The emergence of big sagebrush (Artemisia tridentata) seedlings from 5 gardens where both the seed source and the soils were reciprocated was investigated over a 5-year period in western Nevada. The sites where the study was conducted were located at the arid extremes for mountain (A. tridentata subsp. vareyana) and basin big sagebrush (A. tridentata subsp. tridentata) in the trans-Sierra Nevada area. Soils, sites, and seed sources differed significantly (P=0.01) in seedling emergence. The driest site, where it was difficult to obtain seedling emergence even on a year of above average precipitation, had a soil surface that was very conducive to the germination of seeds of big sagebrush when the seedbed was moved to garden locations with greater environmental potential. Seedbed quality differed markedly among sites with soil derived from decomposing granite versus metavolcanic sources. Big sagebrush seeds were buried in soils derived from granite through a winnowing action. Seeds from a non-granitic soil site were also adapted, apparently through size and shape, to this winnowing self-burial. The dominant microenvironmental factors contributing to seedling emergence tended to be site and seed source specific. Microtopography in the fall, when seeds were dispersed, and seasonal precipitation were dominant factors controlling the emergence of big sagebrush seedlings.

A controlled environment experiment was performed on plants from 2 Agropyron smithii Rydb. (western wheatgass) populations to determine how defoliation at 1-week intervals and graxing history affected total silicon accumulation in shoots, and how Si was distributed within the plant. Plants were collected from a heavily grazed, 10-year-old prairie dog colony and an ungrazed, 40-year-old exciosure at Wind Cave National Park, South Dakota. After 18 weeks, the total amount of Si accumulated in shoots was similar in plants from both populations, regardless of whether or not the plants were clipped. However, the Si concentration in shoots was greater in nondefoliated than defoliated plants of both populations because of Si dilution resulting from greater shoot production in defoliated pIants. In both populations, roots and leaf blades had the highest Si concentrations, rhizomes had the lowest concentrations, and sheaths, crowns, and belowground stems had intermediate concentration.

A major problem in evaluating nutritional quality of the grazing animal’s diet is collecting forage representative of that being grazed. We compared the chemical composition of simulated diet (SD) and mower clipped (MC) forage samples to each other and to fecal chemical composition data. Forage from crested wheatgrass [Agropyron desertorum (Fischer ex. Link) Schuhes], western wheatgrass [Puscopyrum smititii(Rydb.) A. Love], smooth bromegrass (Bromus inermis Leyssor), Russian wildrye [Psuthyrostachys juncea (Fisher) Nevskil, and native range pastures was collected every 2 weeks beginning 14 June and continuing through 20 September 1983. Fresh fecal samples from grazing steers were obtained 2 days following forage collections. Variability among individuals hand clipping forage to simulate a grazing animal’s diet was less than the variability between mower strips for in vitro digestible organic matter (IVDOM), calcium (Ca), and magnesium (Mg). Correlation coeffkients between SD and MC residuals were low. Coefficients between SD and fecal residuals were higher for acid detergent fiber (ADF), IVDOM, Ca, and phosphorus (P) than coefficients for the same variables obtained with MC and fecal data. The highest coefficients using residual data were achieved with fecal Ca and SD ADF, cellulose, Ca, and Mg r = -0.84, -0.81, 0.84, and 0.81, respectively. Interactions Involving pastures and sample dates were significant for the same effects for P, ADF, cellulose, and IVDOM for SD and fecal data. Data suggest that some fecal components, primarily Ca, may be useful in predicting the diet quality of grazing cattle, but these relationships need further examination.

The role that accumulated carbohydrates play in plant regrowth has been discussed for over 60 years. However, few quantitative studies have been published on the importance of carbohydrates for regrowth in early spring after plants have been exposed to periods of either drought or drought plus defoliation. We examined the relationship between total nonstructural carbohydrate (TNC) concentrations and pools (biomass X concentration) and spring regrowth for crested wheatgrass [Agropyron desertorum Fisch. ex Link) Schult.] and bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Love ssp. Spicata; Syn. A. spicatum (Pursh) Scribn. and Smith] with and without clipping under drought, natural, and irrigated conditions. In spring 1985 and early spring 1986, after 1 or 2 years of clipping, crown and root TNC concentrations an IT NC pools per tiller were generally similar for clipped and unclipped plants of both species. Nonstructural carbohydrate concentrations in crowns and roots did not relate to rate or total production of dark regrowth in mid-spring 1985 and early spring 1986. In early spring 1986 following 2 years of repeated treatments, crown and root TNC pools were on average 7 times higher under drought, in both clipped and unclipped plants, than they were under the higher moisture-level treatments for both species. The large pools of TNC in drought-treated plants appeared to enhance the production of dark regrowth when meristematic limitations on growing tillers did not exist in early spring. These results suggest that plants exposed to prolonged periods of drought or drought plus defoliation may have rapid initial regrowth upon alleviation of these stresses because high amounts of TNC may have accumulated in their storage organs during stress. In addition, the results suggest that high TNC availability facilitates growth only when meristematic activity is high.

Three experiments were conducted with grazing and penned animals to evaluate the accuracy and precision of different methods of administering ytterbium (Yb) as a marker to estimate fecal output. A paired t test was used to evaluate differences between marker estimates of fecal output and fecal output measured by total collection. Marker administration methods within an experiment were compared in a one-way analysis of variance using the absolute percentage deviation of the marker estimates from total collection. In Experiment 1, wethers were confined in metabolism crates and orally administered either a pulse dose or a once daily dose. Both methods overestimated fecal output (7.3% for the once daily and 11.2% for the pulse dose method); however, the once daily dose was more precise (SE = .78%) than the pulse dose (SE = 2.17%). In Experiment 2, a crossover design with steers grazing dormant bromegrass pasture was employed to compare estimates of fecal output by pulse dosing and once daily dosing of Yb via rumen cannula. Although both methods underestimated fecal output (4.0% for the once daily and 11.5% for the pulse dose), once daily dosing was more precise (SE = 2.36%) than pulse dosing (SE = 3.64%). In Experiment 3, an intraruminal constant release Yb bolus was compared with daily feeding of Yb-labeled supplement using grazing and pen fed steers. The constant release bolus overestimated fecal output 13.8% on pasture and 41.3% in the pen study. Standard errors for the constant release bolus were 4.02% (pasture) and 4.76% (pen). Although use of Yb in a labeled supplement did not provide an accurate estimate of fecal output (80.1 and 106.0% of total collection on pasture and in pen, respectively), it had a lower SE than the constant release bolus method during both the pasture and pen studies. Once daily dosing was more precise than a pulse dose for estimating fecal output in Experiments 1 and 2. The constant release bolus used in Experiment 3 does not appear to be suitable for estimating fecal output of grazing cattle.

Diet composition, performance, and production of calves and lambs grazing in combination were contrasted between a repeated-seasonal (RSG) (May-Sept.) and a 16-subunit, 1-herd high-performance short-duration grazing (HPSDG) system during 1983 and 1984. Animal numbers were adjusted with put-and-take sets of livestock to attain planned forage use levels for each cycle in HPSDG and comparable end-of-season use levels in both treatments. Diet quality, as estimated from fecal nitrogen (N), was better (P<0.05) for the RSG livestock especially during the first 2 grazing periods. Similarity indices of lamb and calf diet composition indicated compatibility of the lamb and calf mix in both grazing systems treatments. Calves primarily selected western wheatgrass (Agropyron smithii Rydb.) and annual grasses and lambs selected buffalograss (Buchloe dactyloides [Nutt.] Engelm.) and blue grama (Bouteloua gracilis [H.B.K.] Lag. Ex Griffiths). Average daily gain (ADG) of RSG calves was greater in both 1983 and 1984 (0.52 and 0.68 kg/d) compared to HSPDG calves (0.39 and 0.62 kg/d, P<0.05). RSG lamb ADG (72.6 g/d) was greater in 1983 compared to HPSDG (45.4 g/d, P<0.05). Attained stocking rates were 35 and 25% higher in HPSDG during 1983 and 1984, respectively. Gain/ha, however, was greater for the HPSDG calves and combined livestock (calves + lambs) only during 1984 (P<0.05).

Epicuticular wax on the leaves of honey mesquite (Prosopis glandulosa) increased rapidly from May to July and stabilized or decreased by late summer. Pattern of accumulation best fit a second order polynomial regression equation using day of year as the independent variable. Considerable variation in wax accumulation was found among individual trees within populations and appeared to be consistent from year to year. Wax generally increased from about 0.35 g m-2 to more than 1.00 g m-2 during the growing season. A difference in maximum wax accumulation was detected between the 2 years of study and was attributed to differing environmental conditions. These findings may partially explain resistance of honey mesquite to folk-applied herbicides.

The valuable role that healthy riparian ecosystems play in regional diversity of plant and wildlife communities is just beginning to be recognized. Resource managers need to know how degraded riparian areas respond to changes in management, such as reduction and eliiination of grazing. Differences in vegetation structure were examined in a montane riparian zone in north-central Colorado after 30 years of cattle exclusion and continued, but reduced, grazing pressure. In order to assess the changes in the riparian community, canopy coverage, density, and standing crop of important riparian species were measured in 1985 and 1986. Total vascular vegetation, shrub, and graminoid canopy cover was greater (P greater than or equal to 0.05) in the exclosures as compared to grazed areas, while forb canopy cover was similar (P>0.05) between treatments. Exclosures had nearly 2 times the litter cover, while grazed areas had 4 times more bare ground. Willow canopy coverage was 8 l/2 times greater in protected areas than in grazed areas. Kentucky bluegrass (Poa pratensis L.) cover was 4 times greater in grazed areas than exclosures, while the cover of fowl bluegrass (Poa palustris L.) was 6 times greater in the protected sites. Canopy cover of other important riparian species, such as tufted hairgrass (Deschampsia caespitosa (L.) Beauv.), Nebraska sedge (Carex nebraskensis Dewey), and beaked sedge (C. rostrata Stokes), was similar (P>0.05) between treatments. Mean peak standing crop over the 2 years of the study ws 2,410 kg/ha in the exciosures and 1,217 kg/ha in caged plots within grazed areas. Cattle utilized approximately 65% of the current year’s growth of vegetation during the 1985 and 1986 grazing seasons.