“The basis of all technique, considering the vast proportions of the creek valley erosion problem and the lack of funds for expensive construction works, must be some plant or plants which will hold banks…The plants adopted must be susceptible of cheap propagation from cuttings, must stand some drouth, make rapid growth, make a good mat of roots both above and below water table, and should be unpalatable to stock…[t]amarisk…holds out some promise.”
-Aldo Leopold, “The University and The Erosion Problem”, from the Bulletin of the University of Wisconsin (1916)
An increasingly common sight along waterways in the West, tamarisk (Tamarix spp.) looms large on tallies of the country’s most noxious weeds, garnering heaps of opprobrium from ranchers, farmers and conservationists alike—and not least because the plant reaches heights of twenty feet and forms impenetrably dense, scratchy thickets. More odious is its gluttony for water, its worthlessness as forage, its exclusionary growth habits that poison the soil. It is a singularly pernicious weed, supremely adaptive and nigh-invincible.
Introduced from Eurasia as an ornamental in the 1820s, Tamarix species—there are nearly one hundred total; eight so far have become established in Western states—made landfall in New England and thence radiated westward. San Francisco nurseries were offering it in 1850; by 1880 it had thwarted its cultivators and begun turning up, rogue and unwanted, in Texas, Utah and elsewhere.
In theory, planting tamarisk throughout the West seemed like a pretty good idea to homesteaders in the early 20th century: the shrubby trees grew where nothing else did, they provided shade and windbreak and sprays of lovely white to pink blossoms for half the year, and their robust snarls along streambanks seemed likely to curb erosion. But the plants quickly wore out their welcome. They appeared to actively degrade the land wherever they took root. And worse yet, they showed zero inclination to leave.
The reality of tamarisk’s wholesale invasion set in around the 1930s, as people began divining secrets to the weed’s alarming success. Tamarisk is a halophyte, capable of tolerating exceedingly saline soil—hence its common name, saltcedar—and it manages this feat by accumulating and excreting salts from specialized glands in its leaves. These leaves, plumose and briny, drop in the fall and, in decomposing, effectively salt the earth under and around the plant. Little grows in this seasoned soil but more saltcedar.
Tamarisk is also a phreatophyte, sprouting far-reaching roots that tunnel down to penetrate the water table. These taproots sometimes descend ninety feet in their aqueous pursuits. When the plant finally finds water, it uses the stuff prodigiously: A single adult tamarisk can transpire almost 16 gallons a day. Tamarisk is thus like a leaking fire hydrant, a faulty lawn sprinkler in Vegas, drawing down already-low aquifers and spritzing the air in its photosynthetic profligacy. In a drought-prone region, this is tantamount to burning dollar bills for heat—watching a precious resource go up in evapotranspirative smoke.
For several reasons, tamarisk is exceedingly difficult to control. It reproduces by roots, resprouts and seeds—a mature adult can annually produce half a million wind- and water-borne seeds more or less continuously over a season—so any effective treatment must contend with each propagative avenue. It’s fire-adapted and will resprout after a burn (or after cutting), so both measures require an herbicide accompaniment to be effective. It’s unpalatable to most everything except Diorhabda beetles, which have been imported from Eurasia experimentally, with cautiously sanguine results. Much to everyone’s consternation, the tamarisk abides.
Millions are spent annually in Nevada to control tamarisk. Treatment costs range from $50-$300 per acre, and it’s rarely a one-off sort of deal: one must treat, remove and repeat. It’s a tough, salty angiosperm—despite its superficially cedar-like appearance—and it’s dug its heels deep.