BINGHAM CIENEGA NATURAL PRESERVE
THE NATURE CONSERVANCY RESTORATION PROJECT
by Daniel Baker
SITE DESCRIPTION AND HISTORIC NATURAL CONDITIONS:
Bingham Cienega Natural Preserve occupies 285 acres in the Central San Pedro Valley near the small community of Redington, almost due east of Tucson. In 1978 The Nature Conservancy’s Arizona Natural Heritage Program identified Bingham Cienega as one of Arizona’s rarest natural features. In a 1988 Arizona Natural Areas Study, the Arizona State Parks Board identified and ranked Bingham Cienega as the 9th most significant site out of over 300 sites proposed for natural area protection in Arizona. In 1989 the Pima County Flood Control District purchased the Cienega and entered into a 25 year management agreement with The Nature Conservancy.
Bingham Cienega is situated along the banks of the San Pedro River, which has received substantial local, national and international attention. The San Pedro and environs was designated as one of The Nature Conservancy’s "Last Great Places" because it represents one of the last great relatively intact surviving ecosystems. As one of the longest undammed watersheds remaining in the American Southwest, the San Pedro River stretches 140 miles from northern Sonora, Mexico to its confluence with the Gila River. NAFTA’s scientific expert team for the Commission for Environmental Cooperation found that as many as four to five million neo-tropical bird migrants utilize it as their main Western flight corridor between Central and North America. Nearly half of North American birds have been sighted there, and the American Bird Conservancy recognized it as a Globally Important Bird Area. Some of America’s rarest forest types line its banks, principally Fremont cottonwood-Gooding willow forest and mesquite bosques. It also supports the highest number of mammal species in North America.
Bingham Cienega is situated in the Central Basin of the San Pedro. The Central Basin presents the rare sight of a nearly unfragmented landscape with no significant development and a very low human population density (a few hundred) between the fifty-five or so miles separating Benson-Pomerene and San Manuel-Mammoth. It also connects the Rincon-Catalina mountain complex with the Winchesters and Galiuros. Mountain lion, black bear, bighorn sheep, mule and white-tail deer, gray fox, coatimundi and ringtail cats among others traverse these ranges. Animal corridors such as nearby Buehman and Redfield Canyons connect these "sky islands" thereby reducing extinction rates from these habitats, increasing recolonization rates after local extinction, and permitting gene flow between habitats.1
Bingham Cienega is a spring-fed marsh. Rock outcrops from the Catalina Core Complex in the main channel just north of the mouth of Edgar Canyon force underflow to rise up and become streamflow.2 The shallow water table created by the influence of this same block of consolidated sediments is also thought to be responsible for generating outflow at the spring location.3 Bingham Cienega and adjacent agricultural fields occur on the pre-entrenchment flood plain of the San Pedro and are 4 meters above the active channel. The site was not eroded by flooding in 1983 or 1993.
1879 General Land Office surveys of the Preserve and vicinity indicate that historically moister areas in and near the cienega included dense, shrubby willows, while sacaton grasslands, deciduous riparian forests and mesquite bosques lay outside the cienega.4 Pollen analyses show woody riparian vegetation increased during late historic periods, coincident with decreased fire frequency.5 Bingham Cienega is now a lotic system supporting extensive stands of cattails, bullrush and other obligate wetland plants.6 Besides the wetland, mesquite bosque, palustrine wooded swamp and cottonwood-willow riparian forest are on site. Sacaton grass persists along riparian forest edges or in understory. The adjacent floodplain is dominated by riparian species, especially mesquite and salt cedar as well as Fremont cottonwood, Gooding willow, Arizona walnut and velvet ash. The surrounding upland plant communities are Sonoran desert scrub dominated by mesquite, saguaro and cholla cacti species.
Sites like Bingham with perennial flow and diverse riparian habitats are critically important as stepping stones for migratory birds in the intermittent middle and lower San Pedro. Cottonwood-willow forests support the highest densities of birds in the Southwest, and mesquite bosques the second highest, and both support diverse assemblages of invertebrates, reptiles and mammals.7 In Arizona 90% of streamside wetlands have disappeared. In cienega wetlands the losses are estimated to be closer to 95%.8 The remaining are threatened by increased water demands on streamflow and ground-water sources. Despite their small area, over 70% of all species inhabiting this semi-arid region as well as migratory species depend on these systems. 9,10
CHANGES TO SYSTEM RESULTING IN NEED FOR RESTORATION:
Around the turn of the century approximately 70 acres at Bingham Cienega were modified hydrologically by ditching and berming the cienega wetland, and the entire area was cleared for agriculture. These fields are like the thousands of acres of floodplain habitat, especially mesquite bosques and sacaton grasslands, that were cleared and farmed along the San Pedro. The loss of sacaton grassland is especially notable: over 95% of sacaton grassland habitat in Arizona has been lost over the last century.11 Historically sacaton grasslands formed extensive stands along riparian areas within the semiarid grasslands. It has now been replaced by mesquite due largely to fire suppression and declining water tables. Initial site recovery occurred when farming and livestock grazing were stopped in years following the purchase of the cienega by Pima County in 1989. In addition, the berm was breached and the wetland was allowed to reestablish over the abandoned fields. Areal extent and hydrology of the cienega has somewhat stabilized at about 22 acres.
Before 1890 the San Pedro flowed slowly in a shallow narrow channel through marshy environments. San Pedro entrenchment occurred around the turn of the century with a series of large floods. This was apparently due to a variety of causes including climactic changes, timber harvesting, fire suppression, overgrazing, draining of swamps, beaver extirpation and earthquake. Today only isolated pieces of the once extensive marshlands persist; commonly attributed to the arroyo cutting episode, and more recently groundwater development in the form of pumping for agricultural, municipal and industrial uses which has lowered water tables and diminished water supply necessary to maintain wetland habitats.
RESTORATION OPPORTUNITIES, CHALLENGES, APPROACHES:
Part of the opportunity at Bingham Cienega is the potential for local restoration of the lost character of the San Pedro, which historically included sacaton meadows. Since cienega vegetation often occurs in zones or bands that reflect gradients of water availability,12 The Nature Conservancy conducted a "Preliminary Vegetation and Hydrological Analyses for Bingham Cienega."13 Its purpose was to relate hydrological gradients across the agricultural fields to spatial distribution of dominant cienega plant species. Three planting areas were identified to support a different historic riparian community type: deciduous riparian woodland, sacaton grassland and mesquite woodland. The entire upland terrace portion of Bingham Cienega was found to be hydrologically suitable for the restoration of sacaton grassland. If successful, such an effort might provide a model for other recovering areas and abandoned agricultural fields along the length of the San Pedro Valley where sacaton dominated historically.
The conditions that allow this opportunity for riparian deciduous woodland and sacaton grassland restoration are the same ones that make it such a challenge. The lesson of ecology is that all systems and their parts are connected. Bingham is effectively an island in the threatened hydrologic system of the San Pedro. The lack of floods and overbank inundation due to floodplain entrenchment, and which are required to move seeds into sediment, have prevented recruitment and reestablishment of native species.14 Additional inputs of moisture after germination appear to be an important factor in seedling survivorship.15 Competition with exotic weeds including Johnson grass and bermuda which dominate the fields are inhibiting factors as well. Sacaton is also adapted to fire of appropriate timing and periodicity.16 Any controlled burning must match historical timing and intensity of wild fires, as well as be feasible within surrounding environmental and social conditions.
Bingham Cienega Natural Preserve attracts attention for its beautiful, unique and important location and habitat type. It is also interesting for its riparian restoration possibilities. It presents all the opportunities and challenges that constitute the dreams and nightmares of the ecological restoration concept.
1 Gori, D., Unpublished report to the Arizona Nature Conservancy, 1997.
2 Agenbroad, L. D., "Cenozoic Stratigraphy and Paleohydrology of the Redington-San Manuel Area," University of Arizona Ph.D. Dissertation, 1967.
3 Baird, Ronayne and Maddock, Preliminary Vegetation and Hydrologic Analyses for Bingham Cienega, University of Arizona Department of Hydrology and Water Resources, 1997.
4 Fonseca, Julia, "Vegetation Changes at Bingham Cienega," Pima County Flood Control District, 1994.
5 Davis, O. K., "Pollen Analysis of Borderland Cienegas," Unpublished report to the Arizona Nature Conservancy, 1994.
6 Stromberg, J. C., "Southern Arizona Warm-Temperate Riverine Marshes," Stewardship Abstract Responsibility, Arizona Nature Conservancy, 1993.
7 Ohmart, R. D. and Anderson, B. W., "Riparian Habitat" in Inventory and Monitoring of Wildlife Habitat, ed. by Cooperrider, A. Y., Boyd, R. J., and Stuart, H. R., Denver: USDI Bureau of Land Management Service Center, pp. 169-199, 1986.
8 Hendrickson, D. A. and Minkley, W. L., "Cienegas - Vanishing Climax Communities of the American Southwest," Desert Plants, pp. 131-175, 1984.
9,10 Carothers, Mills, and Johnson, "The Creation and Restoration of Riparian Habitat in Southwestern Arid and Semi-Arid Regions, pp. 351-66 in Kustler, J., and Kentual, M., eds., Wetland Creation and Restoration, Island Press, 1990. Naiman, R. J., Decamps, H., and Pollock, M., "The Role of Riparian Corridors in Maintaining Regional Biodiversity," Ecological Applications, pp. 209-12, 1993.
11 Humphrey, R. R., "Forage Production on Arizona Ranges," University of Arizona, Agricultural Experiment Station Bulletin 302, 1960.
12 Hendrickson and Minkley, op. cit.
13 Baird, op. cit.
14 Haughey, 1997.
15 Aldon, E. F., "Establishing Alkali Sacaton on Harsh Site in the Southwest," Journal of Range Management, pp. 129-132, 1975.
16 Bock, J. H. and Bock, C. E., "Habitat Relationships of Some Native Perennial Grasses in Southeastern Arizona," Desert Plants, pp. 3-14, 1986.