Physiognomy and Structure: No Data Available

Floristics: The vegetation is characterized by a fairly open to moderate shrub canopy (18-60% cover) dominated by Sarcobatus vermiculatus with an herbaceous layer dominated by the rhizomatous graminoid Distichlis spicata (10-80% cover). Associated shrubs and dwarf-shrubs may include Ericameria nauseosa, Gutierrezia sarothrae, and Tetradymia canescens. Sporobolus airoides may codominate the graminoid layer, and Hordeum jubatum is common in disturbed stands. Juncus arcticus ssp. littoralis (= Juncus balticus) and Leymus cinereus are also present in some stands. The forb layer is generally sparse and composed of species such as Iva axillaris and Ipomopsis spp. Introduced species, such as Bromus tectorum, Lepidium latifolium, Lepidium perfoliatum, and Bassia hyssopifolia, may be present to abundant in disturbed stands.

The stand described by Baker (1982b) for the Piceance Basin had patches of Sarcobatus vermiculatus alternating with wide expanses of Distichlis spicata (= var. stricta). A few species of annuals also were present but could not be identified. Cover of Sarcobatus in this stand was not high. Baker (1982b) reports that many Sarcobatus-dominated communities are in the literature for Colorado, with understories of exotic annual weeds. His stand was one of only a few stands from western Colorado that still contains a native perennial grass understory.

Data from Costello (1944b) for the San Juan Valley show dominance of Sarcobatus, with >60% cover, and Chrysothamnus spp. are associated. The understory consists primarily of Distichlis spicata and Sporobolus airoides, with Bouteloua gracilis, Iva axillaris, and Muhlenbergia richardsonis (= Muhlenbergia squarrosa) commonly present. Costello (1944b) also reported on Sarcobatus-dominated stands in western Colorado and Wyoming with several associated shrub species, including Artemisia tridentata, Atriplex gardneri, Atriplex confertifolia, and Bassia americana (= Kochia americana). Herbaceous species include Elymus lanceolatus (= Elytrigia dasystachya), Salsola spp., and Sporobolus airoides.

Hanson (1929) reports that the appearance of greasewood stands varies greatly with depth to water table and salt concentration in the soil. It can form almost pure, tall stands, or in places be much more open with shrubs and grasses associated.

Dynamics:  Sarcobatus vermiculatus and Distichlis spicata, like many facultative halophytes, are tolerant of alkaline and saline soil conditions that allow the species to occur in sites with less interspecific competition (Ungar et al. 1969, Branson et al. 1976). Sarcobatus vermiculatus is often found on sites with high water tables that are intermittently flooded. Hansen et al. (1995) reported that it can tolerate saturated soil conditions for up to 40 days. Sarcobatus vermiculatus-dominated vegetation can occur as a narrow band along a stream, a broad floodplain shrubland, or as a mosaic of communities where composition and density of the shrub and understory species vary with depth to water table, salinity and alkalinity, soil texture, and past land use or disturbance. This shrubland may occur as a band of abrupt concentric rings of vegetation around a salt flat or depression. This visible zonation is caused by the change in dominant species and their relative tolerances to soil salinity and depth to groundwater.

The warm-season grass Distichlis spicata is rhizomatous, tolerant of moderate grazing, and its roots resist trampling. Although relatively unpalatable, it can provide valuable winter forage for livestock, if needed. When grazed, Distichlis spicata generally increases because of reduced competition from other less grazing-tolerant species. If grazed heavily, Distichlis spicata will decline and may be replaced by less desirable warm-season grasses such as tumblegrass, Schedonnardus paniculatus, or Hordeum jubatum (Costello 1944b, Jones and Walford 1995). Weeds are generally not a problem because few grow well in saline soils. However, severely disturbed sites are susceptible to invasion by introduced species such as Bromus tectorum, Lepidium latifolium, Lepidium perfoliatum, and Bassia hyssopifolia (Franklin and Dyrness 1973).

Anything that raises the water table of a closed basin will result in an increase in this type, due to the resulting alkalinity of the soils. Grazing of domestic livestock decreases Distichlis and results in its replacement by annual weedy plants such as Bromus tectorum, Chorispora spp., and Lepidium spp. (Baker 1982b).