• Carbon exchange rates in grazed and ungrazed pastures of Wyoming

      Lecain, D. R.; Morgan, J. A.; Schuman, G. E.; Reeder, J. D.; Hart, R. H. (Society for Range Management, 2000-03-01)
      The influence of cattle grazing on carbon cycling in the mixed grass prairie was investigated by measuring the CO(2) exchange rate in pastures with a 13 year history of heavy or light grazing and an ungrazed exclosure at the High Plains Grasslands Research Station near Cheyenne, Wyo. In 1995, 1996 and 1997 a closed system chamber, which covered 1 m(2) of ground, was used every 3 weeks from April to October to measure midday CO(2) exchange rate. Green vegetation index (similar to leaf area index), soil respiration rate, species composition, soil water content, soil temperature, and air temperature were also measured to relate to CO(2) exchange rates of the 3 grazing treatments. Treatment differences varied among years, but overall early season (mid April to mid June) CO(2) exchange rates in the grazed pastures were higher (up to 2.5 X) than in the exclosure. Higher early season CO(2) exchange rates were associated with earlier spring green-up in grazed pastures, measured as higher green vegetation index. As the growing season progressed, green vegetation index increased in all pastures, but more so in the ungrazed exclosure, resulting in occasionally higher (up to 2 X) CO(2) exchange rate compared with grazed pastures late in the season. Seasonal treatment differences were not associated with soil temperature, soil respiration rate, or air temperature, nor was there a substantial change in species composition due to grazing. We hypothesize that early spring green-up and higher early season CO(2) exchange rate in grazed pastures may be due to better light penetration and a warmer microclimate near the soil surface because of less litter and standing dead compared to the ungrazed pastures. When all the measurements were averaged over the entire season, there was no difference in CO(2) exchange rate between heavily grazed, lightly grazed and ungrazed pastures in this ecosystem.
    • Effects of nitrogen fertilization in leafy spurge root architecture

      Ringwall, K.; Biondini, M. E.; Grygiel, C. E. (Society for Range Management, 2000-03-01)
      There is a dearth of information concerning the degree to which the amounts, periodicity, and spatial patterns of N applications can be manipulated to alter the rooting strategy of leafy spurge, and thus make it more susceptible to chemical and biological controls. This study was designed with the following objectives: (1) determine the effect of patchy N fertilization on shoot and root biomass, root distribution by depth, root plasticity, and the ratio of coarse vs. fine roots of leafy spurge; and (2) determine how leafy spurge scales root biomass to root lateral spread and root surface area, as well as how these scaling patterns are affected by N fertilization. The root architecture, plasticity, and response to patchy N fertilization was evaluated in 3 separate experiments conducted in large containers. Patchy fertilization did not alter the morphological characteristics of leafy spurge roots, but did cause a reduction in root biomass and a drastic change in the distribution of the root surface area within the plant's rooting volume. Fertilization both doubled the percentage of roots located in the top 10 cm of soil and shifted it toward the fertilized patches.
    • Grazing effects on spring ecosystem vegetation of California's hardwood rangelands

      Allen-Diaz, B.; Jackson, R. D. (Society for Range Management, 2000-03-01)
      Three watersheds at the University of California's Sierra Foothill Research and Extension Center (SFREC), Marysville, Calif. were selected to study cattle grazing effects on the vegetation surrounding cold-water springs and their downslope creeks. Three spring-creek systems from each of 3 watersheds were randomly assigned to grazing treatments (9 total). Treatments were ungrazed, lightly grazed (1,500 kg(.)ha(-1) residual dry matter), and moderately grazed (1,000 kg(.)ha(-1) residual dry matter) based on degree of use in upland pastures encircling the spring-creek systems. Total herbaceous cover at springs varied significantly among the 6 years only once (greater in 1994 than all others covarying with previous year's rainfall. Grazing intensity did not affect total herbaceous cover at springs. A year X grazing treatment interaction (P 0.05) was detected for total herbaceous cover at spring-fed creeks. Three years after grazing removal, total herbaceous cover on ungrazed creek plots surpassed cover at moderately grazed and lightly grazed plots. Moderately grazed plot herbaceous cover declined steadily throughout the first 3 years, while lightly grazed cover remained relatively stable. Plant community composition and stability by year and grazing treatment were analyzed with TWINSPAN. With few exceptions, stable plant communities persisted on sites regardless of grazing intensity or cover changes. Total herbaceous cover was sensitive to interannual fluctuations, especially under increased grazing intensities. This attribute renders cover a more useful gauge of ecosystem health than plant composition as the latter may not provide evidence of potentially deleterious grazing X climate interactions until after soil erosion or water table characteristics are seriously, perhaps permanently, altered.
    • Herpetofaunal responses to brush management with herbicide and fire

      Jones, B.; Fox, S. F.; Leslie, D. M.; Engle, D. M.; Lochmiller, R. L. (Society for Range Management, 2000-03-01)
      We examined how native herpetofauna of the Cross Timbers in Oklahoma, USA, were influenced by vegetation types derived from combinations of herbicide applications and prescribed burning. Brush management treatments consisted of tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiazol-2-y-1] -N,N'-dimethylurea)-only, tebuthiuron + fire, and untreated pastures of mature hardwood forest (no herbicide or fire). A total of 292 individuals representing 30 species was captured in 1994 and 1995 using time-constrained searching and drift-fence arrays on 3 replicates of the 3 treatments. Relative total abundance and species richness of herpetofauna were similar on all 3 treatment types. However, differences were apparent by taxonomic group. In general, amphibians were most abundant in untreated and tebuthiuron-only pastures, lizards were most abundant on the untreated pastures, and snakes were most abundant on pastures treated with tebuthiuron + fire. Maintenance of a mosaic of habitats in the Cross Timbers may enhance diversity of the native herpetofauna.
    • N-alkane as an internal marker for predicting digestibility of forages

      Sandberg, R. E.; Adams, D. C.; Klopfenstein, T. J.; Grant, R. J. (Society for Range Management, 2000-03-01)
      Independent digestion trials with 5 forages were conducted to compare n-alkane with indigestible acid-detergent fiber (IADF) as internal markers to predict in vivo dry matter digestibility (digestibility). Forages were mixed grasses from subirrigated meadow (meadow), meadow regrowth (regrowth), native range (range), mature mixed grass hay from meadow, and alfalfa (Medicago sativa L.) hay. Meadow, regrowth, and range diets were immature grasses harvested 0.5 hours before feeding. Feces from the meadow hay and alfalfa hay trials were divided to compare freeze drying and oven drying (60 degrees C). All diets were subjected to in vitro fermentation for 0, 48, or 96 hours. N-alkane was separated from samples by 4.5-hour saponification with alcoholic KOH followed by extraction with n-hexane. Indigestible ADF was measured by 96-hour in vitro fermentation followed by ADF extraction. Digestibility estimated by markers was compared with in vivo digestibilities. N-alkane based digestibilities were lower (P < 0.01) than in vivo digestibility for all diets. N-alkanes provided higher estimates of digestibilities than IADF for meadow (P < 0.01), regrowth (P = 0.06), and alfalfa hay (P = 0.06), and lower digestibility for meadow hay (P = 0.02). Digestibilities calculated using n-alkanes for range tended to be higher (P = 0.14) than IADF values. Freeze drying increased (P < 0.01) the amount of n-alkane extracted from alfalfa hay, but did not affect (P = 0.1) the amount extracted from meadow hay. N-alkane disappeared (P < 0.001) from residue collected after 48 hours of in vitro fermentation, but no additional disappearance (P = 0.78) was evident at 96 hours. Neither marker was completely recoverable, although recovery of n-alkane was higher than indigestible ADF for 4 of the 5 forages tested.
    • Rangeland management impacts on soil biological indicators in southern Alberta

      Dormaar, J. F.; Willms, W. D. (Society for Range Management, 2000-03-01)
      Quantitative techniques are needed to determine the effects of cultivation and livestock grazing on biological indicators of soils of the Northern Great Plains. Our objective was to determine how various management practices, which were representative of those used since European settlement in the 1880's, affected 3 biological indicators of soil quality. The study was conducted at 3 sites that are representative of the major grassland ecosystems in Canada: a Mixed Prairie site with Stipa comota Trin. Rupr. dominant in the Brown (Aridic Haploboroll) Soil Zone, a Mixed Prairie site with S. comata Trin. Rupr. and S. viridula Trin. dominant in the Dark Brown (Typic Haploboroll) Soil Zone, and a Fescue Prairie site with Festuca campestris Rydb. dominant in the Black (Udic Haploboroll) Soil Zone. At each site, 6 treatments representing common production practices were imposed and compared with the native community in a randomized complete block design with 4 replicates and a plot size of 3 x 10 m. The treatments included: 1) monoculture seeding of 2 grass species; 2) alfalfa (Medicago sativa L. 'Beaver'); 3) continuous spring wheat (Triticum aestivum L. 'Katepwa'): 4) spring wheat and fallow rotation; and 5) abandoned cultivated land. Our hypothesis that mineralizable-N, and phosphatase and dehydrogenase activities would be influenced by cultivation was confirmed by significant changes in these indicators that were detected after only 180 days after treatment establishment. The pool of readily decomposable organic matter was reduced with cultivation and not replenished over the period of the study. The 3 biological indicators were sensitive to not only time following external management changes, but also to seasonal fluctuations. We conclude that soil biological indicators can be used to quantify temporal and botanical changes in diverse ecotypes within the Northern Great Plains.
    • Residual nitrogen effects on soil, forage, and steer gain

      Berg, W. A.; Sims, P. L. (Society for Range Management, 2000-03-01)
      Nitrogen fertilization is a common practice on introduced grass pastures established on marginal farmland in the Southern Great Plains. The efficiency of N fertilizer use on pastures and concern about nitrate movement into substrata prompted this study of residual N effects following fertilization. The study was conducted on Old World bluestem (Bothriochloa ischaemum L.) pastures on Pratt soil (sandy, mixed thermic Psammentic Haplustalfs) in western Oklahoma where the 57-year average annual precipitation is 566 mm yr(-1). Herbage production and steer gains were quantified over 3 summer grazing seasons on paddocks fertilized annually with 0, 34, 68, or 102 kg N ha(-1) yr(-1) during the preceding 5 years. Peak standing ungrazed herbage yields were 2- to 4-fold greater in paddocks fertilized the preceding 5 years and were linearly related to the total N applied the previous 5 years. Steer weight gain responded linearly to N with an average of 0.63 kg gain over 3 years per kg N applied over the preceding 5 years. No differences (P > 0.05) in soil nitrate concentrations to a depth of 2.8 m were measured among the N rate treatments. Overall, substantial effects of residual N were measured in both herbage mass and steer weight gain for 3 years following 5 years of N fertilization.
    • 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.