Life in the Riparian Zone:

The Hassayampa River Refuge


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The Hassayampa River flows underground for most of its course, but near Wickenburg, crystalline bedrock forces the river above ground. The year round surface flow supports a lush willow cottonwood forest, one of the rarest landscapes in Arizona. According to the Arizona Sonora Desert Museum, only 0.5% of the land of Arizona is riparian. The Nature Conservancy purchased the land to preserve the riparian habitat and protect its biological diversity.

On a weekend in January, Phil and I visited the refuge. In the restored old ranch house which served as the main office, we signed the guest book and chatted with the old gentleman staffing the visitor center. The small staff is supplemented by volunteers who help to maintain the trails and explain that the preserve receives all of its funds from donations, not from the considerably deeper pockets of the International Nature Conservancy.

The Hassayampa preserve was once the Frederick Brill Ranch, a cattle ranch, stagecoach station, and orchard owned by a Russian immigrant around 1871. In 1913 the ranch became a guest ranch, and in 1986 it became a private nature sanctuary owned by the Arizona Chapter of the Nature Conservancy.

Arizona has relatively few free-flowing streams and rivers remaining. The federal government, ranchers and farmers have dammed and diverted streams for power, flood control, and sustenance for crops and livestock. Large metropolitan areas such as Phoenix and Tucson have drained their aquifers and lowered the water table so much that the Salt, Gila, Santa Cruz, Rillito, and Pantano Rivers flow underground except in times of flood. To reduce flooding damage and control erosion, cities have channeled streams and cleared vegetation. The result is faster stream flow and increased flooding downstream. If riparian areas had been allowed to stand, the thick vegetation would have slowed the flow of water, allowing it to sink underground, replenish the aquifer, and provide habitat for hundreds of bird species, fish, amphibians, insects and mammals such as deer, beaver and otter.

At the Hassayampa preserve, Phil and I willingly donated our $5 and picked up a postcard for 20 cents that promised to help us identify the tracks of animals on the trail. It had rained the day before and we were hopeful of seeing traces of wildlife, if not the wildlife itself.

The refuge is renowned for its willow-cottonwood forest, but we couldn't tell the difference between the mostly leafless trees until we read that the cottonwood, at 65 feet or more, towered over most of the other trees. In late spring or summer we would have been able to recognize the willow by its narrow leaf and pink-to-purple orchid-like flower.

Cottonwoods require occasional flooding in order to scour the seeds and deposit them in new, wet sandbars, where they can germinate. With a constant source of water, the seedlings grow quickly to their mature height of up to 100 feet. A large cottonwood transpires 100 gallons of water a day, making cottonwoods rare anywhere in Arizona except along perennial streams. The cottonwoods, along with the willows, seepwillows, tree tobacco, and other lush vegetation, stabilize the soil along the banks of the stream, and provides shade, food and shelter for wildlife.

The cottonwood is one of the favorite nesting places of birds and may explain the abundance of birds and birders at the refuge. Neither of us being birders, Phil and I stared blankly at the bird board at the visitor center, not recognizing a single bird listed. Eventually we did manage to match one bird we spotted with a photograph at the visitor center. The only other wildlife sighting was the spider we saw perched on a sign in the visitor center.

Dusky Flycatcher, I think
Phil and I saw several tracks along the river and decided, upon closer inspection, that the maker of the tracks was a racoon. Other, less defined tracks might have been mule deer or peccary, but Phil heard a cow mooing and decided that it probably had a more domestic source. There were probably mule deer, peccaries, coyotes, rabbits, and skunks nearby, because the visitor center exhibited their scat. Before the rivers had been dammed, drained and diverted, we might have seen otters and beaver along the banks. In 1833 a trapper named James Ohio Pattie camped in a thick grove of timber beside a river which may have been the San Pedro. He trapped 200 beaver in seven days and described ducks and geese on the river. Today, the San Pedro holds little water and no timber or beaver.

According to the Desert Museum's sonorensis, the riparian soils support denser vegetation than surrounding desert because there is more organic matter and enough water to leach salts from the soil. Riparian trees that require moist soil but not flooding, as cottonwoods and willows do, are sycamore, ash, walnut and alder. On the edge of the water you might see grasses and horsetails. In the water you might find endangered native fish such as Gila topminnows, Sonoran chubs and Razorback suckers. On the banks there may be leopard frogs, tree frogs, bullfrogs, garter snakes, Sonoran mud turtles and tiger salamanders. Hunting these small animals might be hawks and bald eagles, coyotes and bobcats.

There is a line of palm trees at the Hassayampa Refuge. Phil was surprised, thinking that palms are not native to the desert but are imports that came with transplanted Californians. There are two native palms in the Sonoran Desert region, however: the desert fan palm and the thread palm. Palms require water at their roots but can survive summer heat and fires. In California, palms often mark a fault line because the fine clays resulting from the grinding of rocks along a fault form an impermeable layer which holds water. This enables the palms to keep their feet in the water and their heads in the sun. In western Arizona, stands of desert fan palms are found in springs, seeps, and desert streams.
The tamarisk, or salt cedar, is an exotic species that threatens native riparian communities. It is extremely hardy to drought and fires and produces a phenomenal number of wind-blown seeds. Its hardiness and reproductive abilities enable it to invade territory that formerly belonged to the cottonwood and willow; it then takes up enormous quantities of water and concentrates salts around its roots, preventing less salt-tolerant plants from establishing themselves. It is almost impossible to eradicate once it has taken over a riparian area. Poisoning is more effective than burning or physical removal ("tammy whacking"), but requires vast quantities of chemicals to clear the rivers. Near the Hassayampa preserve, volunteers are invited to engage in "tammy whacking" periodically to try to prevent tamarisk from invading the refuge.

According to the Nature Conservancy, 90% of the critical riparian areas in the Sonoran Desert have been lost or degraded in the last century, and this loss threatens at least 80% of Arizona wildlife, which depend on riparian areas for survival. The Arizona Chapter of the Nature Conservancy manages the Hassayampa River Preserve as well as eleven other preserves.

Thick tamarisk stands at the rest area just outside the
Hassayampa River Refuge
The flood of 1993 left debris up to this height. Tree Tobacco Termites were here
All pictures were taken at Hassayampa River Refuge, its visitor center, and at the nearby rest stop.
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