A Nevada study found that sites
with sparse native plants are more susceptible to medusahead invasion
than more diverse low sagebrush (Artemisia arbuscula) or woodland/low
sagebrush
communities. If the more diverse communities are degraded
to a "low" seral state, medusahead can invade and occupy the site. Young and
others [119] determined that low sagebrush communities are most susceptible to medusahead
invasion, while big sagebrush (A. tridentata) communities are more resistant [118].
Mule deer generally use medusahead very little. A northeastern
Oregon medusahead-rattail fescue (Festuca myuros)-soft chess (Bromus
mollis) community received some spring
and summer use. However, despite the extensive
stands available, medusahead was still the least preferred forage of mule deer
in winter, summer, and fall, and it ranked low in spring. Communities dominated by medusahead
were of little value to mule deer, while cheatgrass-dominated communities receive substantial
use [14]. The dwarf sagebrush species such as low sagebrush and black sagebrush (Artemisia nova)
are
preferred mule deer browse. Medusahead has established in some dwarf sagebrush communities,
and the invasion of such sites by
medusahead has increased the incidence of wildfire as reduced cover of dwarf
sagebrushes. These sites
had previously been considered "fireproof" because of
reduced herbaceous vegetation caused by excessive grazing [23].
A healthy stand of
perennial vegetation appears to be the best barrier to medusahead invasion [28].
Medusahead invasions are most common on ranges in poor condition. Poor grazing management practices may accelerate the rate of
spread, but proper management alone may not prevent invasion [42]. Cultivated areas are susceptible to
invasion by medusahead, especially old fields. Livestock avoid medusahead when
more palatable forage is available, leading to an abundance of soil-stored
medusahead seed [83]. A combination of treatments including grazing, burning,
mechanical manipulation, herbicide such as atrazine or glyphosate, and/or reseeding are generally necessary to reduce
established stands of medusahead [22,75,79,106].
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©Julie Kierstead
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GENERAL BOTANICAL CHARACTERISTICS:
Medusahead is a nonnative, cool-season annual grass [
49]. Plant
height ranges from 8 to 20 inches (20-50 cm), depending on the site. Plants
produce tillers, but very few leaves [
79,
83]. Medusahead has a
distinctive flowerhead. The inflorescence contains 2 to 3 spikelets per node, and each spikelet contains 1
seed. Plants produce an average of 7.1 seeds per spike [
79,
83]. Medusahead has 2 types of awns: both are flat, but the longer of
the 2 contains barbs that point upward [
79]. Plants in dense stands usually produce
1 spike; in open areas the number of spikes per plant typically increases
to 3 to 5. An exceptional plant in Idaho produced 133 spikes.
Medusahead-dominated
stands usually have more than 100
plants/ft
2. Densities of 1,500 to 2,000 plants/ft
2 have been found
on a valley bottom in southern Idaho [
99,
106].
RAUNKIAER [90] LIFE FORM:
Therophyte
REGENERATION PROCESSES:
Medusahead is
entirely dependent upon seed production for regeneration. It is an extremely capable
seeder because of its large annual
production of viable seed, and because its seed maintains viability in
litter and soil for at least 1 year [
99]. Medusahead maintains a
short-lived seedbank [
10,
62,
99]. Plants produce up to 6,000 seeds/ft
2
of soil, propagating dense
stands in succeeding years [
75]. Medusahead is principally self fertile. Most of the
pollen grains are dispersed within the floret and only a moderate number of
pollen grains are produced in each of the short anthers [
41]. Some
cross-pollination is effected by wind [
18].
Animals, wind, and water disperse the seed, and spread is rapid
[42]. A long, rough awn aids in animal dispersal of seed, and medusahead often 1st establishes along
domestic sheep and cow trails [83]. Seeds are dispersed primarily from the coats
and intestinal tracts of grazing animals [42,75,99,109]. Germinable seeds have been recovered in fecal material 4
to 9 days after ingestion by rabbits and domestic sheep, respectively [99]. Stiff barbs pointing in
1 direction enable the
seeds to work into the duff and top layers of the soil. Seeds may germinate in fall, winter, or
spring;
fall germination is most common [6,99,116]. Seedlings
from all seasons produce seeds by early summer [116]. Seeds germinating
in the top layer of litter without soil contact may die during the 1st dry
spell [61,75]. Medusahead usually germinates faster than its competitors. Germination
has been observed 8 to 10 hours after moistening at 50 degrees
Fahrenheit (10 oC) [49]. Germination rates are often over 90% [99]. Awn removal
increases the percentage of germination [85].
A Nevada study found that medusahead seedling emergence and growth
is favored by soil movement and pitting of the soil surface because these
conditions maintain favorable soil temperatures and moisture levels [35]. Favorable microsites for germination and
establishment of medusahead are created when plant litter covers the soil
surface. In Nevada, emergence of medusahead germinants under litter was 47 times greater
than emergence of germinants on bare ground by the end of March. By the end of the growing season,
medusahead yield was 4 times greater under litter than on bare soil [34].
Moderate temperatures may encourage medusahead growth and yield. Maximum dry matter production of medusahead was
achieved at a moderate day/night temperature regime of 75/52 degrees Fahrenheit (24/11
oC). Its yield was
reduced by 75% with a high day/night temperature regime of 90/61 degrees Fahrenheit (32/16
oC), and reduced by 50% with a
low day/night temperature regime of 61/41degrees Fahrenheit (16/5 oC) [29].
SITE CHARACTERISTICS:
Medusahead grows in areas
that have relatively mild to cold temperatures in winter but are hot in summer [
75,
79].
It is generally found
in areas that receive fall, winter, and spring moisture followed by dry summers
[
108]. It occurs in areas with annual precipitation
of 10 to 40 inches (250-1,000 mm), with an
upper limit of precipitation approximately 50 inches (1,270 mm) [
75,
79,
99]. Infestations
primarily occur in former sagebrush-grass or bunchgrass communities that
receive 10 to 20 inches (250-500 mm) of precipitation [
79,
99]. Areas above 4,500 feet (1,370 m) elevation, and well-drained
coarse soils, may be less susceptible to invasion.
Medusahead often dominates disturbed areas on soils with high moisture-holding
capacities and slow percolation rates [33]. Sites particularly susceptible to medusahead invasion
in the more arid portions of Idaho are either those with well-developed soil
profiles, particularly with high clay content either at or near the surface; or
those occupying topographic positions that receive additional run-off from
adjacent sites. In more mesic climates, moderately well-developed soils are as susceptible
to invasion as well-developed soils. Conversely,
soils with little profile development, particularly those that are well
drained, remain dominated by cheatgrass in early seral stages regardless of
whether they are in a more arid or mesic area [28].
In a northwestern California site where medusahead is prevalent, 60% of the vegetation is grassland
or woodland/grass. The climate is mediterranean, with cool wet winters and hot
dry summers. Mean annual rainfall is 39 inches (980 mm). Soil is fine sandy loam
2 to 3.3 feet (0.6-1.0 m) deep with rapid surface drainage; slope is 10% on a southeast aspect [5,6].
Foothills in southwestern Oregon where medusahead is found have silty clay loam
soil, with 1,600 feet (500 m) elevation and 20-30% slope on a west aspect. On southwest aspects,
medusahead occurs on
5-20% slopes at 2,000 feet (600 m) elevation. The climate has a
mediterranean/maritime pattern with cool, wet winters and hot dry summers and annual
precipitation of 20 inches (500 mm) [14].
Medusahead and cheatgrass are often in
competition with each other, and soil and topographic factors affect
their distribution [28,39]. Each can replace other herbaceous vegetation and
share dominance with the other. Cheatgrass occupies a
larger geographical area than medusahead, extending to drier areas of the
semiarid western U.S. than does medusahead [29].
Cheatgrass will grow in almost any type of soil, although it does best on deep, loamy or
coarse-textured soils and it does not grow as well on fine textured soils (e.g. [32,73,125]).
Medusahead may be more likely to dominate on fine-textured soils in the Intermountain region [118].
In arid conditions, medusahead is more dependent on additional moisture for
survival. This may be because cheatgrass matures when soil moisture is still
plentiful in May, and medusahead does not mature until 3 weeks later when
moisture is more confined to depressions and clay soils [28,39]. Because medusahead matures
approximately 1 month later than cheatgrass, it initially only replaces cheatgrass on soils with
sufficient moisture holding capacity, such as clay textured soils, so that some
soil moisture remains after cheatgrass matures. Medusahead's root system can exploit all soil moisture in the soil profile
[117]. In the Columbia River Basin, medusahead is dominant on
soils high in montmorillonite clay within 10 to 12 inches (25-30 cm) of the surface,
and on soils low in clay but on with favorable topographic positions.
Cheatgrass is dominant on weakly developed soils low in montmorillonite clay.
SUCCESSIONAL STATUS:
Medusahead occurs in seral and late-successional plant communities. It has invaded vast
areas formerly dominated by perennial
grasses. Medusahead often colonizes
portions of range previously dominated by cheatgrass [
27,
57]. The growth
habits, life cycles, and ecological adaptations of medusahead and cheatgrass are
similar, and the annuals typically grow in association until medusahead
becomes dominant and eventually exclusive [
16]. Southwestern Idaho stands in which medusahead was sparse were all seral. In
virtually all cases studied, the sites invaded by medusahead had been occupied
previously by seral species, mainly annuals, which had replaced perennial
bunchgrasses depleted by overgrazing, fire, or cultivation [
64,
79,
102].
Medusahead has potential
for successionally
replacing cheatgrass in the 11-inch (280 mm) and above precipitation zone in the northern
Great Basin and elsewhere [
54]. Medusahead litter impedes cheatgrass establishment, and may do better in low nitrogen environments
than does cheatgrass [
50,
51]. Coexistence of cheatgrass and medusahead is most likely in habitats
low in both nitrogen and phosphorus. Cheatgrass is likely to have
the competitive advantage in more fertile habitats unless other environmental factors
(e.g. high clay content) favor
medusahead [
29]. In the sagebrush steppe of northeastern California,
Russian-thistle (
Salsola kali), tumblemustard
(
Sisymbrium altissimum), and cheatgrass form a seral continuum that closes many sagebrush
communities to the establishment of perennial seedlings. Medusahead has extended the seral
continuum by replacing cheatgrass on some low sagebrush sites on the Modoc Plateau [
118,
124].
Cheatgrass usually grows in dense stands
and readily ignites and carries fire. After
fire strikes a cheatgrass-infested community, cheatgrass usually
flourishes. However, medusahead can thrives in the wake of cheatgrass-driven fires
[
31].
Medusahead is a seral invader after disturbance [102].
Medusahead often grows in dense stands on disturbed
sites where climax perennial grasses have been removed, often to the exclusion
of other species [51]. The abundance of bluebunch wheatgrass has "significantly" decreased
in the Great Basin because of the invasion of
introduced annuals such as medusahead [81]. Past heavy grazing of
foothills, pastures, and rangelands of southeastern Oregon has resulted in
dominance by annual grasses such as medusahead and annual forbs including
yellow starthistle [15].
SEASONAL DEVELOPMENT:
Medusahead is a cool-season annual, and temperature is an important factor in controlling
its phenology. Medusahead germinates during autumn, late winter, or
early spring [
25,
79]. It usually germinates in October and continues to grow
through the winter in mesic climates. During winter, growth is slowed markedly
with low temperatures, and the plant resumes active growth when the temperature
increases at the beginning of spring [
25]. Leaves, stems and roots increase in number through
the winter and roots can reach 40 inches (100 cm) depth by early February [
51]. This allows
medusahead to outcompete desirable grasses such as bluebunch wheatgrass [
44,
51].
Growth accelerates in the spring; by late May or early June, seeds are in the
milk or early dough stage [
42]. Seed are generally mature by late June to early July, a few weeks
later than most annual grasses [
79]. Seeds remain in spikes until dispersal in late summer
or early fall [
99]. Late maturity and greater availability of
soil moisture late in the growing season allow medusahead to reach
maturity and produce large amounts of seeds, which might enhance
site occupation in subsequent generations [
29]. Medusahead phenology was as
follows in northern Idaho [
16]:
Date |
Development |
May 9 |
Leaf |
May 23 |
Flowerbud |
June 6 |
Flower |
June 21 |
Late Dough |
July 3 |
Mature |
FIRE ECOLOGY
SPECIES: Taeniatherum caput-medusae
UPDATE (2019): For a summary of more recently published information (2001-2019) about medusahead’s relationship with fire and response to control methods, see this
annotated bibliography.
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Medusahead establishes after
fire from
the seed bank and from seed dispersed from off-site sources [
10,
62,
99]. Bioassays
of burned soil after a rapidly spreading, wind-driven fire in California found
viable medusahead fruits within lightly charred litter [
10].
Fire regimes: The expansion of exotic annual
grasses such as medusahead has substantially increased frequency of fire in the
western United States [69]. Medusahead has a fine
structure and its herbage dries completely; therefore, its standing dead biomass
is extremely flammable. The hazard of wildfire is further increased by
considerable litter
[41].
Medusahead litter decomposes more slowly than that of most plants [108], therefore
making stands of this annual grass a fire hazard [84]. Slow decomposition
is a result of its high silica content [77,104]: total ash content of
medusahead contains 72 to 89% silica [104]. The long-lasting litter formed by medusahead
is easily ignited and burns readily [79].
Invasion can initiate a cycle where a non-native grass colonizes an
area and provides the fine fuel necessary for the initiation and propagation of
fire. Fires then increase in frequency, area, and possibly severity. Following
these grass-fueled fires, non-native grasses recover more rapidly than native species
and cause a further increase in fire [27]. Frequent fires destroy the shrub component of the
plant community, and
potentially part of the bunchgrass community, without destroying
"significant" amounts of medusahead seed [79].
The non-native grasses cheatgrass and medusahead have invaded the low sagebrush
communities on the volcanic tablelands of northeastern California and northwestern
Nevada. When precipitation is adequate, the interspaces
between sagebrush plants are completely covered by these invasive grasses. The fine fuels of these
plants, and the accumulation of litter of highly
siliceous medusahead, create conditions in which fire is easily
carried. Negative effects of wildfires in this region include erosion of the thin, coarse-textured,
eolian veneer soils
[11]. For example, the herbaceous vegetation of a ponderosa pine/Sandberg bluegrass
in Modoc County, California, included many other native herbaceous species. After a
wildfire, medusahead
excluded almost all other understory species [22].
Historically, the Snake River Plains of Idaho was vegetated with shrub-bunchgrass
communities. The
primary disturbance was patchy stand-replacement fire, occurring every few
decades. Fire usually occurred where sagebrush or other shrubs had grown dense, since bunchgrasses
did not often provide adequate
continuous fuels. With invasion of exotic annuals and increase such as medusahead, historical
patterns of postfire succession have been altered. Fire-free
intervals have been reduced, and shrub-bunchgrass lands are being converted
to annual grassland.
According to Peters and Bunting [88], "the landscape has become more homogenous,
species diversity has decreased, and burns are larger and more continuous."
Xeric big sagebrush (Artemisia tridentata ssp. xericensis), a subspecies with limited
distribution that is sometimes referred to as an ecotype of mountain big sagebrush, is found primarily in western Idaho
and eastern Oregon and is restricted to a zone where the annual precipitation exceeds 12 inches,
the elevation is less than 4,500 feet, and the summers are relatively warm. Many of these
communities are on relatively steep slopes and have a higher potential for human and
lightning-caused fires, resulting in repeated burns. These frequently burned areas are often
dominated by cheatgrass and medusahead [72].
The range of fire intervals reported for some species that dominate
communities in which medusahead occurs are listed below. Find further fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".
Community or Ecosystem |
Dominant Species |
Fire Return Interval Range (years) |
California chaparral |
Adenostoma and/or Arctostaphylos spp. |
< 35 to < 100 |
sagebrush steppe |
Artemisia tridentata/Pseudoroegneria spicata |
20-70 [86] |
basin big sagebrush |
Artemisia tridentata var. tridentata |
12-43 [96] |
mountain big sagebrush |
Artemisia tridentata var. vaseyana |
20-60 [3,21] |
Wyoming big sagebrush |
Artemisia tridentata var. wyomingensis |
10-70 (40)** [115,122] |
blue grama-needle-and-thread grass-western wheatgrass |
Bouteloua gracilis-Hesperostipa comata-Pascopyrum
smithii |
< 35 |
cheatgrass |
Bromus tectorum |
< 10 |
California montane chaparral |
Ceanothus and/or Arctostaphylos spp. |
50-100 |
western juniper |
Juniperus occidentalis |
20-70 |
Rocky Mountain juniper |
Juniperus scopulorum |
< 35 |
wheatgrass plains grasslands |
Pascopyrum smithii |
< 35 |
pinyon-juniper |
Pinus-Juniperus spp. |
< 35 [86] |
Rocky Mountain lodgepole pine* |
Pinus contorta var. latifolia |
25-300+ [1,2,95] |
Sierra lodgepole pine* |
Pinus contorta var. murrayana |
35-200 |
Pacific ponderosa pine* |
Pinus ponderosa var. ponderosa |
1-47 [2] |
mountain grasslands |
Pseudoroegneria spicata |
3-40 (10)** [1,2] |
Rocky Mountain Douglas-fir* |
Pseudotsuga menziesii var. glauca |
25-100 [2] |
coastal Douglas-fir* |
Pseudotsuga menziesii var. menziesii |
40-240 [2,82,91] |
California mixed evergreen |
Pseudotsuga menziesii var. m.-Lithocarpus
densiflorus-Arbutus m. |
< 35 [2] |
*fire return interval varies widely; trends in variation are noted in the
species summary
**(mean)
POSTFIRE REGENERATION STRATEGY [103]:
Ground residual colonizer (on-site, initial community)
Initial off-site colonizer (off-site, initial community)
FIRE EFFECTS
SPECIES: Taeniatherum caput-medusae
IMMEDIATE FIRE EFFECT ON PLANT:
Fire kills mature medusahead plants. Immature plants may be only top-killed by
early-season fire, and regenerate by tillering [
79,
83]. Fire also destroys many viable medusahead seeds, but sufficient numbers remain uninjured
that reduction in plant density is usually temporary [
76,
99].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No entry
PLANT RESPONSE TO FIRE:
UPDATE (2019): For a summary of more recently published information (2001-2019) about medusahead’s relationship with fire and response to control methods, see this
annotated bibliography.
Medusahead increases under frequent fires at the expense of native species and
sometimes, cheatgrass. It promotes further frequent fire by increasing fuel
loads [
27,
76]. Accumulated medusahead litter enables stand-replacement fires to occur in
ecosystems such as low sagebrush sites that,
under "pristine" conditions, may have been fire-resistant
[
11,
116,
119,
122]. Wildfires in medusahead-infested
areas usually minimally damage
soil surfaces and soil erosion is limited, but enough medusahead seed survives to
produce thinned, vigorous stand of multiculmed medusahead plants the following year. Within
a few years, stand densities approach prefire levels [
54].
In cheatgrass and medusahead wildfires, accumulation of litter and the rapidity at which the litter
combusts lead to soil heating of
such short duration that nitrate levels may increase. Wildfire-induced increases
in soil nitrate in cheatgrass and medusahead-dominated areas are undesirable: Medusahead is nitrophilic
and readily germinates in seedbeds with high nitrate levels. Near Alturas, California, a wind-driven wildfire
rapidly spread across a medusahead-dominated area. The litter did not completely
ash and there were still viable medusahead fruits in the lightly
charred litter. Bioassays of the burned soil found over 6.2x106
germinable seeds of medusahead per acre (unpublished data; R. R. Blank, USDA/ARS,
Reno, NV) [10].
Fire eliminates some medusahead seed and removes medusahead litter. It also places the
remaining seed in contact with mineral soil where it can germinate and
subsequently be destroyed by future treatments such as tillage and herbicide use
[108]. Contact with aqueous slurries of heated soil significantly (p<0.05) reduced the rate
and success of emergence of medusahead
seedlings compared with a control [12].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Attempts have been made to destroy medusahead by
prescribed burning in soft-dough stage to destroy the seed crop. Medusahead stands in the milk or early
dough stage (late May or early June) are
cured enough that they can carry a "light" fire that burns through the slender culms
and arrests seed development [
42]. However, a "substantial" number of seeds
are not killed by fire [
52]. Burning followed by seeding of perennial
grasses may suppress medusahead [
17]. If postfire revegetation efforts of
medusahead-infested areas are not timely, erosion will expose the clay subsoil
that the species frequently inhabits [
11]. A controlled burn in early June on a ranch in the
Redwood Valley, California, almost completely eliminated medusahead, and the area was still
"relatively" free of medusahead 2 years later [
42]. Another California
study found that medusahead cover was significantly reduced (p=0.03) by 74% with
prescribed burning in ungrazed prairie. Coverage was greatest with either summer
grazing or no
grazing and fire exclusion (p=0.013) [
71].
FIRE MANAGEMENT CONSIDERATIONS:
Wildfires facilitate replacement of native grasses with
these annual grasses [
38,
80]. However, burning may be an effective means of reducing dominance if
plants are burned early enough in the season to scorch culms and seeds, preventing seed
maturation [
30]. Compared to chemical or cultivation treatments, burning provides a relatively
economical, although highly variable, means of controlling medusahead [
83].
Preliminary results from Oregon indicate that glyphosate treatment and mowing 1 year
following summer prescribed burning were equally effective at reducing medusahead and
cheatgrass cover [
89]. The heat of
the fire should be concentrated to burn as many seeds in the head as
possible. This can be achieved by having the fire move slowly so as to
obtain complete fuel consumption. Slow, "hot" fires kill the greatest number of
seeds, and this can be achieved by burning downhill or into the wind [
75,
77,
83].
Early-season burns, conducted before medusahead seeds have ripened, are effective if
associated plants have dried enough to provide fuel for a fire [75]. Burning
medusahead during the soft dough stage is effective because the high moisture content in the seed
increases the effects of burning
[77]. Dense patches of green medusahead will often remain unburned unless previously sprayed
with oil. Some recommend later-season burns, after medusahead seeds have ripened
but before they drop. Seeds of most herbaceous species will have dropped by
then,
and will be less susceptible to fire damage [75]. An
effective management strategy in central Oregon is burning medusahead in late
spring or early summer before the seeds have dropped off the plant, and
following the next spring with an herbicide treatment of glyphosate after remaining seeds have
germinated. However, this herbicide treatment is not recommended when reseeding is required since
it is a broad-spectrum non-specific treatment [79]. It is recommended that reburning
not occur more than once every 2 to 3 years if an adequate stand of forage
plants is to be established [75]. A California study found medusahead burned
well at relative humidity of 40 to 50% and temperature 60 to 70 degrees
Fahrenheit (16-21 oC); however, a temperature of 90 degrees Fahrenheit (32
oC) and relative
humidity of 30% was considered too severe [42]. In another test, best burning
conditions for consuming medusahead were experienced around noon with air
temperature of 99 degrees Fahrenheit (37 oC), relative humidity 23%, and wind
speed of 11 mph (17 km/hr). Other California studies suggest that relative humidity of about
40% is not optimal for igniting dry grass [42,77].
Fire's effectiveness in reducing stands of medusahead on rangeland depends
on burning conditions, including time of day and season of burn. Fire
can be an effective tool in removing old medusahead litter, reducing density of medusahead stands, reducing the medusahead
seed bank, and
minimizing damage to desirable associated species. The following are
conditions present during burns of medusahead-infested rangeland at the R. E.
Shellhammer Ranch in Solano County, California 1959 [77].
Date and time |
oF (oC) |
Relative humidity (%) |
Wind velocity (mph) |
Fuel moisture (% ) |
Type of burn |
Speed of fire (ft/min) |
Duration of fire
at pyrometer(sec) |
Aug. 26
|
|
|
|
|
slow/fast |
slow/fast |
slow/fast |
|
|
|
Aug. 28
|
|
|
|
|
slow/fast |
slow/fast |
slow/fast |
|
|
|
Aug. 31
|
|
|
|
|
slow/fast |
slow/fast |
slow/fast |
|
|
|
Mean
|
|
|
|
|
slow/fast |
4/53 |
53/18 |
Slow, hot fires are most desirable for reducing medusahead. In this
study, the most effective control of medusahead was obtained by late
afternoon fires that burned slowly (into a mild wind), ignited when seed was in the soft-dough
stage [77].
Blaisdell and others [9] suggest that each situation be carefully examined and evaluated before
burning can be prescribed as a plant control measure, and emphasize that areas with a poor stand
of desirable perennials prior to burning will probably require seeding to provide satisfactory
forage production and delay return of sagebrush or other unwanted species such as medusahead,
cheatgrass, or halogeton (Halogeton glomeratus) [71]. Young and Evans [120,121] determined that 2 perennial grass plants per square foot
(2.5 per m2) is the minimum necessary to preempt invasion by nonnative annual species and/or
shrub seedlings.
Small roadside burns in southeastern Los Angeles
ponderosa pine woodlands often become dominated by medusahead and cheatgrass. These
communities often accumulate fuel contributing to repeated and increasingly
larger fires. These cycles can be interrupted by immediate seeding
in the burned areas with perennials.
However, if the annuals are established, competition must be reduced before
desirable perennial herbs, shrubs, and/or trees can establish. On
sites marginal for conifers, a combination of all 3 is often desirable [
22].
Taeniatherum caput-medusae: References
1. Arno, Stephen F. 1980. Forest fire history in the Northern Rockies. Journal of Forestry. 78(8): 460-465. [11990]
2. Arno, Stephen F. 2000. Fire in western forest ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 97-120. [36984]
3. Arno, Stephen F.; Gruell, George E. 1983. Fire history at the forest-grassland ecotone in southwestern Montana. Journal of Range Management. 36(3): 332-336. [342]
4. Arredondo, J. Tulio; Jones, Thomas A.; Johnson, Douglas A. 1998. Seedling growth of Intermountain perennial and weedy annual grasses. Journal of Range Management. 51(5): 584-589. [35483]
5. Bartolome, James W. 1979. Germination and seedling establishment in California annual grasslands. Journal of Ecology. 67: 272-281. [28345]
6. Bartolome, James W.; McClaran, Mitchel P. 1992. Composition and production of California oak savanna seasonally grazed by sheep. Journal of Range Management. 45(1): 103-107. [17434]
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