Ungulate Browsing of Two Populations of
Rubber Rabbitbrush
Sherel Goodrich
E. Durant McArthur
Allen Huber
Jeffrey E. Ott
Abstract—Utilization of willow-leaf rubber rabbitbrush (Chrysothamnus nauseosus ssp. salicifolius) was determined by twig measurements in spring and fall at two populations in Duchesne
County, Utah. These measurements indicted ungulates used between 38 and 59% of twig growth in 2 years at two sites. Use was
mostly in winter when mule deer (Odocoileus hemionus) and elk
(Cervus elaphus) were present. Cattle (Bos taurus) were also present
in summer and fall. Most of the cattle use appeared to be in the fall.
Use of two color morphs (white and green) was compared at one site.
There was no significant (P > 0.05) difference between use of marked
twigs of the color morhps. However, the percent branches browsed
did show highly significant seasonal differences between the color
morphs (P < 0.01 for three of the four dates but P > 0.2 for the fourth
date).
Rabbitbrush (Chrysothamnus) is generally considered low
preference and low forage value for ungulates. However,
the genus is far too complex for standard criteria of universal
application. Anderson (1986a) listed five sections, 16 species, and 39 subspecies for the genus, with 22 subspecies for
rubber rabbitbrush (C. nauseosus). Within the great variation of the genus are found some taxa of high forage preference by at least some ungulates. Moderate use and value of
yellowbrush or mountain low rabbitbrush (Chrysothamnus
viscidiflorus ssp. lanceolatus) has been noted by Sampson
(1919), Lommasson and others (1937), and Dayton (1931).
However, decades have passed with this plant still often
considered, by association with its relatives, to be of low or
worthless forage value, and most often studied as an object
of range control (McArthur and Meyer 1987). Although large
stands of some taxa of rubber rabbitbrush show little, if any,
ungulate use, other populations are moderately to heavily
used annually. In general, narrow-leaved plants with green
or yellow stems are less used by herbivores than are wideleaved plants with white stems (Hanks and others 1975;
In: McArthur, E. Durant; Ostler, W. Kent; Wambolt, Carl L., comps. 1999.
Proceedings: shrubland ecotones; 1998 August 12–14; Ephraim, UT. Proc.
RMRS-P-11. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station.
Sherel Goodrich is an Ecologist, Ashley National Forest, Vernal, UT 84078.
Durant McArthur is Project Leader and Supervisory Research Geneticist,
Shrub Sciences Laboratory, Rocky Mountain Research Station, Forest Service, U.S. Department of Agriculture, Provo, UT 84606. Allen Huber is a
Range Conservationist, Duchesne District, Ashley National Forest, U.S.
Department of Agriculture, Duchesne, UT 84021. Jeff Ott is a Biological
Technician, Shrub Sciences Laboratory, Rocky Mountain Research Station,
Forest Service, U. S. Department of Agriculture, Provo, UT 84606.
196
McArthur and others 1979a). The study reported in this
paper is focused on wide-leaved plants with both green and
white stems. We entered the study assuming these plants
were willow leaf or mountain white rubber rabbitbrush (C.
nauseosus ssp. salicifolius). However, we wondered if the
green-stemmed plants were a different taxon.
Study Locations ________________
Based on previous observations of use of rubber rabbitbrush, two sites were selected in Duchesne County, Utah.
One site is at Bear Gulch, West Tavaputs Plateau, about 32 km
and 232 degrees from Duchesne, Utah, at 2,455 m elevation
(fig.1). This site is on an alluvial bottom with calcareous,
gravelly, loam soils developed from the Uinta Formation.
The shrubs are associated with seeded grasses (mostly
smooth brome) on the canyon bottom. Slopes adjacent to the
bottom support contrasting communities with Douglas-fir
(Pseudotsuga menziesii) on cool (northerly) aspects. Colorado pinyon (Pinus edulis), Utah juniper (Juniperus osteosperma), Alder-leaf mountain-mahogany (Cercocarpus
montanus), and Salina wildrye (Elymus salinus) are common on warmer aspects.
The other site is near Round Grove (Red Rock), Farm
Creek drainage at the south flank of the Uinta Mountains,
about 18 airline kilometers and 358 degrees from Tabiona,
Utah, at 2,350 m elevation (fig. 1). This site is also on an
alluvial bottom where basin big sagebrush (Artemisia
Figure 1—Study site locations.
USDA Forest Service Proceedings RMRS-P-11. 1999
tridentata ssp. tridentata), snowberry (Symphoricarpos oreophilus), Kentucky bluegrass (Poa pratensis), and thickspike
wheatgrass (Elymus lanceolatus) are common species. The
adjacent uplands support an abundance of alder-leaf mountain-mahogany and other browse species.
Methods _______________________
At the Bear Gulch site 10 rubber rabbitbrush plants were
selected for study. For each plant, 12 branches were selected for measurements. Only unbrowsed twigs were selected in the fall of each year. Heavy plastic tape was used
to mark a point on each selected twig below the point of
anticipated browsing (fig. 2). Data were collected on four
dates (22 Oct. 1991, 12 May 1992, 13 Oct. 1992, and 20 May
1993) so seasonal patterns of use and growth could be
documented. Primary and secondary twigs were measured
from the tape upward on each of these twigs in the fall after
growth had stopped and in spring before initiation of
growth for 2 years for a total of four readings. We recorded
two primary branch measurements; the first one was total
length of the branch distal to the stem and the second one
(included in the first) was that portion of the branch
between the tape and the first secondary branch. Secondary branches were only recorded if they were longer than
5 cm. Fecal group counts in three 1 by 50 m plots were made
to give an indication of relative ungulate presence at the
site (table 1). Fecal groups were swept from the plots after
they were counted. At the Round Grove site 20 rubber
rabbitbrush plants were selected with 10 plants having
greenish stems and 10 plants having whitish stems. These
plants were paired, e.g., each white-stemmed plant was
paired systematically with a green-stemmed plant of similar size within a 2 meter radius. Branch measurements and
pellet group counts were made as described above. Also 30
additional small branches per plant were observed for
utilization. Branches were recorded as used if they had any
obvious use by ungulates. Those with no obvious use were
recorded as not used. Results are shown in table 2. Mean
values that are followed with + indicate mean + standard
error of the mean. To compare the white and green color
morphs at Round Grove a paired t-test was performed
(Woolf 1968). Percent values were arcsine transformed for
data analysis but are reported herein as percent values.
Figure 2—Sampling scheme for branch measurement. The 2nd primary branch (2nd 1°) was included
in the regular primary measurement and is not discussed further in the study.
Results ________________________
Contrast of branch length between fall and spring readings indicated about 55% use at the Bear Gulch site in both
winters. This contrast indicated 59 and 36% use of the whitestemmed morph and 47 and 38% of the green-stemmed
morph at Round Grove in the winters 1991-1992 and 19921993 respectively (tables 1, 2). Use of branches on individual
Table 1—Ungulate fecal groups.
Ungulate fecal groups
Date
Ungulate
Total
Round Grove
Percent
of total
05/92
Deer
Elk
Cow
9
0
0
100
0
0
0.060
0
0
10/92
Deer
Elk
Cow
4
0
25
14
0
86
0.027
0
0.167
1
18
34
2
34
64
0.007
0.120
0.227
05/93
Deer
Elk
Cow
6
18
2
23
69
8
0.040
0.120
0.013
0
29
1
0
97
3
0
0.123
0.007
USDA Forest Service Proceedings RMRS-P-11. 1999
Number
per M2
Total
Bear Gulch
Percent
of total
Number
per M2
197
Table 2—Paired t-tests for white and green morphs for ungulate use.
Date
10/91
05/92
10/92
05/93
Percent of branches browsed
(n = 30/plant)
White
Green
90.3
98.0
99.7
100.0
30.3
68.0
73.6
99.0
t
6.6
4.0
4.7
1.4
P
<0.01
<0.01
<0.01
>0.20
shrubs varied from 34 to 72% at Bear Gulch and 18 to 80%
for the white morph and from 6 to 92% for the green color
morph at Round Grove (data not shown). The 30 twig
comparisons of the white and green morphs at Round Grove
were temporally different (table 2). White morphs ranged
from 90-100%; green morphs from 30-90%. Fall readings
showed greater use of the white morph than of the green one.
Spring readings shows less difference in use between the 2
morphs than fall readings. Figure 3 documents the use and
regrowth of primary and secondary branches of willowleaf
rubber rabbitbrush at Bear Gulch and Red Rock (Round
Grove). Note that primary branches are much longer (~2x) at
Red Rock but the secondary branches (per primary branch)
are much longer (~3x) at Bear Gulch.
Discussion _____________________
Cattle were present in summer at the Round Grove site and
in one summer at the Bear Gulch site. Cattle use of this shrub
appeared to be quite limited except in the fall just before they
were removed from the sites. Considerable cattle use of
willow-leaf rubber rabbitbrush was observed in other canyons
of the Tavaputs Plateau in the fall. Pellet group counts
indicated most browsing of these shrubs at the Bear Gulch
site was a function of elk use, and at Round Grove it was
mostly a function of mule deer use in winter of 1991-1992
and elk and deer use in winter of 1992-1993 (table 3). We
suspect the different growth forms at Bear Gulch and Round
Grove are a result of more elk and cattle use on a sustained
basis at Bear Gulch so the plant’s main central stem is
harvested more frequently than at Round Grove. The mule
deer at Round Grove apparently strip more secondary branches
(fig. 3).
At the Bear Gulch site, use was observed to take place as
soon as wild ungulates moved on the area in late fall or early
winter. Considerable use of this shrub occurred prior to or
concurrent with use of alder-leaf mountain mahogany on
adjacent slopes. Preference or selectivity equal to or greater
than for alder-leaf mountain mahogany is indicated for this
population. We have observed similar use of rubber rabbitbrush early in the winter season at Taylor Flat, Daggett
County, where other browse species are available. This
location in Daggett County was seeded with rubber rabbitbrush seed from a palatable population of C. nauseosus ssp.
hololeucus from Salt Creek, Juab County, Utah.
The two color morphs at Round Grove are apparently both
willow-leaf rubber rabbitbrush. Subspecies of rubber rabbitbrush are often sympatric (McArthur and others 1979b;
Anderson 1986b) but in this case the two morphs behave
quite similarly and are eaten by ungulates much the same.
The stems of the green morph are light green and not as dark
as many rubber rabbitbrush subspecies. The difference in
stem color and temporal difference in twig end browsing
(total stem browsing was not different) may be due to a small
genetic difference within the population. Readings in the fall
showed considerably higher use of twigs of the white morph
than for the green one. However, by spring the difference
was smaller. This indicates preference for the white morph
and acceptance of the green morph as preferred forage had
evened out during the winter. Early use of preferred plants
and delayed acceptance of less preferred plants as winter
progresses seems reasonable. Such a relationship has been
noted by Welch and others (1981) and Hutchings and Stewart
(1953) for ungulates and by Welch and others (1991) for sage
grouse. This relationship is not reflected in our branch
utilization measurements that compare growth with utilization at the end of winter. Had measurements been taken to
compare late fall or early winter use, branch utilization data
might have reflected preference for the white morph.
In addition to rubber rabbitbrush use, we observed use
of yellowbrush at the Bear Gulch and Round Grove sites
where it was moderately to closely hedged after each winter
browsing season.
Table 3—Summary of branch lengths and percent Use.
Date
10/91
10/92
5/93
BearGulch
Branch length (cm)
Percent usea
16,404
—
7,522
55.5 ± 4.3
11,925
—
5,255
54.5 ± 2.8
Red Rock (Round Grove)
White morph
Branch length (cm)
Percent usea
5,604
—
2,178
59.0 ± 5.4
5,736
—
3,240
36.4 ± 5.2
Green morph
Branch length (cm)
Percent usea
5,511
—
2,686
47.4 ± 8.1
6,007
—
3,780
38.5 ± 2.7
a
198
5/92
Based on individual samples, 10 plants per population and 12 branches per plant.
USDA Forest Service Proceedings RMRS-P-11. 1999
Figure 3—Branch lengths over the course of the study. Left—Bear
Gulch, Right—Red Rock (Round Grove).
Apparently by association with large stands of unpalatable rabbitbrush, all rabbitbrush is sometimes considered of
no forage value or at best of low value. This complex of plants
is far too variable to fit such a simplified standard criteria.
In addition to selectivity demonstrated by some ungulates at
least at some times of the year, nutritional value is indicated
to be high. In a study of seven subspecies of rubber rabbitbrush, Bhat and others (1990) found crude protein levels
about equal to that of other high-protein shrubs such as big
sagebrush and fourwing saltbush. Protein levels found in
this study exceeded protein requirements of wintering mule
deer and sheep of about 7.5-8.9% (Welch 1989). On the
Wyoming Red Desert, crude protein values of 9.7 and 6.8%
were found for summer and winter, respectively (Krysl and
others 1984). Phosphorus levels and in vitro dry matter
digestion also rated high compared to some other winter
browse species (Bhat and others 1990).
Complexity of this group of plants as well as rangelands in
general demonstrate the need to go beyond simplified standard criteria designed for universal application. Observations passed on from one generation to the next without
critical review has greatly suppressed the understanding
and use of valuable resources to be found in the rabbitbrush
complex.
References _____________________
Anderson, L. C. 1986a. An overview of the genus Chrysothamnus
Asteraceae. In: McArthur, E. D.; Welch, B. L., comps. Proceedings—symposium on the biology of Artemisia and Chrysothamnus; 1984 July 9-13; Provo, UT. Gen. Tech. Rep. INT-200. Ogden,
UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 29-45.
Anderson, L. C. 1986b. Sympatric subspecies in Chrysothamnus
nauseosus. In: McArthur, E. D.; Welch, B. L., comps. Proceedings—symposium on the biology of Artemisia and Chrysothamnus; 1984 July 9-13; Provo, UT. Gen. Tech. Rep. INT-200. Ogden,
UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 98-103.
USDA Forest Service Proceedings RMRS-P-11. 1999
Bhat, R. B.; Welsh, B. L.; Weber, D. J.; McArthur, E. D. 1990. Midwinter protein, phosphorus, and digestibility of Chrysothamnus
nauseosus subspecies. Journal of Range Management. 43: 177-179.
Dayton, W. A. 1931. Important western browse plants. Misc. Pub.
101. Washington, DC: U.S. Department of Agriculture. 214 p.
Hanks, D. L.; McArthur, E. D.; Plummer, A. P.; Giunta, B. C.;
Blawer, A. C. 1975. Chromatographic recognition of some palatable and unpalatable subspecies of rubber rabbitbrush in and
around Utah. Journal of Range Management. 28: 144-148.
Hutchings, S. S.; Stewart, G. 1953. Increasing forage yields and
sheep production on Intermountain winter ranges. Circular No.
925. Washington DC: U.S. department of Agriculture, Forest
Service. 63 p.
Krysl, L. J.; Sowell, B. F.; Hubbert, M. E.; Plumb, G. E. et al. 1984.
Horses and cattle grazing in the Wyoming Red Desert, II. dietary
quality. Journal of Range Management. 37: 252-256.
Lommasson, T.; Park, B. C.; Kutzleb, C. A. and others. 1937. Range
plant handbook. Washington, DC: U.S. Department of Agriculture.
McArthur, E. D.; Blauer, A. C.; Plummer, A. P.; Stevens, R. 1979a.
Characteristics and hybridization of important Intermountain
shrubs III. INT-RP-220. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 82 p.
McArthur E. D.; Tiernan, C. F.; Welch, B. L. 1979b. Subspecies
specificity of gall forms on Chrysothamnus nauseosus. Great
Basin Naturalist. 39: 81-87.
McArthur, E. D.; Meyer, S. E. 1987. A review of the taxonomy and
distribution of Chrysothamnus. In: Johnson, K. L. Proceedings
of the Fourth Utah Shrub Ecology Workshop, the genus Chrysothamnus; 1986 September 17-18; Cedar City UT. Logan, UT:
Utah State University, College of Natural Resources: 9-17.
Sampson, A. W. 1919. Plant succession in relation to range management. U.S. Department of Agriculture Bull. 791. Washington,
DC: U. S. Department of Agriculture. 76 p.
Welch, B. L. 1989. Nutritive value of shrubs. In: McKell, C. M., ed.
The biology and utilization of shrubs. San Diego: Academic Press
Inc.: 405-424.
Welch, B. L.; McArthur, E. D.; Davis, J. N. 1981. Differential preference
of wintering mule deer for accessions of big sagebrush and for black
sagebrush. Journal of Range Management. 34: 409-411.
Welch, B. L.; Wagstaff, F. J.; Roberson, J. A. 1991. Preference of
wintering sage grouse for big sagebrush. Journal of Range Management. 44: 462-465.
Woolf, C. M. 1968. Principles of Biometry. Princeton, NJ: D. Van
Nostrant Co., Inc. 359 p.
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