Ciénegas Rare Oases in the Desert
by: Shannon Fehlberg, Ph.D., Dorrance Family Foundation Conservation Biologist
Andrew Salywon, Ph.D., Assistant Herbarium Curator, Research Botanist
Kimberlie McCue, Ph.D., Program Director, Conservation of Threatened Species and Habitats
As we head into the heart of another Phoenix summer, the thought of cool, wet, green spaces may seem like just another wishful daydream. It isn’t an unattainable dream, however. Although it may be hard to believe, the state of Arizona is home to an amazing variety of wetlands. Marshes, ciénegas, bosques, tinajas, playas, and other specialized habitats that harbor water all occur within the boundaries of our state. They also constitute some of the rarest and most threatened habitats we have: more than a third of our original wetlands have been lost just since the 1800s, due to drainage for conversion to other uses and the indirect effects of cattle ranching, wildlife management practices, and groundwater pumping. Only one percent of Arizona’s land still contains wetlands, yet these areas possess a cultural and biological significance disproportionate to their limited geographic scope.
If you know where to look, wetlands can be found in most regions of Arizona. The unique type we will focus on in this story is found only in southeastern Arizona (as well as southwestern New Mexico and northern Mexico). These are the ciénegas, a habitat type that results from a specific combination of a permanent water source, topography, and water-bearing soils. Amongst all the threatened wetland types, ciénegas are considered to be the most imperiled, with close to 95% of ciénegas in southern Arizona having been destroyed in historical times.
What Happened to the Ciénegas?
Because ciénegas are sources of perennial water within semiarid landscapes and are good habitat for wildlife, they have been important to humans since prehistoric times. There is little doubt that Native Americans modified or manipulated ciénegas to some extent for farming activities, usually by stream diversion and through vegetation removal. Then, with the introduction of livestock by Spanish colonists in the early 1700s, many ciénegas were substantially impacted by overgrazing. By the early 1800s, the Spanish missionary and military activities in the area decreased and as a result so did livestock grazing. This reprieve did not last long, as by the 1880s the railway had opened up the region to an influx of Anglo-Americans, many of whom engaged in cattle ranching. The ensuing extensive overgrazing, coupled with a persistent drought around 1900, denuded the landscape throughout the Southwest and led to disastrous consequences. Renewed rainfall on the parched landscape resulted in severe erosion and stream cutting—which precipitously lowered the water table (Hendrickson and Minkley 1985). Thus, water that normally fed the ciénegas dried up and ciénegas habitat was significantly diminished. A key species that once functioned to maintain ciénegas is the beaver. Prior to the late 1800s, beavers were common along streams and ciénagas in Arizona. The dams they built created ponds that prevented erosion and trapped sediments. The dams also raised local water tables and helped establish and perpetuate ciénagas. The loss of beaver populations due to trapping in southern Arizona has negatively impacted ciénagas.
Groundwater pumping and water diversions for cities, agriculture, and mining have dropped water tables as well and are threats to many ciénegas. For example, San Simon Ciénega once stretched nearly five miles long and a half-mile wide in a valley bottom in Cochise County, along the Arizona/New Mexico border. This wetland was partially destroyed just before the turn of the 20th century by overgrazing and stream cutting, which lowered the water table. Then, in the 1950s, groundwater pumping for irrigated farming completely depleted the aquifer that fed the ciénega. It is now totally dry and no wetlands remain in the valley (Sivinski in press).
Arizona’s remaining ciénegas provide critical habitat for an abundance of beautiful, distinctive, and rare species of plants and animals–especially native fish, reptiles, and amphibians. Some of these species occur in the Las Ciénegas National Conservation Area (about 40 miles southeast of Tucson) and are highlighted on the webpage of the FROG Conservation Project. Included are the Gila topminnow (endangered species), which grows 1 to 2 inches long and was once the most widespread and common fish in the Gila River basin, but is now restricted to several ciénegas and drainages; the Gila chub (endangered species), which grows 1.5 to 14 inches long, and is restricted to just a few drainages; the Chiricahua leopard frog, once extremely abundant in southeastern Arizona but now listed as a threatened species; and the Mexican garter snake, a primarily aquatic snake, is a candidate threatened species because of declining numbers, in part due to invasive species such as bullfrogs that eat the snakes.
Native Plant Species in Distress
Of essential importance to all the other forms of life in ciénegas are the native plant communities. The most common plants of southwestern ciénegas are bulrushes (Scirpus), cattails (Typha), sedges (Carex), rushes (Juncus) and saltgrasses (Distichlis), but there are a number of threatened and endangered plants that also thrive in ciénegas.
The Canelo Hills ladies’ tresses orchid (Spiranthes delitescens) is an Arizona endemic, occurring here and nowhere else in the world. Known from only four populations existing in ciénegas of southeastern Arizona, it was listed as an endangered species in 1997. This herbaceous plant with long, thin leaves grows on moist slopes and can be easily detected in July and August when it produces a long stalk (approximately 20 inches tall) bearing up to 45 spirally arranged white, tubular flowers. The Canelo Hills ladies’ tresses orchid is a mycotrophic plant, meaning that it depends on a close association with fungi for its germination, growth, and nourishment. This dependency on fungi has made it extremely difficult to maintain any living collections outside of its native environment. In the past, the Desert Botanical Garden partnered with the Center for Conservation and Research of Endangered Wildlife, in Cincinnati, Ohio, to attempt to propagate the orchid via tissue culture. The efforts met with limited success, but we may be revisiting this challenge soon.
Desert Botanical Garden Contributes Preservation Efforts
As members of the Center for Plant Conservation network and stewards of the Huachuca water umbel, we maintain a living collection of these plants in our conservation greenhouse. In addition, we are working with the Department of Defense and a local environmental consulting firm on two projects aimed at increasing the likelihood of long-term survival of populations of the Huachuca water umbel. First, from our living collection, we have propagated more than 60 plants that have been reintroduced to three sites in Fort Huachuca, Arizona. Second, we have initiated a study of the genetic characteristics of Huachuca water umbel populations. This conservation genetic research may lead to a greater understanding of the basic biology of Huachuca water umbel and help answer questions about how much genetic variation is found within populations, how different populations are from one another, how much genetic exchange takes place among populations, and how prevalent vegetative (from rhizomes) and sexual (flowers and fruits) reproduction are within populations. This knowledge will help inform conservation strategies by providing information about which populations face the greatest risk of extinction and which populations are genetically unique. Furthermore, this knowledge will benefit reintroduction efforts because it will help ensure that reintroduced populations harbor sufficient genetic variation and possess the genetic composition best-suited for the area of reintroduction.
As important as ciénegas and other wetland types are for biodiversity in Arizona, there is still relatively little known about the life forms harbored in these areas. Because of this we are actively seeking partnerships with the Bureau of Land Management to conduct surveys of the plants found in southwestern ciénegas in order to document unique species before they are permanently lost, and to develop a baseline for future monitoring of the health of the ciénegas. The more knowledge we have, the greater the possibilities for developing strategies to protect the natural heritage of these oases in the desert.
Hendrickson, D. A. and W. L. Minkley. 1985. Ciénegas - Vanishing climax communities of the American Southwest. Desert Plants 6: 131-175.
Sivinski, R. (in press) Southwestern ciénegas: Rare habitats for endangered wetland plants. Proceedings from the 5th Southwest Rare Plant Conference, Salt Lake City, UT.