Killing tamarisk frees water

  • TRANSFORMATION: Spring Lake before treatment

    Keith Duncan photo
  • Spring Lake after treatment

    Keith Duncan photo
 

Note: This article is a sidebar to this issue's feature story.

Sometimes it takes a miracle to wake people up to an invasion. Sometimes it takes a lawsuit.

For the ranchers and farmers who make a living along the Pecos River in southern New Mexico, it took both.

The miracle occurred in 1991, when a body of water called Spring Lake rose from the dead. For years the 13-acre lake, which lies in the same valley as the Pecos, had been a popular destination for water-skiers.

But in the mid-1960s, tamarisk began crowding the shore, and within a few years the woody exotic had taken over every square foot of shore. Finally, the entire lake dried up, says Keith Duncan, a brush and weed specialist from New Mexico State University. "And I'm talking about a lake that was 40 to 45 feet deep."

The dry lake bed and the tamarisk along its shore persisted for the next two decades. Then in 1986, came the settlement of a jolting lawsuit brought by the state of Texas against New Mexico over Pecos River water. Under the settlement, New Mexico, the upstream state, had to provide Texas with substantially more water than was currently trickling across the border.

That sent New Mexico water officials scrambling. First, they began a water-leasing program, in which the state buys water from willing farmers and then delivers it to the Texas border, says Tom Davis, manager of the Carlsbad Irrigation District. The program has met the short-term need, but worried ranchers, farmers and irrigation companies kept looking for other sources.

Their thoughts naturally turned to tamarisk, which seemed to be the culprit in the death of Spring Lake, and which lined the banks of the Pecos. As an experiment, the group hired Duncan in 1989 to kill the tamarisk along the shores of Spring Lake with an aerial application of herbicides. At the time, the water table had dropped more than 20 feet below the lake bed's surface, says Duncan, but "within 33 months of the spray, the tamarisk was totally gone and we had water back on the surface."

Flush with the Spring Lake miracle, local water interests formed a more formal alliance to push for larger-scale tamarisk removal. Thus was born the Pecos River Native Riparian Restoration Project, perhaps the largest tamarisk removal project in the West. The project has garnered nearly a million dollars in state and federal funding, and for the past three years, project workers have sprayed some six miles of shoreline.

"If we could get just another foot of water per acre, that would be 20,000 to 30,000 acre-feet of water," says Davis, who serves as the project's president. "That's substantial water here in the Chihuahuan desert."

Duncan and Davis say it's too early to tell if they are getting water. They will monitor wells for the next three years, both for water quality and quantity. But this winter, water surfaced in an area where it hadn't been seen for a quarter century, says Davis, "and it hasn't even been a particularly wet year down here." He suspects that natural springs usually sucked dry by tamarisk may now be reaching the surface.

Environmentalists, keen on returning some plant diversity for wildlife along the Pecos, have generally supported the project. But some voice concerns about the herbicides used to kill tamarisk - a mixture of Arsenal (imazapyr) and Roundup (glyphosate) - and question the commitment of the agricultural interests to the revegetation effort.

But Davis says members of the Pecos River restoration project are intent on restoring native vegetation. This summer, crews will burn some of the dead tamarisk and sow seeds from a couple of varieties of native grass, he says. He hopes the weather will cooperate.

"It's a shot in the dark. If we hit it right (with the summer rains) the grasses will grow and we'll be heroes and take the credit; if we don't, well, we'll find someone else to blame it on," jokes Davis.

Besides bad weather, there is also the chance of re-invasion by tamarisk, especially since the plant's seeds can travel in water and air, and the Pecos River above the control site is full of tamarisk. Duncan says that a flood could wreak the most damage, because it would spread tamarisk seed over the entire site, even though in other places in the West, managers are using controlled floods to give native plants an advantage over tamarisk.

"We've got a number of reservoirs which we think we can use to prevent floods," he says. "But I'm not worried about floods or re-invasion if we can get the natives re-established."

Some scientists question whether removing tamarisk will really yield more water in the long run, especially if the native vegetation comes back. "All plants take up water," says ecologist Bob Ohmart of Arizona State University, especially native cottonwoods and willows. "Federal scientists have never been able to show that tamarisk use a drop more water than our natives."

But Davis and Duncan maintain that cottonwoods and willows never lived in great abundance along the Pecos because of the river's high salinity levels. Instead, a variety of more shrubby plants, including four-winged saltbush, grew along the river, and these species do not use as much water, Davis believes.

If the project yields water and returns native vegetation to the banks of the Pecos, Davis says the coalition will likely expand its destruction of tamarisk. "We've got 30,000 acres more of the stuff just waiting out there."

You can contact ...

* Keith Duncan at New Mexico State University, 505/748-1228, e-mail: erbc@nmsu.edu