MOJAVE DESERT FIELD TRIP
Stanley D. Smith
David J. M. Bradney
At this site, we also examined well-developed desert pavement that had desert varnish surfaces estimated to be
at least 8,000 years old. The mosaic structure of Mojave
Desert vegetation (shrub-clump, fertile islands surrounded
by bare areas of desert pavement) and caliche formation
were also discussed at this site.
The third stop was at 1,087 m and was in a blackbrush
(Coleogyne ramosissima)-dominated community. Blackbrush forms a distinct elevational belt between creosotebush desert along the lower bajadas and pinyon-juniper
woodland in the mountains over much of the Mojave Desert
region. Subordinate shrubs in the blackbrush community
were Joshua tree (Yucca brevifolia), winterfat (Eurotia
lanata), Mohave yucca, creosotebush, turpentine bush
(Thamnosma montana), desert almond (Prunus fasciculatus ), and purple sage (Salvia dorrii). A large wash near
the site had a distinct community dominated by rabbitbrush (Chrysothamnus nauseosus), catclaw acacia, cheesebush (Hymenoclea salsola), and desert willow (Chilopsis
linearis).
Just past the third stop, we took a detour by hiking up
a steep south-facing slope to a series of caves in a dolomite
outcrop (1,160 m elevation). In these caves are located a
series of woodrat (genus Neotoma) middens dating from the
present to 15,000 years old. We examined a present-day
woodrat midden and the process of packrat behavior leading to midden formation. The active midden was found to
contain plant materials similar to those observed within a
30-m radius of the caves: yucca leaf parts, twigs from various shrubs, and cactus spines. We then examined several
intermediate-age fossil midden materials, which also contained desert-type plant material. Last, we examined the
15,000-year-old midden deposit, and observed primarily
pinyon and juniper needles in the deposits, indicating that
this cave site was once pinyon-juniper woodland. These
observations led to a discussion of Southwestern biogeography and the migration of plant communities as a function
of climatic change.
About 2 miles above the packrat midden area, we stopped
again within the blackbrush community to examine a
10-year-old burn. The burn site was completely devoid of
blackbrush, but was instead dominated by small subshrubs
such as brittlebush (Encelia virginensis) and desert mallow
(Sphaeralcea ambiqua). The site also had a denser cover of
brome grasses (both Bromus tectorum and B. rubens) than
did the adjacent, nonburned blackbrush community. The
group took some time to discuss fire ecology in the lowland
Mojave Desert and the role of introduced brome grasses in
the fire cycle.
The fourth stop was a canyon site at 1,510 m elevation
near the base of Mount Potosi in the Spring Mountains.
The zonal vegetation on the slopes of the mountains was
an association of singleleaf pinyon (Pinus monophylla)
and Utah juniper (Juniperus osteosperma), both of which
ABSTRACT
The all-day Mojave Desert field trip described in this
summary includes four main stops. These cover an elevationa[ range from 715 to 1,510 m and species compositions
varying from a simple creosotebush (Larrea tridentata) and
bursage (Ambrosia dumosa) community to dramatically
more complex zonal desert-mountain communities. The
field trip also featured postburn plant community compositions and fossil packrat middens for the interpretation of
past plant distribution.
INTRODUCTION
An ali-day field trip was taken along an elevational gradient from Mojave Desert shrub associations in the Las
Vegas Valley to pinyon-juniper woodland in the Spring
Range west of Las Vegas. The field trip traveled from
Las Vegas along the Blue Diamond-Pahrump Highway.
Various desert communities were examined, including
several recent burn sites along the gradient. Additionally,
a side trip was made to a 15,000-year-old packrat midden
that shows evidence of pinyon-juniper woodland occurring
where desert shrub associations occur today. Figure 1
depicts the gradient in vegetation and shows the four primary community types that were examined and are discussed below.
THE FIELD TRIP
The first stop on the field trip was at a simple twospecies Mojave Desert community at the bottom of the
Blue Diamond gradient. The site was at 715 m elevation
and included creosotebush (Larrea tridentata) and white
bursage (Ambrosia dumosa) as the only woody plants on
the site. The site was extremely open and thus typical of
the Lower Sonoran Zone of the Mojave Desert.
The second stop, at 805 m elevation, was a mixed Mojave
Desert community that was again dominated by creosotebush and white burs~e. However, in this community we
also found a significant number of subordinate perennials,
includiQg Nevada ephedra (Ephedra nevadensis), Rosemary eriogonum (Eriogonum fasciculatum), Mohave yucca
(Yucca schidigera), catclaw acacia (Acacia greggii), beavertail cactus (Opuntia basilaris ), pencil cholla (Opuntia ramosissima), and indigo bush (Psorothamnus fremontii).
Field trip held in conjunction with the Symposium on Cheatgrass Invasion, Shrub Die-Off, and Other Aspects of Shrub Biology and Management,
Las Vegas, NV, April 5-7, 1989.
Stanley D. Smith is Associate Professor and David J. M. Bradney is a
Graduate Student in the Department of Biological Sciences, University of
Nevada, Las Vegas, NV 89154.
350
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
6,000
Singleleaf Pinyon
Utah Jumper
Big Sagebrush
Apache Plume
Rabbitbrush
Green Mormon Tea
Singleleaf Ash
-
Pinyon-Juniper
Woodland
5,000
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4,000
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3,000
Stop#4
.
4,960 ft (1,512 m~
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Joshua TreeBiackbrush
Desertscrub
Creosotebush
White Bursage
Nevada Mormon Tea
Rosemary Eriogonum
Mohave Yucca
Catclaw Acacia
Beavertail Cactus
Pencil Cholla
Indigo Bush
1..
Stop#2
2,640 ft (805 m)
2,000
I
Joshua Tree
Winterfat
Turpentine Bush
Desert Trumpet
Blackbrush
Creosotebush
Ground Thorn
Desert Almond
Purple Sage
Desert Willow
Rabbitbrush
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0
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Spring Mountain Pass
5,502 ft (1 ,677m)
Creosotebush
Desertscrub
Stop#1
2,350 ft (716 m)
Figure 1-Field trip stops and a depiction of elevational changes in plant community composition along the
Blue Diamond-Pahrump Highway.
extended into the canyon bottom. Also abundant in the
canyon were big sagebrush (Artemisia tridentata), Apache
plume (Fallugia paradoxa), rabbitbrush, desert almond,
green Mormon tea (Ephedra viridis ), and singleleaf ash
(Fraxinus anomola). We stopped at Spring Mountain Pass
(1,675 m elevation) for lunch, taking the time to enjoy the
midday shade of a well-developed pinyon-juniper woodland.
Mter lunch, we descended into the Pahrump Valley west
of the Spring Mountains. Along the western slope of the
mountains, in a transitional area between blackbrush and
pinyon-juniper woodland, we stopped at a more recent,
351
2-year-old burn that had eliminated virtually all the
Joshua trees, pinyons, and junipers from the area. We
examined and discussed this early successional stage,
and compared it to the older burn on the other side of
the Spring Mountains.
ACKNOWLEDGMENT
The figure used to describe the Mojave Desert gradient
was drawn and kindly donated by Dr. Joseph McAuliffe of
UNLV's Department of Biological Sciences.
iT U.S. GOVERNMENT PRINTING OFFICE: 1990-573-041/21012