Browsing Society for Range Management Journal Archives by Title
Now showing items 9491-9510 of 9715
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Weight-Length Relations in Flowering Dogwood TwigsRatios of twig weight or twig plus leaf weight to twig length in flowering dogwood plants vary meaningfully by season, geographic location, and year. Where the weight of new growth is predicted from twig lengths, the ratio of weight to length should be determined for the population being studied.
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Western Coneflower—A Noxious Species?In laboratory tests, dilute foliar extracts of western coneflower (Rudbeckia occidentalis Nutt.) inhibit germination and seedling growth of seeded grasses as do those of some supposedly innocuous species. Under natural conditions on aspen range, measurements of plants of mountain brome growing in close association with coneflower gave doubtful evidence of suppressed growth. Large doses of dried aerial parts of coneflower force-fed to sheep produced no evidence of toxicity or other distress. We found no evidence of coneflower posing any special threat on mountain range, except as a relatively unpalatable increaser species.
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Western juniper expansion on adjacent disturbed and near-relict sitesWe determined rates of western juniper (Juniperus occidentalis spp. occidentalis Hook.) density and cover change during the period 1951 to 1994 at 3 adjacent sites with nearly identical elevation, slope, aspect, soils, plant communities, and climate, but different land-use histories. The 3 sites are located in central Oregon at the confluence of the Deschutes and Crooked Rivers. Two of the sites are typical of central Oregon rangelands in that they have a history of anthropogenic disturbance including active fire suppression and domestic livestock grazing. The third site is a relict mesa that is a protected Research Natural Area and has experienced minimal anthropogenic impacts. We used large scale aerial photography to determine cover and density of western juniper in 1951, 1956, 1961, 1972, 1982, and 1994. We found that western juniper density and cover during the last 4 decades increased at all sites, with changes on the relict site similar to those on one of the disturbed sites. We suggest that even though 2 of the traditionally cited causes of western juniper expansion since the late 1800s (altered fire regimes, domestic livestock grazing) may have contributed to expansion on our disturbed sites, these mechanisms can not explain expansion on the near-relict mesa. Further, we examined climatic changes since 1900 in the region and concluded that the data did not fully support a climate-driven mechanism for the expansion. In seeking to explain western juniper expansion on semiarid rangelands, we suggest that all potential causal mechanisms (e.g., fire history, biological inertia, climate, domestic grazing, atmospheric CO2 enrichment) be considered.
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Western ragweed effects on herbaceous standing crop in Great Plains grasslandsWestern ragweed [Ambrosia psilostachya DC. ], a major forb species in mixed and tallgrass prairies, is considered to have little value for cattle grazing but is an important food item for bobwhite quail [Colinus virginianus]. While often thought to be a strong increaser with grazing pressure, information on the actual relationship between western ragweed and grasses is contradictory. Our objectives were to 1) determine the effect of western ragweed on grass standing crop, and 2) determine the effect of vegetation type and grazing on survival and shoot morphology of western ragweed. Western ragweed did not appear to reduce grass standing crop. Instead, standing crop (40 to 620 kg ha-1) and density (6 to 41 shoots m-2) of western ragweed were positively related to grass and grass-forb standing crop in mixed prairie. Standing crop of western ragweed was not related to grass standing crop in tallgrass prairie. Competitive thresholds for western ragweed in mixed and tallgrass prairies appear to be above the levels observed in this study. Density of western ragweed shoots decreased over the growing season under both grazed and ungrazed treatments. Survival of western ragweed shoots from June to September was greater in mixed prairie (81%) than in tallgrass prairie (63%) and was greater in ungrazed (76%) than grazed plots (68%). Western ragweed shoots weighed less per unit of height in tall grassprairie. Western ragweed shoots in ungrazed plots were taller than shoots in grazed plots but weighed less per unit of height. These differences in shoot morphology are consistent with increased competition for light in tallgrass prairie and in ungrazed sites. Western ragweed may not directly reduce grass standing crop but, rather, increase only when grasses are reduced by other stresses such as improper grazing.
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Western Ranching, Trade Policies, and Peak OilSkyrocketing trade deficits coupled with depletion of oil and natural gas reserves could make rangeland livestock production essential to food security in the United States.
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Western Wheatgrass Germination as Related to Temperature, Light, and Moisture StressGermination of western wheatgrass was best when seeds were held for 16 hr at temperatures between 55 and 75 F and 8 hr at temperatures between 75 and 90 F daily. Germination was independent of light but was severely reduced by moisture stresses above 1.0 atm.
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Western Wheatgrass Responses to Simulated GrazingTo evaluate responses of range grasses to herbage removal, removal patterns should simulate those under grazing. We compared responses of western wheatgrass (Agropyron smithii Rydb.) in mixed-grass range to no clipping, conventional clipping, and clipping which simulated continuous grazing. Two years of simulated grazing did not affect herbage production or tiller numbers, but both declined under conventional clipping. Belowground phytomass decreased as herbage removal increased. Total nonstructural carbohydrate concentration in rhizomes decreased when utilization exceeded about 40%, but that of roots and crowns decreased only when utilization exceeded 60-70%.
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Wet-Dry Cycle Effects on Warm-Season Grass Seedling EstablishmentA series of 14-day field experiments were conducted to evaluate seedling establishment characteristics of Bouteloua, Erogrostis, and Panicum grass species with controlled wet-dry watering combinations. The objective of the study was to validate previously published greenhouse data of Frasier et al. (1985) on the effects of the first wet-dry watering sequence following planting on seedling emergence and survival. Seedling survival numbers were different between the field and greenhouse experiments but the same general responses to watering sequences were measured. With short wet periods (2 days), seeds generally did not germinate but survived the subsequent dry period as viable seeds. Most seeds germinated with 5 wet days and produced seedlings that were able to survive drought periods of 5 to 7 days. Fewer seedlings survived with 3 days wet than with either 2 or 5 days wet. High rates of soil moisture evaporation in a spring field experiment made it difficult to maintain adequate soil moisture for seed germination, and seeds which germinated failed to produce seedlings. Seedlings were successfully established in 2 experiments conducted later in the summer following the onset of summer rains, which increased the relative humidity and reduced the rate of soil moisture evaporation. This effect was verified in a greenhouse study. In both the greenhouse and field experiments, seedlings were established when the relative humidity exceeded 50% for over one-half of the time during the initial wet-dry period.
