Hill Country Natives Are Smarter Than You Think

Habitat Enhancing Land Management

“Texas is a land of perennial drought, broken by the occasional devastating flood.”

—Unnamed Texas Meteorologist, 1927

Christine Middleton

The first part of this 1927 quote from an unnamed Texas meteorologist certainly describes 2022 so far. The first half of this year was the fifth driest on record, and this summer hasn’t been any better. Most of us don’t remember the “drought of record,” that period from 1949 to 1957, when Texas received 30% to 50% less rainfall than normal. But many can recall 2011, deemed the driest year since Texas began recording rainfall 128 years ago. Got us to wondering how Hill Country native plants weather the storm, or more accurately the lack thereof.

Drought stress occurs when water loss from a plant exceeds the ability of its roots to absorb water. The result is a reduction in a plant’s water content to the point that it interferes with normal plant functions. Animals can move around in search of water. But plants are sessile, meaning they are anchored to one spot. However, you’d be surprised how much native plants in Hays County know about surviving droughts. How exactly do our native plants cope with stress caused by a prolonged period without water? It’s complicated and pretty amazing.

Water is Essential to Plant Development

Photosynthesis: 6H2O + 6CO2 → C6H12O6 + 6O2

Plants depend on water for the biological processes that support life. In particular, six molecules of water plus six molecules of carbon dioxide are recombined to create one molecule of sugar and six molecules of oxygen. The sugar becomes the food that supports plant growth. The oxygen is released into the air – lucky for us humans who like to breathe. As we all learned in school, this process is called photosynthesis.

For photosynthesis to happen, water must be transported from the roots to the leaves. The roots are designed to absorb water and other nutrients contained in the soil. The water then moves upward towards the leaves through a system of tubules called xylem. This transported water, which also bolsters the cell walls of the plant’s stem, is referred to as turgor, and without it most plants wilt.

Once water reaches the leaves, a small portion of that transported water is used in photosynthesis. The rest of the water is released by the leaves and other plant parts into the atmosphere through a process called transpiration. The openings through which the water is released are called stomata. Stomata are generally located on the leaves of plants but can also be on the stems, petals, or other plant parts. The stomata are small openings formed when two guard cells create an opening in response to turgor pressure. When stomata are open, water escapes along with the oxygen that was created as a byproduct of photosynthesis. The open stomata also enable the carbon dioxide needed for photosynthesis to enter the plant.

Drought Tolerant Plants Are Rare

Few plants are truly drought tolerant. Plants aptly termed “resurrection plants” can tolerate low water content in their cell tissues, can survive that way for several years, and recover without physiological damage. One species of resurrection plant here in Texas, Selaginella lepidophylla, is a member of the Spike-moss family and is native to the Chihuahuan Desert. A common name for this species is Flower of Stone, likely because one of the main places it grows is north-facing rock crevices. The amazing thing about this species and other so-called resurrection plants is that during extended periods of dryness the plants dry up and go dormant. To the untrained eye, such plants appear dead. But when rain finally comes, these plants quickly green up, sometimes in as little as 24 to 48 hours. Then the revived plants start growing again as if the prolonged period with no rain never happened.

Texas Natives Cope With Drought

Hill Country natives aren’t as drought tolerant as resurrection plants. But most have developed some form of drought resistance. Over time, our native species have adapted to vagaries of Texas weather— feast or famine in terms of rainfall. And, in the process, these natives have developed an array of strategies for coping with droughts, both those that are seasonal and more prolonged periods without much rain. Strategies vary considerably from species to species but generally fall into two categories: drought avoidance and drought resistance. The quintessential example of drought avoidance is seen in the Badlands region of the American West. Most of the year that landscape is arid with little vegetation. But for brief periods when conditions are just right, the desert wasteland explodes with colorful wildflowers.

Many of our Texas native plants suppress flowering during times of drought. It makes sense as a way to conserve energy and reduce dependency on water. While not nearly as dramatic as the Badland’s display, when the rains finally return, you’ve probably noticed lots of natives burst into bloom. What comes into bloom depends on the timing of the rain. But two of the most noticed examples are the Evening Rain Lily (Copperia drummodi) and Cenizo (Leucophyllum frutescens). Cenizo (popularly known as Texas Sage though not actually a Salvia) is often seen blooming just before or just after a good rain. Evening rain lilies proliferate in the days following a much needed spring rain. Interestingly, rain lilies don’t respond in the same way to artificial watering. So something else is going on, and it might be these plants’ ability to detect the changes in barometric pressure associated with coming storms. That’s likely what is happening with Cenizo, sometimes called Texas Barometer Bush. But just like barometric pressure readings, this plant’s predictive powers are not infallible.

Hill Country natives have evolved other characteristics that provide protection from the historic vagaries of Texas weather. For example, Texas Bluebonnets (Lupinus texensis) time their lifecycle to coincide with the most likely periods of rain. Fall rains trigger seed germination. Cooler winter temperatures enable the bluebonnets to grow and develop roots. Come spring, this Texas icon bursts into bloom. Then each plant produces lots of seeds. That’s another way the species assures continuance in the face of adversity. Only a fraction of the seeds produced in a given year sprout the following fall. The remainder remain dormant and viable for several years. So this well-loved Texas native keeps on blooming along our Texas highways despite some years when fall rains fail to materialize. With climate change in full gallop, will this now happen more often?

Other Hill Country natives have evolved physical characteristics that enable them to maintain relatively higher tissue water content despite reduced water availability. Some like Pasture Heliotrope (Euploca tenella) have sparse, skinny leaves and small flowers and so less surface area for transpiration to take place. And then there are cacti such as Texas Prickly Pear (Opuntia engelmanii var. lindheimeri), whose leaves have evolved into spines and whose stems have enlarged into thick fleshy receptacles where water can be stored for long periods.

Plants have also figured out clever ways for limiting water loss in real time. You may have noticed that on hot days the petals on Engelmann’s Daisy (Engelmannia peristenia) become tightly curled. Then, come cooler evening temperatures, the flowers unfurl and look perfectly normal again. That’s happening because stomata on the petals are closing, limiting transpiration. But closing the stomata during the day means the plant can’t take in the carbon dioxide necessary for photosynthesis. So in the evening when the stomata reopen, the plant takes in carbon dioxide, which is stored for use the following day.

But behaviors like this, designed to limit water loss, result in reduced photosynthesis. Plants may grow more slowly or may even stop growing. Flowers may be smaller or even completely absent at a time when the species would normally be in bloom. Leaves may be less green, offering less chlorophyll for photosynthesis. Foliage may begin to die back. Roots may trim themselves back. Sometimes the leaves of deciduous plants acquire their fall colors, drop their leaves, and go dormant long before summer is over. Come late August, one of our favorite natives, American Beautyberry, is likely to adopt this strategy. It’s easy to believe the bush has died. But next spring you’ll likely be surprised when it begins to sprout new leaves.

So don’t despair! Your landscape might be looking pretty grim about now. But be comforted that Hill Country plants are doing what they are supposed to do when rain is scarce: they are conserving resources. A few won’t make it. And we don’t yet know the full impact of the prolonged period of extreme heat we are experiencing this summer. But when the rains return—hopefully soon—we expect most plants will spring back again for all the wildlife that depend on them for food and shelter— and for our delight!

Spring flowers on resting grazing land, Central Hays County, Texas Photo: Mimi Cavender

With this record-breaking summer heat upon us, we have suspended our HELM property visits. But come September we’ll be back at it. If you would like the HELM team to visit your Hays County property to provide insights into land stewardship concerns you might have, go to https://beautifulhayscounty.org/helm/ and fill out our request form.

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