Habitats of the Llano Estacado
Sanddunes
Introduction
Sanddunes are found between the Pecos River and the Llano Estacado. These sanddunes were formed by the constant southwest wind blowing sand out of the river valley. Most of the sand is stopped by the western edge of the Llano Estacado, the Mescalero Escarpment. There are two different sand dune formations – the older formation has reddish soil due to iron oxide stains on the sand grains. The younger dunes are cream colored, and will form transverse (nearly straight sand ridges at right angles to the prevailing wind) and barchan (crescent shaped) dunes where there are open dune fields.
Some of the sand makes it to the top of the Llano Estacado. On top of the Llano Estacado are smaller areas of sanddunes, usually north and northeast of the draws (watercourses that only run after a rain.) Some of the sand comes from the Pecos Valley, and some is from erosion along the draws. There are a few small areas of open dunes on top of the Llano Estacado (in Midland and Cochran Counties.)
East of the Llano Estacado are also regions of sandy soil – some of this sand comes from the top of the Llano Estacado, and some comes from the creek and river valleys of the “breaks.” There are no open dune fields in this region.
Most of the sanddunes are vegetated. It is unknown why some dune fields do not become vegetated – the dunes at Monahans State Park have been open sand for over a hundred years. Shinnery (Quercus havardii) and Sandsage (Artemisia filifolia) are the indicator plants of sanddune soil – if either plant is seen, a person is in sanddune habitat. There are several dozen species of plants that are only found in the sanddune regions. Marbled Whiptail Lizards are an indicator reptile of the habitat. In some areas the rare Sagebrush Lizard is found, but not in all of the sanddune areas. Lesser Prairie Chickens are found in many of the sanddune areas, but not all, and can be found away from sandy soil at times.
When the wind is above 30 miles an hour, sand grains will begin to move – bouncing along a few inches at a time. (This is known as saltation.) After three hours of a 40 mile an hour wind, sand can either pile up or erode over 3 inches. In 24 hours as much as three feet of sand can move. There is always space between the sand grains, so rainwater quickly goes into the soil. The rainwater goes about four feet deep into the sand and then begins to trickle down the slope of the dune. Down at this depth a number of species of algae and microscopic animalcules survive, for there is just enough filtered light penetrating the sand grains to promote photosynthesis for the algae.
In many places the water will trickle down to the hardpan soils beneath the sand, and go no further. As a result, in a number of areas small pools of water can be found between the dunes. Even if there is no water visible at the surface, its presence is indicated by black willow (Salix nigra) growing in the dunes. Animals will dig where black willow is to be able to get a drink of water.
Adaptations of plants to the sanddune environment
Dune plants have high rates of photosynthesis, and therefore can grow rapidly. The worst windstorms occur in March and April, and thanks to winter moisture, dune plants are stimulated for growth during the windy season. Many dune plants are unusually large and vigorous -- a condition called gigantism. Saltbush, normally 3-4 feet tall on tighter soils can reach 6-8 feet in the dunes.
Many plants form adventitious roots – if their stems are covered by sand, the stems sprout roots. Roots need oxygen, and deeply buried roots can not get the oxygen needed. Adventitious roots allow the plant roots to still get oxygen. Black willow, yucca, and mesquite all have such roots. When the sand blows away, the plants appear to be on stilts – stuck way up in the air on “long legs.”
Shinoak and mesquite form hummocks – large mounds. The hummocks become cemented together with the organic material (dead leaves and wood). Mesquite has nitrogen fixing bacteria in its roots, and those bacteria can extract the nutrients from the organic material. Purple three-awn (Aristada purpurea) also use nitrogen fixing bacteria – it exudes a slimy glue to form sandy sheaths around the roots and the bacteria live inside of the sheaths.
Sand reflects light and heat – so plants have a number of adaptations to combat that foe as well. Many dune plants are either hairy or have silvery leaves. The hair shades the leaf, and the silvery color reflects the light. Often such plants are green in the spring, when growth is of utmost importance, but then they turn gray and much hairier in the long hot summer.
Some plants, especially the annual wildflowers, produce incredible numbers of seed. Instead of one bloomspike, such plants will have dozens of bloom spikes. Some plants do not “release” their seeds – they stay in a capsule attached to the plant. When the plant dies, and is eventually covered over with sand, the seeds will germinate where the parent died.
Other plants produce large seeds – larger than those of related species in different habitats do. Shinoak acorns are over an inch and a half long. Shinoak is endemic to our sanddunes – it grows no other place in the world. Sanddune regions have more species of endemic plants than habitats in other regions due to the constantly changing habitat and the isolation of one dune field to another. The forest of shinoak from Crane to Fort Sumner is the largest oak forest in the world.
Related Resources
The following resources for learning more about the Sanddunes habitat are available on this website:
Essays
- Exploring the empty country of Los Medanos
- The gangsters of Wink
- Jerusalem Crickets
- Coyote Trailing in the Sanddunes
- New Species of beetle in the sanddunes
- Bringing back the boom Tympanuchus restoration and protection
- Maljamar sanddune archaeology
- Apache-Comanche treaty at Willow Springs
- A kangaroo rat meets a family that camps and rides ATVs in the sanddunes - Unpublished | Related questions
- Notrees to Kermit to Wink to Andrews
- Before civilization came to West Texas, traders served as news reporters
- Do you have a personal story of prairie chickens?
- This weekend – daytrip in the dunes and hear about the Comanche War Trail
- It is good to honor the memory of those that have served their people
- Charlie Goodnight, Prairie Chickens, and Fire; It only could happen on the Llano Estacado
- Bringing back the boom – “I love them prairie hens!”
- Help the Texas Parks and Wildlife Department find out where the prairie chickens live
- Cochran County was the last frontier of Texas
- Small town schools are great places for students to learn
- Revisit the horrors at Buffalo Soldier Hill June 23rd
- Will the Mallet Ranch become an Outdoor Education center?
- The 1953 exhumation of the Midland Woman in the Monahans Draw sanddunes
Photoessays
- Los Medanos, the red sanddunes
- On the trail of the lesser prairie chicken
- Critters of the sanddunes
- Plants of the sanddunes
- Scenes, oddities, and artifacts of the sanddunes
- Signs of Modern Man in the sanddunes
- Dunes in July
- What glories August rains bring
- Yoakum County, January, 2007
- The Lesser Prairie Chicken
- The Sanddune Lizard
- Radio Tagging
- Tadpoles and Toads in the sanddunes
- Vegetated Sanddunes
- Adaptations to the wind in sanddunes
- The mammals of the shinoaks
Pre-visit activity
This is a previsit activity for visitors who visit the Sibley Nature Center to learn about the sanddunes of the region. The answers to the following questions can be found on the Sibley Nature Center website either in the Essays section, or the Recommended Day Trips section.
1. Where do you find sanddunes in West Texas?
2. What is the most common tree or shrub that grows on the sanddunes?
3. What bird prefers to live in the sanddunes?
4. What insect opens its holes after a rainy spell in the fall in the sanddunes?
5. From where did the sand of the sanddunes come?
6. What was the name of the waterhole where Magoosh and Mow-way made a treaty?
7. What trees are found near the waterholes of the sanddunes?
8. If there is no standing water in the dunes, how do the animals get their water?
9. The few towns located in the sanddunes of the region were settled because of what natural resource discovered in the dunes?
10. Did Indians ever live year around in the sanddunes?
11. What are fulgurites?
12. What is the favorite activity of people of the 21st century when they visit the sanddunes?
13. Why do most woody plants die when they grow in the shifting and blowing sand?
14. Name three public parks west of the Llano Estacado where a person can visit sanddunes.
15. What owl takes over kangaroo rat burrows?
16. What colors can the hardpan soil between the dunes be?
17. How are spiders in the sanddunes camouflaged?
18. What does the nina la tierra eat?
19. What animal was accidentally released into the sanddunes near Monahans after a train wreck?
20. What do male sanddune staghorn beetles do to find mates?
21. What plant is always found with Tympanuchus?
22. Name a wildflower only found in the sanddunes (at least on this side of the Pecos River.)
23. What is the adaptation of sensitive briar to blowing sand?
24. What might cause the formation of the hardpan soil in the sanddunes?
25. What species of fox specializes in eating kangaroo rats?
26. What butterfly needs the shinoak for its larval food?
27. What common plant besides shinoak can survive being covered by sand?
28. Instead of using windmills to pump water, what do many modern ranchers use?
29. How big can shinoaks become?
30. How did early Indians process shinoak acorns to make them edible?