• Seasonal chemical composition of saltbush in semiarid grasslands in Jordan

      El-Shatnawi, M. K. J.; Mohawesh, Y. M. (Society for Range Management, 2000-03-01)
      Saltbush (Atriplex halimus L.), a native shrub which is adapted to arid rangelands, was transplanted to the semiarid grassland at Jordan University of Science and Technology Campus in 1986. Our objective was to determine the seasonal changes in the chemical composition of the annual growth of leaves and stems of saltbush (Atriplex halimus L.) during 1995-96 and 1996-97. A strong positive correlation was found among P, Ca, crude protein, and nitrogen free extract and a strong negative correlation was found between fiber and P, Ca, crude protein, and nitrogen free extract. Nitrogen free extract (NFE) had a strong positive linear correlation with P, Ca, and crude protein. P, Ca, Ca:P ratio, crude protein, and NFE contents were found to be higher in leaves than in stems on all the occasions. Leaves had relatively higher concentrations of P, Ca, crude protein, and NFE during the growing season (February to April). Crude protein of leaves reached its maximum in March (22.7% ). The concentrations decreased, however, to 15% during the dry period (June to October). Crude protein content of stems ranged from 11.3 to 12.2%. Fiber content of leaves was lowest during February and March (16.9 to 18%), and reached maximum values during August and October. Saltbush is a good protein source for sheep during the dry season; however, P content would not meet nutritional requirements of ewes.
    • Spatial distribution of economic change from Idaho ranches

      Harp, A. J.; Loucks, R. R.; Hawkins, J. N. (Society for Range Management, 2000-03-01)
      Economic impacts from federal grazing policy frequently figure in public debate about federal land in the American West. The spatial and economic level of aggregation at which impacts are estimated is a significant issue, both politically and methodologically. We present an input/output model incorporating spatial detail at the sub-county level. Seven community-level economies are portrayed and contrasted with the aggregated 2-county economy. Our argument is that economic dependencies, notably dependencies on the range cattle industry, differ significantly between communities and that this differentiation is completely masked when the 2 county area is examined as 1 economy. The sub-county breakdown illustrates the degree to which communities are differentially vulnerable to reduced cattle prices and a reduction in available federal forage.
    • Spotted knapweed and grass response to herbicide treatments

      Sheley, R. L.; Duncan, C. A.; Halstvedt, M. B.; Jacobs, J. S. (Society for Range Management, 2000-03-01)
      Picloram at 0.28 kg ai ha(-1), clopyralid plus 2,4-D at 0.21 kg ai ha(-1) plus 1.12 kg ai ha(-1), or dicamba plus 2,4-D at 0.56 kg ai ha(-1) plus 1.12 kg ai ha(-1) were applied to spotted knapweed (Centaurea maculosa Lam.) at the spring-rosette, bolt, bud, flower, or fall-rosette growth stages in 1991 on 2 sites in Montana. Treatments (3 herbicide treatments, 5 growth stages) were applied in a randomized-complete-block design and replicated 3 times at each site. Effects of herbicides on mature and seedling spotted knapweed density depended upon spotted knapweed growth stage at the time of application and the number of years after application. Picloram consistently reduced mature spotted knapweed density to low levels (5 plants m(-2)), regardless of growth stage, and its effect persisted through 1994. Clopyralid plus 2,4-D applied at the bolt or bud stage reduced spotted knapweed densities similar to that of picloram (95%) at the Avon site, while providing about 50% reduction in density 3 years after application at Missoula. This treatment may provide an alternative to picloram in environmentally sensitive areas. Dicamba plus 2,4-D was most effective when applied during the bud and bolt growth stages, and least effective when applied during the spring- and fall-rosette stages. In most situations, picloram and clopyralid plus 2,4-D provided greater control of spotted knapweed than dicamba plus 2,4-D. Herbicide treatments increased perennial grass biomass from 173 kg ha(-1) in the nontreated controls to 494,880, and 1,309 kg ha(-1) for dicamba plus 2,4-D, clopyralid plus 2,4-D and picloram, respectively.
    • Supplementation of yearling steers grazing Northern Great Plains rangelands

      Karn, J. F. (Society for Range Management, 2000-03-01)
      Growing yearling steers on summer rangelands as part of a cow-calf-yearling operation would allow producers to maximize forage utilization, and selling yearling steers when forage was in short supply would minimize potential genetic losses in the cow herd. A series of summer supplementation and intake studies were conducted from 1988-1992 to determine if weight gains of grazing yearling steers could be increased by supplemental energy (ground barley), phosphorus (P), or crude protein. Studies were conducted at 2 locations on pastures of approximately 51 ha each, which contained quite different mixtures of forage species. Forage P, crude protein and IVDOM levels were monitored throughout the grazing season. Supplementation results varied among years and between locations. There were significant (P < 0.14) location by treatment interactions in 1989 and 1990 because steers at the WEST location tended to respond more to supplementation than steers at the EAST location, but EAST location steers had the highest rates of gain. Providing supplements at gradually increasing rates produced results comparable to supplementing at a constant rate all summer. Supplemental crude protein showed no significant benefit, but crude protein levels in pasture forage were generally above steer requirements. Weight gains averaged over all 5 years were greater (P < 0.05) for steers supplemented with barley or barley and P, compared to unsupplemented control steers. The response to supplementation should be beneficial most years, but results may vary with the quantity and quality of available forage.
    • Switchgrass growth and development: water, nitrogen, and plant density effects

      Sanderson, M. A.; Reed, R. L. (Society for Range Management, 2000-03-01)
      Switchgrass (Panicum virgatum L.), an important component of the tallgrass prairie, is a productive warm-season forage grass. Interest in growing switchgrass for alternative uses has raised questions about resource use during production. The objective of our study was to examine how resource inputs affected interspecific plant competition in switchgrass. 'Alamo' switchgrass was established from seed in outdoor lysimeters in May 1993 and grown under 22 or 112 kg N ha(-1), and under field capacity or water-deficit conditions until August 1994. Plant spacing varied systematically from 10 to 70 cm. Plants were harvested in late summer each year and individual plant dry weight, tiller number, leaf area, and morphological development stage were measured. Soil moisture tensions below -45 kPa reduced switchgrass photosynthetic rates and xylem pressure potential. As plant spacing increased, tiller number, leaf area, plant dry weight, and morphological development stage increased. Plant dry weight and tiller number in the establishment year was not affected by N input. Established plants in 1994, however, responded to high N input at low plant densities with 50 to 100% greater leaf area and up to 3-fold greater plant dry weight compared to the low-N treatment. The increased plant dry weight at high N input resulted from increased individual tiller weight and not increased tiller number. Our data indicate that competitive responses of switchgrass plants at high plant densities were controlled by competition for aboveground resources, as plant yield and morphology at high densities were not affected by water or N inputs.
    • Technical note: Estimating aboveground plant biomass using a photographic technique

      Paruelo, J. M.; Lauenroth, W. K.; Roset, P. A. (Society for Range Management, 2000-03-01)
      We present a non-destructive, photographic method to estimate biomass in semiarid grasslands. Though the method needs to be calibrated, it allows for a dramatic increase in the number of samples compared with the clipping method. The method is based on a relationship between the percentage or "green pixels" in a digital image and green biomass. We identified "green pixels" as those satisfying the following condition: G/B > 1 and G/R > 1, where G, B and R are the intensities of a particular pixel in the green, blue, and red bands respectively. The percentage of green pixels of the image and green grass biomass showed a correlation of 0.87 (n = 36, p < 0.001) when data were pooled from 3 sample dates. The relationship was slightly curvilinear and a log transformation of green biomass yielded a better correlation (r = 0.91, n = 36, p < 0.001). The percentage of green pixels showed a lower correlation with total green biomass than with grass biomass (r = 0.59) for the linear model and 0.73 for the log transformed model). The relationship between the percentage of green pixels and either green grass or total green biomass changed during the growing season. Both the slope and the Y-intercept of the model differed significantly among dates. Correlation coefficients for different dates ranged between 0.76 and 0.95.
    • Ungulate herbivory on Utah aspen: Assessment of long-term exclosures

      Kay, C. E.; Bartos, D. L. (Society for Range Management, 2000-03-01)
      The role of livestock grazing and big-game browsing in the decline of aspen (Populus tremuloides Michx.) in the Intermountain West has long been questioned. All known aspen exclosures (n=8) on the Dixie and Fishlake National Forests in south-central Utah were measured during late summer of 1995 and 1996 to determine aspen stem dynamics, successional status, and understory species composition. Five of the exclosures were of a 3-part design with a total-exclusion portion, a livestock-exclusion portion, and a combined-use portion which permitted the effects of deer (Odocoileus hemionus) and elk (Cervus elaphus) herbivory to be measured separately from those of livestock. Aspen within all total-exclusion plots successfully regenerated and developed multi-aged stems without the influence of fire or other disturbance. Aspen subjected to browsing by wildlife, primarily mule deer, either failed to regenerate successfully or regenerated at stem densities significantly lower (2,498 stems ha(-1)) than that on total-exclusion plots (4,474 stems ha(-1)). On combined wildlife-livestock-use plots, most aspen failed to regenerate successfully, or did so at low stem densities (1,012 stems/ha(-1)). Aspen successfully regenerated on ungulate-use plots only when deer numbers were low. Similarly, ungulate herbivory had significant effects on understory species composition. In general, utilization by deer tended to reduce shrubs and tall palatable forbs while favoring the growth of native grasses. The addition of livestock grazing, however, tended to reduce native grasses while promoting introduced species and bare soil. Thus, communities dominated by old-age or single-age trees appear to be a product of ungulate browsing, not a biological attribute of aspen as has been commonly assumed. There was no evidence that climatic variation affected aspen regeneration. Observed differences are attributed to varied histories of ungulate herbivory.