|Abstract or Summary
- Studies were conducted from 1962 to 1966 to investigate the
effectiveness of several practices in manipulating medusahead
(Taeniatherum asperum (Sim. ) Nevski) infested and/or dominated
ecosystems by releasing competition in favor of perennial grasses.
Several herbicide treatments were evaluated for selective
control of medusahead and cheatgrass (Bromus tectorum L. ) and the
subsequent release from competition of perennial grasses on
deteriorated sagebrush (Artemisia tridentata Nutt. ) /bluebunch wheatgrass
(Agropyron spicatum (Pursh) Scribn. and Smith) range in the
Snake River hills of eastern Oregon.
On foothill range in western Oregon, sheep grazing and mowing treatments were applied in attempt to selectively control medusahead dominance in favor of suppressed perennial grasses, primarily California oatgrass (Danthonia californica Boland).
Effectiveness of all treatments, including control, was
evaluated by measuring vegetative changes in species density,
reproductive vigor, and plant bulk, and interpreting these in terms
of plant succession.
Herbicides were applied in spring and fall, 1962 and spring,
1963. Annual vegetation and the small, tufted perennial Sandberg's
bluegrass (Poa secunda Presl. ) were measured for frequency of occurrence in 50 nested plots of 2²-inch and 1²-foot quadrat sizes,
randomized in 8 by 50-foot macroplots (8 by 25 feet at one site) four
times for each treatment at each of three experimental sites. For perennials, frequency was measured in 1²-foot quadrats only, and
in addition, percent canopy cover was determined. Frequency
measurements were taken from 1963 to 1966 at one site and 1964 to
1966 at two other sites. Canopy cover measurements were excluded
in 1966 due to extreme drought-and foraging by grasshoppers.
Much variation occurred for annual species due to climatic
conditions and herbicide treatments. Cheatgrass was dense and
vigorous only in 1963. Medusahead was more sparse and patchy but
made vigorous growth in 1963, 1964, and 1965. Being about three
weeks later in phenology than cheatgrass, medusahead was able to
benefit from late spring precipitation in 1964 and 1965. Both were
practically absent in 1966 from drought. Fiddleneck (Amsinckia intermedia Fisch. and Mey) and sunflower (Helianthus annuus L. )
were the dominant annuals in 1964 and 1965, except where medusahead was co-dominant in patches.
Frequencies of Sandberg's bluegrass were higher in 1963 but
lower and static the remaining years. Herbicides isocil and atrazine
at rates of 1 and 2 lb/acre reduced Sandberg's bluegrass to low frequencies. Under different environmental conditions, atrazine, at
rates of 1/2 and 3/4 lb/acre, harmed bluegrass to only a small degree.
Sandberg's bluegrass was resistant to bromacil at a rate of 1/2 lb/acre,
whereas the closely related herbicide, isocil, was quite harmful.
Atrazine increased vigor, height, and number of reproductive
stems of bluebunch wheatgrass for three consecutive years following
application. Wheatgrass plants responded to atrazine as if they had
received a nitrogen fertilizer treatment. This was manifested by
darker green, denser, and leafier clumps than those observed in
Atrazine, at rates of 1/2 to 2 lb/acre, caused no apparent injury
to bluebunch wheatgrass. Since atrazine is most harmful at the seed
ling stage, young seedlings perhaps were killed from residual atrazine.
Other factors such as grasshoppers, poor seed crops, and inadequate
climatic conditions could have contributed in part, or solely, to static
wheatgrass frequencies during the period of study.
In western Oregon, sheep grazing treatments in mid April, mid April - followed by late May, and late May; and mowing treatments in mid April and mid April - followed by late May were
applied from 1963 to 1965 on randomized 1/20-acre paddocks, replicated three times. Frequency of all species were measured following treatment each year and in 1966 in 50 nested plots of 2²-inch, 6²-inch, and 1²-foot quadrat sizes. Basal area of California oatgrass, yields
of medusahead, oatgrass, other herbage, and total herbage were
measured in 1966 for all treatments.
From relationships of vegetation data and habitat factors of
soil, degree of slope, and exposure, two distinct ecological sites
were noted at the main study area at the Hill Pasture. These were
referred to as the mesic site and xeric site. Frequencies of medusahead and California oatgrass were higher on the xeric and mesic site,
The early-late grazing was highly effective on both the xeric
and mesic site for utilizing medusahead. The late grazing was effective on the mesic site but extremely poor on the xeric, even with
heavier grazing pressure applied. Medusahead had a high density
in 1966 on paddocks where both treatments had been applied, and
was again dominant.
The early-late mowing effectively reduced medusahead to near
absence, improved California oatgrass vegetative and reproductive
vigor markedly, and shifted dominance to California oatgrass. Low frequencies of medusahead were recorded in 1966.
The early grazing and early mowing were both ineffective for
reducing medusahead frequencies each year. Medusahead was
readily consumed when grazed early. This reduced the buildup of
litter to some extent.
Vegetation-habitat relationships were investigated at 12 other
hill range sites along the western edge of the Willamette Valley and
were related to the mesic and xeric sites at the Hill Pasture. Under
conditions of the treatments applied, results of the Hill Pasture study
could be extrapolated to all but two of the 12 sites as a means of
gaining rapid range improvement.