks to recover. Another approach could be mowing just small sections each year. This would also provide a way to observe the vegetative response to different treatments. Experimentation is a good approach to honing a maintenance plan. Climatic conditions are also a factor. Grasses tend to grow more slowly during periods of drought. So skipping a mow cycle at such times may be a wise decision. Aesthetics are also a consideration but should not trump ecological function.
Controlling woody encroachment and invasives
Mowing is not the only tool landowners have for assisting nature in restoring ecological balance to their grassy areas. Woody plant encroachment refers to the increase, over years and decades, in the abundance of indigenous woody plants, such as shrubs and bushes, at the expense of herbaceous plants and grasses. It’s a natural phenomenon that can be intensified by land use practices such as overgrazing and fire suppression. Climate change may also play a role. Like burning, mowing helps control woody encroachment albeit to a lesser extent. So especially in places that are mowed infrequently or not at all, manual control may be called for. And it’s fun to walk your land, clipper or loppers in hand, doing a little routine maintenance while observing the wildflowers and the butterflies you love.
Ashe juniper is much easier to control when only a few inches tall. And fortunately, if all upper growth is removed down below the soil line, below the little growth nub, the basal stem “bud,” juniper doesn’t re-sprout. Other woody plants such as mesquite do. So you might also bring along a small container of herbicide and a paintbrush. Just dab the cut with a little to prevent new growth without harming surrounding vegetation. But don’t get carried away! Keep in mind, the Hill Country always was a mix of grasslands and woodlands. And, as discussed in Part One, patches of trees and shrubs are a characteristic of our grassland savannas. So any clearing of woody species should be done slowly and thoughtfully, keeping in mind the ecological functions they serve.
News Flash! The spread of invasive species is not only woody encroachment! So while you are enjoying your property, also be on the lookout for invasive grasses and forbs such as Johnson Grass or Malta Thistle. Pull what you can. But remember seeds and roots likely remain. So revisit that same site occasionally to monitor progress and pull any new upstarts. For larger areas, solarization is a potential approach that requires a minimum of expense, a bit of labor, and patience while letting the sun do its work. The process, best done in summer (June-August), uses the sun’s heat to kill the roots and seeds of herbaceous plants. Austin Water’s Wildland Conservation Group has successfully used solarization to control Johnson grass. Here are their detailed instructions.
Black plastic being removed after 11 months of solarization at Prospect Park in San Marcos. The area was then seeded with natives and the plastic reused for another project. Photo: Lance Jones
As you walk your land, also note places where thatch has built up. What is thatch? It is the un-decomposed or partially decomposed layer of living and dead grass stems, roots, rhizomes, stolons, and other organic material found between the surface of the soil and the living grass blades. The right amount of thatch is a good thing. It protects soil and roots from extreme temperatures and holds in moisture. Eventually, as these materials break down, organic matter is added back into the soil. But too much or too little thatch can be detrimental. Too much thatch inhibits the germination of native grasses and forbs. With too little thatch, the soil is more exposed to the elements, meaning seeds find it harder to germinate.
If you see places with too much or too little thatch, make a mental note. Then bring a rake along on your next outing. Make use of any thatch you rake up by placing it on the bare areas you spotted. Bare areas are prone to erosion, so encouraging revegetation before that happens is always good. Other approaches that offer seedlings a measure of protection include covering a bare area with a thin layer of the woody vegetation you removed or with mulch you have produced. If erosion has already started, you will find more on how to address the problem in an earlier article titled Don’t Go With The Flow!
Jumpstarting recovery
Healthy ecosystems are characterized by complex interactions among a wide variety of plants and animals. As discussed in Variety is the Spice of Life, and That Goes for Plants Too!, much of our rich diversity has been lost due to abusive land practices and other assaults on Hays County ecosystems. Recovery often takes time. After disturbance, revegetation goes through stages during which different species thrive. First come the colonizers, things that spread rapidly, usually via either prolific seeding or rhizomes. Often these are things we tend to regard as weeds. However, they serve important functions, such as fixing nitrogen and restoring fungi. Unfortunately, early succession (colonization, species recovery) is often a time KR and other invasives can take hold. As the land recovers, mid-succession grasses like Silver Bluestem (Bothriochloa laguroides) begin to move in. Finally, climax grasses begin to take hold. That’s when you start seeing Little Bluestem and the other tallgrass species.
Hairy grama is often seen growing in sparsely vegetated patches.
The timeframe from early succession to climax varies depending on local conditions, such as soil condition, rainfall, and remaining seed bank. Often the process takes years and even decades. But we humans can be an impatient bunch. Seeding and transplanting native grasses and forbs can both speed recovery and increase diversity. These methods also help in discouraging the influx of invasive species. One member of our HELM team reported success in using seeding to eliminate KR bluestem! How? First by weeding out as much as possible from a stand of KR. Then seeding with fast growing, early succession grasses such as Sideoats gramma (Bouteloua curtipendula) and Texas cupgrass (Eriochloa sericea). A lot of KR seeds were still present in the soil. But because these particular native grasses spread quickly, they proved strong competitors. And soon these same natives spread on their own to other portions of the property. Success!
Wildflower seeds are best spread in the October/November timeframe. But the optimum time for spreading native grass seed is between January and April. Be aware that dry conditions will likely influence germination and growth rates. So watch the weather for prediction of a rainy spell before spreading valuable seeds. Also, the more locally sourced the seed is, the more likely the plants produced are adapted to local conditions. So gathering seed from your own property or that of a neighbor is always the best option. That’s what they do at the Austin Water Quality Protection Lands (WQPL). For more on seed gathering at the WQPL, see Collecting Seeds to Protect an Aquifer in last month’s Hays Humm.
Seed gathering at the Austin Wildlands Preserve at Onion Creek
One of the reasons our native grasses are so resilient is the symbiotic relationship they have with certain fungi growing on their roots. The lack of that particular fungi can be detrimental. It can take time for fungi to return to degraded soil. But that too can be jumpstarted.
Author David Hillis signs books for Lauralee Harris and Dick McBride at the September 2023 HCMN Chapter meeting.
In his book, Armadillos to Ziziphus: A Naturalist in the Texas Hill Country, David M. Hillis suggests transplanting a few whole plants containing symbiotic fungi into an area sown with their seeds. Live roots are another option offered by some growers. But live roots and transplants often require supplemental water over some period of time to stay alive. So that approach may be something to attempt only when wet years have returned.
Slow and steady wins
In a given season, think about implementing these management practices to only a portion of a property. Makes the job a lot easier for sure and allows for experimentation. But there are ecology-based reasons for this approach as well. For example, bees, butterflies, and other insects overwinter in dry stems or in leaf litter. So mowing in the wintertime can severely impact next spring’s populations. Disrupting the entire site can reduce the area’s population of pollinators. Birds may also have a hard time finding enough insects to support their offspring, and fewer nestlings will make it to maturity. As a general rule, you might consider managing less than 30% of your property at a time. Untreated areas will thus provide the needed habitat and serve as a refuge as species begin to recolonize that year’s managed portion.
Daytime temperatures are becoming more tolerable. The HELM team is gearing up to resume our visits with Hays County landowners. And what will we do when we come out to your property? We will walk it with you, identifying grasses and other plants as we go. We will make suggestions on improving soil and controlling erosion. We will provide helpful advice on attracting birds and other wildlife, preventing oak wilt, and much more. So, if you own acreage in Hays County and would like us to include you on our fall schedule, go to https://www.beautifulhayscounty.org/helm/ and fill out our request form. And please help us spread the word!
Photo: Lance Jones