Effects of unmanaged populations of large mammalian herbivores, especially elk (Cervus elaphus on vegetation is a concern in Yellowstone National Park, since wolves (Canis Lupus) are extirpated, ungulate migrations are altered by human activities and the disruption of natural process is possible. Stands of low, hedged (height-suppressed) willows (Salix spp.) are observed throughout the greater Yellowstone National Park area where high densities of wintering elk or moose (Alces alces) exist. The height of 47% of the willow stands surveyed on Yellowstone's northern winter range has been suppressed. Mean leader use of willows of all heights was (P < 0.05 in the winter of 1987-88, increased to 60% in winter 1988-89, following the drought and fires of 1988, then declined to 44% in 1989-90 and winter 1990-96. Height-suppressed willows (43 +/- 2 cm, mean +/- SE) were about one-half as tall as tall willows (83 +/- 4 cm). Percent twig use of suppressed willows in summer (25%) and winter (59%) was significantly more than for intermediate or tall stands (P < 0.05). Suppressed willows produced about one-fourth the aboveground annual biomass compared to taller willows; even after 27 or 31 years of protection, previously-suppressed willows produced only one-third the aboveground biomass of taller willows, suggesting suppressed willows grow on sites with lower growth potential. Growth conditions for willows on the northern winter range may have declined due to a warmer and drier climate this century, locally reduced water tables—because of the decline on beaver (Castor canadenis), or fire suppression may be responsible for the observed changes. Tall and intermediate-height willows contained higher concentrations of nitrogen and they exhibited more water stress than height-suppressed willows of the same species. More xeric growth conditions this century than last century, especially during the decades of the 1920's, 1930's, and 1980's, may explain the low growth rates and lower chemical defenses against ungulate herbivory for height-suppressed willows. We propose a more xeric climate and locally-reduced water tables likely contributed to the willow declines on the northern winter range, but that the proximate factor in the declines was herbivory by native ungulates.

Grazing trials were conducted during early and late spring of 1988 and 1989 to evaluate the impact of sheep grazing duration and stocking density on grazing efficiency and forage selectivity in tall fescue (Festuca arundinacea Schreb.)-subclover (Trifolium subterranum L.) hill pastures near Corvallis, Ore. Grazing treatments were 2, 6, and 10 days duration with corresponding stocking densities 380,130, 78, and 1,390, 460, and 280 ewes/ha during early and late spring trials each year, respectively. Grazing efficiency was generally greater (P < 0.05) for the low density/longer duration (10-day) than for higher density/shorter duration (2-day) treatments. Greater grazing efficiency as duration increased largely reflected higher rates of intake rather than lower levels of non-consumptive forage destruction. Stocking density within a constant grazing duration (2 days) had little effect on grazing efficiency. Within the 10 day grazing treatment, grazing efficiency was highest during the last 4 days and lowest during the first 2 days (P < 0.05). Although short duration/high density grazing is considered to be non-selective, sheep were equally or more selective under very short duration/very high density compared to longer duration/lower density treatments in this study. These results suggest that the very short duration with very high stocking density was not an attractive management option since grazing efficiency was low and sheep were more selective.

Tarbush (Flourensia cernua DC.) is an abundant but generally unpalatable shrub native to the Chihuahuan Desert. The objective of this study was to examine the leaf surface chemistry of tarbush in relation to degree of use by ruminants. Mature tarbush leaves were collected on 2 sites during 2 periods approximately 2 weeks apart from plants exhibiting either high (> 45%) or low (< 10%) use when browsed by cattle, sheep, and goats confined to a small area (5 plants per use category for each site/period combination). A greater (P < 0.05) concentration of epicuticular wax was detected on the leaf surface of plants that were used to a lower degree (82 and 10.3% of the leaf dry matter for high- and low-use plants, respectively). Several leaf surface compounds were related to period, while site and degree of use were seldom related to individual mono- and sesquiterpenes measured in this study. Camphene and 10 unidentified compounds differed between periods (P < 0.10). Two unidentified compounds were related to site (P < 0.10) and 2 others were related to use (P < 0.10). In summary, individual leaf surface compounds on tarbush do not appear to greatly affect degree of use of tarbush by livestock, but collectively (based on epicuticular wax data), these compounds may influence the diet selected by browsing ruminants.

The importance of western ragweed (Ambrosia psilostachya) DC.) in the diet of bobwhites (Colinus virginianus Merr.) and their high dietary requirement for essential amino acids prompted us to explore the use of disking and fertilization (nitrogen and phosphorus) to improve its nutritional quality on deep, unfertile, sandy-soil rangelands in western Oklahoma. Fertilization (55 kg N ha-1, 56 kg P ha-1 as diammonium phosphate) of disk strips did not readily increase seed production of western ragweed. Fertilizer had no detectable effect on nutritional quality of seeds, which contained an average of 13% crude protein and 21% fat. Conflicting results reported on the effect of fertilizer on the quality of plant proteins within the literature could be attributable to differences of climate and soils, growth habits of different plant species, type and rates of fertilizers, and stages of maturity when plants are harvested for analysis.

The objective of this research was to characterize the life-histories of cheatgrass (Bromus tectorum L.) and yellow starthistle (Centaurea solstitialis L.) growing in association. Biweekly demographic attributes were monitored during 1991 (moist spring) and 1992 (dry spring). Data were arranged into life-history tables, and sensitivity analysis was performed to determine key transition phases. The entire cheatgrass seed crop reached the soil surface, 41% of yellow starthistle's seed output was lost during seed rain. Frost heaving reduced winter seedling populations of cheatgrass (53%) more than yellow starthistle (40%). All cheatgrass seedlings surviving the frost heaving period became adults. Yellow starthistle density was reduced by 75% during the juvenile phase. Cheatgrass adults appeared about 6 weeks before yellow starthistle adults. Cheatgrass seed output remained about 7,000 m2 with moist and dry spring conditions. Yellow starthistle seed output was about 21,600 m2 and 5,200 m2 with moist and dry spring conditions, respectively. Reduction of yellow starthistle seed output with dry spring conditions suggest oscillatory community dynamics. Key processes associated with life-history transitions were interference (competition), resource acquisition rates and duration, and reproductive allocation.

A 2 year study in south central North Dakota determined the responses of (1) litter and root decomposition and nitrogen (N) release, and (2) soil N mineralization to grazing intensity. The treatments were: long term not grazed, moderate grazing, and heavy grazing. The moderate grazing and the heavy grazing treatments removed 45% and 77% of annual above-ground growth respectively. The moderate grazing treatment resulted in higher decomposition and soil N mineralization rates, and lower N releases via decomposition than the long term not grazed and heavy grazing treatments. No consistent differences were found between the long term not grazed and heavy grazing treatments. Annual litter and root decomposition rates in the moderate grazing treatment averaged 55% for 1989-1990 and 63% for 1990-1991 while the long term not grazed and heavy grazing treatments had rates for the same periods of 13% and 19%. The moderate grazing treatment had a net soil N mineralization of 60 micrograms.g-1 and 269 micrograms.g-1 during the 1989 and 1990 growing seasons whereas the long term not grazed and heavy grazing treatments had net soil immobilization for the same periods of -59 micrograms.g-1 and -115 micrograms.g-1. Annual N release from litter and root decomposition in the heavy grazing and long term not grazed treatments averaged 70% and 38% respectively during the 1989-1990 incubation period, and 51 % and 23% during 1990-1991. The equivalent values for the moderate grazing treatment were 47% and -6% (net N immobilization) for 1989-1990 and 41% and 23% for 1990-1991. Results from this study seem to indicate that the standard grazing rule of "take half leave half" may have a significant impact in N conservation and the supply of mineral N for plant growth.

Two digestion trials, using 20 ram lambs (Experiment 1) and 8 cows (Experiment 2) provided ad libitum access to mature prairie grass hay, were conducted to evaluate controlled release intraruminal chromic oxide boluses and alkaline hydrogen peroxide lignin as markers for estimating forage intake by the fecal output/indigestibility ratio. A soybean meal and 3 urea based supplements were fed to lambs in Experiment 1. For both experiments, daily fecal output was weighed and sampled for 6 days (Experiment 1) and 5 days (Experiment 2) beginning 7 days after oral administration of controlled release boluses. Rectal fecal grab samples were also collected at 1000 daily and at 4-hour intervals on day 4 of collections for Experiment 2. For both experiments Cr2O3 excretion rates based on total collections were used to evaluate Cr2O3 controlled release boluses and alkaline hydrogen peroxide lignin predictive value in place of manufacturer's stated release rate. In experiment 1, fecal Cr2O3 output was 224 mg/day +/- 3.9 compared to the manufacturer's stated release rate of 201 mg Cr2O3/day. Fecal alkaline hydrogen peroxide lignin recovery was 97.8% +/- 1.9. Samples composited over the 6-day collection period predicted fecal output, apparent dry matter digestibility, and dry matter intake similar (P = .44, .15 and .55; respectively) to actual values. Supplemental treatment and dry matter intake had no effect (P > .38) on daily fecal Cr2O3 output or alkaline hydrogen peroxide lignin recovery. In Experiment 2, fecal Cr2O3 was 1,662 mg/day +/- 63 compared to the manufacturer's stated release rate of 1,505 mg Cr2O3/day. Fecal alkaline hydrogen peroxide lignin recovery was 95.9% +/- 7. Using 5-day composited samples, predicted fecal output, dry matter digestibility, and dry matter intake were similar (P = .49, .21 and .49; respectively) to actual values. Increasing the number of daily grab samples increased R2 values between actual and predicted fecal output and dry matter digestibility. Fecal grab samples and total fecal collection samples provided a similar relationship (R2=.71) between actual and predicted dry matter intake when each were composited over 5 days. Time of day did not affect fecal Cr2O3 or alkaline hydrogen peroxide lignin concentrations. These results suggest that grab samples collected once daily on 5 consecutive days can be used to predict fecal output when Cr2O3 controlled release boluses are used. Although recoveries of fecal alkaline hydrogen peroxide lignin were near 100% in these experiments, digestibility estimates using this internal marker were variable and adversely influenced predictions of dry matter intake.

Annual grasslands in the Pacific Northwest are being invaded by Eurasian weeds, such as yellow starthistle (Centaurea solstitialis L.). Plant-plant interactions influence community dynamics and plant establishment. The objectives of this study were to quantify the effects of interference between seedlings of cheatgrass (Bromus tectorum L.) and yellow starthistle and to compare growth of isolated individuals of these species. Isolated individuals and addition series mixtures with total stand densities ranging from 20-20,000 plants m-2 were grown in an environmental chamber (10 degrees C, 12-hour daylength). Individuals were harvested on 4-day intervals between 10 and 46 days, and mixtures were harvested 37 days after planting. Shoot weight, root weight, leaf area, and total root length of isolated individuals were similar. Yellow starthistle roots penetrated deeper into the soil than did cheatgrass roots 22 days after planting. Intraspecific interference was greater than interspecific interference for both species, and resource partitioning via rooting depth was evident. The yellow starthistle root:shoot ratio and the cheatgrass lower (below 200 mm): upper (above 200 mm) root ratio increased with increasing densities. Yellow starthistle and cheatgrass minimize interspecific interference as seedlings through differential growth and rooting depth. Invasion of cheatgrass rangelands by yellow starthistle increase resource partitioning and reduce our ability to revegetate rangelands by conventional means.

Winterfat [Eurotia lanata (Pursh) Moq.] is a chenopod shrub often used in range seedings because of its palatability and nutritive value. Environmental conditions influence winterfat germination and seedling vigor and, therefore, seedling success. We tested the hypothesis that seed imbibition at warm temperatures damages seed membranes, resulting in lower post-imbibition concentrations of seed cations. Energy-dispersive x-ray microanalysis of Cl uptake and fresh weight increase over time gave evidence that winterfat seeds imbibe more rapidly at 25 than at 4 degrees C. However, imbibition of seeds at 20 degrees C did not result in consistently lower post-imbibition cation concentrations. Although imbibition is more rapid at warm temperatures, the post-imbibition concentration of cations in seeds imbibed at 20 degrees C does not justify the conclusion that warm imbibition damages winterfat seed membranes.