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MEDUSAHEAD:NATURALSUCCESSOR
TO THE CHEATGRASS TYPE IN THE
NORTHERN GREAT BASIN
M.Hironaka
The appearance of mature medusahead is menacing.
The long, wavy, retrosely barbed awns on the glume and
seed make the seed head physically unattractive to livestock. In addition, it is of low palatability. The high silicon dioxide content is suspect for its unattractiveness, being more than 10 percent of the dry weight and probably
contributes to its low palatability and slow rate of decomposition (Bovey and others 1961). The large amount of old
growth because of avoidance by livestock and slow decomposition is especially conspicuous. Accumulations of several thousand pounds per acre of old growth and litter are
common. The accumulation delays soil warming in the
spring and retards soil surface evaporation, and contributes to shifting the competitive advantage to medusahead
over cheatgrass. The slow decomposition of old growth
slows nutrient cycling, especially nitrogen, and this is
thought to favor medusahead (Brannon 1972) over cheatgrass. Needless to say, medusahead provides excellent
ground cover.
ABSTRACT
Medusahead ('l'aeniatherum asperum) has replaced
cheatgrass (Bromus tectorum) and other annual grasses
over eztensive areas in California, Idaho, Oregon, and
Washington during the past 40 years. It has low palatability, injurious and pesky awns, and completely dominates affected areas. Avoidance by livestock and resistance
to rapid decomposition result in medusahead stands with
thick accumulations of old growth. Wildfires are common. Recovery to preburn levels of biomass and density is
achieved in a few years. One perennial-grass candidate to
replace medusahead is bottlebrush squirreltail (Sitanion
hystrix). Seedlings of this grass possess some needed
traits to endure the stresses of annual grass competition
during the first growing season.
INTRODUCTION
Medusahead (Taeniatherum asperum) was first reported in the Pacific Northwest near Roseburg, OR, in
1887 (Furbush 1953) and shortly thereafter in eastern
Washington near Steptoe in 1901 (St. John 1937). The
introduction of medusahead to the Palouse region was
only a few years after cheatgrass (Bromus tectorum)
(Mack 1981).
The spread ofmedusahead was not as spectacular as
that of cheatgrass. In the Great Basin, medusahead was
first collected near Payette, ID, in 1944 by J. F. Pechanec,
about 300 miles south of G. R. Vasey's 1901 collection site
(St. John 1937). After its discovery by Pechanec, it had
spread rapidly in southern Idaho and adjacent Oregon.
A 1957 Bureau of Land Management report indicated
that more than 700,000 acres were infested with medusahead in southern Idaho (Bovey 1959). Today, a conservative estimate of infested acreage in the Intermountain region would more than double that amount.
Medusahead is a winter annual grass that has the
potential of successionally replacing cheatgrass in the
11-inch and above precipitation zone in the northern
Great Basin. Nearly all of the spread ofmedusahead has
been at the expense of cheatgrass and associated bromes.
The invasion has been and continues to be restricted to
the higher precipitation zones of the cheatgrass type. At
the drier edge of its infestation, medusahead tends to be
associated with swales and heavier textured soils (Dahl
and Tisdale 1975).
REPLACEMENT PROCESS
The process as to how medusahead has been able to
replace cheatgrass has been of great interest. The replacement process is not the same as the Russian tbistlemustard-cheatgrass sequence reported by Piemeisel
(1951). The growth development of cheatgrass and medusahead is lock-step from germination to resumption of
shoot growth in the spring. Even the root growth activity
of the two during winter is similar (Harris 1967; Hironaka
1961). After resumption of aboveground growth in the
spring, cheatgrass develops much more rapidly and
reaches seed maturity 10 to 20 days earlier than medusahead. This earlier maturity of cheatgrass suggests that
cheatgrass would have the advantage in the lower precipitation zones, but does not explain how medusahead replaces it where moisture is sufficient for both.
After testing for allelopathic effects, which proved negative, no apparent reason for the rapid replacement of
cheatgrass could be found. Though not tested with a
critical experiment, it was found that the overwintering
mortality of cheatgrass was consistently higher than medusahead by 5 to 10 percent. This differential in overwintering mortality, coupled with reduced seed production per unit area for cheatgrass because of fewer and
smaller plants due to shared density with medusahead,
rapidly favors domination by medusahead. This differential in winter mortality is believed to be the primary mode
of population shift that favors medusahead.
The rapidly diminishing seed production of cheatgrass
due to replacement by medusahead leads to a prolonged
Paper presented at the Symposium on Ecology, Management, and Restoration of Intermountain Annual Rangelands, Boise,ID, May 18-22, 1992.
M. Hironaka is Professor Emeritus, Range Resources, University of
Idaho, Moscow,ID 83843.
89
domination by medusahead, until it is successionally replaced by another species. During medusahead domination, the most noticeable thing is the accumulation of old
growth and litter during the early years. However, after
some years, one notices a decline and stabilization in the
amount of old growth. It is speculated that the soil microbial populations gradually catch up and old-growth accumulation is greatly reduced.
The large amount of fine fuel material associated with
medusahead brings with it the problem of fire. Wildfires
are common occurrences, which periodically devastate
large continuous blocks of rangeland in certain years.
Normally, soil surface damage is minimal, and soil erosion is generally not a serious problem. Enough caryopses
escape damage to produce a thinned, vigorous stand of
multiculmed plants the year following fire. Within a few
years stand densities approach what they were before the
fire.
Overwinter root activity of medusahead is similar to that
of cheatgrass (Hironaka 1961).
SQum.RELTAIL COMPETES
A native bunchgrass whose seedlings are able to successfully compete with medusahead is bottlebrush
squirreltail (Sitanion hystri%), a relatively short-lived
perennial (Hironaka and Sindelar 1973). Preliminary
studies indicate that squirreltail seedling roots are Capable of growth under low soil temperature conditions.
This enables squirreltail seedlings to have root penetration as deep as the roots of medusahead and cheatgrass
by the beginning of the spring season. Bluebunch wheatgrass is unable to do this (Harris 1967).
Squirreltail seedlings establish with difficulty in medusahead communities, but some are able to establish in
spite of the competition. Each succeeding year, the established individuals become larger and because of their
perenniality gain an additional edge on the use of resources, as well as physically depriving annuals of space.
Once mature, the squirreltail plant becomes an annual
seed source for the site. The gradual takeover of site by
squirreltail makes for a wholly different environmental
condition for seedlings of other long-lived perennials species. It is probable that site occupancy by squirreltail provides a different moisture-depletion regime than when annual grass dominance prevails, even though there may be
little difference in the total amount of son moisture utilized. The altered moisture depletion regime would improve the chances of perennial seedlings surviving in a
squirreltail community, while they could not establish
in medusahead- and cheatgrass-dominated communities.
Under these new conditions, it is likely that the slowdeveloping wheatgrass seedlings would have a better
chance of establishing in a squirreltail community and,
once established, gradually replace the squirreltail grass.
This last scenario has not been observed in the field,
but with a little encouragement with seed introduction
and coverage, the chance of safe site opportunities
(Harper 1977) for bluebunch wheatgrass or other longlived perennial grasses would be greatly increased. With
well-planned management, long-lived perennials could be
inserted in squirreltail communities, and gradually they
would again dominate the difficult and rugged landscapes
presently dominated by medusahead.
REPLACEMENT PROSPECTS
To control and replace medusahead with a more desired
species is slow and difficult. Much of the medusahead
type is on terrain that is too steep or rocky for rangeland
tillage and seeding equipment. For areas where medusahead competition can be controlled and seeding is economically feasible, seeding to perennial grasses with introduced perennial grasses is recommended For the most
part, however, this is wholly impractical and other strategies must be considered.
Succession, natural and assisted, seems to be the only
practical alternative. Options to effectively reduce medusahead competition directly by treatment to enhance
and encourage establishment of perennials are prohibitive
due to costs or legislation. For example, the use of herbicides to temporarily control medusahead might have been
feasible and acceptable 20 or 30 years ago, but it is no
longer an available option on public lands because of environmental concerns. Moreover, economics with respect to
land value and cost of land treatment reduce the number
of options available.
Establishing perennials by successional replacement
might be more easily accomplished in the medusahead
type than the drier cheatgrass type in the northern Great
Basin. The greater amount of precipitation associated
with the medusahead type means we have more latitude,
ecologically speaking. In the natural replacement process
each succeeding community is dominated by species individuals that have longer longevity. Perennials, once established, are difficult to dislodge, and for the species to
gain dominance in the community they need only to establish individuals when the suitable conditions arise. Annuals, on the other hand, must reestablish yearly or frequently to hold their place in the community.
Harris (1967) and Harris and Goebel (1976) provided
an explicit explanation as to why the native bluebunch
wheatgrass (Agropyron spicatum), the climax bunchgrass
that had been replaced, was not able to return in the face
of cheatgrass competition. Bluebunch wheatgrass seedling roots remain inactive over winter, whereas roots of
cheatgrass seedlings continue to grow, enabling cheatgrass to be competitively superior for soil moisture.
REFERENCES
Brannon, T. A. 1972. Some interaction between nitratenitrogen and temperature in portions of the life cycle of
four range grasses. Pullman, WA: Washington State
University. 69 p. Thesis.
Bovey, R. W. 1959. A study of growth, composition and
environmental factors in the control and utilization of
Elymus caput-medusae L. Moscow, ID: University of
Idaho. 97 p. Thesis.
Bovey, R. W., LeTourneau, D.; Erickson, L. C .. 1961. The
chemical composition ofmedusahead and downy brome.
Weeds. 9: 307-311.
90
Hironaka, M. 1961. The relative rate of root development
of cheatgrass and medusahead. Journal of Range Management. 14: 263-267.
Hironaka, M.; Sindelar, B. W. 1973. Reproductive success
of squirreltail in medusahead infested ranges. Journal
of Range Management. 26: 219-221.
Mack, R. N. 1981. Invasion of Bromus tectorum L. into
western North America: an ecological chronicle. AgroEcosystems. 7: 145-165.
Piemeisel, Robert L. 1951. Causes affecting change and
rate of change in a vegetation of annuals in Idaho.
Ecology. 82: 58-72.
St. John, Harold. 1987. Flora of southeastern Washington
and of adjacent Idaho. Rev. ed. 1956. Pullman, WA:
Student Book Corp. 560 p.
Dahl, B. E.; Tisdale, E. W. 1975. Environmental factors
related to medusahead distribution. Journal of Range
Management. 28: 463-468.
Furbush, P. 1953. Control of medusa-head on California
ranges. Journal of Forestry. 51: 118-121.
Harper, J. L. 1977. Population biology of plants. London:
Academic Press. 892 p.
Harris, Grant. 1967. Some competitive relationships between Agropyron spicatum and Bromus tectorum. Ecological Monographs. 37:89-111.
Harris, G.; Goebel, C. J. 1976. Factors of plant competition in seeding Pacific Northwest bunchgrass ranges.
Res. Cen. Bull. 820. Pullman, WA: Washington State
University, College of Agriculture. _ p.
91