Drought, ‘invader’ trees killing cottonwoods : The government and Rio Grande Valley citizens are joining forces to curb the loss of the native bosque.

On a late spring afternoon, the Rio Grande Nature Center offers a welcome respite from the heat and hassle of the city.

Winding paths shaded by tall, graceful cottonwood trees lead to the banks of the river, muddy and swollen with snowmelt. A breeze wafts the sweet incense of Russian olive blossoms through feathery stands of tamarisk in the forest clearings.

Here in the Rio Grande bosque--the world’s largest cottonwood forest--people and wildlife share a high-desert oasis.

But something is wrong with this picture.

All along the 160-mile Middle Rio Grande Valley, the native cottonwoods are failing to reproduce, steadily giving way to Russian olive and tamarisk trees--aggressive, drought-tolerant plants from Eurasia that were introduced for erosion control early in the 20th Century.

Experts warn that within decades the cottonwoods will be overtaken by the invaders, and some native animal species are likely to vanish from the area as a result.

“As soon as the cottonwoods die out, there’s going to be something there to replace them,” said Anne Cully, a U.S. Fish and Wildlife Service plant ecologist.

Cully and other biologists say the cottonwoods are declining because of lack of water.

For most of the past 5 million years, melting snow in the southern Rocky Mountains fed spring floods that spread through the bosque and adjoining wetlands, scouring debris from the forest floor and replenishing soil nutrients.

When the floodwaters receded, patches of damp, bare earth lay ready for cottonwood seedlings to take root.

But flood-control and land-reclamation projects have drained thousands of acres of wetlands in the last 70 years and confined the once-meandering Rio Grande to a narrow, straightened channel.

As invader trees have crowded into forest clearings and the water table has dropped in the absence of flooding, suitable habitat for young cottonwoods has disappeared.

There is a growing consensus among valley residents and elected officials that something must be done.

Sen. Pete V. Domenici (R-N.M.) has been a moving force from the start. Domenici, who grew up near the river, said he realized the seriousness of the bosque’s plight only a few years ago.

As a result, Domenici convened a citizens’ task force, which pinpointed a number of political and technical problems. He also helped secure $1.4 million from the federal government for a study of the bosque by a team of government and university scientists.

In a report last fall, the study team set forth 20 recommendations, chief of which was that upstream dam operators should mimic the river’s natural flow by releasing enough water to flood the bosque each spring.

Cully, who helped write the study, says scientists understand that the dams, levees and irrigation ditches along the river will not be removed.

Every drop of the river’s water is spoken for, destined for downstream farmers, the state of Texas and Mexico.

At the same time, sundry agencies and political entities, each with a different mission, claim some authority over the river.

River-management changes must win support from the U.S. Army Corps of Engineers, the federal Bureau of Reclamation, the Fish and Wildlife Service, the Middle Rio Grande Conservancy District (which delivers irrigation water to farmers), the city of Albuquerque and other communities and six Native American pueblos.

“The way things are now, letting out enough water for over-bank flooding to get some (natural) processes back is not going to be possible,” Cully said.

Likewise, she said, scientists know the invader species are here to stay.

“We aren’t really ever going to be able to get rid of salt cedar (tamarisk) and Russian olive,” she said. “But we can try to prevent them from becoming the dominant species.”

Albuquerque’s Open Space Division, which administers the 5,000-acre Rio Grande Valley State Park, has re-established cottonwoods in areas that have been burned out or cleared of invader trees, says superintendent Rex Funk.

Funk says he hopes that current research into cottonwood regeneration--including a program of controlled flooding at Bosque Del Apache National Wildlife Refuge near San Antonio, N.M.--yields practical solutions.

Meanwhile, a state Bosque Management Task Force is recommending the creation of a new governmental entity to advocate on the behalf of the bosque in future river-management decisions.

This new body would probably be a management council made up of the interested communities and government agencies, said Laurence Lattmanm, chairman of the task force.

“There are groups that speak for various people,” he said. “But no one speaks for the bosque.”