The alien saltcedar - tamarisks

American Forests, Jan-Feb, 1995 by Peter Friederici

Tough, prolific, and exclusionary, the tamarisk is "planta non grata" in the Southwest, but it's apparently here to stay.

It's probably just as well that the name of the first person to plant a saltcedar in the Southwest is lost to history. He, or she, was no doubt praised some 200 years ago for the inspiration that brought a source of shade and wood to the sun-baked desert. But today's reaction would be quite different.

In two centuries the alien saltcedar has established itself along numerous rivers and reservoirs, where biologists and land managers regard it as a noxious plant pest. It stands accused of degrading wildlife habitat, ruining the recreational amenities of riparian areas, wasting scarce water, and even increasing the severity of floods. Its impact has been especially great on riparian woodlands, which support the greatest quantity and diversity of life--both animal and human--in the desert landscape, and which are among the most imperiled ecosystems in North America.

Saltcedar's negative effects are a direct reflection of exactly those qualities early settlers in the Southwest found so positive. Its roots stabilize streambanks against the flooding typical of desert washes and rivers. Its foliage provides precious shade for poultry and livestock. It can be cut for firewood. Its abundant sprays of white or pink flowers provide some ornamentation in an area where the vegetation often seemed alien, if not outright hostile, to new immigrants.

And it is remarkably hardy. "It'll grow anywhere it can get its feet in water," says Mary Irish, director of horticulture at the Desert Botanical Garden in Phoenix. "It's extremely tolerant of any soil, including salty soil, and it doesn't mind the heat at all."

The tamarisk family is native to southern Eurasia, and over time, several species were introduced here. One--the evergreen athel tamarisk or Tamarix aphylla--grows at least 50 feet high and is a valued shade tree. Beekeepers say its flowers produce excellent honey. The other species, which are deciduous, are referred to as Tamarix chinensis, T. ramosissima, and T. parviflora. Because they appear to hybridize, and are virtually impossible to tell apart, some botanists consider them all to be members of the same species.

This is the shrub or tree called saltcedar, a name whose latter half refers to tiny, scaly leaves that resemble cedar scales. And it is saltcedar because the plant exudes salt from glands on its leaves. Grab a branch, and you end up with a residue thick enough to taste. When the leaves drop in the autumn, they pass that salt to the soil, which may eventually become too saline to support most native plant species.

Given ample water and space, a saltcedar can become a medium-sized tree--the largest known in the U.S. is a 44-footer in New Mexico. In the wild, though, it more commonly forms dense thickets of many-branched shrubs, all growing to a height of 15 or 20 feet. The foliage is so dense that almost nothing can grow under it.

Saltcedar is not really adapted to aridity. It grows only where water runs near the surface, and it is spendthrift--a large specimen uses perhaps 200 gallons a day. It has been estimated that all the saltcedar in the Southwest uses, per year, twice as much water as all the cities of southern California.

Dense stands of saltcedar trap sediment during floods, narrowing water channels and perhaps increasing the severity of subsequent floods. Along the Colorado River, saltcedar thickets have overgrown many beaches long favored for camping and recreation.

Wildlife is far less abundant in saltcedar thickets than in supplanted native woodlands, largely because native plants act as host to many more insect species. A study along the lower Colorado River showed that during the winter an undisturbed native woodland of cottonwood and willow supported an average of 154 birds per 100 acres. Only four birds lived in an equivalent area of saltcedar. Few birds nest in saltcedar, perhaps because the feathery leaves do not provide the same protection from intense summer heat as do the broad leaves of cottonwoods and willows.

It is extremely difficult to destroy an established thicket. "After any environmental calamity it comes back stronger than before," says William Neill, a saltcedar-control advocate in southern California. "It is not balanced by natural predation or diseases, so it displaces the native species. It survives extreme environmental conditions very well--fire, salinity, immersion, drought, dense shade."

And its reproduction is copious: A single saltcedar can produce up to half a million winged seeds in a year--seeds so tiny it takes 100,000 to make up a gram. When they sprout, the seedlings can grow up to 10 feet in a year.

Given such profligacy, it's no surprise that saltcedar escaped the homesteads and pastures where it had been introduced; by the early 20th century it was spreading quickly. On Lake McMillan, a reservoir on New Mexico's Pecos River, saltcedar was unknown before 1912. By 1915 it had spread to 600 acres of delta land. By 1925 it covered 12,300 acres.