Rio Grande Cottonwood
The Rio Grande cottonwood is also popularly known as the Fremont cottonwood, common cottonwood, valley cottonwood, marsh cottonwood, alamo and alamillo. Its scientific name reflects its membership in the poplar family, which includes the poplars, the aspens and the other cottonwood species. Like many Southwestern plants, its scientific name also bears the stamp of John C. Fremont, the famed 19th century "Pathfinder of the West."
The Water Tree
The Rio Grande cottonwood, a welcome sight to pioneers in the desert because it often signaled water, typically reaches 50 to 60 feet in height, with a trunk of three feet in diameter. Some of the grand old cottonwoods in the Rio Grande Valley have reached 90 feet in height, with trunks five feet across. In open areas, the tree may divide into branches near its base, producing a spreading crown. In closed stands, the trunk may ascend tall and straight, nearly free of branches near the base, producing a comparatively small crown. The tree has roughly deltoid-shaped, toothed leaves which are attached alternatively along the stems. The flattened leaf stems, or petioles, permit the leaves to twist in a breeze, producing a soft rustling or fluttering sound. The wood is moderately light, soft and relatively weak. It is uniform in texture and usually straight grained.
The Rio Grande cottonwood reproduces by seeding, unlike many other flood-plain trees which regenerate by sprouting. It flowers in the spring, before it leafs out. It releases its seeds, each carried by a downy white tuft, or "parachute," in anticipation of traditional spring floods and winds, the principal mechanisms for dispersion. A mature Rio Grande cottonwood can produce as many as 25 million seeds in a season, covering wide areas with a blanket of "cotton."
Once free, a seed, with a viable life of no more than a few days to a few weeks, begins a desperate, and usually a hopeless, race for survival. It must land on moist alluvial soil and swiftly extend roots toward subsurface water. If the soil dries too quickly, the seedling dies. Given sufficient moisture, however, the seedling may put down roots three- to five-feet deep in the course of a summer. If it survives trampling, fire, flood and animal feeding, it will become a fast-growing tree, always heavily dependent on a reliable water supply. (The Rio Grande cottonwood’s cousin, the eastern cottonwood, is the fastest growing tree in North America.) When fall comes, the Rio Grande cottonwood pays with gold leaves for its purchase of water.
Its Ecological Role
Rio Grande cottonwood seedlings and saplings provide food for deer, rabbits and field mice. Larger trees provide food for beavers as well as wood for the animals’ dams and lodges. Mature trees provide nesting for a variety of birds. Stands provide habitat for wildlife.
Prior to the Spanish entradas, which began in the late 16th century, the Rio Grande cottonwood dominated many of the low land riparian or, stream-side forests of the Southwest, from western Texas and northern Mexico north to southern Colorado and west to California. It grew at elevations ranging from 2500 to 7000 feet.
Today, the Rio Grande cottonwood, as well as the riparian forests, are under intense assault. Along rivers and streams throughout the Southwest, man has dammed, re-channeled and regulated stream flow, often holding back the spring floods which would otherwise disperse Rio Grande cottonwood seeds and water the river bottoms. He has drawn down water tables, putting them beyond the reach of Rio Grand cottonwood roots. He has cleared watersheds, allowed detrimental salt and mineral buildups, developed roads, opened mines, effected intense overgrazing, polluted the water, trampled and overrun new forest growth, introduced aggressive alien species, and eliminated or severely reduced beavers and other wildlife. The Southwest’s riparian forests are now among the most threatened woodlands of North America.
Surprisingly, the Rio Grande cottonwood, the "water tree," has found a home in south-central New Mexico’s White Sands National Monument, an environment too harsh for 75 percent of the plants from the surrounding Chihuahuan Desert. In this area of little annual rainfall, blistering summer heat, relentless spring winds, impoverished soil and eastward marching sand dunes, the Rio Grande cottonwood has eked out a tortured existence by capturing and securing soil in the interdune flats and extending roots to a relatively shallow water table.
The Rio Grande cottonwood’s affinity for water became a metaphor for Southwestern pueblos’ reliance on water. Pueblo carvers shape the tree’s roots the conduit to water into kachina dolls, spiritual icons of the deeply religious agricultural peoples of an arid land. Originally, carvers took the roots from trees which had been undercut and swept down rivers and streams by flood waters. Today, as the cottonwoods and riparian forests vanish, the carvers must often buy their wood, frequently at exorbitant prices.
The Rio Grande cottonwood’s disappearance from the banks of Southwestern streams and rivers can now be regarded as a metaphor for our relentless abuse of the environment of the desert Southwest.
Jay W. Sharp
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