What is a playa? "Playa," and its synonym "playa lake," are a couple of those vague terms like "swamp" or "marsh" that are generally used to describe some type of wetland. Playa is also a Spanish word with an English translation of shore or beach. Unfortunately, this translation provides little help in describing a playa. If the question about playas is asked relative to a particular geographic region, such as New Mexico, it becomes somewhat easier to answer; although the result is still not certain. This is because individuals use wetland terms like swamp, playa, or lake and understand their intention for a local region, but individuals from outside these local areas cannot be sure of their meaning. A farmer in Wisconsin would likely form a much different vision of "lake" than a west Texas farmer. The Texas farmer might envision a wet, shallow low spot in a field or pasture, whereas the Wisconsinite would likely see a deep fishing lake.

Regardless of this potential confusion, scientists have used the terms playa and playa lake to describe various types of shallow wetlands in prairie, semiarid, or arid environments throughout the world. Their descriptions vary because the ecology, hydrology, and geology of playas varies greatly among geographic regions. Because playas are most abundant in the Great Plains of the United States the description here will focus on these unique prairie sites. In the Great Plains playas are defined as "shallow depressional recharge wetlands that are formed through a combination of wind, wave, and dissolution processes with each wetland existing in its own watershed." As the words depressional and recharge imply, Great Plains playas only receive water from precipitation and runoff. Naturally water is only lost through evaporation, transpiration, and recharge. Wetlands in the Great Plains that have springs or receive groundwater additions to their surface water are generally not considered to be playas. Because playa watersheds are not connected to one another and storms can be very localized in the Great Plains, a playa in one location may be full of water while only a short distance away other playas are dry. Playas are shallow, usually only 5 feet deep at most, and have erratic hydroperiods, frequently drying and filling with water in most years.

Until relatively recently, few playas were thought to exist in the Great Plains outside the Southern Great Plains. The Southern Great Plains of southeastern Colorado, southwestern Kansas, west Texas, the panhandle of Oklahoma, and eastern New Mexico was traditionally referred to as the "Playa Lakes Region" by many agencies and in many scientific papers. Playas occur almost continuously from the Southern Great Plains into northwestern Kansas, northeastern Colorado, eastern Wyoming, and western Nebraska but in reduced numbers (and density). The majority of these playas occur in the shortgrass prairie. True to playa form, however, they cannot be easily categorized because some playas also exist further east in the mixed and tallgrass prairies. Indeed, the Rainwater Basin wetlands of south central Nebraska to the east of the shortgrass prairie are classified as playas.

The exact number of playas that exists in the Great Plains is unknown but certainly exceeds 25,000 because this number has been counted from soils maps in the Southern Great Plains alone. When one includes the playas of eastern Wyoming, Nebraska, northeast Colorado, and northwest Kansas, it is likely that there are more than 30,000 playas in the Great Plains. Regardless of the exact number, when one considers there are more than 25,000 playa wetlands, covering more than 445,000 acres, in a mostly semiarid to arid, highly agriculturalized environment with few other wetlands, it is obvious playas are a keystone ecosystem central to the ecological integrity of the entire Great Plains.

The entire floral and faunal composition of a playa can change within a few days. If a playa has been dry for more than a year often only a thin layer of grass and spindly forbs remain in the basin. In early May thunderstorms can occur over the playa, and more importantly, its surrounding watershed, resulting in the basin being covered with 2 feet of water. Within days, aquatic plants begin to germinate, there is an explosion of aquatic invertebrates such as clam shrimp, toads and frogs begin emerging and calling in earnest, shorebirds immigrate to feed on the invertebrates, and duck pairs which are now courting will subsequently nest on the playa margin. This is a typical sequence in the life history of a playa and can occur in thousands of playas each year. The unpredictable climate of the Great Plains dictates this condition.

Playas need this hydrologic disturbance (flooding, drying) to remain productive and be the key sites of biodiversity that they are. Indeed wetlands by definition periodically dry out. Among other things this enhances decomposition, allows other plant and animal communities to emerge, and recolonize and coexist with those species that require a more aquatic or a more terrestrial condition. The general public, many ecologists, and natural resource managers assume the aquatic condition is more beneficial, probably because it is more transient and full of life than the drier state. However, this drying and flooding allows two vastly different communities and their integrades to exist on the same site, increasing the diversity of the wetland and the prairie. Further, among other ecosystem processes, the cycling of nutrients provided by the hydrologic disturbance is required by the various biotic communities.

When most people consider "flora" they usually think of higher vascular plants while others may think of algae, but few consider fungi, mosses, bacteria, and viruses as "flora". There are few studies investigating these latter groups in playas and we know little of their diversity. Studies of vascular plants in the Southern Great Plains indicate that at least 346 species occur in playas and 212 species in the Rainwater Basin of Nebraska. This distinct flora would not exist in the prairies if not for the existence of playas.

As with the flora, the animal life existing in playas not only depends on the current, but also the historic hydroperiod. For example, invertebrates occurring in playas may have been existing as eggs in the soil for years, the result of some historic dispersal and precipitation event. Invertebrates in playas are a particularly diverse group with more than 170 taxa identified. Many of these taxa are identified only to the family level because of the difficulty of species identification. Indeed new invertebrate species exist in playas that have yet to be described.

The most diverse vertebrate group existing in playas are birds with more than 250 species having been recorded. Most of these occur during spring and fall migration with abundances of certain groups, such as waterfowl, in the millions. Amphibians are not a very diverse vertebrate group in playas with only 13-15 species being present. However, in the summer they may be the most abundant vertebrate with more than 40,000 individuals occurring in a single wetland. Although many reptiles occur in dry-moist playas only the yellow mud turtle is considered to require an entirely wet playa for a short period of time each year. Finally, no truly aquatic mammals exist in Southern Great Plains playas, but muskrat and mink do occur in the Rainwater Basin. The abundance and diversity of mammals in dry or moist playas, however, can be quite high. No fish naturally occur in playas but many have been introduced.

To preserve a truly functioning western Great Plains prairie we must conserve some key sites of diversity, such as playas and river/stream corridors. Because the biggest past and immediate threat to playas has been sedimentation associated with cultivation of the surrounding watershed, restoration of watersheds and purchase/easement of remaining native sites will be a key component of conservation. Sedimentation fills in playas and does not allow them to hold water for as long as they could because the water is spread out over a larger area increasing evaporation and shallow soil infiltration. Any change to the potential hydroperiod can drastically affect the plants and animals that exist there. For example, playas with cultivated watersheds and much higher sediment loads have a plant community that has a much higher percentage of exotic species and annuals than playas with native prairie watersheds.

There has been significant conservation of Rainwater Basin playas in south-central Nebraska but efforts to protect playas outside of that region have been weak. For example, only two of more than 19,000 playas in Texas have been protected by purchase or easement in the past 15 years. Meanwhile the status of playas has declined further during this time period. Public and private conservation groups throughout the region should focus their efforts on these unique opportunities. Texas Tech University has conducted most of the research in playa conservation and ecology. For further information on that research contact l.m.smith@ttu.edu or link to Loren Smith’s website:  www.rw.ttu.edu/smith/Smith_L.htm

* Portions excerpted from "Playas of the Great Plains" with permission of University of Texas Press.  www.utexas.edu/utpress/books/smipla.html