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Spacing Patterns in Mojave Desert Trees
and Shrubs
Matthew Fidelibus
Raymond Franson
David Bainbridge
may have poor moisture holding capacity (Fidelibus, unpublished data). As a result, belowground interactions may be
different in revegetation sites than in native systems. At
Viceroy Gold Corporation's Castle Mountain Mine, revegetation success will be determined by comparing plant
diversity and density of revegetated lands to undisturbed
sites 10 years after revegetation is completed. If transplants
are placed too close together or in antagonistic relationships,
revegetation goals may not be met.
To facilitate selection and placement of transplants at the
mine site, a study was initiated to determine inter- and
intra-specific shrub spacing patterns in areas not disturbed
by current mining. Point to plant and nearest neighbor
methods were used to determine species density and dispersion patterns, and examine inter- and intra-specific neighbor preferences. This data will be used to determine species
composition, juxtaposition and distancing when replanting
disturbed areas.
Abstract-Planting shrubs at an excessive density or planting
incompatible species together may reduce desert revegetation success. As part of the revegetation program at a Mojave Desert mine, a
study was initiated to detennine spacing patterns among the woody
perennial species in areas not disturbed by the current mining
activity. Shrub density ranged from approximately 9,000-14,000
individualslha. Most shrubs were found to be randomly dispersed;
however, larger shrubs such as creosote bush (Larrea tridentata), and
Joshua tree (Yucca brevifolia), were regularly dispersed and widely
spaced. Plants were found to often associate with con specific neighbors. Data on species composition, density, dispersion, and neighbor
preferences will be used in mine site revegetation.
Climatic conditions favorable for germination and establishment of native perennials are infrequent and unpredictable in the Mojave Desert (Barbour 1968), limiting the value
of direct seeding for desert revegetation (Bainbridge and
Virginia 1990; Lippitt and others 1994). Fortunately, nursery stock can be successfully transplanted in hot deserts
(Bainbridge and Virginia 1990; Fidelibus and Bainbridge
1994; Romney and others 1989), facilitating recovery and
speeding visual relief. Factors such as poor substrate quality, lack of plant protection and drought have been found to
limit initial survival oftransplants on bare areas (Bainbridge
and Virginia 1990; Bainbridge and Fidelibus 1994). Plant
interactions occurring several years after planting, however, may ultimately determine transplant success.
Previous studies have shown that competition in the
desert is limited to belowground interactions (Cody 1986;
Rundel and Nobel 1991). Fonteyn and Mahall (1981) have
documented competition for soil moisture between creosote
bush (Larrea tridentata) and bursage (Ambrosia dumosa).
Chew and Chew (1965) found that creosote bush density is
correlated with mean annual rainfall suggesting intra-specific competition. Furthermore, Cody (1986) has shown that
some Mojave Desert shrub species may "prefer" or "avoid"
specific species as neighbors, possibly because of competitive
interactions between plants with similar root structure.
Mine spoils and other disturbed substrates are often deficient in nutrients, organic matter, and microsymbionts, and
Methods
-----------------------------------
Current mining operations will disturb approximately
343 ha (at an average elevation of 1,300 m). Vegetation was
classified into three major communities by Everett (1991),
based upon the descriptions of Holland (1986). The communities in order of decreasing acreage are: Joshua tree (Yucca
brevifolia) woodland (JTW), blackbrush (Coleogyne
ramosissima) scrub (BBS),andMojavemixedsteppe(MMS).
An on-going study is determining substrate qualities, elevation, slope, and aspect of undisturbed communities in order
to determine which assemblages of native plants will be best
suited for the modified substrates and new topography
created by mining operations. It is expected that each
community type will be recreated within the mine site. Sites
for vegetation sampling were chosen to include each major
community and were coordinated with the soil study.
Seventeen 50 m by 50 m quadrats were established within
areas which were judged to be representative ofthe community sampled; 11 quadrats in JTW, 4 quadrats in BBS, and
2 quadrats in MMS. The JTW and BBS quadrats were
established on relatively flat substrates of similar (within
community type) elevation and substrate to insure that
slope, aspect, elevation, or substrate differences were not
responsible for observed vegetation patterns. The MMS
community occurs on steep, rocky, slopes. For these sites,
quadrats were established on slopes of similar aspect, elevation, and grade.
In each quadrat, twenty sampling points were selected
using stratified random coordinates. At each point, the
distance to the nearest perennial shrub was measured, and
In: Barrow, Jerry R; McArthur, E. Durant; Sosebee, Ronald E.; Tausch,
Robin J., comps. 1996. Proceedings: shrubland ecosystem dynamics in a
changing environment; 1995 May 23-25; Las Cruces, NM. Gen. Tech. Rep.
INT-GTR-338. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Intermountain Research Station.
Matthew Fidelibus is Biologist, San Diego State University Foundation,
5500 Campanile Dr., San Diego, CA 92182. Raymond Franson is Ecologist,
Viceroy Gold Corporation, Castle Mountain Mine, P.O. Box 68, Searchlight,
NV 89046. David Bainbridge is Restoration Ecologist, San Diego State
University, 5500 Campanile Dr., San Diego, CA 92182.
182
distances from this shrub to its first and second nearest
neighbor and its nearest conspecific (if the nearest neighbor
was a different species) were also recorded. For each species,
the average point to plant distance (m) was calculated, and
this value was used to estimate species density (# individualslha) following the methods of Cottam and Curtis (1956).
The observed mean distance between conspecifics was
compared to the expected mean distance (generated by
assuming a random distribution of each species at their
measured density). Departure from randomness was then
determined by the ratio ofthe observed mean distance to the
expected mean distance as described by Clark and Evans
(1954).
To determine if a specific species was a nearest or second
nearest neighbor more or less frequently than would be
expected based upon their density, chi-square analyses were
performed (Cody 1986). Species are described as "preferred"
neighbors if they occur as neighbors more often than would
be expected by chance (p < 0.05), and "avoided" if they occur
as neighbors less often than expected by chance. If species
were found to be neighbors as often as would be expected by
chance alone (p > 0.05), then their relationship is described
as "neutral." The mechanisms behind preferred, avoided or
neutral relations were not investigated.
Revegetation of Joshua trees is an important goal at the
mine, and because the species is present in lower densities
than other perennials, the distance from each random point
to the nearest Joshua tree, and the distance to the nearest
neighbor Joshua tree, were also recorded (if Joshua trees
were within 10 m of a point) to insure an adequate data set
for this species.
Results -----------------------------------Density
Shrub density varied among community type (table 1).
The BBS community had the highest shrub density (14,800
shrubslha), but the lowest diversity (9 species). The JTW
community had the lowest shrub density (8,900 shrubslha)
but the highest species diversity (26 species). The MMS had
intermediate shrub density (12,500 shrubslha) and diversity values (12 specie~). Relative shrub densities often differed dramatically among communities, and some species
were characteristic of, or limited to, specific communities.
The density of blackbrush, for instance, was nearly 9,000
individualslha in the BBS community; a density greater
than the overall shrub density in the JTW community (table 1).
By contrast, blackbrush occurred only infrequently in JTW,
and was absent from the MMS sites.
Few species (other than blackbrush) were found in their
highest relative densities in the BBS community (table 1);
however, Mormon tea (Ephedra nevadensis), Pima rhatany
(Krameria erecta) and Anderson's thornbush (Lycium
andersonii) were equally abundant in BBS and MMS, occurring in JTW at lower relative densities (table 1). The arborescent monocots, Mojave yucca (Yucca schidigera) and Joshua
tree, were found to occur at identical densities across the
BBS andJTW communities. Cooper's goldenbush (Ericameria
cooperi), a very abundant species in JTW (2,952lha), was
much less common in BBS (561lha).
Table 1-The density (# of individualslha) of selected shrub species in three different plant
communities surrounding Castle Mountain Mine, in the east Mojave Desert.
Common name
Anderson's thornbush
Beavertail cactus
Blackbrush
Buckhorn cholla
California barrel cactus
California buckwheat
Cooper's goldenbush
Creosote bush
Joshua tree
Mojave prickly pear
Mojave yucca
Mormon tea
Pima rhatany
Total shrub densitt
Species name
Lycium andersonii
Opuntia basilaris
Coleogyne ramosissima
Opuntia acanthocarpa
Ferocactus cylindraceus
Eriogonum fasciculatum
Ericameria cooperi
Larrea tridentata
Yucca brevifolia
Opuntia erinacea
Yucca schidigera
Ephedra nevadensis
Krameria erecta
BBS1
1,684
0
8,984
0
0
187
561
936
374
0
374
1,123
749
14,800
JTW2
1,011
202
647
121
40
40
2,952
1,051
364
243
364
647
566
8,900
MMS3
1,562
0
0
0
1,562
2,500
625
1,875
0
0
625
1,250
0
12,500
lBBS = Blackbrush Scrub.
2JTW = Joshua Tree Woodland.
3MMS = Mojave Mixed Steppe.
4The calculation of total shrub density is based upon all observed species, including several less common shrubs not
displayed in this table.
183
Table 2-Average distance (m) and standard error between the nearest neighbor (NN)
and the nearest conspecific (NCSP) of several
species of shrubs surrounding Castle Mountain Mine.
BBS
Species
Anderson's thornbush
Beavertail cactus
Blackbrush
Buckhorn cholla
California barrel cactus
California buckwheat
Cooper's goldenbush
Creosote bush
Joshua tree
Mojave prickly pear
Mojave yucca
Mormon tea
Pima rhatany
MMS
JTW
NCSP
NN
NCSP
NN
0.40 ± 0.06
1.24 ± 0.46
0.61 ± 0.03
1.39 ± 0.60
0.79±0.13
0.50 ± 0.22
0.62 ± 0.07
1.83 ± 1.00
0.77 ± 0.09
1.02 ± 0.30
1.1 ± 0.3
3.40 ± 0.98
6.97 ± 0.69
0.47 ± 0.22
0.72 ± 0.30
0.38 ± 0.13
5.67 ± 0.03
1.03 ± 0.49
0.98 ± 0.31
0.70 ± 0.06
1.07 ± 0.13
0.74±0.19
0.45 ± 0.17
0.79 ± 0.16
0.51 ± 0.11
1.79 ±
5.39 ±
1.05 ±
6.48 ±
1.05 ±
1.83 ±
6.97 ±
3.55 ±
10.31 ±
2.72 ±
1.50 ±
0.29
1.88
0.17
2.79
0.16
0.29
0.69
0.77
1.96
0.70
0.34
NN
NCSP
0.50 ± 0.11
1.04 ± 0.31
0.72 ± 0.17
0.53 ± 0.08
1.02 ± 0.78
0.69 ± 0.10
2.01 ± 0.73
0.59 ± 0.09
2.17 ± 0.61
1.64 ±0.29
1.10±0.76
0.62 ± 0.29
7.27 ±2.13
1.15 ± 0.55
Neighbor Preference or Avoidance
The density data indicates that Joshua tree woodland
is primarily composed of a variety of small shrub species
(table 1), with Joshua trees occurring at relatively low
densities (374lha, nearly the same density as in BBS).
Cooper's goldenbush was the most abundant species, occurring at a density nearly three times that of the two next most
abundant species in JTW; Anderson's thornbush and creosote bush (Larrea tridentata).
In the MMS community Joshua trees were absent, while
Mojave yucca occurred at a density nearly equal to the
combined density of both Yucca species in BBS or JTW.
There were few species of cacti in MMS, aside from the
California barrel cactus, (Ferocactu8 cylindraceus), a dominant plant on rocky slopes surrounding the mine (table 1).
Neighbor preference or avoidance was only observed with
a few species, and positive interactions (neighbor preferences) were more common than negative interactions (neighbor avoidances). Conspecific preferences were observed for
Anderson's thornbush, blackbrush, California buckwheat,
Cooper's goldenbush, creosote bush, Mormon tea, and pima
rhatany. Avoidance was observed between Anderson's thornbush and creosote bush, Cooper's goldenbush, and pima
rhatany. The significant neighbor preferences and avoidances for Cooper's goldenbush are displayed as an example
(table 4).
Distance Between Plants
Table 3-Dispersion pattern of common shrubs in three plant
The average distance between shrubs and their nearest
neighbors was found to be similar among communities (table 2).
Most shrub species were found to grow within 0.5-1.0 m of
another shrub. The average distance between conspecifics
was typically much higher than the average distance to a
nearest neighbor.
communities near Castle Mountain Mine, in the East
Mojave Desert (p < 0.05).
Species
Anderson's thornbush
Beavertail cactus
Blackbrush
Buckhorn cholla
California barrel cactus
California buckwheat
Cooper's golden bush
Creosote bush
Joshua tree
Mojave prickly pear
Mojave yucca
Mormon tea
Pima rhatany
Dispersion
Most shrubs were found to be randomly dispersed (table 3).
A regular dispersion pattern was observed for some large
shrubs for example, blackbrush, California barrel cactus, creosote bush, Joshua tree, and Mojave yucca; table 3). California
buckwheat (Eriogonum fasciculatum) was the only species
tested which showed a clumped distribution.
184
BBS
random
regular
JTW
MMS
random
random
random
random
random
regular
clumped
regular
regular
random
random
random
random
regular
random
regular
random
random
random
random
Table 4-Selected results of chi square analysis of first and second nearest neighbor data for Cooper's
goldenbush. Results with a Chi square value greater than 3.88 indicate significance at
p < 0.05. Insignificant results are not displayed.
Cooper's goldenbush
Neighbors
Cooper's goldenbush
Creosote bush
Discussion
Expected
24.88
8.86
NN1
Observed
42
3
Expected
11.77
3.88
27.54
9.8
NN2
Observed
49
a
16.72
9.8
expected based upon mean density (approximately 1 plantim2 ).
We also observed that the nearest conspecific was usually
much further away (1.0-7.0 m) than the nearest neighbor (of
any species). These findings are consistent with the observations that shrubs may form small groups or "islands" where
plants are more densely packed, and that these islands may
often be composed of several shrub species. Shrub islands
are common in the deserts of the Southwest, and they play
an important role in the ecology of desert shrubs (Goodall
and Perry 1979). Thus, planting inter-specific assemblages
of shrubs may bean effective revegetation strategy.
-------------------------------
Density
High shrub densities were found in BBS and MMS communities (12,500-14,800 individualslha;table 1). These findings agree with Lei and Walker (1994) who reported that
blackbrush were "extremely abundant" within BBS communities (in southern Nevada), and Holland (1986) who characterized MMS as being a "fairly dense" plant assemblage.
Everett (1991) also noted that density and diversity increase
in MMS sites with increased grade and rockiness, and these
sites were rocky and relatively steep grade. Cody (1986)
noted that species diversity and density is related to sampling area. Consequently, more species may have been noted
in BBS and MMS communities if sampling intensity were
higher.
Although less abundant than BBS or MMS, plant density
in JTW (table 1) was similar to, but higher, than values
reported by Cody (1986); 8,900 plants/ha vs. 7,000 to 8,000
plants/ha. However, much of the desert surrounding the
mine is free range, and JTW suffers the most intense grazing
pressure. Evidence of grazing is expressed as heavily browsed
grasses and shrubs and well marked cattle trails. Thus,
plant density may be reduced in JTW because of herbivory.
If the 900 acres of disturbance were revegetated at a
density similar to that of an undisturbed community (approximately 1 plantim 2 ), more than 3.6 million shrubs would
be required. Producing and planting this many shrubs
would be impossible; however, plant spacing and neighbor
interactions are still important.
Dispersion and Neighbor Preference
The results of the dispersion and neighbor preference data
analysis indicates that shrubs are generally randomly dispersed (in relation to other individuals of the same species),
with a few larger shrub species being regularly dispersed
(table 3). A random dispersion may simplify revegetation at
the mine provided that shrubs are not planted near incompatible neighbors. The mechanism(s) creating a regular
dispersion of trees, such as Joshua trees, is unknown but
using the wide spacing observed in nature may be important
for revegetation success. The clumped dispersion of California buckwheat is probably the result of the rocky terrain
where sites for plant establishment are not uniformly distributed across the quadrat.
The results of the nearest neighbor analysis are less clear.
Conspecific preferences were noted for several species including blackbrush, and Cooper's goldenbush (table 4), although these interactions are less common for second nearest neighbors than they are for first nearest neighbors. It is
possible that observed conspecific preferences are the result
of clonal growth forms, however, this hypothesis is not
supported by distances to nearest conspecifics (which are
typically longer than distances to the nearest neighbor).
Diversity
The low species diversity found in BBS was also noted by
Lei and Walker (1995) who attributed the low diversity in
BBS to blackbrush abundance. Species diversity in JTW (26
species) was similar to Cody's (1986) findings (35 species);
although Cody's study, unlike ours, included perennial grass
species. Much of the diversity in JTW comes from small
shrubs. Larger shrubs such as creosote bush, Mojave yucca,
and Joshua tree are visually important, however, they were
found to grow in low densities (table 1). The revegetation
program's emphasis on species diversity appears to be an
ecologically sound management criteria.
Conclusions
-----------------------------
Species composition and patterns in vegetation are often
difficult to distinguish without performing systematic sampling. Vegetation sampling should be conducted to improve
the chance of revegetation success by detecting spacing
patterns and neighbor interactions, and to avoid focusing on
charismatic mega-flora. Natural plant assemblages in desert
systems may be slope, aspect, or substrate dependent, and
belowground relations may be altered on disturbed substrates. However, belowground competition has been documented and should be considered when planning revegetation projects.
Distance
Distance to nearest neighbor data (table 2) show that
many shrubs grow closer together (0.5-1.0 m) than might be
185
Acknowledgments
Fonteyn, P. J. and B. E. Mahall. 1981. An experimental analysis of
structure in a desert plant community. Journal of Ecology.
69:883-896.
Goodall, D. W. and R. A Perry, eds. 1979. Arid Land Ecosystems:
Structure, Functioning, and Management, Vol. 1, (International
Biological Programme 16). Cambridge University Press. 881 pp.
Holland, R. F. 1986. Preliminary Descriptions of the Terrestrial
Natural Communities of California. State of California. The
Resources Agency. Department ofFish and Game. Sacramento,
CA 156 pp.
Lei, S. A and L. R. Walker. 1995. Composition and distribution of
(Coleogyne ramosissima) communities in southern Nevada. In:
Roundy, Bruce A; McArthur, E. Durant; Haley, Jennifer S.;
Mann, David K., comps. 1993. Proceedings: wildland shrub and
arid land restoration symposium; 1993 October 19-21; Las Vegas,
NY. Gen. Tech. Rep. INT-GTR-315. Ogden, UT; U.S. Department
of Agriculture, Forest Service, Intermountain Research Station.
pp:192-195.
Lippitt, L., M. W. Fidelibus, and D. A Bainbridge. 1994. Native seed
collection, processing, and storage for revegetation projects in the
western United States. Restoration Ecology. 2(2):120-131.
Romney, E. M., A Wallace, and R. B. Hunter. 1989. Transplanting
of native shrubs on disturbed land in the Mojave Desert. In:
Wallace, A, E. D. McArthur, and M. R. Haferkamp, comps.
Proceedings-Symposium on Shrub Ecophysiology and Biotechnology, Logan, Utah, June 30-July 2, 1987. pp: 50-53.
Rundel, P. W. and P. S. Nobel. 1991. Structure and function
in desert root systems. In: Plant Root Growth: An Ecological
Perspective. D. Atkinson, ed. Blackwell Scientific Publications.
London. p. 349-378.
-----------------------
We thank John Tiszler, Robert MacAller, and Debbie
Waldecker for field assistance and helpful editorial suggestions.
References -------------------------------Bainbridge, D. A and M. W. Fidelibus. 1994. Treeshelters improve
woody transplant survival on arid lands (California). Restoration
and Management Notes. 12(1): 86.
Bainbridge, D. A and R. A Virginia. 1990. Restoration in the
Sonoran Desert. Restoration and Management Notes. 8(1):3-14.
Barbour, M. G. 1968. Germination requirements for the desert
shrub Larrea tridentata. Ecology. 50: 679-685.
Chew, R. W. and A E. Chew. 1965. The primary productivity of a
desert-shrub (Larrea tridentata) community. Ecological monographs. 35:355-375.
Clark, P. J. and F. C. Evans. 1954. Distance to nearest neighbor as
a measure of spatial relationships in populations. Ecology.
35(4 ):445-453.
Cody, M. L. 1986. Spacing patterns in Mojave Desert plant communities: near-neighbor analyses. Journal of Arid Environments.
11:199-217.
Cottam, G. and J. T. Curtis. 1956. Use of distance measures in
phytosociological sampling. Ecology. 37:451-460.
Everett, R. G. 1991. Castle Mountain Mine Project, San Bernadino
County, CA, Vegetation Analysis. California Desert Studies Consortium, Fullerton, CA
Fidelibus, M. W. and D. A Bainbridge. 1994. The effect of
containerless transportation on desert shrubs. Tree Planters'
Notes. 45(3):82-86.
186