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River Lost, River Found: The Colorado and San Pedro Rivers.

by Tom Leskiw

Somewhere along the line, cottonwoods became my favorite tree. It’s natural to want to root for the underdog: of the 106 forest types in North America, the Fremont cottonwood/ Goodding willow association is considered the most threatened. In Arizona, a scant 10% of this original habitat remains. Causes for its demise are many: dams, overuse of surface and groundwater supplies, cattle grazing, the elimination of beaver, clearing for agriculture, and the invasion of exotic plants. The insidious connection between dam building and the disappearance of old-growth cottonwood forests is this: successful cottonwood seed germination depends on clean seedbeds created by high, flushing flows. Dams, which are constructed to modulate flows, eliminate larger-scale floods. In addition, they trap sediment, robbing the river system of the material needed to form bars that support streamside vegetation.

  Cottonwoods at Grand Canyon National Park.
  Cottonwoods growing at Burro Spring on the Tonto Platform, Grand Canyon National Park.
Photo courtesy National Park Service.

Riparian areas—those narrow bands of green vegetation along the banks of rivers and streams and near springs, bogs, lakes, and ponds—are critically important to the health of arid lands. In Arizona and New Mexico, at least 80% of all vertebrate wildlife species use riparian areas at some stage of their lives, and more than half of these species are considered riparian obligates. In the Southwest, riparian areas support a higher breeding diversity of birds than all other western habitats combined. Many of the areas that once supported Fremont cottonwoods have been colonized by tamarisk (Tamarix sp.), an aggressive, water-sucking invader from Eurasia, also known as salt-cedar. Research confirms that most birds shun streamside areas where tamarisk is the dominant plant. From any perspective—total avian density, number of birds present, bird species diversity—Tamarix chinensis groves have a lower value to birds than any type of native tree community.

In 2001, I attended the 3rd biennial conference of the Association for the Study of Literature and the Environment. I was eager to go, in part because I’d signed up for a post-conference 15-mile float trip down the Colorado River. Still on a high brought on by activities such as a writing workshop by ethnobotanist Gary Paul Nabhan, a poetry reading by Simon Ortiz, and keynote slideshow by singer, actress, and river runner Katie Lee, I boarded the bus for the put-in at the base of Glen Canyon Dam.

What kind of wacko floats the Colorado, silently seething, “Man, where are all the cottonwoods? They should be here.” A wacko that bears a striking resemblance to me. Granted, much of the river flowed through a narrow bedrock canyon—unsuitable for the formation of bars. However, in those areas where sediments had been deposited, cottonwoods were virtually nonexistent. I tallied the number I saw: fifteen miles of river and one lone cottonwood to show for it. Tamarisk, however, was abundant.

I’m proud to be a scientist, but there’s a downside. The techniques we use—those lenses through which we examine our world—are both a blessing and a curse. We’re trained to look beyond today’s “snapshot” of a landscape. It’s a good gig, really: getting paid to have visions. Good scientists are capable of conjuring and maintaining these visions— “desired future condition” and “natural range of variability” in jargonspeak. Why couldn’t I just let go, float the river like everyone else? Be content with the sacred triad of sun, water, and camaraderie?

Colorado River at Grand Canyon.  
Prehistoric granaries above Nankoweep in Marble Canyon, Grand Canyon National Park.
Photo by Mark Lellouch, courtesy National Park Service.

The media has trumpeted recent attempts by the U.S. Bureau of Reclamation to mimic spring flood flows on the Colorado. However, the 1996 controlled flood was smaller than all but 10% of pre-dam floods between 1922 and 1962. The amount of water being released is insufficient to accomplish the work that the river needs to do—scouring bars, uprooting exotic or decadent vegetation, and creating fresh seedbeds. While the trip down the river was enjoyable, my memories are of sterile salt-cedar flats, instead of the previous lush river groves that supported yellow-billed cuckoos. The Colorado—Spanish for red-colored—no longer lives up to its name. Robbed of sediment, it is often verde, a shade of green—reduced to a shadow of its primal power.

Conference over, I rendezvoused with my wife Sue in Phoenix. Her conference had been in Denver. We loaded the rental car and set out for southeastern Arizona. Despite the late-June heat, there was a place that I just had to share with her.

The San Pedro River originates in Mexico, flowing northward to its confluence with the Gila River near Winkleman, Arizona. The San Pedro’s claims to fame are numerous: it is the only permanently undammed river in the southwestern United States, supports 75% of the nesting gray hawks in this country. Over one hundred of the 355 species of birds recorded here remain to breed along this narrow ribbon of life. In addition, the river serves as stopover habitat for an estimated 5-10 million migratory songbirds annually. For these reasons, it was the first Globally Important Bird Area to be designated by the American Bird Conservancy, in 1996.

Colorado River, brush, and Grand Canyon.  
Brush and small trees along the Colorado River as it leaves the Grand Canyon.
Photo by Rhett Butler, MongaBay.com.

Acquired by the U.S. Bureau of Land Management in 1987 from the Tenneco Corporation, the 56,000-acre preserve is arguably the most successful modern-day conservation story in Arizona. The area is by no means pristine: by the late 19th century, an estimated 100,000 cattle grazed within the headwaters of the San Pedro River Valley. A series of events that, in sum, constitute a veritable watershed “management” Murphy’s Law, speaks to the marvelous capacity for riparian areas to at least partly recover, given time. A drought between 1890 and 1893 caused cattle to die by the thousands. Meanwhile, fur trappers removed an estimated one million beaver from the area. The extirpation of beaver—a keystone species—in 1900 was especially devastating to the watershed.

Over the past 30 years, scientists have clarified the definition of a keystone species:

  • Its members have a large effect on community structure and function (i.e., high overall importance)
  • These effects are disproportionately large relative to abundance (i.e., high community importance)

Beavers, through their dam-building efforts, had reduced the erosive power of the San Pedro. The resulting stair-stepping watercourse buffered the watershed during seasonal floods. Large pools spread the water outward, fostering a network of wetlands that were effective in recharging the water table.

The devastated rangeland, shorn of grasses by too many horses and cows, had lost its ability to hold soil in place when the rains returned in 1893. The once stable, slow- moving, marshy perennial river transformed into an unstable, flood-prone, intermittent stream. Stream downcutting largely eliminated the wetlands, resulting in a lowering of the water table. In 1870, Arizona rancher H.C. Hooker had described the San Pedro River Valley as “having an abundance of timber with large beds of sacaton and grama grasses. The river bed was shallow and grassy … its banks with luxuriant growth of vegetation.”

San Pedro River.
  The San Pedro River in the San Pedro National Riparian Area.
Photo courtesy Bureau of Land Management.

His description of the same area in 1900 told a different story: “… The river had cut 10 to 40 feet below its banks with its trees and underbrush gone, with the mesas grazed by thousands of horses and cattle.” Native Americans had dwelled for 11,000 years along the San Pedro with little impact, yet a mere 20 years was all that was needed for Anglos to wreak major changes.

Then, in 1988, the BLM instituted a 15-year grazing moratorium, eliminating the season-long cow-calf regime of 6,500-13,000 animals. The rapid rate of vegetative recovery along the San Pedro has stunned even seasoned ecologists. Since 1988, 24 of the 47 bird species deemed to have a riparian affinity have increased significantly, with only three species experiencing significant declines.

Sue and I arrived at the San Pedro House—the hub for a network of trails—on a day that dawned clear and warm. Being heat wimps, we like to hit the trail early, reveling in the frenetic bird activity that occurs before the temperature rises. Fire-engine-red male summer tanagers foraged on the serrated, delta-shaped leaves of Fremont cottonwoods. As the air heated, the vaguely similar songs of dueting yellow-billed cuckoos and white-winged doves melded into one. An impossibly red male vermilion flycatcher hawked insects. Suspended languidly in the water, a Sonoran mud turtle poked about slowly, "going nowhere in plenty of time," as N. Scott Momaday would say. Blue grosbeaks sang from their perches. Below them, hopping through the crisp cottonwood leaf litter, were scores of juvenile toads.

We continued our way upstream, the trail soon bringing us to Kingfisher Pond. Green kingfishers are sometimes here, so we carefully scanned likely perches along the pond’s margins. Beaver had been reintroduced, and their numerous calling cards—chewed cottonwood stumps—could be seen poking out of the still water. Experiencing such abundance breathed life, feather, fur, and bone into additional attributes of the San Pedro: the highest densities of breeding birds in all of North America have been reported from southwestern riparian woodlands. In addition, the San Pedro hosts the largest concentration of Yellow-billed Cuckoos in the western United States.

As we continued along the loop trail that paralleled Garden Wash, I reflected on the activities—past, present, and future—of those who call this area home. After experiencing the altered, diminished riparian areas along the Colorado River, our visit to the San Pedro was a much-needed tonic. However, the river’s future isn’t assured, owing to rapid groundwater withdrawals and the re-evaluation of the grazing moratorium that is currently underway.

Aerial photo: San Pedro River.   Aerial photo: San Pedro riparian corridor.  
San Pedro River and San Pedro riparian corridor.
Photos by Adriel Heisey, courtesy The Nature Conservancy.

A dream came true for me in January 2004, when we found property to buy a long stone’s throw from the banks of the San Pedro. I returned in early March to close escrow and perform some repairs. It was snowing the day that escrow closed. The next day, the bright Arizona sunshine was back in action, melting the snowpack in the Huachuca Mountains. My timing was fortuitous, as the nearby city of Sierra Vista was hosting the 11th Annual High Desert Gardening and Landscaping Conference the next weekend. During the conference, I received a wealth of information on plants that I could expect to flourish in our yard.

For me, though, the best part of the conference was the active participation of the University of Arizona’s Cooperative Extension, which had a very informative booth. Furthermore, staff members were available to visit one’s property, evaluate the conditions at the site, and offer suggestions for appropriate plants to use (i.e., those that demand little water). Their suggestions regarding easy-to-incorporate techniques of water conservation, re-use, and water harvesting made perfect sense. I left the conference feeling positive about the prospects for our culture to make some overdue course corrections about our attitudes toward water. In my mind, the death of the San Pedro just isn’t acceptable.

San Pedro River: Last Great Place poster.
  The Nature Conservancy's Last Great Place campaign includes the San Pedro River.
Graphic courtesy The Nature Conservancy.

Several weeks later, my working vacation winding down, I drove out to the river. March had been unusually warm. Cottonwood buds had broken, their nascent green leaves foreshadowing the waves of migratory birds soon to follow. The snow-capped peaks, looming above a desert river, were stunning. Mountain canyons—Miller, Carr, Ramsey, and Sawmill—whispered seductively. I’ll return soon, I promised. The sight of a snowy eastern escarpment towering above a glistening desert river triggered in my mind a scenic analog that once existed in my adopted home state, California. A place of beauty, where a shining range of light casts shadows upon a desert watercourse: the Sierra Nevada and the Owens River.

The tale of how L.A.’s thirst for water diminished the Owens River and obliterated Owens Lake should serve as a cautionary message for those of us who grapple with water issues today. Buying a second home in the Desert Southwest was not an easy sell to Sue. Not wanting to contribute to the problem, she had resisted the idea of spending even part of the year in this land of little rain. However, friends who live in southeastern Arizona say that they will welcome our presence, especially because we expect to be involved in spreading the dharma of water conservation and re-use.

Will we wind up being part of the problem or part of the solution? Is there a middle ground? It’s my hope that, by exercising foresight and creativity, we can bequeath a healthy San Pedro River to future generations.


Tom Leskiw works as a hydrologic/biologic technician for Six Rivers National Forest in Northern California. When not in the field observing two of his favorite subjects—birds and trees—he is likely to be found at his computer writing about them.
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Friends of the San Pedro River

Grand Canyon National Park

Grand Canyon National Park Foundation

Rivers Foundation of the Americas

San Pedro Riparian National Conservation Area

San Pedro River Factsheet by Southwest Center for Biological Diversity

The Nature Conservancy's The Last Great Places: San Pedro River

Tour the San Pedro River with the Summer Tanager

Upper San Pedro Partnership

U.S. Fish & Wildlife Service Southwest Region




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