phyte mounds, and dunes on the playa surface. When
many playas (Neal and Motts 1967), are raised accumu-
vegetation is present along the edge of a playa, it is
lations of soil and vegetation, ranging in height from 1
often found on coarse textured mounds (Blank et al.
to 5 m (3.28 to 16.40 ft) and having a 2- to 10-m (6.56- to
1992) and varies from less than 1 percent to as high as
32.8 ft-) circumference, which protect the plants from
25 percent areal coverage (Barbour and Billings 1988)
adverse effects of flooding. These are found on and
with a low species diversity. The macrophyte species
adjacent to many playas. Phreatophyte mounds are
found on soft and hard playas differ greatly, although
formed when wind-blown sand and silt accumulate
the central portions of both are devoid of vegetation.
around a phreatophyte growing at the level of the pla-
In general, plant communities on hard playas vary from
ya surface and build successively upward. Pioneer
plants such as Kochia californica or Suaeda fruticos
xerophytic vegetation, which is stunted and shrubby
compared to its conspecific upland counterparts, to
may be initial colonizers; as aeolian material develops
around them they may be replaced by Atriplex torreyi,
halophytes of the alkaline sink scrub vegetation type.
A. confertifolia, or Haplopappus acradenius as the
In contrast, soft playas are more typically vegetated with
succulent chenopodes (e.g., Allenrolfea occidentalis
mound increases in size (Vasek 1983). Concentric cracks,
[Stone 1956, Lichvar et al. 1995]) of the alkaline sink
or ring fissures (Cooke et al. 1993), similar to desicca-
scrub. The dominant vegetation of many of the playas
tion cracks in the playa surface, may form around these
in southern California is enumerated by Stone (1956).
mounds after desiccation or lowering of the ground-
The vegetation found on and around playas (as well
water level. Lines (1979) similarly reports that on other-
as in some similar habitats) has been classified as "alka-
wise puffy ground, hard, compact areas may form
around iodinebush (Allenrolfea occidentalis) because
line scrub" by Thorne (1976) and generally consists of
scattered scrub of halophytic plants mostly in the
of the reduction of groundwater level. Such mounds
Chenopodiaceae. On occasion, representatives of the
have finite life expectancies; as the mound accumulates
Asteraceae, Brassicaeae, Fabaceae, and Poaceae are
aeolian sediment and increases in height, the distance
found, but none are dominants (Barbour and Billings
over which roots can extract groundwater is surpassed
1988). Barbour and Billings (1988) also state that about
and the plants die. Following plant death, the mound
20 percent of this vegetation type consists of mosaics
may erode. Neal and Motts (1967) suggest that surface
of monocultures of single-perennial-species dominance.
flooding accelerates the erosion and destruction of
These habitats are typically described as poorly drained,
these mounds. Unfortunately, no data exist on the relative
heavy soils, usually with an underlying hardpan, of
numbers or extent of phreatophyte mounds, associated
mesas, flats, playas, and sinks located throughout the
cracks, or erosion rates on inundated vs. noninundated
Great Basin, Death Valley, and Panamint Deserts, Owens
portions of playas. Further, the location of the wetland
Valley, and the Great Central Valley. This classification
boundary is distorted by the occurrence of phreato-
unit may be further broken down: (1) Shadscale scrub--
phytes because these FACW species typically seek out
generally Atriplex confertifolia, which dominates alka-
groundwater from up to 1 m (3.28 ft) or more in depth
line, heavy soils, usually with a shallow hardpan. Asso-
(Hunt 1966, West 1983), which is a depth greater than
ciated plants are low and shallow rooted and include
required to meet wetland hydrology criteria.
Grayia spinosa, Ceratoides lanata, Haplopappus
acradenius, Kochia california, Artemisia spinescens,
Hydrology/vegetation interactions
Mendora spinescens, Gutierrezia sarothrae, and
Coleogyne ramosissima. (2) Alkalai sink scrub--A suite
While a considerable body of literature exists on a
of species lower and more sparse than shadscale scrub
range of topics relating to vegetation around playas (tax-
generally found over playas, alkaline flats, and dry lakes
onomy, biogeography, physiological ecology--includ-
where there is little drainage. Chief species include Atri-
ing drought and salinity tolerance), there appear to be
plex spp., Salicornia subterminalis, Suaeda fruticos,
no studies of use vegetation in predicting playa areas
S. torreyana, Sarcobatus vermiculatus, Allenrolfea oc-
that are intermittently inundated. Some anecdotal infor-
cidentalis, and Nitrophila occidentalis. (3) Alkalai
mation exists on the relationship between vegetation
meadow and aquatic--This group consists of halophyt-
and areas that flood periodically. For example, Went and
ic species that grow in alkaline soils where springs and
Westergaard (1949) describe vegetation of hard and soft
seeps maintain meadows, pools, and small lakes. Rep-
playas in Death Valley, California, after inundation (see
resentatives include Distichlis spicata, Muhlenbergia
Table 1). West (1983) provides mutually exclusive spe-
asperifolia, Phragmites australis, Sporobolus airoides,
cies lists of plants in "lowland" (free water table at least
Juncus cooperi, J. mexicanus, Scirpus nevadensis, S.
occasionally present at the surface) and "upland" (water
americanus, S. paludosus, Allenrolfea occidentalis,
table > 1 m [3.28 ft] below surface) salt-desert habitats
and Anemopsis californica.
(Table 1). The lowland group of species is mostly rated
Phreatophyte mounds, as found on and adjacent to
as Facultative Wetland (FACW) (Reed 1988) and is dom-
13
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