Photo Essay
Clay playas - The most important ecological feature of the Llano Estacado
Over 10,000 clay playas dot the Llano Estacado - averaging at least one per square mile. Most have watersheds of less than a square mile, and some only a watershed of a hundred acres. The smaller the watershed, the less often a clay playa will fill with water. Before settlement, animals and Indians congregated at the playas when they were filled with water. Often a person could dig a few feet down and find water, and many of the early hand-dug water wells were first located at the edge of a playa.
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Most clay playas on ranch land are grazed. During a drought the only place a cow can find green grass is in the bottom of a clay playa.
Ungrazed clay playas often have curly dock (the black plant), the light blue spiny aster, and other tall weeds.
This clay playa has had brush invade the bottom - and it will remain until a heavy rain fills the playa and causes the shrubs to die. In the foreground is seepwillow, which moved onto the southern Llano Estacado in the rainy 1980s, and in the background is salt cedar and black willow. The green in between is a perennial ragweed. Only the black willow could survive standing in water for over a month.
Clay playas in the southern Llano Estacado have Lipan Clay - which in drought, will crack as it dries.
In the spring ( as early as late February) the non-native London Rocket Mustard will cover the bottom of the playa - especially if a long drought has killed the perennial grasses normally found there.
The bright green rescue grass, an annual, is also non-native. It was brought to the United States to provide winter grazing. The dead weed stalks of the previous year are seen to the right, but some just-leafing black willows survived the long drought that eliminated the perennial grasses.
On the bare soil, verbena bracteata is often found, and it starts blooming as early as late February.
In the rainy 1980s salt cedar invaded many of the clay playas on the southern Llano Estacado. In recent years the Natural Resources Conservation Service has been cost sharing with landowners to eradicate the shrub, which will often form dense thickets and suck up any rainwater that falls.
Salt cedar blooms produce millions of seeds, as seen in this photo. The seeds can travel great distances during strong windstorms, but they have to land in wet soil for germination - if they dry out any length of time, they do not germinate.
Ragweed produces copious amounts of pollen in late August and September. A stray damselfly settled down on this ragweed during its search for a stock pond with permanent water where it might find a mate. The dust like seeds travel during stong sandstorms.
Purple Texas Thistle is often found in a clay playa because of the extra moisture from what rains do come. When plenty of rain falls, the species is found in almost every habitat in west Texas. The seeds fly on strong winds.
Purple Nightshade is also common in clay playas. Its perennial rhizomatous roots spread and sometimes dense patches of the plant can be found. Its green berries were used to make asadero cheese - the juice of the berry splits milk into curds and whey.
Tumbleweeds often end up in a clay playa as well, and sometimes the bottom of a playa is completely carpeted with tumbleweed (and it is a non native plant, too.) This caterpillar remains unidentified by the staff of Sibley Nature Center.
When the soil stays wet long enough, the "nuts" (storage roots) of nutsedge send out leaves and roots. The "nuts" of sedges are important duck food, and can live even when water covers them. Sometimes the plant is not visible in a clay playa for years, and when conditions are finally appropriate, up comes the plants. The bluish leaf is that of blueweed, a perennial member of the sunflower genus. Farmers hate it, for it also has rhizomatous roots and is almost impossible to kill, just like nightshade.
In the foreground the small yellow blossoms of the blueweed. Surrounding it is the gray leaves of espantes vaqueros (ghost cowboys), an annual with one of the sweetest scents of the Llano Estacado.
Cocklebur is another plant that grows in playas, draws, and barditches. Its new leaves are poisonous to livestock. The species is reputedly the natural model for velcro - the seedpods stick together.
With enough moisture the nutsedge will bloom.
Kochia is another non-native plant. It was introduced as summer cypress, an ornamental plant grown for its fiery red and orange leaves in the fall. It also is another major pollen producer, bringing misery to allergy sufferers.
Careless weed is a native allergen, and will germinate in bare soil. Its new leaves, like those of tumbleweed, have been used as greens. Some species of careless weeds produce thousands of small seeds, and are sold today as amaranth - to be used like oats in a mush.
Chaff flower is more common south of the Llano Estacado, but has established itself in playas, bar ditches, city parks, and schoolyards.
Frogfruit is a perennial groundcover common in playas. It is the larval food source for small blue butterflies, and has been used as an ornamental groundcover. The grass is sideoats grama, the state grass of Texas.
Buffalo grass is the common grass in grazed playas, and in clay playas where prairie dogs live on the surrounding slopes. The tiny male blooms dance above the leaves. Blueweed grows among the buffalo grass.
Common annual sunflowers are a common feature of clay playas.
After an inch rain, the lowest part of a clay playa has filled with water. If no permanent water is near, toads come to mate and lay eggs.
Some clay playas cover several hundred acres. In such playas thousands of toads come to lay eggs, and afterwards millions of baby toads will hop away in two to four weeks, depending on the species. At least five species of toads use the clay playas of the southern Llano Estacado.
In the background is a circle of ripples, and the tadpole that came to the surface to gasp air is about ready to leave the water. When the tadpole begins to grow legs, it becomes an air breather.
Sometimes when a baby toad (toadlet) leaves the water, it still has a tail.
The toadlets are often met by garter snakes, hognose snakes, night herons, great blue herons, green herons and other predators. They will soon dig into the soil, after eating their weight in termites, and possibly not emerge again for a year.
Tadpole shrimp eggs lay dormant in the soil of the playa until it is filled, then they hatch, grow for a week or two, mate, and then die.
Tadpole shrimp filters the muck in the bottom of the playa for organic material and this one has a shore fly riding its back.
In shallow water, dying tadpole shrimp turn upside down, and sandpipers and other predators feast.
When the shallow water was inspected, a small green invertebrate moved about, but when the observer tried to catch it, it disappeared into the muck underneath.
On the leeward side of a big playa, the organic material from rotting vegetation forms a thick scum. This toadlet sank underneath when approached.
Floating in the water is larger pieces of organic material, and then foam created by the chemical reactions of decay lines the shore. Beyond is more organic material, now beginning to dry out.
Examined closely, the foam is attractive.
An oily sheen from the decaying organic material slings together in filmy sheets beyond the floating scum.
Running along the shore of the playa, on dirt that had become bare after being covered with water, this tiger beetle hunts smaller insects that come to the rotting vegetation. It is a different species from that found at salt playas.
In September, the first of the ducks that migrate to the playas for the winter have arrived, and they stand on the shore, sleeping after feasting on the rich and fecund life provided by the playa filling with water.
A black tern swoops over the playa, dipping its beak to catch fairy shrimp and other aquatic invertebrates. They migrate through the Llano Estacado every year, but if the playas are not full, they pass on through without stopping.
Summer resident Blacknecked Stilts nest along the shores of playas. When disturbed they fly around the intruder, fussing loudly.
Three coots bob in the water, with the ubiquitous West Texas oil pumpjacks in the background.
In the fall, phalaropes stop in the filled playas, and spin in the water, causing the aquatic invertebrates to be brought to the surface so the birds can eat.
As the water recedes, a person notices the small mesquite shrubs that invaded the playa during drier years have died because of having their roots inudated, and no oxygen left in the soil underneath.
Along the receding shoreline, bird tracks mix with fox tracks.