Category Archives: Landscapes

The big picture.

Just Add Water: Annual Wildflowers in the Chihuahuan Desert

Prairie evening primroses dot a pasture near Fort Davis, Texas.

My friend, John Karges, and I were talking yesterday about the amazing spring that we’re having. He laughed and said “Add water and the desert will stir itself.”

How true.

We’ve had an extraordinarily wet winter and spring this year. Deep, soaking rains and frequent snow (and ice) storms encouraged a wildflower display that few can remember ever seeing in the Chihuahuan Desert region. Big Bend bluebonnets create a blue haze on the hillsides; the delicate, white petals of prairie evening primrose look like a tissue-box explosion in pastures; and mustard plants emit a perfume so sweet it’s cloying at times.

Big Bend Bluebonnets along the River Road in Presidio County Texas.

Even the stems of the cacti are so swollen with water they look like they’re going to burst. Instead, they’ve burst with flowers, dozens of blossoms covering a single plant.

The desert is in bloom. It’s a marvelous sight to behold.

Mustard wildflowers carpet a pasture in the Chihuahuan Desert near Marathon, Texas.

But where do all these flowers come from?

Most of the time, the Chihuahuan Desert is a pretty harsh environment. It’s dry (especially in the winter) and the rain that we do receive tends to come in the summer during highly localized thunderstorms that may drench one spot but leave a broad area dry as a bone.

To cope with the heat and the unpredictable precipitation patterns, desert plants have an amazing array of adaptations aimed at holding on to moisture: small leaves, fine hairs that protect the leaf surface, and a splendidly specialized photosynthetic process.

But during years like this one, we’re reminded of the most amazing adaptation of all: being an humble annual.

Annual plants are those that go from seed to seed in a very short time. When conditions aren’t favorable, the seed just doesn’t sprout. It sits in the soil, waiting for the perfect combination of moisture and warmth that will increase its chances of survival.

Dense patches of the annual wildflower curvepod scrambled eggs were common at higher elevations in the Chihuahuan Desert.

This life cycle isn’t unusual—in fact, approximately 13% of the world’s flora consists of annuals. But if you look at the flora of a typical desert, you’ll find something very different. In the aridlands of the world, annuals can make up 40% or more of the desert flora. Think about it. Nearly half of the plants growing in a desert won’t even make an appearance until there’s some hope of surviving long enough to be pollinated and set seed.

The seed of many desert annuals can survive for years—decades even—before the conditions are perfect for growth. On occasion, they get fooled, though. A good soaking rain followed by heat, wind, and dry conditions may spell doom for an overeager annual.  Long-term survival depends on mechanisms that discourage a portion of seed from growing even when conditions are just right.

But sometimes, spring conditions are just too favorable for any plant to remain snug in its seed jacket. This is one of those years. Good rains and warm day-time temperatures have encouraged the growth of hundreds of thousands of annuals. Early in the spring, clay flats in the Big Bend region were covered with turtleback—its gray-green leaves and cream-colored flowers forming a soft carpet across the landscape. Stands of lyreleaf twistflower (you’ve just got to love the name) sent their spikes of purple, urn-shaped flowers above the grasses, and curvepod scrambled eggs had even the plant enthusiasts scratching their heads. Where did they all come from?


Naked turtleback creates a green haze in the Chihuahuan Desert of Big Bend National Park, Texas.

 

Naked turtleback in the clay flats of Big Bend National Park, Texas.

The desert is truly spectacular this year and every week it changes. We’re still getting rain, so the show will go on. If you’ve been putting off your annual pilgrimage to the Chihuahuan Desert, it’s time to quit procrastinating, pack your camping gear, and come on out. This truly may be a once in a lifetime experience.

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White on White

Sunset at White Sands National Monument

Imagine this.

You’re standing in the Tularosa Basin of New Mexico during the last ice age—let’s say about 30,000 years ago. A huge lake shimmers in the background. Herds of mammoth and camels squelch through the mud leaving long lines of tracks. Packs of saber-toothed cats and dire wolves follow, waiting for the opportunity to hunt.

The lake is not unusual for this time period, nor this geologic setting. The Tularosa Basin is completely enclosed, bound by mountains to the east, west, and south; and Chupadera Mesa to the north. Water that drains into the basin has nowhere to go, so—depending on the climate—it either accumulates or it evaporates.

During the last ice age, water accumulated. Temperatures were cooler, evaporation wasn’t as rapid, and there was simply more water. At least eight lakes dotted the basins of the northern Chihuahuan Desert in Arizona, Texas, and New Mexico.

But the giant lake of the Tularosa Basin (now known as Lake Otero) is different. Although the water sparkles and shimmers, it’s not “pure.” The mountains surrounding the basin are partially composed of gypsum deposits hundreds of feet thick. As rain or snowmelt flows across the surface, the water slowly but surely dissolves the minerals of the rocks, and carries them away in solution to eventually accumulate in the lake.

Now, jump forward about 20,000 years. The climate is changing. Temperatures are rising and there is less precipitation. The mammoths and camels no longer roam the lake shores. The dire wolves and saber tooth cats have disappeared. The lake is drying up.

As the free water evaporates, millions of tons of dissolved minerals become concentrated in less and less water. Knife-like crystals of selenite begin to grow in the supersaturated muds of the lake bed. Eventually, the water of the lake is gone and the crystals lie exposed. Battered by the wind, cracked during freeze/thaw cycles, broken as animals walk across them, tiny chips and flakes of gypsum from the crystals are ground down into pure white, sand.

The wind picks up the sand grains and bounces them across the landscape. They begin to accumulate around rocks, bushes, and anything stable enough to stop their movement. Sand dunes begin to form.

Take another giant step through time. Pay your admission and enter White Sands National Monument, an amazing system of gypsum sand dunes. These gypsum dunes are quite rare. They require a set of specific conditions to form: a source of gypsum, arid conditions (so the gypsum won’t just dissolve away), and the wind to pile everything up. The three largest gypsum dune systems in the world are in the Chihuahuan Desert (White Sands, Guadalupe Mountains National Park, and Cuatro Cienegas, Mexico).

Although the dunes seem barren, they’re actually teaming with life. But you need to be on your toes (or more likely, your knees) to see much. Many of the animals spend their days dug into cool burrows in the sand or tucked into the shade of a bush.

But the main reason that you may not see anything is because the animals have changed color to blend with their environment. Instead of the normal browns and tans of the desert, the animals of white sands are bleached blondes.

This color adaptation is exciting to researchers. After all, the dunes are only about 7,000 years old, so to find white versions of common animals shows speciation moving along at a fairly rapid clip.

The Bleached Earless Lizard (Holbrookia maculata ruthveni) shows the greatest adaptation to its environment of all the lizards at White Sands. On the dark, volcanic rock surrounding White Sands National Monument, the earless lizard is a dark brown. The populations at White Sands are nearly pure white.

Bleached Earless Lizard

A Bleached Earless Lizard blends into the white sand.

This adaptation was probably originally a matter of natural selection. A dark animal on white sand is an easy target for a predator. Since the Bleached Earless Lizard is active during the day and prefers open habitats, the darker lizards would have been removed from the environment, leaving lighter and lighter animals to breed.

Today, predators are probably still picking off darker lizards, but the lizards themselves have changed their way of looking for a suitable mate. Field and experimental studies have shown that White Sands males will display preferentially to the lighter White Sands females when given a choice, thus continuing the selection for lighter animals. Although the Bleached Earless Lizard is considered a subspecies of the general population of Holbrookia maculata, these behavioral changes may indicate that a new species is in the making.

Bleached Earless Lizard

Bleached Earless Lizard (Holbrookia maculata ruthveni)

While other reptiles and animals such as pocket mice and crickets all show adaptation to the white sand, perhaps the most astounding group (evolutionarily speaking) are the moths.

Not much was known about the moths of gypsum dunes until 2006 when lepidopterist Eric Metzler was invited to conduct a long-term study at White Sands National Monument. He established a three km-long transect that cut across the four habitat types within the dune field: open dunes with no vegetation, interdunal spaces, the edge of the dunes, and open habitat outside the dune field.

Using light traps, Metzler and his colleagues collected moths at 11 sample sites along the transect. What they found was astounding. Among the thousands of moths collected were 24 undescribed species in 7 families. As you would expect, many of the new moth species are white or very pale in color.

As Metzler’s study shows, there is still much to be learned in the gypsum dune fields of the Chihuahuan Desert. So the next time you visit White Sands National Monument or venture out into the gypsum dunes at Guadalupe Mountains National Park, take a moment to wander. Watch for movement and holes in the ground. Imagine the life under your feet and admire the resourcefulness of the plants and animals that live here. Perhaps you, too, will discover a new species.

Also posted in Animals, Chihuahuan Desert, Geology, Insects Tagged , , |