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EFFECTS OF FIRE ON JUNIPER
WOODLAND ECOSYSTEMS IN THE
GREAT BASIN
Stephen C. Bunting
Schott and Pieper 1987; Tress and Klopatek 1987), western juniper (Burkhardt and Tisdale 1969; Johnson and
Smathers 1976; Martin 1978; Miller and others 1992;
Young and Evans 1981), eastern redcedar (Juniperus
virginiana L.) (Owensby and others 1973), Ashe juniper
(J. ashei Buchholz) (Wright and Bailey 1982), and
others. In the West, juniper has been noted to invade
into sagebrush-grass, dry mountain meadow, curlleaf
mountain-mahogany (Cercocarpus ledifolius Nutt.),
and aspen (Populus tremuloides Michx.) vegetation.
ABSTRACT
Juniper has invaded adjacent vegetation types through·
out much of its worldwide range and is characteristic of
these woodlands. In the Western United States this veg·
etation change has affected millions of hectares. Fire his·
tory studies for juniper·dominated areas indicate that fire·
free intervals of 50 years or less would probably have
checked this advance during the pristine period. However,
the number of fire ignitions we currently receive does not
seem adequate given the dissected nature of the topogra·
phy and the discontinuous fuels of these areas. Alternative
scenarios are suggested to explain this inconsistency.
ACCEPTED CAUSES
The causes for the invasion of juniper into adjacent
communities have generally been credited to: (1) change
in climate, (2) effects of livestock grazing on plant competition and fire potential, and (3) wildfire suppression
(Blackburn and Tueller 1970; Burkhardt and Tisdale
1976; Gruel11986; Wright and Bailey 1982; Young and
Evans 1981). The latter two are usually given as the most
likely causes. Livestock grazing reduces abundance of
fine fuel and therefore the fire potential. Livestock grazing may affect the rate of invasion, but the eventual outcome for both grazed and ungrazed sites will be the same
in the absence of fire.
Reintroduction of fire onto the juniper-dominated site
has often resulted in increases in herbaceous productivity
(Aro 1971; Despain 1987; Wink and Wright 1973) and species diversity (Tress and Klopatek 1987). Recent reviews
of the effects of fire in the juniper woodlands on specific
plant species and postfire succession have been written by
Bunting and others (1987), Everett (1987), Koniak (1985),
Martin (1978), and Wright and Bailey (1982).
Few detailed fire history studies have been completed
for areas with juniper- or pinyon-juniper-dominated vegetation. The most complete study is that in western juniper in southwestern Idaho by Burkhardt and Tisdale
(1969, 1976). Their data indicate that mean fire-free intervals (FFI) for old stands of juniper between the years
1650 and 1900 were 25 to 30 years. However, one site
had an FFI of 13 years. There were a number of years
that several sites burned during the same year even
though the sites were a considerable distance apart.
Few fires were documented for the stands of juniper
that were invading sagebrush-grass communities. Young
and Evans (1981) evaluated the fire history of a western
juniper-dominated site in northern California. They
found evidence of three large fires during the 1650-1900
interval. They concluded that FFI's less than 50 years
INTRODUCTION
Juniper woodlands are a m~or vegetation type found in
most of the Western States. The term "pinyon-juniper" is
commonly used for the woodlands in aggregate, although
junipers (Juniperus spp.) are more common and significant portions exist that do not have a pinyon (Pinus spp.)
codominant. Common juniper species included are oneseed (J. monosperma [Engelm.] Sarg.), Utah (J. osteo·
sperma [Torr.] Little), redberry (J. pinchoti Sudw.), and
alligator juniper (J. deppeana Steud.). The western juniper (J. occidentalis Hook.) woodland is located primarily
in the northwestern Great Basin and Columbia Basin and
has no pinyon associate. Additional juniper woodlands
occur in North America on the northern Great Plains,
southern mixed and tall grass prairies (Wright and Bailey
1982); and in southern Europe (di Castri and others1981;
Polunin and Walters 1985), Asia (Walter and Breckle
1986), and northern Africa (di Castri and others 1981).
During pristine times dense juniper stands composed
of large trees were often restricted to rocky areas or areas
with dissected topography (Burkhardt and Tisdale 1976;
O'Rourke and Ogden 1969). Large trees may have also occurred in adjacent sites but in open savannahlike stands.
The reduction of fire occurrence, in most juniper woodlands, resulted in increased density of juniper, an advance
ofjuniper into adjacent vegetation types, and the concomitant reduction in the productivity and species diversity of
herbaceous and shrub species. This has been noted for
southwestern pinyon-juniper (Arnold and others 1964;
Paper presented at the Symposium on Ecology, Management, and Res·
toration of Intermountain Annual Rangelands. Boise, ID, May 1S.22, 1992.
Stephen C. Bunting is Professor of Range Resources, College of For·
estry, Wildlife and Range Sciences, University ofldaho, Moscow, ID.
53
Table 2-lnfluence of fall-applied glyphosate + 2,4-0' on forage
production of wheatgrasses at Fargo, NO
Species
Cultivar
fallow technique was developed to control downy brome
during the renovation of rangelands in Nevada (Eckert
and others1974). Atrazine applied at 1.1 kglha in late
fall controlled downy brome and most other vegetation for
1 year. A significant advantage of this technique was the
accumulation of soil moisture that was available for germination and growth of perennial range grasses seeded 1 year
after the atrazine was applied. This technique required
the use of deep-furrow drills to move the treated soil away
from the seeded grasses. The furrows had an added benefit
of protecting the new seedlings from drought and coldtemperature stress. Broadleaf weeds such as Russian
thistle (Salsola iberica) and mustards (Sisymbrium and
Descurainia spp.) were controlled during the year of grass
establishment with 2,4-D. Unfortunately, the use of this
technique was limited, and atrazine is no longer registered
for use on rangelands. Since the early 1970's, several new,
highly active herbicides such as hexazinone and sulfonylureas have become available that may be adaptable to the
chemical-fallow technique of renovating rangelands.
Glyphosate is a foliage-active herbicide that will control
small downy brome at rates as low as 0.3 kglha. Research
in Wyoming has shown that glyphosate and paraquat applied in May at low rates controlled downy brome with
minimum injury to established range grasses (Whitson and
others 1991). To be effective, treatments had to be applied
after downy brome emergence was complete. In North
Dakota, glyphosate applied at 0.2 kglha in" the spring did
not reduce forage production of western wheatgrass, blue
grama (Bouteloua gracilis), and Stipa spp., whereas glyphosate applied in the fall reduced forage production of
western wheatgrass (Lym and Kirby 1991). Cutlivars of
crested, western, intermediate, and thickspike wheatgrasses (Elymus lancerolatus ssp.lanceolatus) differed
greatly in response to applications of glyphosate plus
2,4-D (table 2). Therefore, any research on the tolerance
of perennial grasses to herbicides such as glyphosate needs
to include cultivars with germplasm diversity. Glyphosate
may be useful for reducing the downy brome seed bank in
rangelands and should be evaluated extensively.
.
As mentioned earlier, chlorsulfuron and metsulfuron will
suppress downy brome in winter wheat. Comes (1985-87),
conducting research in the low-rainfall area of Washington,
has shown that new seedings of Nordan crested wheatgrass
Forage production
Percent of nontreated
Crested
Nordan
Fairway
Parkway
Ruff
Hycrest
Western
Walsh
Rodan
Intermediate
Mandan759R
Slate
103
46
Thickspike
Sodar
Critana
135
76
129
91
127
93
90
68
68
'Giyphosate + 2.4-D applied at 0.4 + 0.7 kglha on September 19, 1989, at
Fargo, NO.
brome control in wheat is based on positional selectively.
This herbicide must be incorporated mechanically, as it
does not leach into soil. Wheat must be planted with
drills that place the wheat seed below the treated zone.
The soil-persistent sulfonylurea herbicides such as chlorsulfuron and metsulfuron applied preemergence to downy
brome have suppressed downy brome 30 to 40 percent in
winter wheat, but rates used are generally too low to control this weed consistently.
In no-till winter wheat, a granular formulation of triallate plus trifluralin (BuckleTM) applied to the soil surface before planting wheat has controlled downy brome.
The granules are not absorbed by surface litter in no-till
fields and thus are more effective than liquid formulations
of these herbicides. Selective use of this treatment is dependent on some movement of the herbicide away from
the wheat row during the planting operation and on placement of the wheat seed at least 3 to 4 em deep. Diclofop
applied to the soil surface after planting wheat no-till has
controlled downy brome selectively but can be absorbed by
excessive surface residues and requires rain soon after application for activation. Under ideal conditions, weed control and crop yield response to the use of diclofop in no-till
systems can be dramatic.
Pronamide applied in late fall will control downy brome
selectively in established (1 year or older) slender wheatgrass (Elymus trachycaulus ssp. trachycaulus), tall wheatgrass (Elytrigia elongata), western wheatgrass (Pascopyrum smithii), crested wheatgrass (Agropyron desertarum), intermediate wheatgrass (Elytrigia intermedia),
creeping foxtail (Alopecurus arundinaceus), and orchardgrass (})actylis glomerata) grown in Conservation Reserve
Program (CRP) lands. The current label for pronamide
use on CRP lands prohibits the grazing of treated grasses.
However, this herbicide may be useful in an integrated
rangeland renovation program to prevent downy brome
seed production and thus reduce the soil weed seed bank.
Downy brome is very competitive in new seedings of perennial rangegrasses and as few as 40 plants per m2 will
reduce shoot biomass of crested wheatgrass by 62 percent
(Evans 1961). In the 1970's an atrazine-based chemical
Table 3--Control of downy brome and Russian thistle in new
seedlings of Covar sheep fescue at Und, WA
Herbicide
Nontreated
Bromoxynil
+COC2
Quizalofop
+COC
Quizalofop
+bromoxynil
+CCC
Rate
Downy
brome
Russian
thistle
kg/ha
- - Percent control· •
Cover
sheep fescue
No.IIT'I
Vigo~
0.0
.28
0
0
0
93
227
235
2.5
2.8
.11
97
0
323
3.5
.11
+.28
99
86
253
3.0
'COC .. Crop oil concentrate (1 percent v/v).
2\Jigor rating: o... plants dead; 5 .. plants normal and vigorous.
54
will tolerate preemergence applications of chlorsulfuron
applied at up to 0.05 kglha. Forage dry weight of crested
wheatgrass was similar to the hand-weeded controls during the year of establishment and was increased up to 200
percent during the second year when the controls were not
hand weeded. Similar results were achieved with a number of other range grasses. Davison and others (1984) reported that Nordan crested wheatgrass grown in the greenhouse would tolerate 0.16 kgllia of chlorsulfuron applied
either preemergence or postemergence. Additional research on the use of chlorsulfuron in rangelands is needed
to determine the full potential of this and related herbicides.
developed must be integrated into a total rangeland system
that recognizes biological, economical, and environmental
concerns.
REFERENCES
Bolton, F.; Appleby, A. P. 1992. [Unpublished data.]
Corvallis, OR: Oregon State University.
Comes, R. D. 1985-87. [Unpublished data.] Prosser, WA:
U.S. Department of Agriculture, Agricultural Research
Service.
Davison, J. C.; Krall, J. M.; Johnson, W. S. 1984. Theresponse of selected range grass species to chlorsulfuron.
Proceedings, Western Society ofWeed Science. 37:210.
(Abstract).
Devlin, D. L.; Gealy, D. R.; Morrow L. A 1987. Differential metabolism of metribuzin by downy brome (Bromus
tectorum) and winter wheat (Triticum aestivum). Weed
Science. 35: 741-745.
Eckert, R. E., Jr.; Asher, J. E.; Christensen, M. D.; Evans,
R. A 1974. Evaluation of the atrazine fallow technique
for weed control and seedling establishment. Journal of
Range Management. 27(4): 288-292.
Evans, R. A 1961. Effects of different densities of downy
brome (Bromus tectorum) on growth and survival of
crested wheatgrass (Agropyron desertorum) in the
greenhouse. Weeds. 9:216-223.
Hanks, E.; McWhorter, C. G. 1991. Variables affecting the
use of positive displacement pumps to apply herbicides
in ultralow volume. Weed Technology. 5: 111-116.
Lym, R. G.; Kirby, D. R. 1991. Effect ofglyphosate on
introduced and native grasses. Weed Technology.
5:421-425.
Mack, R. N. 1981. Invasion of Bromus tectorum L. into
western North America: an ecological chronicle. AgroEcosystems. 7: 145-165.
McWhorter, C. G.; Barrentine, W. L. 1988. Spread of paraffinic oil on leaf surfaces of Johnsongrass (Sorghum
halepence). Weed Science. 36: 111-117.
Mitich, L. W.; Kyser, G. B. 1987. WSWS survey of common and troublesome weeds in twelve western states.
Proceedings, Western Society ofWeed Science. 40:
36-59.
Morrow, L.A.; Stahlman, P. W. 1984. The history and distribution of downy brome (Bromus tectorum) in North
America. Weed Science. 32(supplement 1): 2-6.
Ogg, A. G., Jr. [Unpublished data.] Pullman, WA: U.S.
Department of Agriculture, Agricultural Research
Service.
Stahlman, P. W. 1984. Downy brome (Bromus tectorum)
control with diclofop in winter wheat (Triticum
aestivum). Weed Science. 32:59-62.
Swan, D. G.; Whitesides, R. E.1988. Downybrome (Bromus tectorum) control in winter wheat. Weed Technology. 2:481-485.
Thill, D. C.; Beck, K. G.; Callihan, R. H. 1984. The biology
of downy brome (Bromus tectorum). Weed Science.
32(supplement 1): 7-12.
Whitson, T. D.; Fink, G. E.; Barnard, S. E. 1991. Annual
report: Rangeland research and extension demonstrations. Laramie, WY: University of Wyoming: 8-9.
RECENT DEVELOPMENTS
In recent years, a new group of herbicides has been developed that will control most annual grass weeds, including downy brome, in fine-leaved fescues. Quizalofop applied postemergence (1990-91) at 0.1 kg/ha plus crop oil
concentrate controlled downy brome selectively in seedling
Covar sheep fescue (Festuca ovina) (Ogg, unpublished).
Similar results were obtained with fluazifop for barnyardgrass CEchinochloa crus-galli) control in Durar hard fescue
(Festuca trachyphylla). When these herbicides were tankmixed with bromoxynil, most seedling broadleaf weeds
were controlled also (table 3). The use of these and related
herbicides needs to be investigated more fully under rangeland conditions.
Herbicide cost and sprayer efficiency are major economic
considerations in most croplands and are important especially in rangeland. Recently, a new sprayer has been developed that uses 2 to 5 L of total volume per ha (0.25 to
0.50 gallons per acre) and may enhance herbicide activity
(Hanks and McWhorter 1991). Referred to as air-assist
sprayers, these sprayers use compressed air delivered to
each nozzle at 28 to 55 k Pa (4 to 9 psi) to propel the spray
solution. Herbicides are dissolved in oil instead of water
and micro-metering pumps deliver the herbicide-oil mixture to the nozzles. Spray droplet size is maintained at
about 250 microns with this system. Because herbicides
are dissolved in oil, coverage of leaf surfaces is improved
and spray solutions do not dry as rapidly as water-based
sprays (McWhorter and Barrentine 1988). These conditions have enhanced the activity of some herbicides. The
air-assist sprayer would appear to have excellent applicability to rangeland conditions and should be evaluated
thoroughly.
The most significant problems that need to be addressed
in the use of herbicides on rangelands include:
•
•
•
•
•
Cost of herbicides.
Selectivity in mixed species.
Inactivation of herbicides by surface litter.
Weed seed longevity.
Environmental concerns.
It should be emphasized that total reliance on one
method of control, for example herbicides, is rarely successful and is never sustainable. An approach that integrates all available methods (cultural, mechanical, biological, and chemical) is much more likely to produce effective
weed control. In addition, the weed management system
55