INDICATOR VALUE OF LICHEN
COVER ON DESERT SHRUBS
Roger Rosentreter
ABSTRACT
Europe (Ferry and others 1973). As an epiphyte, this
lichen receives nutrients from the air and from the substrate on which it grows. Other species in this genus
commonly occur below bird nests or perch sites because
of the nitrogen or eutrophication of the environment.
Therefore, orange lichen is considered nitrophilous in
its habitat selection.
Unlike many other lichens, orange lichen reproduces
relatively rapidly. It puts much of its energy into asexual
reproduction in the form of specialized fragments called
soredia. Soredia are coarse, granular, flourlike fragments
of lichen containing both algal and fungal components.
These reproductive fragments oflichens are dispersed
by winds and any physical abrasion. They can colonize
substrates within a few years (2-5) (Barkman 1958).
Swinscow (1968) correlated substrate stability with lichen
colonization rates. Although lichens may rapidly become
established and play pioneering roles in succession, tree
bark colonization by lichens was relatively slow (Barkman
1958). An older tree has had more time to be colonized by
lichens and generally has a higher lichen cover (Barkman
1958). Other factors such as canopy cover or bark sloughing may, however, actually result in a decrease in lichen
cover in older age-class trees (Culberson 1955; McCune
1979).
Desert shrubs are useful indicators of ecological site
conditions and potential biomass productivity. Sagebrush
(subgenus Tridentatae of Artemisia) is used to illustrate
many of the ecological relationships involved with desert
shrubs and their resulting lichen cover. Subspecies of big
sagebrush (Artemisia tridentata) are ideal for this because
they cover thousands of square miles of rangeland in the
western United States and their habitat selection reflects
the soil's depth, structure, drainage, chemistry, moisture,
and temperature (Fosberg and Hironaka 1964; Barker
and McKell 1983). In addition, it was found that the
amount oflichen cover on each subspecies of sagebrush
may indicate the site's productivity and history to a
greater degree and with a finer resolution than merely
the subspecies of sagebrush alone.
Sagebrush typically has shredded bark, a result of
weak phloem cells (Diettert 1938), and therefore does
not provide a stable substrate for lichen colonization.
Diettert (1938) reported that eccentric (asymmetrical)
growth of the stem could cause some portions to grow
more slowly and some parts may die. Consequently, the
rate of bark expansion can vary. A centric stem, in contrast to an eccentric one, would shed its bark more frequently on all sides, resulting in a less stable substrate.
A young eccentric shrub may have a section of dead cambium, which provides a stable substrate for lichen growth
similar to that on older shrubs. Thus, the stem growth
pattern relates to the bark's stability.
Ecological factors affecting the amount of lichen cover
on desert shrubs are discussed. Canopy density, shrub
growth rate, bark stability, pH, and ecological sites are
correlated with the amount of lichen cover on shrubs.
Knowledge of these relationships can indicate site characteristics useful in interpreting and managing shrub
sites. Common lichen species growing on desert shrubs
are briefly discussed. Anthropogenic and shrub dieoff
effects that increase lichen cover densities are explained.
The big sagebrush (Artemisia tridentata) complex in
southern Idaho is used to illustrate many of the ecological
relationships involved with shrubs and their resulting
lichen cover.
INTRODUCTION
The orange lichen (Xanthoria fallax [Hepp] Am.) commonly occurs on sagebrush and other shrubs in the arid
steppes of western North America. This common lichen
occurs in many other parts of the world. It is prevalent
throughout the Great Basin on many desert shrubs. In
the arid climate of Zion National Park in Utah, it was
the third most dominant lichen on trees (Rushforth 1982).
Some shrubs commonly occupied by orange lichen are
greasewood, juniper, sagebrush, and several types of
rabbi thrush.
Physiological adaptations of this orange lichen to dry
sites have been studied by Kershaw (1972). He demonstrated that orange lichen could maintain higher photosynthetic rates at a lower moisture content than many
other lichen species. Variation in pigment concentrations
and algal cell numbers may allow it to grow in both sun
and shade habitats (Peard 1983). Leblanc and DeSloover
(1970) found orange lichen to be the dominant lichen on
isolated deciduous trees around Montreal, Canada, and
it appeared to be the species most capable of adapting to
dry, exposed habitats.
In Europe, orange lichen is known to occur in the lichen association called Xanthorian (Ferry and others
1973). This association is best developed along coastal
areas, on bird perching rocks, and on trees with bark with
relatively high pH values. The eutrophication of the atmosphere in the form of fertilizer dust from farming has
extended the range of the orange lichen association in
Paper presented at the Symposium on Cheatgrass Invasion, Shrub
Die-Off, and Other Aspects of Shrub Biology and Management, Las Vegas,
NV, April 5-7, 1989.
Roger Rosentreter is the Idaho State Office Botanist for the Bureau
of Land Management, U.S. Department of the Interior, 3380 Americana
Terrace, Boise, ID 83706.
282
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
equation ( I a - b I /a + b = stem ratio) compensated for
comparisons between various sized shrubs. This stem
ratio was used as an index of the bark's relative stability.
Soil type was determined for 38 of the transects from
a profile obtained by digging a soil pit in the shrub stand.
The soil pit descriptions are on file with the Idaho branch
of the Soil Conservation Service, Boise, ID (Owyhee
County Survey in preparation). Soil types by moisture
were rated as either aridic (drier) or xeric.
The big sagebrush complex consists primarily of the
three common subspecies, basin, Wyoming, and mountain
big sagebrush (Artemisia tridentata ssp. tridentata, ssp.
wyomingensis, and ssp. vaseyana, respectively). The
three subspecies are found in areas having different
moisture regimes (Fosberg and Hironaka 1964; Winward
1970). Basin big sagebrush occurs on relatively deep,
well-drained soils, Wyoming big sagebrush on warmer
and often drier sites with shallower, sometimes slightly
saline soils, and mountain big sagebrush in areas of
higher moisture and lower temperatures.
Paired Transects
In 34 cases, the basic transect was paired with a basic
transect in another nearby stand. These pairs were used
to compare the influences of slope, taxon, or live vs. dead
shrubs on the amount of lichen cover. Data were collected
the same as above.
STUDY AREA
The study area was limited to Ada, Elmore, and
Owyhee Counties in southwestern Idaho. This area has
a climate fairly typical of the Great Basin desert with dry,
hot summers and moist, cold winters. The area consists
of two floristic divisions, one being the Snake River Plain
and the other the Owyhee Desert. Both areas are dominated by sagebrush grasslands in the lower elevational
positions, while mountain shrubs, western juniper
(Juniperus occidentalis), and Douglas-fir (Pseudotsuga
menziesii var. glauca) dominate at higher elevations.
Elevational Transects
The influences of precipitation and temperature on
lichen cover were evaluated by transects established at
regular intervals of increasing elevation. The Mudflat
Road and the Bockman Grade, approximately parallel
ascending roads on the north side of the Owyhee Mountains, were the elevational transects, with 15 basic transects sampled per elevational transect. Each elevational
transect began at 3,500 ft and continued up to 5, 700 ft,
encompassing the distributional range of all three big
sagebrush subspecies. Basic transects were done at elevationa} changes of approximately 150 feet.
Voucher specimens were collected of the lichens encountered, as well as one big sagebrush specimen per
transect. These were deposited in the University of
Montana Herbarium (MONTU). Leaves from the voucher
specimens were chemically analyzed to verify the field
identifications. Other epiphytic lichens encountered
on sagebrush are listed by subspecies in Appendix A.
Nomenclature of lichens follows Egan (1987).
METHODS
Basic Transect Sampling
Homogeneous shrub stands varied in size from 10
square meters to several square hectares. Decadent
stands and areas of heavy disturbance were avoided in
sampling. A total of 186 basic transects were sampled.
The basic line transect within a stand was composed of
the first 15 mature shrubs encountered along a random
compass bearing. The location, date, elevation, taxon,
shrub age, stem growth pattern, soil type, percent shrub
cover, and lichen cover value per shrub were recorded for
each transect. Lichen cover values on shrubs were estimated using a scale of 0-4, similar to Esseen's (1981)
study of epiphytic lichens on trees in Sweden. Lichen
cover values were rated as:
Cover value
Onone
1 sparse
2 moderate
3 rich
4 dense
Data Analysis
Independent variables were of two types: one continuous and the other discrete. Some environmental variables
were continuous, such as elevation, stem growth pattern,
and age. Other variables were discrete, or at least collected as discrete data, such as soil type, slope, and taxon.
These variables were correlated against the dependent
variable lichen cover using the Statistical Package for
the Social Sciences (SPSS).
Percent cover
0
0-0.5
0.5-5
5-20
20-100
Only the foliose orange lichen was considered in the
lichen cover rating. Other incidental foliose and crustose
lichens were not rated.
Shrubs lacking bark were not sampled. Shrub age was
determined by cutting at the base three of the 15 shrubs
in a transect, then counting the annual rings by wetting
the cross section, and using a lOx hand lens for improved
visibility of the rings (Ferguson 1964). The stem growth
pattern was sampled by tracing outlines of the cross sections and marking the initial point of growth onto the
data sheet. The longest and shortest radii of each stem
were measured to determine a stem growth ratio. If a =
the shortest radius and b =the longest radius then the
RESULTS AND DISCUSSION
Lichen cover differed strongly among the respective
big sagebrush subspecies (fig. 1). Wyoming big sagebrush
had the highest lichen cover, followed by basin and then
mountain big sagebrush. Lichen cover was significantly
greater on dead than living shrubs of basin and mountain
big sagebrush subspecies at the paired sites (table 1).
In contrast, lichen cover was similar on dead and living
shrubs of Wyoming big sagebrush (table 1). Both live and
283
Apparently, lichen growth is favored by the wetting/
drying cycles created by an open canopy. When a lichen
is dry, both the algal and the fungal components are inactive (Kershaw 1972). Physiologically, lichens need a high
moisture content to be photosynthetically active and to
have a positive carbon budget (Kershaw 1972). At low
thallus moisture content photosynthesis by the algae is
inactive, but respiration by the fungi is still high. This
results in a net carbon loss. Since lichen thalli are approximately 70 percent fungal hyphae it is advantageous
for a lichen to be fully moistened and then quickly dried
(Adams and Risser 1971; Lechowicz 1981). Laboratory
work on lichens has suggested that frequent wetting and
drying cycles were important for maintaining lichen vigor
(Ahmadjian 1967; Pearson 1970).
A live shrub's relatively closed canopy is disadvantageous for the lichen because it prevents saturation of the
lichen during light rain. After heavy precipitation, the
closed canopy decreases the air circulation and slows
drying. The prolonged moisture condition caused by
closed, dense canopies has been shown to decrease the
lichen cover on trees (McCune and Antos 1982). A denser
shrub canopy reduces humidity fluctuations, thereby
encouraging lichen parasitism by fungi (Pearson 1969;
Hawksworth 1982). Mountain big sagebrush, with the
lowest lichen cover (fig. 1), has a flatter topped, and
denser, canopy structure than the other two subspecies
(Winward and Tisdale 1977).
X
w '3
0
~
0:::
w
>
0
u
zw
::r:
u
2
::J
SUBSPECIES
Figure 1-Lichen cover on big sagebrush by
subspecies (±1 s.d.).
Table 1-Comparison of lichen cover between live and dead big
sagebrush shrubs from paired sites
N
Subspecies
Mean
S.E.
T-value
Probability
Shrub Age
Wyoming
live
dead
4
4
2.7
2.5
0.31
.46
0.59
0.599
Basin
live
dead
6
6
.6
1.8
.15
.41
-3.33
.02
.03
.41
-3.91
.01
Mountain
live
dead
24
24
.02
.64
It is often assumed that an older substrate supports
more lichen cover because lichens are slow to colonize
and grow. Esseen (1981) reported higher lichen cover
and biomass on larger (diameter at breast height, d.b.h.)
trees than on smaller trees. Similarly, McCune and Antos
(1982) reported increased lichen cover on larger d.b.h.
Douglas-fir, but they also found decreased cover on larger
d.b.h. grand fir (Abies grandis ). Changes in canopy structure and bark texture were suggested as being responsible
for the respective differences in lichen cover.
On blackjack oak (Quercus marilandica) the average
number of species per size class of tree did not vary significantly for size classes greater than 3.5 ft d.b.h. (Adams
and Risser 1971). The bark of blackjack oak becomes less
stable with age, and therefore it was less suitable as a
substrate for lichen colonization.
Sagebrush bark appears to be comparable to the
situation with blackjack oak. There was no correlation
between lichen cover and shrub age for big sagebrush
(fig. 2). Apparently, the bark of actively growing sagebrush falls off with increasing age, counteracting the
positive influences of age.
dead Wyoming big sagebrush shrubs are favorable for
lichen growth, perhaps because they tend to have more
open canopies resulting in more frequent wetting and
faster drying microhabitats. Wyoming big sagebrush
occurs in shallower soils with lower biomass productivity
than do the other subspecies. Wyoming big sagebrush
does not occur in such dense stands, and its growth habit
and branching patterns are more open than those of the
other subspecies. A dead sagebrush shrub has an open
canopy due to its lack ofleaves and allows greater penetration of moisture and solar radiation and freer air circulation (McCune and Antos 1982). Therefore, dead shrubs
may contain effectively drier sites for lichen epiphytes
than do live shrubs.
284
Legend
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YEARS
---ECCENTRIC->
Figure 3-Lichen cover on big sagebrush vs. stem
growth ratio.
Figure 2-Lichen cover by shrub age for big
sagebrush.
Stem Growth Pattern
The stem growth pattern was recorded as a ratio between the longest and the shortest radii of each shrub's
stem growth from the point of initial growth. This ratio
reflects the relative stability of the bark as a habitat,
regardless of the shrub's size (see Methods). The more
stable the bark, the more time for lichen colonization and
growth to occur. The eccentric stem growth ratio strongly
correlated with lichen cover (fig. 3, r 2 = 0. 72). This suggested that nearly 72 percent of the increase in lichen
cover could be explained by the stem growth ratio as an
indirect measure of habitat stability. The mean ratio of
stem eccentricity differed among big sagebrush subspecies
(fig. 4, table 2). This may reflect each subspecies' preference for different soil sites (Fosberg and Hironaka 1964),
which produced different rates and types of stem growth.
The stem growth ratio also strongly correlated to soil
moisture types for all subspecies (fig. 5). Drier aridic soils
had shrubs with more eccentric stems than the more
moist xeric soils. Diettert (1938) suggested that eccentricity may result from mechanical damage, death of
flower-bearing branches, or differential growth. Aridic
soils are drought stressed more often than xeric soil sites,
and it seems possible that drought stress could cause
differential cambium death resulting in differential or
eccentric growth.
Shrub cross sections were measured at the base. Generally, if the base was eccentric then the rest of the shrub
had eccentric stem growth. In most shrubs analyzed, the
eccentric pattern spiralled up the branch, although in
other shrubs the eccentricity varied randomly along the
branch. Basin big sagebrush can be found in both soil
moisture types and is more sensitive to soil texture and
drainage than to the soil moisture content (Fosberg and
Hironaka 1964; Winward and Tisdale 1977). The wider
range in stem growth ratios (0.05-0.94) for basin big
0.8
1\
.I
u
a:=
I-
0.6
I
I
I
0.4
z
w
u
u
w
0.2
SUBSPECIES
Figure 4-Stem growth ratio for big sagebrush
subspecies (±1 s.d.).
Table 2-Scheffe's method of pairwise comparisons of
eccentric stem growth ratio by subspecies of
big sagebrush. Significant differences at the
5 percent level are marked by an asterisk
Wyoming
Wyoming
285
Basin
Mountain
Mean
ratio
0.87
Basin
.58
Mountain
.17
sagebrush (fig. 6) may reflect its wider range in soil habitat selection. The other two subspecies are not distributed over as wide a range of soil habitats (Winward and
Tisdale 1977; Hironaka and others 1983). The stronger
correlation (,-2 = 0. 73, fig. 6) between lichen cover and
stem growth ratio for basin big sagebrush may be due
to this more widely distributed range of this subspecies.
This wide range in soil type tolerance and in stem growth
ratios of basin big sagebrush may account for the large
variation in the lichen cover values found on this subspecies (fig. 1).
Lichen cover was strongly correlated to soil moisture
type (fig. 7). The previous discussion indicates that soil
moisture types influenced the stem growth ratio, which
in turn appears to influence the lichen cover. It appears
that the drier aridic soils support shrubs with higher
eccentric stem growth ratios, resulting in stable bark that
can support greater lichen cover. In addition, aridic soil
sites often have more bare soil, dust storms, lower humidity, and faster drying rates. These additional factors,
though unrelated to the stem growth ratio, may also positively influence lichen cover.
0.8
1\
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cr:
r- 0.6
z
w
u
u
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XERIC
ARIDIC
SOIL TYPE
Figure 5-Stem growth ratio of big sagebrush by
soil moisture type (±1 s.d.).
t}
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ssp. wyomingensis
ssp. tridentata
0.2
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0.8
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---ECCENTRIC->
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Legend
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ssp.vaseyana
LowPr 957. C.l.
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o.4
o.6
o.s
---ECCENTRIC->
Figure 6-Lichen cover on big sagebrush subspecies by
stem growth ratio.
286
0.8
4-
CZI ARIDIC
X
w
3-
4-
~XERIC
X
w
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Legend
r2 =.40
SOIL TYPE
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0-~------------~~------~~~--------~~------~----~
2000
3000
4000
5000
6000
7000
ELEVATION (FEET)
Figure 7-Lichen cover on big sagebrush by
soil moisture type (±1 s.d.).
Figure 8-Lichen cover on big sagebrush relative
to elevation.
Elevation
cover= 2.19 + 2.66 (stem ratio)- 0.00050 (elevation), with
an r 2 = 0. 77. Nearly 77 percent of a shrub's lichen cover
can be explained by the relative stability of its habitat
(stem ratio) and the precipitation and temperature regime
(elevational position). These data showed that the relative stability of the shrub bark was more significant in
controlling lichen cover than the prevailing moisture and
temperature regimes.
The above regression equation allows us to predict the
amount oflichen cover likely to occur on an individual or
stand of big sagebrush (fig. 9). This suggests that conditions favorable for lichen growth are unfavorable for general site productivity of the vascular plants. Therefore,
the percentage oflichen cover may indicate productivity
by shrubs. Aridic soil sites supporting high lichen cover
were at low elevations with low precipitation, producing
shrubs with slow eccentric stem growth and open canopies. Xeric soil sites lacking lichen cover occur at high
elevations with higher precipitation, producing shrubs
with relatively fast-growing centric stems and closed,
dense canopies.
The amount of orange lichen cover can indicate the
site's potential productivity beyond the indicator value
of the subspecies of sagebrush. The more orange lichen,
the less the potential productivity. Lichen cover can be
used to evaluate a given site, a small stand of shrubs, a
small patch of shrubs, or even an individual shrub. This
bright orange lichen can easily be identified year round,
providing an additional diagnostic characteristic for the
identification of the subspecies of big sagebrush. Lichen
cover reflects long-term environmental conditions rather
than an individual year's moisture. Using lichen cover
to evaluate sites is easier than many other methods. For
example, a site's productivity is more quickly evaluated
by looking at the amount of lichen cover on shrubs than
it is by digging soil profiles or cutting down shrubs and
analyzing the stem growth patterns.
Elevational transects were used to infer the influences
of temperature and precipitation on lichen cover. Lichen
cover on sagebrush decreased with increasing elevation
(r 2 = 0.40, fig. 8). This decrease may be attributed to abiotic conditions associated with elevational change, so that
elevational position may be a factor controlling the abundance of lichen cover on big sagebrush. A similar lichen
species, Xanthoria candelaria, was also found by Adams
and Risser (1971) to decrease with increasing precipitation. Lichen cover may decrease with increasing precipitation due to the decreasing frequency and the slower
rate of drying. In general, leaf area increases with
greater moisture thus creating greater canopy density,
which is not favorable for lichen cover. Frequent periods
of desiccation are required by Xanthoria (Kershaw 1972).
Pearson and Henriksson (1981) reported that lichens in
growth chambers became less active or became moldy
in the absence of frequent wet/dry cycles. Field studies
in Montana forests showed that long durations of high
humidity may favor a few lichen species, but these conditions also eliminated many others (McCune and Antos
1982). Orange lichen was more abundant on sagebrush
growing in drier sites, as shown by elevational analysis
(fig. 8) .. Perhaps this distribution pattern may have been
caused by the dual influence of pathological and physiological factors.
Mountain big sagebrush is the dominant subspecies
at elevations above 5,500 ft in the study area. It had the
least lichen cover and the smallest mean stem growth
ratio of the three subspecies studied (figs. 1, 4). These
two factors, elevation and stem growth pattern, appeared
to be complementary and were important parameters
controlline the extent oflichen cover on big sagebrush.
A multiple regression analysis of these two variables
sampled independently provided a prediction equation
for lichen cover on big sagebrush. This equation is lichen
287
dramatically if dust and climatic conditions are favorable
for lichen colonization and growth. Some people have
questioned whether the lichens were responsible for the
shrub dieoff. My observations do not support this idea.
In contrast, the shrubs died first and the lichen cover
densities increased on these dead shrubs secondarily.
centric
(1) Stem growth
Prob = 0.0001
r 2 = 0.72
I No lichen cover I
ACKNOWLEDGMENTS
high
(2) Elevation
Prob = 0.0001
r 2 = 0.40
The author thanks Dr. Bruce McCune, Department
of General Science, Oregon State University, Corvallis,
for his help and insight into quantitative and statistical
analysis of ecological relationships. He also thanks
Dr. Rick Kelsey of the USDA Forest Service, Pacific
Northwest Research Station, Corvallis; Ann DeBolt of
the Boise, Idaho, District, Bureau of Land Management;
and Dr. Mason Hale of the Smithsonian Institution for
their constructive comments.
1
lichen cover
(3) Canopy structure
live vs. dead shrubs
Prob. = 0.01
T-value = 3.42
open
REFERENCES
Figure 9-Dependence model of epiphytic lichen
cover by stem growth pattern, elevation, and
canopy structure for big sagebrush.
Adams, D. B.; Risser, P. G. 1971. Some factors influencing
the frequency of bark lichens in north central Oklahoma. American Journal of Botany. 58:752-757.
Ahmadjian, V. 1967. The lichen symbiosis. Lexington,
MA: Ginn and Co. 152 p.
Anderson, D. C.; Harper, K. T.; Holmgren, R. C. 1982.
Factors influencing development of cryptogamic soil
crusts in Utah deserts. Journal of Range Management.
35(2): 180-185.
Barker, J. R.; McKell, C. M. 1983. Habitat differences
between basin and Wyoming big sagebrush in contiguous populations. Journal of Range Management. 36:
450-454.
.
Barkman, J. J. 1958. Phytosociology and ecology of cryptogamic epiphytes. Assen, The Netherlands: Van Gorcum
and Co. 628 p.
Culberson, W. L. 1955. Qualitative and quantitative studies on the distribution of corticolous lichens and bryophytes in Wisconsin. Lloydia. 18(1): 25-36.
Diettert, R. A. 1938. The morphology of Artemisia tridentata Nutt. Lloydia. 1: 3-74.
Egan, R. S. 1987. A fifth checklist of the lichen-forming
lichenicolous and allied fungi of the continental United
States and Canada. The Bryologist. 90(2): 77-173.
Esseen, P. A. 1981. Host specificity and ecology of epiphytic macrolichens in some central Swedish spruce
forests. Wahlenbergia. 7: 73-80.
Ferguson, C. W. 1964. Annual rings in big sagebrush.
Paper of Lab. of Tree Ring Res. #1. Tucson, AZ: University of Arizona Press. 211 p.
Ferry, B. W.; Baddeley, M. S.; Hawksworth, D. L., eds.
1973. Air pollution and lichens. London: Athlone Press.
389p.
Fosberg, M. A.; Hironaka, M. 1964. Soil properties affecting the distribution of big and low sagebrush communities in southern Idaho. Amer. Soc. Agron. Spec. Publ. 5:
230-236.
Hawksworth, D. L. 1982. Secondary fungi in lichen
symbiosis: parasites, saprophytes, and parasymbionts.
Journal of the Hattori Botanical Laboratory. 52:
357-366.
Lichen Enrichment
Epiphytic lichens are not directly influenced by soil
mineral conditions because they are not attached to the
soil. Dust input was of greater importance than soil to
epiphytes (Barkman 1958). Barkman found that Xanthoria species exhibited maximum production in areas
high in nitrogen compounds. Murray (1975) conducted
a detailed mineral cycling study in southern Idaho on
big sagebrush. He considered atmospheric nutrient input
to the mineral cycle significant where large dust storms
occur two to three times a year. Significant amounts of
dry particulate matter from dust storms were deposited
in his catch basins. Potassium and nitrogen were deposited in the greatest quantities at sites oflower precipitation. His data suggest that dust storms and modern
fertilizing practices may positively influence the distribution of orange lichen.
During this study, several areas were found which
showed unusually high enrichment of lichen cover on
desert shrubs. The apparent cause of this enrichment
appears to be related to (1) agricultural fertilizers,
(2) agricultural dust, or (3) dust from dirt roads. These
anthropogenic factors.. in concert with the other environmental factors addressed in this study, can produce areas
of enrichment of orange lichen cover on shrub stands,
fenceposts, and other stable substrates in arid western
North America. Arid areas with fine, silty soils that experience dust storms periodically will tend to have more
Xanthoria lichen cover than will areas with coarse, loamy
soils.
Shrub Dieoff
Shrub stands killed by insects, flooding, drought, or
other causes create open shrub canopies with stable bark.
Such dead shrub stands will increase their lichen cover
288
Kershaw, K. A. 1972. The relationship between moisture
content and net assimilation rate of lichen thalli and
its ecological significance. Canadian Journal of Botany.
50: 543-555.
LeBlanc, S.C.; DeSloover, J. 1970. Relationship between
industrialization and the distribution and growth of
epiphytic lichens and mosses in Montreal. Canadian
Journal of Botany. 48: 1485-1496.
Lechowicz, M. J. 1981. The effects of climatic pattern
on lichen productivity: Cetraria cucullata (Bell.) Ach.
in the arctic tundra of northern Alaska. Oecologia
(Berlin). 50: 210-216.
McCune, B. 1979. Comparative ecology of structural
groups: compositional patterns in the Swan Valley
forests, Montana. Missoula, MT: University of Montana. 94 p. Thesis.
McCune, B.; Antos, J. A. 1982. Epiphytic communities
of the Swan Valley, Montana. Bryologist. 85(1): 1-12.
Murray, R. 1975. Effect of Artemisia tridentata removal
on mineral cycling. Pullman, WA: Washington State
University. 109 p. Thesis.
Peard, J. L. 1980. The ecophysiology of the lichen Xanthoria fallax (Hepp) Arn. growing on trunks of Rocky
Mountain junipers near Boulder, Colorado. Boulder,
CO: University of Colorado. 96 p. Thesis.
Pearson, L. C. 1969. Influence of temperature and humidity on distribution of lichens in a Minnesota bog. Ecology. 50(4): 740-746.
Pearson, L. C. 1970. Varying environmental factors to
grow intact lichens under laboratory conditions. American Journal of Botany. 57(6): 659-664.
Pearson, L. C.; Henriksson, E. 1981. Air pollution damage
to cell membranes in lichens. II. Laboratory experiments. Bryologist. 84: 515-520.
Rushforth, S. R.; St. Clair, L. L.; Brotherson, J. D.;
Nebeker, G. T. 1982. Lichen community in Zion
National Park. Bryologist. 85: 185-192.
Swinscow, T. D. V. 1968. Pyrenocarpous lichens: 13.
Freshwater species of Verrucaria in the British Isles.
Lichenologist. 4: 34-54.
Winward, A. H. 1970. Taxonomic and ecological relationships of a big sage complex in Idaho. Moscow, ID: University of Idaho. 80 p. Thesis.
Winward, A. H.; Tisdale, E. W. 1977. Taxonomy of the
Artemisia tridentata complex in Idaho. For., Wildlife
and Range Exp. Stn. Bull. 19. Moscow, ID. 15 p.
APPENDIX A: EPIPHYTIC LICHEN SPECIES
OCCURRING IN SOUTHERN IDAHO ON BIG
SAGEBRUSH BY SUBSPECIES
wyomingens is
Buellia punctata
Caloplaca fraudans
Candelaria concolor
Candelariella rosulans
C. vitellina
Hypogymnia physodes
Lecanora cf. varia
Lecanora sp.
Lecidea plebeja
Lepraria neglecta
Letharia vulpina
Melanelia exasperatula
Melanelia incolorata
Physcia dimidiata
Physcia sp.
Physconia detersa
Physconia grisea
P. muscigena
Rinodina sp.
Usnea sp.
Xanthoria candelaria
X fallax
X polycarpa
X sorediata
X
tridentata
vaseyana
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
289
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X