No. 18. Desert Playa and Salt Scrub Shrublands

Rex C. Crawford and Jimmy Kagan

Geographic Distribution. The desert playa and salt scrub habitat centers on the Great Basin of Nevada and Utah. In the Pacific Northwest, it is most common and abundant in the larger, alkaline lake basins in southeastern Oregon, although it is represented throughout the Columbia Plateau, Basin and Range, and Owyhee Provinces. 

Shadscale salt desert shrub and mixed salt desert shrub range from southeastern Oregon south into Utah and Nevada. Black greasewood salt desert scrub and alkaline/saline bottomland grasslands and wetlands appear throughout the Columbia Plateau of Washington and Oregon.

Physical Setting. This habitat typically occupies the lowest elevations in hydrologic basins in the driest regions of the Pacific Northwest. Elevation range is highly variable, from 3,000 to 7,500 ft (914 to 2.286 m) in southeastern Oregon to 500 to 5,500 ft (152-1,676 m) in central Washington. Structural and compositional variation in this habitat are related to changes in salinity and fluctuations in the water table. Areas with little or no vegetative cover have highly alkaline and saline soils and are poorly drained or irregularly flooded. Other arid soil types include desert pavement and barren ash. The wettest variants of the habitat are usually found at the mouth of stream drainages or in areas with some freshwater input into a playa. These have finer, deeper alluvial soils that occur in low alkaline dunes, around playas, on slopes above alkaline basins or in small, poorly drained basins in sagebrush steppe. Topographically, this habitat occurs on playas or desert pavement, or on low benches above playas with occasional low alkaline dune ridges.

Landscape Setting. This habitat is typically surrounded by shrub-steppe habitat. It forms a habitat mosaic of playas, salt grass meadows, salt desert shrublands and sagebrush shrublands. This habitat may be associated with Herbaceous Wetland habitat. Local land use can result in juxtaposition with Agriculture or Eastside Grasslands habitat. Most of this habitat provides rangeland for livestock, particularly as winter range. Portions of this habitat associated with water are most attractive to livestock. Other portions of this type are designated wildlife refuges.

Structure. This habitat is structurally diverse, ranging from dense shrublands to sparse grasslands to non-vegetated flats. Generally, low to medium-tall alkali or saline tolerant shrubs form an open layer over a grass and annual, often succulent, forb undergrowth. Deciduous shrubs, when present, usually create <50% cover but occasionally can exceed 70% on previously disturbed ground. Ground cover between shrubs is variable, ranging from widely spaced tall, medium-tall, or short bunchgrasses to dense, short rhizomatous grasses. Other areas have no shrubs and support a fairly continuous cover of graminoids, occasionally with widely spaced bunchgrasses. Sites can have extensive bare ground, usually gravelly flats, ash, desert pavement, or low alkaline dune ridges. Typically, this habitat is a mosaic of open medium-tall to low shrubland communities, patchy grasslands or herb lands, and sparsely to non-vegetated areas.

Composition. Characteristic medium-tall shrubs that dominate well-drained sites are shadscale (Atriplex confertifolia), bud sagebrush (Artemisia spinescens), and hopsage (Grayia spinosa). Characteristic low shrubs are greenmolly (Kochia americana), saltbush (Atriplex gardneri or A. nuttallii), and winter fat (Krascheninnikovia lanata). Other medium-tall shrubs, big sagebrush (Artemisia tridentata), horsebrush (Tetradymia nuttallii or T. glabrata), Mormon tea (Ephedra viridis), or rabbitbrush (Chrysothamnus nauseosus or C. viscidiflorus) can be co-dominant. The medium-tall shrub black greasewood (Sarcobatus vermiculatus) or low shrubs, iodinebush (Allenrolfea occidentalis) or Mojave seablite (Suaeda moquinii) can be dominant or co-dominant on less well drained, generally more saline parts of this habitat.

Herbaceous indicators of salt desert habitats appear in various habitats. On densely vegetated sites, native bunchgrasses, basin wildrye (Leymus cinereus), curly bluegrass (Poa secunda), and needle-and-threadgrass (Stipa comata) are important, usually with shrubs in this habitat. Basin wildrye is also a common and diagnostic grass in sites with less alkaline, deeper soils and some movement of water. Indian ricegrass (Oryzopsis hymenoides) and bottlebrush squirreltail (Elymus elymoides) are dominant grasses on the alkaline dunes. Introduced plants, particularly, cheatgrass (Bromus tectorum) or halogeton (Halogeton glomeratus) often dominate overgrazed sites. Saltgrass (Distichlis spicata) is a common, diagnostic native sod-forming grass on more saline sites that often dominates large areas with and without shrubs. Pickleweed (Salicornia virginica) is found in wetter, saline areas. Alkaline sites have mat muhly (Muhlenbergia richardsonis), alkali bluegrass (Poa secunda ssp. juncifolia), beardless wildrye (Leymus triticoides), and Lemmon’s alkaligrass (Puccinella lemmonii). Common reedgrass (Phragmites australis), bulrush (Scirpus americanus, S. maritimus), and creeping spikerush (Eleocharis palustris) are diagnostic of the wettest parts of this habitat.

Other Classifications and Key References. Popular literature refers to this habitat as shadscale, salt desert scrub, and saltflat desert. This habitat encompasses the "Desert or Salt Desert Shrub" and "Distichlis stricta Associations on Saline-Alkali Soils" in Franklin and Dyrness ⁸⁸ and Saltbush-greasewood in Kuchler ¹³⁶. The Oregon Gap II Project ¹²⁶ and Oregon Vegetation Landscape-Level Cover Types ¹²⁷ that would represent this type are salt desert scrub shrubland and alkali playa. Other references describe this habitat ^{29, 30, 52, 60, 123, 131, 147, 175, 184}.

Natural Disturbance Regime. Fire plays a minor role over much of the distribution of the type because of sparse vegetation and lack of fuel. Many of these areas are prone to irregular flooding and prolonged droughts; both factors lead to a redistribution of component species and creation of sparsely or unvegetated areas.

Succession and Stand Dynamics. Many of the dominant shrub species sprout following fire, herbicide treatments, or heavy grazing ⁴. The characteristic shrubs of this habitat increase with grazing and can invade adjacent big sagebrush communities with intense grazing.

Effects of Management and Anthropogenic Impacts. Several exotic species invade this habitat with grazing. Halogeton, a toxic exotic plant, is found most commonly in this habitat. Other noxious but nontoxic exotics that increase with grazing are Russian thistle (Salsola kali), tall tumblemustard (Sisymbrium altissimum), and cheatgrass. These can replace native grasses and change the structure of the native habitat.

Status and Trends. Agricultural development is generally not feasible; consequently, little of this habitat is converted to other uses. Most of this habitat is used for livestock grazing, which overall has increased shrub and annual cover and decreased bunchgrass cover. Quigley and Arbelbide ¹⁸¹ concluded that the Salt Desert Shrub cover type is less abundant now than before 1900. They further noted that the cover type has undergone a moderate level of change, so that some successional pathways have been unaltered. Approximately one third of Pacific Northwest salt desert and related community types listed in the National Vegetation Classification are considered imperiled or critically imperiled ¹⁰.