Stand on the bald knob of Emory Peak and you’ll see the Chihuahuan Desert rolled out below you with wave upon wave of mesas and mountains reaching out to the rim of the world. You can see for hundreds of kilometers in all directions. Not a house, not another human being, no living thing moves. Big Bend looks round, complete, as timeless and permanent as planet Earth itself and as beautiful and barren as the Moon. But Big Bend isn’t just one world, and it isn’t lifeless. It is many different worlds inhabited by countless creatures both great and small pursuing an extraordinary variety of lifestyles. These worlds may be as narrow as the mosquitofish’s spring-fed pool, as wide as the cougar’s hunting range, as dry as the pocket mouse’s burrow, as wet as the beaver’s pond, as open as the mule deer’s golden grassland, or as canopied as the Colima warbler’s forested canyon.
And the Big Bend world is not as changeless as it seems. Over an unthinkably long span of geologic time, and sometimes overnight, Big Bend has experienced sweeping changes that carried off whole communities of plants and animals. The great order of dinosaurs died out, and no one knows why, yet the scorpion and turtle have lived on here virtually unchanged through countless ages. Other plants and animals have staked survival on the long, slow process of adaptation to a changing environment. While one ancient lily evolved into grass, for example, another became the giant dagger we see today. Cholla cactus shades itself with thorns and the kangaroo rat manages never to take a drink.
In Big Bend as elsewhere, what animals live where is largely determined by what plants grow where. This in turn depends on such variables as the type and condition of the soil, elevation, climate, temperature, humidity, amount of cloud cover and direct sunlight, exposure to the wind, availability of water, and the drastic changes for bad and for good wrought by man. Yet there is nothing clear-cut or fixed about the edges of the different plant communities. The floodplain goes green or returns to dust depending on the river’s rise or fall. The shrub desert, the grasslands, and the woodlands all crawl uphill or down, putting out skirmishers along their lines of march. Within the national park natural forces are once again free to shape and reshape Big Bend’s different worlds. The battle seesaws back and forth between drought and ponderosa pine, tarbush and tabosa-grass, the eater and the eaten, the river and the rock, and the sun and the ageless land.
Broadly speaking there are four North American deserts: the Great Basin, Mohave, Sonoran, and Chihuahuan. The park lies within the Chihuahuan. This desert is bordered on three sides by mountains; the fourth abuts vast semi-arid plains. The Sierra Madre Oriental (East Mother Range) blocks winds from the Gulf of Mexico, except as spinoffs of summer hurricanes. The Sierra Madre Occidental (West Mother Range) blocks the westerlies. How can you recognize Chihuahuan Desert? By the lechuguilla plant (see [page 32]), which grows only in this desert.
In Big Bend you can turn back your personal clock to a time when mankind was still very obviously part of nature. You can walk in the desert and drink solitude as sweet as spring water or sit on the edge of a mountain meadow knee-deep in grass. You can watch the whitetail deer drift through the forest in a silence as perfect and ethereal as song, watching you but expressing no fear. For in the park you are just one more of nature’s creatures free to live and to grow in Big Bend’s self-healing, life-renewing world.
For many people the spirit of the desert is embodied in the vulture tirelessly circling empty skies above a bleak and barren land, the harvester of death keeping watch over desolation. But the desert is far from lifeless or the vulture wouldn’t be on patrol. The meager shrubs are miracles of adaptation and those seeming barren wastes rustle under the feet of countless busy creatures. Across the eons evolutionary selection has produced a different design for living within each species, yet all are subject to the same law.
Heat and aridity are the chief factors controlling all Chihuahuan Desert life. Most desert creatures stay in hiding during the day, keeping out of the sun in underground burrows, under rocks, or in the shrubs’ sparse shade. Many birds and most larger mammals don’t even visit the desert during the heat of the day. And although plants cannot crawl out from under the sun, nature has protected them by different means.
Probably the best way to see the living desert is to get out and walk and look. Study a plot of shrub desert in a single day and night. The most obvious desert dwellers, and sometimes the only living things you will see, are the plants. These vary from one stretch of desert to another because different species prefer different living conditions. But you will likely find plants in several categories, including woody and fibrous shrubs, cactuses, and other succulents. All have their own ways of resisting heat and drought, and all provide food or shelter to one or another special animal.
If success can be judged by sheer numbers, then the most successful desert shrub must be creosotebush, an evergreen bush that can make a living on the poorest and driest soils. You cannot mistake it for any other. The ground around it is apt to be bare and the individual bushes so evenly spaced that they look hand planted. This characteristic creosotebush pattern is probably caused by root competition for scant moisture. Each creosotebush has a long taproot reaching down maybe 9 meters (30 feet) to find underground water, while a network of shallow roots spreads far and wide to capture every drop of surface moisture. The plant protects itself from moisture loss by giving its dark green leaves a light-reflecting coat of resin. In the springtime, and often after rain, it bursts into brief yellow flower. It fruits in fuzzy little white balls, and you sometimes see a plant bearing both fruits and flowers.