Vegetation changes of communities containing medusahead (Taeniatherum asperum (Sim.) Nevski) following herbicide, grazing, and mowing treatments

Graduation date: 1969Studies were conducted from 1962 to 1966 to investigate the\ud effectiveness of several practices in manipulating medusahead\ud (Taeniatherum asperum (Sim. ) Nevski) infested and/or dominated\ud ecosystems by releasing competition in favor of perennial grasses.\ud Several herbicide treatments were evaluated for selective\ud control of medusahead and cheatgrass (Bromus tectorum L. ) and the\ud subsequent release from competition of perennial grasses on\ud deteriorated sagebrush (Artemisia tridentata Nutt. ) /bluebunch wheatgrass\ud (Agropyron spicatum (Pursh) Scribn. and Smith) range in the\ud Snake River hills of eastern Oregon.\ud 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).\ud Effectiveness of all treatments, including control, was\ud evaluated by measuring vegetative changes in species density,\ud reproductive vigor, and plant bulk, and interpreting these in terms\ud of plant succession.\ud Herbicides were applied in spring and fall, 1962 and spring,\ud 1963. Annual vegetation and the small, tufted perennial Sandberg's\ud bluegrass (Poa secunda Presl. ) were measured for frequency of occurrence in 50 nested plots of 2²-inch and 1²-foot quadrat sizes,\ud randomized in 8 by 50-foot macroplots (8 by 25 feet at one site) four\ud times for each treatment at each of three experimental sites. For perennials, frequency was measured in 1²-foot quadrats only, and\ud in addition, percent canopy cover was determined. Frequency\ud measurements were taken from 1963 to 1966 at one site and 1964 to\ud 1966 at two other sites. Canopy cover measurements were excluded\ud in 1966 due to extreme drought-and foraging by grasshoppers.\ud Much variation occurred for annual species due to climatic\ud conditions and herbicide treatments. Cheatgrass was dense and\ud vigorous only in 1963. Medusahead was more sparse and patchy but\ud made vigorous growth in 1963, 1964, and 1965. Being about three\ud weeks later in phenology than cheatgrass, medusahead was able to\ud benefit from late spring precipitation in 1964 and 1965. Both were\ud practically absent in 1966 from drought. Fiddleneck (Amsinckia intermedia Fisch. and Mey) and sunflower (Helianthus annuus L. )\ud were the dominant annuals in 1964 and 1965, except where medusahead was co-dominant in patches.\ud Frequencies of Sandberg's bluegrass were higher in 1963 but\ud lower and static the remaining years. Herbicides isocil and atrazine\ud at rates of 1 and 2 lb/acre reduced Sandberg's bluegrass to low frequencies. Under different environmental conditions, atrazine, at\ud rates of 1/2 and 3/4 lb/acre, harmed bluegrass to only a small degree.\ud Sandberg's bluegrass was resistant to bromacil at a rate of 1/2 lb/acre,\ud whereas the closely related herbicide, isocil, was quite harmful.\ud Atrazine increased vigor, height, and number of reproductive\ud stems of bluebunch wheatgrass for three consecutive years following\ud application. Wheatgrass plants responded to atrazine as if they had\ud received a nitrogen fertilizer treatment. This was manifested by\ud darker green, denser, and leafier clumps than those observed in\ud other treatments.\ud Atrazine, at rates of 1/2 to 2 lb/acre, caused no apparent injury\ud to bluebunch wheatgrass. Since atrazine is most harmful at the seed\ud ling stage, young seedlings perhaps were killed from residual atrazine.\ud Other factors such as grasshoppers, poor seed crops, and inadequate\ud climatic conditions could have contributed in part, or solely, to static\ud wheatgrass frequencies during the period of study.\ud 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\ud 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\ud of medusahead, oatgrass, other herbage, and total herbage were\ud measured in 1966 for all treatments.\ud From relationships of vegetation data and habitat factors of\ud soil, degree of slope, and exposure, two distinct ecological sites\ud were noted at the main study area at the Hill Pasture. These were\ud referred to as the mesic site and xeric site. Frequencies of medusahead and California oatgrass were higher on the xeric and mesic site,\ud respectively.\ud The early-late grazing was highly effective on both the xeric\ud and mesic site for utilizing medusahead. The late grazing was effective on the mesic site but extremely poor on the xeric, even with\ud heavier grazing pressure applied. Medusahead had a high density\ud in 1966 on paddocks where both treatments had been applied, and\ud was again dominant.\ud The early-late mowing effectively reduced medusahead to near\ud absence, improved California oatgrass vegetative and reproductive\ud vigor markedly, and shifted dominance to California oatgrass. Low frequencies of medusahead were recorded in 1966.\ud The early grazing and early mowing were both ineffective for\ud reducing medusahead frequencies each year. Medusahead was\ud readily consumed when grazed early. This reduced the buildup of\ud litter to some extent.\ud Vegetation-habitat relationships were investigated at 12 other\ud hill range sites along the western edge of the Willamette Valley and\ud were related to the mesic and xeric sites at the Hill Pasture. Under\ud conditions of the treatments applied, results of the Hill Pasture study\ud could be extrapolated to all but two of the 12 sites as a means of\ud gaining rapid range improvement