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The humble creosote bush proves its adaptability


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Southwest Wildlife

An Uncommon Common Plant

The humble creosote bush proves its adaptability over
tens of thousands of square miles of southwestern desert.

Story and Photos by Jay W. Sharp

 

 

Although the creosote bush (Larrea Tridentata) has exotic features something like you might anticipate finding only in a rare species, it is probably, in fact, the most dominant and widely distributed shrub of our southwestern deserts.

creosote 1
Creosote bushes grow in a wide range of Southwest desert environments like, for instance, this community on a rocky desert hillside. (All photos by Jay W. Sharp)

It covers literally tens of thousands of square miles.

As William G. McGinnies noted in his Discovering the Desert, the creosote bush's ability to adapt to diverse and harsh conditions exceeds that of "any other desert plant." Moreover, it ranks high on the list, if not at the top, of the longest-living organisms on the planet earth. It hosts a varied assortment of wildlife guests. It has even served, since prehistoric times, as a natural pharmacy for medications used by Native American and other peoples to cure a variety of ailments.

For all its exotica, the creosote bush — one of the most stable members of the desert plant community — will appear in force to greet you in almost any walk or drive through a Southwestern desert landscape.

 

 

Chosen Environments

 

creosote 2
In times of drought, the creosote’s leaves turn from dark green to golden brown.

As McGinnies indicated, the creosote bush can prosper — sometimes in pure stands — in a wide range of difficult environments. It can, for example, make its home hundreds of feet below sea level, for instance, in California's Death Valley, or more than 8,000 feet above sea level, in Mexico's Zacatecas mountain ranges. It grows quite happily "on well-drained deep alluvial soil, on the edges of alkaline flats, on sandy plains, and on the rocky slopes of volcanic hills." It not only dominates plant communities across the natural landscapes of our Chihuahuan Desert as well in the Sonoran and Mojave Deserts; it has asserted control of desert grasslands that have been overgrazed by domestic livestock or disturbed by development or by the plow.

It has survived events that offer us stunning insight into the resilience of life. In Gathering the Desert, for example, Gary Paul Nabhan recalled how ecologist Janice Beatly found that 20 of 21 creosote bush plants incinerated — at ground zero — by a thermonuclear explosion at Yucca Flat, Nev., in 1962 had fully recovered by 1972.

 

 

The Plant

 

An evergreen shrub that may range from 3 feet up to 12 or 13 feet in height, the creosote bush produces a spray of branches from its root crown with leaf clusters near the ends. In our Chihuahuan Desert, which usually receives slightly more rainfall than the Sonoran and Mojave Deserts, the creosote typically grows in a roughly spherical shape, leaving a fair amount of stem and leaf detritus and a slightly more nitrogen-enriched soil beneath the plant canopy.

creosote 3
In times of adequate rainfall, the creosote bears a good cover of dark green leaves.

The leaves — two quarter- to half-inch-long leaflets joined at the base — bear a resinous coating. They exude a creosote-like smell if crushed between your fingers or soaked by a shower. (Spanish-speaking peoples sometimes call the creosote bush the "hediondilla," or "little stinker.")

Creosote blooms — inch-long, yellow flowers with five petals — can light up the plant soon after a decent rain, especially from spring through the fall. Its fruits — grayish brown, fuzzy and corn-kernel sized — are composed of five fused one-seeded carpels, or reproductive organs. Once dropped, the fruits spread, not by floating on desert breezes nor by attaching to animals' coats, but rather by wind-blown tumbling across the earth's surface. They may resist breaking apart to release the seeds for some period of time.

The plant's root system includes a tap root that may extend several feet deep, often just reaching the caliche hardpan that underlies much of our desert region, and it has fibrous and relatively slender secondary roots that extend laterally for perhaps 10 to 12 feet and only about a foot beneath the surface.

 

 

Reproduction

 

The creosote bush can propagate either by seed germination or by cloning. Surprisingly, although the shrub produces abundant fruits, it reproduces relatively rarely by seed germination, according to the US Forest Service. This is because its fruits (shed during the fall here in the Chihuahuan Desert) release their seeds reluctantly, and then usually at the wrong place and at the wrong time for germination.

creosote 4
The bush’s blooms — inch-long, yellow flowers with five petals — can light up the plant soon after a decent rain, especially from spring through the fall.

A creosote bush seed, once it is released, probably stands the best chance of germinating if it is lucky enough to have been gathered, scarred and buried by a rodent in a burrow located in broken soil on a sloping surface — provided that fortuitous event happens concurrently with moderate rainfall and temperature. A seed that lies in topsoil through the desert summer, exposed to drought, high temperatures and daytime sunlight, will, most likely, simply die.

By comparison, an established creosote bush frequently produces new shoots — clones — from the outer edge of its root crown, according to the Desert Ecology website. Although the heart of the crown eventually dies, shoots continue to "gradually move outwards in a circle and then become separate plants, all derived from the original one." In effect, an original plant, from a germinated seed, continues its life through its clones.

 

 

Drought Tolerance

 

"Creosote is the most drought-tolerant perennial plant of North America," according to Desert Ecology. "It can live for at least two years with no water at all." A creosote bush can survive seasonal temperature swings from several degrees below zero Fahrenheit in the winter to several degrees above 100 in the summer.

During the hot summer season, as the day progresses, the creosote effectively keeps the margins, not the flat surfaces, of its leaves turned toward the desert sun. It thereby minimizes the leaves' exposure to solar heat and transpiration (the loss of water though a leaf's stomata, or pores). During extreme drought, the creosote's leaves turn from dark green to golden brown, and the plant effectively prunes itself, shedding many of its leaves and even branches to minimize its water requirements.

 

 

 

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