The East Of Sierra Nevada Region
Author: David Stoms
Plant Community Types
The East of the Sierra Nevada (ESN) Region of the Great Basin
Province encompasses 13,128 km², consisting principally of
three basins: the Owens Valley, the Mono Basin-Long Valley Caldera,
and the Walker River drainage in Mono and northern Inyo counties
(Figure ESN-1). The primary ranges area the Sweetwater Mountains
and the White-Inyo Mountains, plus the lower escarpment of the eastern
flank of the Sierra Nevada. The upper elevational limit of the western
edge of the region occurs at the transition between pinyon-juniper
of the ESN with the Jeffrey pine of the Sierra Nevada. At its southern
extremity, the boundary with the Mojave Desert is the transition
from sagebrush to creosote bush scrub. The region is artificially
truncated by the California-Nevada border on the eastern side.
Shaded relief image of the East of the Sierra Nevada Region.
is cooler than the Mojave Desert to the south, causing most of the
precipitation to be winter snow (Schoenherr 1992). The Sierra Nevada
range creates a rain-shadow effect, however, so the region is extremely
dry. Bishop, in the Owens Valley, receives an annual average of
just 14 cm of precipitation. The crest of the Sierra Nevada and
White Mountain Peak both exceed 4,000 m, while the intervening Owens
Valley is only ~1,500 m. Thus the high relief of the region produces
a wide diversity of habitats. Alpine dwarf scrub and subalpine conifer
forests of Bristlecone and Limber pines occur at the highest elevations.
Below this is a band of pinyon-juniper woodland, consisting of Singleleaf
pinyon and either Western juniper on the eastern face of the Sierra
Nevada or Utah juniper elsewhere. There is also extensions of Jeffrey
pine and other conifer forests in the Sweetwater Mountains and south
of Mono Lake. Blackbush scrub is found in the Owens Valley below
the pinyon-juniper zone, and below that is the hallmark of the Great
Basinsagebrush scrub, often in conjunction with Antelope Brush
(Purshia tridentata). Shadscale (Atriplex confertifolia)
replaces sagebrush on more alkaline soils closer to intermittent
lakes. In the wettest locations in these alkaline basins, alkali
sink scrub communities with succulent leaves form. Some communities
characteristic of the Mojave Desert occur at the margins of the
region, such as creosote scrub and Joshua tree woodland. Wetland
and riparian communities are extremely critical in this arid environment,
including montane meadows, alkali meadow, freshwater and alkali
marshes, aspen, black cottonwood, and riparian scrub.
harshness of the environment, the region has nevertheless experienced
significant human impacts on its biodiversity. Water is a primary
resource conflict, with competition between urban consumers, recreationists,
and wildlife. A large proportion of water in the Owens River system
has been diverted since 1913 by the City of Los Angeles Department
of Water and Power aqueduct. This diversion has resulted not only
in a significant drop in the water level in Mono Lake, but has also
changed the volume and timing of flows in streams, which in turn
has affected riparian habitats. Since the 1970s, groundwater has
also been exported to supplement surface water diversions into the
Los Angeles Aqueduct. Groundwater pumping has adversely affected
or eliminated phreatophytic shrubs and grasses that depend on groundwater
in favor of species with lower water requirements, including many
weedy species (Groeneveld 1992).
is the lifeblood of the regional economy. Fishing is extremely popular,
adding to the demands for water resources. The ESN region is also
the gateway to the recreational resources of the Sierra Nevada,
from skiing at Mammoth Mountain and June Mountain to the eastern
entrance to Yosemite National Park. Many tourists come to enjoy
the scenery and natural history of such unusual attractions as Mono
Lake and the ancient Bristlecone pine forests in the White Mountains.
Livestock grazing was once extremely intensive, especially sheep
which were moved as vast herds. Overgrazing in sagebrush communities
leads to a decline in Purshia tridentata which was preferred by
native browsers. Fire suppression may also favor sagebrush over
P. tridentata and perennial grasses. Mining was once an important
economic activity but its main legacy is in historical ghost towns
like Bodie. Logging in Jeffrey pine forests does occur on USFS lands
but is not nearly as important economically as it is on the Modoc
Plateau portion of the Great Basin province.
designations and expansions to National Parks made by the California
Desert Protection Act of 1994 were incorporated from a preliminary
digital map of the Bureau of Land Management (BLM) state office.
The Bishop Resource Area office of BLM provided digital coverages
of the Areas of Critical Environmental Concern under its jurisdiction.
Management status of lands in the East of Sierra Nevada Region. See
text for definitions of management levels.
manage almost the entire ESN region (94.5%), distributed among USFS
(43.1% of the region), BLM (31.1%), NPS (6.8%), Indian reservations
(0.1%), California Fish & Game and other state agencies (1.0%),
and local governments (11.1%, largely managed by the City of Los
Angeles Department of Water and Power in the Owens Valley). The
remainder is privately owned (5.5%) or water bodies (1.2%). Private
land occurs mostly in the Antelope and Bridgeport valleys at the
northern end of the region.
Table ESN-1. Area
and percentage of land surface by management status level of the East
of the Sierra Nevada Region.
profiles by elevation zone are somewhat atypical in the ESN region
compared to other regions where higher elevations tend to be better
represented than lower elevations. In the ESN (Figure ESN-3), all
zones except between 2000-2500 m are represented proportional to
their area. This pattern of less status 1 and 2 management at middle
elevations reflects the allocation of biodiversity management at
the lower elevations in Death Valley National Park and the wilderness
areas and botanical areas in the White-Inyo Mountains.
Proportion of management status of lands in the East of the Sierra
Nevada Region by elevation zones.
on the eastern flank of the Sierra Nevada range south of Mono Lake
were generalized from the 1980 Vegetation Resource Inventory (U.
S. Forest Service, unpublished maps). The White-Inyo Mountains were
mapped from the Landsat TM-based Inyo National Forest vegetation
map. The floor of the Owens Valley was derived from the 1:24,000
scale BLM-SCS soil-vegetation mapping. The remaining areas were
delineated subjectively by photointerpretation of patterns in the
satellite imagery in conjunction with the CALVEG map (Parker and
Matyas 1981), another BLM soil-vegetation map published in the Bodie/Coleville
Grazing EIS for the Bodie and Antelope Valley areas, and the VTM
maps. Final delineation of a landscape unit was an iterative process
based on evidence from the satellite imagery, existing vegetation
maps, and field reconnaissance.
was derived mainly from the Inyo Vegetation Resource Inventory,
the BLM soil-vegetation maps, unpublished maps produced by the VTM
survey and from our own field survey. These sources all contained
dominant species data. For the White Mountain area, the Forest Service
map was classified by CALVEG type (Parker and Matyas 1981). We ascribed
dominant species to each of the vegetation types because we felt
the types were relatively simple and consistent. The BLM-SCS data
for the Owens Valley represented plots which they extrapolated to
landscapes of the same community type. Researchers at UCSB then
summarized the three dominant species associated with each community
type. Of the 1,371 landscapes in the region, 175 were visited in
the field during 1995, covering 44% of the region. These landscapes
tend to be larger than average because of the absence of detailed
information ranged widely in date and reliability, the current database
is uneven in both level of detail and accuracy. We did not have
the resources to assess the statistical accuracy of the vegetation
map and associated database. However, we have appraised the product
using less formal methods that have guided our use of it. Classes
are probably more accurate than species data in the White Mountains
where species were inferred from CALVEG classes. Forest Service
maps depict Pinyon-juniper types which may contain patches dominated
by either species alone or co-dominated by both. In the absence
of field data to the contrary, both species were coded in the database
and assigned to the more general Great Basin Woodlands type. Subalpine
Sagebrush Scrub, which is well-developed in the White-Inyo Mountains
(Holland 1986), was not identified in existing map sources; therefore
this type does not appear in the gap analysis database. Portions
of the region without existing vegetation maps such as east of the
White Mountains have the least spatial detail and were assigned
species attributes from sparse field reconnaissance. These areas
will tend to be the most generalized and least accurate.
12,191 km² (92.8%) of the ESN region as vegetated other than
agricultural or horticultural land cover. In other words, 7.2% has
been converted to urban or agricultural uses or contains open water
or bare ground. The vegetation layer was delineated into 1,371 landscape
units with an average size of 967 ha. Distributional information
is provided on 72 dominant plant species, 38 community types and
9 land use/land cover types.
Based on our
system for converting dominant species assemblages into natural
community types, we mapped 38 community types within the ESN region.
Twenty-four of the 38 types were mapped with an area greater than
25 km². Great Basin Woodlands, Great Basin Mixed Scrub, and
Shadscale Scrub are the most extensive types, covering 2,429 km²,
2,223 km², and 1,053 km², respectively. Eight community
types contribute 76% of the region's total vegetated area. Two new
community types were described by the Gap Analysis project to supplement
the Holland (1986) classification for this regionLow Sagebrush
Scrub and Cercocarpus ledifolius Woodland.
Table ESN-2. Percent
area of each CNDDB community type at each management status level
in the East of Sierra Nevada Region. * indicates an addition to the
standard CNDDB classification (Holland 1986).
Community Name (Holland 1986)
Mapped Distribution (km²)
Creosote Bush Scrub
Mixed Woody Scrub
Basin Mixed Scrub
Sagebrush Scrub *
ledifolius Woodland *
or Alpine Meadow
Black Cottonwood Riparian Forest
Basin Cottonwood-Willow Riparian Forest
Basin Riparian Scrub
Live Oak Woodland
Pinyon and Juniper Woodlands
Live Oak Forest
Pine-Lodgepole Pine Forest
Total (incl nonvegetated)
community types mainly on status 4 (primarily private) lands.
Because most of the region is publicly owned, few of the 38 types
have the majority of their distributions on private land. The two
exceptions are Transmontane Freshwater Marsh and Montane Black Cottonwood
Riparian Forest, although the latter covers slightly less than 25
and herbaceous types mainly located in unprotected areas. Three
of the 21 scrub and herbaceous types were mapped with areas greater
than 25 km² and with less than 10% of their distribution in
Status 1 and 2 managed areas, which are designated for conservation
of native biodiversity. These include Blackbush Scrub, Low Sagebrush
Scrub, and Montane Meadow. Blackbush (Coleogyne ramosissima)
is a paleoendemic or a relict species whose range was formerly much
wider (Stebbins and Major 1965). Mojave Mixed Woody Scrub also meets
these criteria but is considered to be a marginal type in this region.
Alkali Meadow has 10.9% of its mapped area in managed areas but
is also of concern because of the potential adverse impact of groundwater
pumping. Lowering the water table can reduce cover or eliminate
entirely the native grasses and Atriplex lentiformis ssp. torreyi
(Groeneveld 1992). Other wetland and riparian types also appear
poorly represented on Status 1 and 2 lands but have mapped distributions
below the criterion. Therefore, we have less confidence in the accuracy
of their management profiles. Slight errors in mapping could make
significant differences in whether or not they appear protected.
and woodland types mainly located in unprotected areas. Three
of the 16 forest and woodland types were mapped with areas greater
than 25 km² and with less than 10% of their distribution in
Status 1 and 2 areas. These include Aspen Riparian Forest, Aspen
Forest and Jeffrey Pine Forest. These types are almost exclusively
on public lands, and are of management concern primarily because
of grazing, which is widespread. Lodgepole Pine Forest and Whitebark
Pine-Lodgepole Pine Forest also meet these criteria but are more
characteristic of the Sierra Nevada and tend to be outliers in the
types that appear well-protected. Five types were mapped with
areas greater than 25 km² and with more than 25% of their distribution
in Status 1 and 2 areas. These include Mojave Creosote Bush Scrub,
Desert Saltbush Scrub, Desert Sink Scrub, Joshua Tree Woodland,
and Bristlecone Pine Forest. These types represent the lower elevation
sites in Death Valley National Park and the higher elevations in
the White-Inyo Mountains. These types are of relatively low priority
for additional land acquisition or allocation to Status 1 and 2.
Other types common in the Great Basin such as sagebrush and the
piñon-juniper woodlands are also relatively well-represented
but not to the same level as the types listed above.
The ESN Region
is the southernmost portion of the Great Basin Province in California
(Hickman 1993). The management status of community types in the
ESN region may not be representative of the province as a whole.
Therefore, our findings should be considered tentative and apply
only to the California portion of the ecoregion. However, most Great
Basin types are not well-represented in managed areas in other states
within the ecoregion either (Caicco et al. 1995. Edwards et al.