• Oxalate and tannins assessment in Atriplex halimus L. and A. nummularia L

      Abu-Zanat, M. M.; Al-Hassanat, F. M.; Alawi, M.; Ruyle, G. B. (Society for Range Management, 2003-07-01)
      The study was conducted at 3 locations in the arid region of Jordan to assess the seasonal changes of oxalate and tannins in Atriplex halimus L. and A. nummularia L. plants commonly used for revegetation of degraded rangelands. During spring and fall seasons, 20 shrubs of each species were selected randomly at each location, 20 similar twigs per shrub were clipped and analyzed for oxalate and tannins. Atriplex halimus contained higher levels of oxalate (7.00%) compared with A. nummularia plants (6.20%) (P < 0.001). Oxalate levels averaged 8.29 and 4.92% in spring and fall season, respectively. Plants of A. halimus accumulated more oxalate in spring than those of A. nummularia. Clipping had no effect on oxalate concentration. The seedlings of A. nummularia contained more oxalate than old plants whereas old shrubs of A. halimus contained more oxalate than the young seedlings. The browse of A. halimus contained more condensed and hydrolyzable tannins (1.05% and 0.67%, P < 0.0001) than A. nummularia (0.80% and 0.39%, P 0.0001), respectively. Clipping had no effect on the levels of tannic phenols, condensed and hydrolyzable tannins. Young plants of the 2 species had higher levels of condensed tannins compared to older plants. However, seedlings of A. nummularia contained significantly higher levels of condensed tannins compared to A. nummularia seedlings (1.57% and 1.47%, respectively). Atriplex halimus synthesized more oxalate, tannic phenols, condensed and hydrolyzable tannins than A. nummularia. These secondary metabolites may explain the low palatability of Atriplex halimus compared to A. nummularia.
    • Perennial grass abundance along a grazing gradient in Mendoza, Argentina

      Gonnet, J. M.; Guevara, J. C.; Estevez, O. R. (Society for Range Management, 2003-07-01)
      The study analyzed the basal area and density of perennial grasses along a cattle grazing intensity gradient away from a water development. Several mechanisms explaining combinations of changes in basal area and density with increasing grazing intensity were proposed. There was a curve-linear gradient of decreasing utilization of grasses at greater distances from water, and that gradient declined at greater distances from water. Basal diameter and density of 8 grasses were recorded at 11 distances from water ranged from 0.1 to 4.6 km within 16, 1-m2 plots for each distance. Circular basal area for each species was derived from its mean basal diameter. Plant density was estimated counting each tussock for bunchgrasses and each tiller as an individual for the 1 rhizomatous grass. The abundance of basal area and density to the gradient of distance from water was analyzed for grasses grouped according to their selectivity by cattle (undesirable, preferred, desirable, and secondary preference) and for the major preferred grass, Chloris castilloniana Lillo Parodi and the 2 undesirable grasses, Aristida inversa Haeck. and A. mendocina Phil. Distance from water was regressed separately on basal area and on density for each selectivity group and each individual species. Basal area of total, undesirable, and desirable grasses increased up to intermediate distances from water and decreased at sites farther from water. Basal area of both the preferred grasses combined and the major preferred species increased linearly with distance from water. Basal area of A. inversa showed the same trend as the undesirable grasses while basal area of A. mendocina showed no definite pattern with increasing grazing intensity. Basal area of secondary preference species showed no definite pattern with distance from water. Density of total and desirable grasses increased up to intermediate distances from water and decreased at sites farther from water. Density of preferred species combined and the major preferred grass increased linearly with distance from water. Density of the 2 undesirable grasses and the secondary preference grass showed no definite trend with increasing grazing intensity. The combined patterns of basal area and density across the grazing intensity gradient suggest that the expression of recruitment, mortality, and plant growth (or shrinkage) in relation to grazing intensity varies among species and at different levels of grazing intensity. However, controlled experiments are needed to decipher the relative contributions of grazing intensity, neighboring species composition, or vegetation patterns existing before the establishment of the livestock water in the patterns of abundance.
    • Research observation: Effects of rangeland ecological condition on scaled quail sightings

      Joseph, J.; Holechek, J. L.; Valdez, R.; Collins, M.; Thomas, M. (Society for Range Management, 2003-07-01)
      Scaled quail (Callipepla squamata) numbers were evaluated during and after a 2-year drought period using strip census techniques on 2 pastures in late seral rangeland ecological condition and 2 pastures in mid-seral rangeland ecological condtion. This study was conducted on the Chihuahuan Desert Rangeland Research Center (CDRRC) in south-central New Mexico on 4 adjoining pastures that were similar in size and terrain. During part of the study (August 1994 to April 1997) all 4 pastures were destocked due to depletion of perennial grass cover and biomass from a combination of drought and heavy cattle grazing. Scaled quail sightings pooled across sampling periods (9) were different (P = 0.08) on high and low rangeland ecological condition treatments. They averaged 10.72 birds per pasture on late-seral and 4.22 birds per pasture on mid-seral rangeland ecological condition treatments. Autumn perennial grass cover and standing biomass levels was higher (P < 0.10) on late seral than on mid-seral rangeland ecological condition pastures during both years of study. Availability of scaled quail foods such as leatherweed croton and broom snakeweed did not differ (P > 0.10) between treatments. Our study indicates that during extended dry periods livestock grazing at moderate intensities may adversely affect scaled quail populations in the Chihuahuan Desert by depleting perennial grass cover. However, in years of above average precipitation there is evidence scaled quail prefer mid-seral pastures over late-seral pastures. Maintaining a mosaic of conservatively (late-seral) and moderately (mid-seral) grazed pastures should best meet the habitat needs of scaled quail in the Chihuahuan Desert.
    • Restoring riparian corridors with fire: effects on soil and vegetation

      Blank, R. R.; Chambers, J. C.; Zamudio, D. (Society for Range Management, 2003-07-01)
      In many riparian corridors of the semi-arid west, stream incision has resulted in lowered water tables, basin big sagebrush (Artemisia tridentata var. tridentata Nutt.) encroachment and the loss of the dominant herbaceous vegetation. To determine the potential for restoring basin big sagebrush-dominated riparian corridors to greater herbaceous cover, a fall prescribed burn on sites with relatively shallow (-153 to -267 cm) and deep (-268 to or = -300 cm) water tables was conducted. We evaluated the separate and interacting effects of water table depth and burning on total soil C and N, soil nutrient availability, and soil enzyme activities by microsite (sagebrush subcanopy, sagebrush interspace), and soil depth (ash/liter, 0-2, 2-5, and 10-20 cm). Three years after the prescribed burn, tissue nutrient content in silvery lupine (Lupinus argenteus Pursh) and Douglas sedge (Carex douglasii Boott), by microsite, growing in burned and unburned areas of 1 shallow water table site was measured. Influence of fire on soil attributes was largely limited to the top 5 cm. As a consequence of prescribed burning, deep water table sites lost relatively more N and C from litter horizons and released more aqueous-soluble Ca+2 from 0-2 cm mineral horizons than did corresponding horizons from shallow water table sites. Overall, compared to unburned controls, burning: (1) increased aqueous-extractable SO4(-2), K+, and KCl-extractable NH4+, (2) decreased activities of the enzymes asparaginase, urease and acid-phosphatase, and (3) decreased KCl-extractable NO3- and aqueous-soluble ortho-P. Out of 16 measured soil attributes reported, 7 were influenced by a microsite main effect and/or interaction. New tissue of silvery lupine on burned plots had greater N, greater Zn and Fe (only on subcanopy microsites) and less Ca than plants on control plots; new tissue of Douglas sedge had greater S and less Na, P, and Zn. The results indicate that burning alone is an appropriate restoration treatment for shallow water table sites because of minimal C and N loss and increased available nutrients for regrowth of understory herbaceous species. Deep water table sites require a burning prescription that minimizes fire severity because of higher potential C and N loss, and reseeding due to a lack of perennial understory herbaceous species and more xeric conditions.
    • Sustainability of Inner Mongolian grasslands: application of the Savanna model

      Christensen, L.; Coughenour, M. B.; Ellis, J. E.; Chen, Z. (Society for Range Management, 2003-07-01)
      The sustainability and resilience of an Asian typical steppe grazing ecosystem was assessed by determining thresholds and stable states with an ecosystem simulation model. This analysis used the Savanna model to simulate spatial climate, vegetation, and livestock grazing dynamics, at 14 different stocking rates (5.5-59.8 AUY km-2). Grazing effects on vegetation were assessed, including effects on primary production, vegetation composition, and root biomass. Simulations were run for 100 years: 50 years to examine sustainability and 50 years to examine resilience of the system. Results showed that a grazing intensity (1-g/u; g = biomass in grazed area, u = biomass in ungrazed area) of 0.49 was sustainable for this particular system. This region was resilient to grazing up to the intensity of 0.49, where the system remained dominated by herbaceous production. Grazing intensities higher than 0.49, in combination with low precipitation events, resulted in decreased herbaceous net primary production and root biomass, and increased shrub net primary production and root biomass. Herbaceous vegetation was unable to gain a competitive advantage over shrubs in areas where grazing intensities were above 0.49; consequently, the system shifted to a stable shrub-dominated state that could not return its original composition even without further grazing.
    • The economic logic of prescribed burning law and regulation

      Yoder, J.; Engle, D. M.; Tilley, M.; Fuhlendorf, S. (Society for Range Management, 2003-07-01)
      Prescribed burning has long been recognized as a useful tool in rangeland management, but with it comes the risk of fire and smoke damage to the property of others. All but 2 states have codified laws specifying criminal penalties or liability rules for prescribed burning, but the laws in a number of states have changed in recent years or are under review. We develop an economic model of the incentive and welfare effects of prescribed burning law and regulation in which the likelihood and extent of external damage can be reduced by precautionary effort on the part of both the burner and/or the victim. The model provides implications regarding the comparative advantages to the public of strict liability versus negligence rules. We conclude that the relative effectiveness of a liability rule depends in large part on the relative ability of burners and other landowners to mitigate the probability and extent of damage, as well as the legal costs associated with implementing a given liability rule.
    • Ungulate herbivory on buckbrush in an Arizona ponderosa pine forest

      Huffman, D. W.; Moore, M. M. (Society for Range Management, 2003-07-01)
      Monitoring processes that affect plant population dynamics and determine community structure is central in forest restoration ecology. To study effects of mule deer (Odocoileus hemionus) and elk (Cervus elaphus) on buckbrush (Ceanothus fendleri Gray), we built exclosures around 90 plant-centered plots in 3 ponderosa pine (Pinus ponderosa Laws.) forest restoration management units and compared vegetative and flowering characteristics with unprotected plots for 2 years. On unprotected plots, 69% of the current-year branches were browsed during the first year and 44% were browsed the second year. There was no difference in number of aerial stems or current-year branches in the first year, yet stems on protected plots were longer (24.1 cm; P < 0.01) and retained more than 4 times the current-year biomass (1.4 g stem-1; P < 0.01) than those on unprotected plots (12.9 cm and 0.3 g stem-1, respectively). Stem number, length and diameter, number of current-year branches, and current-year biomass on protected plots were all greater (P < 0.01) than on unprotected plots in the second year. Stems on protected plots had significantly higher (P < 0.01) length-diameter ratios and had fewer current-year branches per unit length (P < 0.05) than unprotected stems. Flowering stems were found on significantly (P < 0.05) more protected plots (55%) than unprotected plots (8%) in the second year. Effects of ungulate herbivores on buckbrush size, stem recruitment, morphology, and flowering represent important constraints to early understory development and restoration in this Southwest ponderosa pine forest.
    • Utilization and grazing distribution of cattle at 4 stocking densities

      Burboa-Cabrera, F. R.; Schacht, W. H.; Anderson, B. E. (Society for Range Management, 2003-07-01)
      The relationship between stocking density and grazing distribution was studied in eastern Nebraska pastures seeded to a warm-season, tall-grass mixture and grazed at 4 stocking densities: 9, 18, 27, and 54 steers ha-1. Each of 4 pastures was divided into 4 paddocks ranging in size from 0.18 to 1.12 ha. Paddocks within each pasture were grazed rotationally by 10 steers averaging 282 kg during 3 consecutive cycles (12, 36, and 24 days) from early June to late August in 1995 and 1996. Transects 12-m long were established in a grid pattern in each paddock. Six tillers each of big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicum virgatum L.) were marked permanently in each transect. Height and leaf length of marked tillers were measured before and after grazing in the last 2 grazing cycles in both years. Utilization was estimated by the reduction in tiller height or leaf length. Estimates of grazing distribution were based on a uniformity index, which was calculated by summing the absolute differences of tiller height or leaf length between adjacent transects. Stocking density generally did not affect (P > 0.05) tiller height reduction which ranged from 19 to 22 cm and from 29 to 38 cm among the stocking densities in 1995 and 1996, respectively. In most grazing cycles, leaf length reduction for big bluestem was greater (P < 0.05) than for switchgrass while tiller height reduction was similar between species. Spatial grazing distribution was not affected (P > 0.05) by stocking density but big bluestem was grazed more evenly (P < 0.05) than switchgrass in the last cycle in each year. Stocking densities as high as 54 steers ha-1 on warm-season, tall-grass mixtures do not appear to be a major factor in affecting spatial grazing distribution or forage plant selection.
    • Vegetation indices, CO2 flux, and biomass for Northern Plains grasslands

      Frank, A. B.; Karn, J. F. (Society for Range Management, 2003-07-01)
      Native grasslands are a sink for atmospheric CO2 sequestration, but ways for extending site-specific CO2 flux measurements to a regional scale are lacking. Objectives of this study were to determine the utility of using canopy radiometric reflectance for estimating CO2 fluxes for semiarid grasslands. The relationship between the normalized difference vegetation index (NDVI) calculated from spectral reflectance data obtained with hand-held radiometers was compared to CO2 flux calculated from Bowen ratio/energy balance measurements. Carbon dioxide flux was measured during the plant growing season over a nongrazed prairie, grazed prairie, and a shrub dominated prairie site near Mandan, N.D. Measurements were also made of evapotranspiration (ET), green biomass, and green leaf area index (LAI). Correlation coefficients of NDVI with vegetation parameters of biomass and LAI for each site and year exceeded 0.84 in 1999, 0.74 in 2000, and 0.91 in 2001; with CO2 flux correlations exceeded 0.63 in 1999, 0.68 in 2000, and 0.69 in 2001; with ET correlations exceeded 0.91 in 1999, 0.92 in 2000, and 0.90 in 2001. Regression analysis over all years and sites produced a nonlinear relation between NDVI and both biomass (R2 = 0.83) and LAI (R2 = 0.77) and a linear relationship between NDVI and both CO2 flux (R2 = 0.51) and ET (R2 = 0.81). The relationships between NDVI and biomass, LAI, CO2 flux, and ET for the 3 grassland sites, which differed in management and vegetation, were generally quite similar suggesting that NDVI has potential for use in predicting canopy CO2 flux rates for semiarid grasslands in the Northern Great Plains.