Big Bend National Park

Desert Plants
Gorp.com

The popular image of desert-dwelling plants is the cactus—uncommonly adept at getting water and then miserly about hanging onto it. But there are other strategies or adaptations. One is waiting. Many desert annuals, unlike their counterparts in temperate climes, simply wait out the rains in their seed stage of life. If the rains don't come one year, the seed simply remains dormant. The mechanism is a germination inhibitor. Unless enough rain falls to remove this inhibitor, the seed ignores the wetting. This ensures that the developing plant will have enough water to complete its life cycle and develop new seeds before the next dry spell. This chemically patient seed may wait more than a year to germinate, but once it does, the plant will develop, flower, and fruit much more rapidly than a temperate annual would.

Creosote bushes ply another strategy. These regularly spaced shrubs look as though human beings had planted them, because their roots produce toxins that discourage the roots of other plants from intruding on their growing space. The small creosote bush leaves are coated with a resin so that they lose little moisture to the air. These combined strategies make creosote bush the most prevalent shrub in the park and enable it to prosper in all North American deserts. Creosote bushes that grow along a road tap pavement runoff and may grow twice as tall as those one row back from the road.

The chief indicator plant of the Chihuahuan Desert is lechuguilla, appearing as a clump of dagger blades protruding from the desert floor. The coarse, strong fibers of the lechuguilla are used in matting ropes, bags, and household items, which are, in a way, products of the Chihuahuan Desert. The lechuguilla illustrates an often misunderstood fact about the desert: The desert is a life zone, despite its aridity.

Cacti exemplify the survival strategy of water conservation. Instead of water-losing leaves, all cacti have spines. These also protect the plants from being trampled or eaten. (When you're all stem, you can't afford to be nibbled on!) The thick and fleshy stem presents reduced surface area and bears a waxy coating that inhibits evapotranspiration. The shallow root system spreads in a wide pattern to intercept rainwater as soon as it enters the ground. Cacti store water, serving as their own reservoirs for surviving long droughts.

The ocotillo is not a cactus; it's in a family by itself. With rain, the ocotillo develops leaves, but drops them when conditions are dry. This may happen several times per year. Wax extracted from the candelilla, or wax plant, is used in the manufacture of candles, waxes, gum, and phonograph records. In the rainy season, the stem fills up with a thick sap that, in the dry season, coats the stem as a wax and prevents evaporation. The wax seals in moisture, protecting the plant from drought. Desert plants display their most profuse flowering in springtime, which hits the lowlands in February and slowly ascends to the mountain heights by May. One glimpse of this floral richness and your image of the desert changes forever.

The mountainous regions of the park also host their own unique plant species. Some plants here are found nowhere else in the world. The Chisos oak grows only in Blue Creek Canyon. The Chisos agave, apparently a hybridized century plant, grows only in these mountains. A number of other plant species, such as the drooping juniper, which appears to need a good watering, grow in the United States only in the Chisos Mountains, but are also found in Mexico and elsewhere.


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