• Pre-laying nutrition of sage grouse hens in Oregon

      Barnett, J. K.; Crawford, J. A. (Society for Range Management, 1994-03-01)
      Diet, dietary selection, and nutritional composition of the food of sage grouse (Centrocercus urophasianus) hens were determined during the pre-laying period in southeastern Oregon in 1990 an 1991. We collected 42 female sage grouse during a 5-week period preceding incubation (4 March-8 April). Sagebrush (Artemisia spp.) was the most common among 21 foods consumed but forbs composed 18 to 50% of the diet by weight. Desert-parsley (Lomatium spp.), hawksbeard (Crepis spp.), long-leaf phlox (Phlox longifolia Nutt.), everlasting (Antennaria spp.), mountain-dandelion (Agoseris spp.), clover (Trifolium spp.), Pursh's milk-vetch (Astragalus purshii Dougl.), buckwheat (Eriogonum spp.), and obscure milk-vetch (A. obscurus) were the primary (greater than or equal to 1% of the diet by weight) forbs consumed. Forbs were used selectively over sagebrush in both low and big sagebrush cover types. All forbs were higher in crude protein and phosphorus and many were higher in calcium than sagebrush. Consumption of forbs increased nutrient content of the composite diet. Substantially fewer forbs were present in the diet in 1991 than in 1990, which coincided with reduced sage grouse productivity on the study area. These results suggest that consumption of forbs during the pre-laying period may effect reproductive success by improving nutritional status of hens.
    • Productivity of long-term grazing treatments in response to seasonal precipitation

      Milchunas, D. G.; Forwood, J. R.; Lauenroth, W. K. (Society for Range Management, 1994-03-01)
      Estimates of forage production for long-term ungrazed, lightly, moderately, and heavily grazed treatments (0, 20, 40, 60% removal of annual forage production) established in 1939 in shortgrass steppe communities were subjected to multiple regression analyses to assess long-term temporal trends resulting from grazing and short-term sensitivities to abiotic factors. Average production based upon all data from 1939-1990 was 75, 71, 68, and 57 g m-2 yr-1 for ungrazed, lightly, moderately, and heavily grazed treatments, respectively. Variability in forage production was explained mostly by cool-season precipitation, and magnitude of forage production was more sensitive to annual fluctuations in precipitation than to long-term grazing treatments. Production per unit increase of precipitation was greater for cool-season than warm-season precipitation, but only when cool-season precipitation was above average. This was attributed to differences in evaporative demand of the atmosphere resulting in different utilization-efficiencies of small and large rainfall events in the 2 seasons. Based upon a regression model constructed using data from 1939 through 1962, forage production was not affected by grazing to 20 to 35% removal. For pastures of average relative productivity, grazing at 60% level of consumption for 25 years resulted in a 3% decrease in forage production in wet years and a 12% decrease in dry years. Estimates of productivity after 50 years of heavy compared to light grazing treatment were -5 and -18% for wet and average y precipitation, respectively.
    • The effect of Quercus douglasii removal on understory yield and composition

      Bartolome, J. W.; Allen-Diaz, B. H.; Tietje, W. D. (Society for Range Management, 1994-03-01)
      The canopy of Quercus douglasii H. & A. (blue oak) has been variously reported to enhance or suppress understory production. The effects of canopy removal have been reported only for the northern portion of blue oak's range. We removed all blue oaks from 6 plots in the central coast of California and found no significant change in understory biomass over 3 years. Understory herb cover averaged 32.6% on cleared plots, compared to 24.3% on uncut plots, but composition changed little with the exception of an increase in Erodium cicutarium (L.) L'Her. Clearing did not produce the distinctive species composition and forage enhancement under Q. douglasii canopy reported in other studies, an based on comparisons between unmanipulated canopy and adjacent grassland. Our results suggest that the canopy effect could instead be caused by differences in sites occupied by trees. Clearing of Q. douglasii in regions with 50 cm or less of mean annual precipitation is not recommended for increasing forage production.