• Quantification and simulation of soil water on grazed fescue watersheds

      Chanasyk, David S.; Mapfumo, Emmanuel; Willms, Walter D.; Naeth, M. Anne (Society for Range Management, 2004-03-01)
      A 2-year study was conducted at the Agriculture and Agri-Food Canada Stavely Range Substation, Alberta. The objective was to quantify and simulate the soil water status of small grassland watersheds under 3 grazing intensities and 4 topographic positions. The grazing treatments were ungrazed (or control), heavy (2.4 AUM ha-1) and very heavy (4.8 AUM ha-1) grazing and the topographic positions were upperslope, midslope, lowerslope and 5 m away from the collector drain. Moisture readings were taken every 2 weeks between spring and fall using a CPN 503 moisture neutron probe. Readings were taken at the soil surface and at 15-, 25-, 35-, 45- and 55-cm depths. Total annual precipitation in 1998 and 1999 was 648 and 399 mm, respectively. In both years grazing treatments did not affect total soil water in the 0-50 cm (TSW50) depth interval for the upper, middle and lower slope positions, but TSW50 close to the collector drain was significantly (P ≤ 0.05) greater for the heavy grazed compared to the very heavy grazed treatment. Within each grazing treatment, TSW50 differences among slope positions occurred mainly under the heavy grazed treatment. Simulation of soil water at each soil depth and watershed was conducted using the Versatile Soil Moisture Budget Model (VB2000). Statistical and graphical evaluations of the model results were conducted using the volumetric soil water data collected for 1998 and 1999. The statistics determined included average error (AE), root mean square (RMS), coefficient of residual mass (CRM), modeling efficiency (EF) and coefficient of determination (CD). All statistics varied with each soil depth and watershed, indicating the transient nature of the data. This is reflected in the mostly negative CRM values, which ranged between -1.0 and 0.16. Overall model fitting to the whole data for all depths, watersheds and years gave values of CRM = -0.08 and EF = 0.19, indicating a slight over-prediction by the model. Spatial variation due to presence of rocks or cracks and averaging across slopes may have partly contributed to the discrepancies between model results and observed data.
    • Response of mountain meadows to grazing by recreational pack stock

      Cole, David N.; Van Wagtendonk, Jan W.; McClaran, Mitchel P.; Moore, Peggy E.; McDougald, Neil K. (Society for Range Management, 2004-03-01)
      Effects of recreational pack stock grazing on mountain meadows in Yosemite National Park were assessed in a 5-year study. Yosemite is a designated wilderness, to be managed such that its natural conditions are preserved. Studies were conducted in 3 characteristic meadow types: shorthair sedge (Carex filifolia Nutt.), Brewer's reed grass (Calamagrostis breweri Thurber), and tufted hairgrass [Deschampsia cespitosa (L.) Beauv.]. Horses and mules grazed experimental plots at intensities of 15 to 69% utilization for 4 seasons. In all 3 meadows, grazing caused decreases in productivity. The mean reduction after 4 years of grazing was 18% in the shorthair sedge meadow, 17% in the Brewer's reed grass meadow, and 22% in the tufted hairgrass meadow. Grazing also caused shifts in basal groundcover (usually a reduction in vegetation cover and increase in bare soil cover), and changes in species composition. Productivity and vegetation cover decreased as percent utilization increased, while bare soil cover increased as utilization increased. Changes in species composition were less predictably related to differences in grazing intensity. Passive management of grazing is insufficient in wilderness areas that are regularly used by groups with recreational stock. Wilderness managers need to monitor meadow conditions and the grazing intensities that occur. Our study suggests that biomass and ground cover are more sensitive indicators of grazing impact than species composition. Managers must make decisions about maximum acceptable levels of grazing impact and then develop guidelines for maximum use levels, based on data such as ours that relates grazing intensity to meadow response.
    • Seedling recruitment of perennial grasses in degraded areas of the Patagonian Monte

      Bisigato, Alejandro Jorge; Bertiller, Monica Beatriz (Society for Range Management, 2004-03-01)
      The recruitment of perennial grass seedlings in degraded areas of the Patagonian Monte was analyzed. Recolonization of large bare-soil areas by dwarf shrubs or perennial grasses was hypothesized to create favorable microsites for grass seedling recruitment. Under natural field conditions, soil moisture (0-20 cm), root biomass (0-20 cm), the soil seed bank of perennial grasses, and density of perennial grass seedlings in the center of large bare soil areas and in microsites neighboring isolated plants of perennial grasses and dwarf shrubs were assessed. A manipulative experiment was conducted to evaluate seedling recruitment at the 3 microsites with identical density of seed addition of perennial grasses, under situations of root exclusion, and water addition. Under natural field conditions, root biomass did not differ among microsites. Soil moisture, seed density, and seedling density of perennial grasses were higher near perennial grasses than in bare soil or next to dwarf shrubs. Recruitment of perennial grass seedlings did not differ among microsites when the density of seeds did not vary among them or roots of the established plants were excluded. Water increased perennial grass seedling recruitment at all microsites. In degraded areas of the Patagonian Monte the spatial distribution of the soil seed bank followed by water availability are the main limiting factors of seedling recruitment of perennial grasses. Managerial practices oriented to maintain and increase the soil seed bank of perennial grasses, such as grazing exclusion during the grass reproductive period, might contribute to promote the re-establishment of perennial grasses.
    • Sheep gain and species diversity: in sandy grassland, Inner Mongolia

      Zhao, Ha-Lin; Li, Sheng-Gong; Zhang, Tong-Hui; Ohkuro, Toshiya; Zhou, Rui-Lian (Society for Range Management, 2004-03-01)
      A grazing experiment was conducted from 1992 to 1996 at a sandy grassland in the Horqin sandy land, located in the northeastern part of China. The grassland had been grazed by sheep for many years before the experiment at an intensity of 4.5 sheep ha-1. The experiment consisted of 4 grazing treatments: no grazing (0 sheep ha-1), light grazing (2 sheep ha-1), moderate grazing (4 sheep ha-1) and overgrazing (6 sheep ha-1). Plant species diversity, plant biomass, soil properties, and sheep liveweight under various grazing treatments were examined. Overgrazing resulted in considerable decreases in both species diversity and plant biomass. As a result, sheep liveweight gain decreased significantly in the last 3 years of the experiment in the overgrazing treatment. No grazing and light grazing treatments had higher species diversity as well as higher biomass production than moderate grazing and overgrazing treatments. The results indicate that light sheep grazing is sufficient for the recovery of overgrazed grassland in this region and for the maintenance of plant species diversity. The proper grazing intensity should be 2-3 sheep or sheep equivalents per hectare for the sandy grassland in Inner Mongolia.
    • Shrub regrowth, antiherbivore defenses, and nutritional value following fire

      Schindler, Jason R.; Fulbright, Timothy E.; Forbes, T. D. A. (Society for Range Management, 2004-03-01)
      Prescribed fire is a commonly used as a follow-up procedure to mechanical top growth removal methods such as mowing and roller chopping, but the effects of fire on spinescence and tannin content of shrub sprouts produced after mechanical top growth removal are unknown. Following mowing, (1) height, spinescence, and tannin content in sprouts produced after burning; (2) nutrient and fiber contents in sprouts of the 3 study species; and (3) utilization of sprouts of each species in burned and unburned plots were determined in each of blackbrush acacia (Acacia rigidula Benth.), honey mesquite (Prosopis glandulosa Torr.), and spiny hackberry (Celtis pallida Torr.). Averaged across sampling periods, burned blackbrush acacia and honey mesquite had 54% and 94%, respectively, shorter thorns than unburned plants. Burned and unburned spiny hackberry plants had similar thorn lengths. Averaged across species, sprouts of burned plants had similar tannin levels as unburned plants 6 and 12 weeks after burning. Sprouts of burned blackbrush acacia had higher levels of tannin than sprouts of unburned plants 34 weeks after burning. Leaf material from sprouts of burned spiny hackberry plants had higher crude protein and digestible protein than leaf material from unburned plants. Blackbrush acacia sprouts in burned plots contained lower digestible dry matter and digestible energy than plants in unburned plots. Honey mesquite sprouts in burned plots contained higher digestible dry matter and digestible energy than plants in unburned plots. Burning appears to be a desirable follow-up treatment to mowing because it temporarily increases nutritional value of shrub sprouts, decreases physical defenses, and suppresses growth of shrub species that have low palatability to white-tailed deer.
    • Spatio-temporal rainfall variation and stock management in arid Namibia

      Ward, David; Saltz, David; Ngairorue, Ben T. (Society for Range Management, 2004-03-01)
      The high inherent variability in rainfall and forage availability in arid regions makes it very difficult for a rancher to establish a herd size that is suited to the environment and also complicates management decision-making regarding the distribution of animals within and between areas of a single ranch. We recorded the temporal and spatial variability in rainfall and grass production on a local scale on 3 ranches in arid Namibia over 3 years, to determine their effects on potential stocking density, stock movement decisions and timing of grazing. We conducted a 3-year experiment to test the effects of the timing of grazing on grass regrowth. Furthermore, we tested the reliability of a rule-of-thumb used by ranchers to ascertain whether a drought year is likely and whether they should sell some of their cattle in advance of drought. We expanded the scale of the study to include 31 ranches over a 700 km-long rainfall gradient to determine the reliability of extrapolating conclusions obtained at a local scale to a larger geographic scale. We found that rainfall and grass production varied widely, resulting in recommended stocking densities up to 10-fold smaller than those currently recommended by the Namibian Ministry of Agriculture. We found that there is no optimal spatial or temporal scale of ranch management, and that ranchers could do no better than a simple rule of “move the cattle to wherever there is most grass”. This simple rule's validity was reinforced by the results of our experiment, which showed that there was no significant effect of timing of grazing on grass regrowth. Statistical analyses of long-term rainfall records indicated that the ranchers' rule-of-thumb regarding approaching drought was unreliable and that this could lead to substantial loss of profit if adhered to.
    • Stocking rate, precipitation, and herbage production on sand sagebrush-grassland

      Gillen, Robert L.; Sims, Phillip L. (Society for Range Management, 2004-03-01)
      Knowledge of the relationship between stocking rate or grazing intensity and plant production is fundamental to the sustainable management of rangelands. The general management paradigm is that plant production declines as stocking rate increases. Our objective was to determine the impact of stocking rate on herbaceous production of a sand sagebrush (Artemisia filifolia Torr.)-grassland. Stocking rates averaging 43, 57, and 85 animal-unit-days ha-1 (AUD ha-1) for year-round grazing were applied from 1941 to 1961. Herbaceous plant production was determined by sampling standing crop in temporary exclosures at the end of the growing season from 1958 to 1961, the last 4 years of the grazing study. Total herbaceous production averaged over stocking rates and years was 1,490 kg ha-1. Grasses contributed 89% of the total while forbs contributed 11%. Total production averaged 1,540, 1,470, and 1,450 kg ha-1 for stocking rates of 43, 57, and 85 AUD ha-1 y-1, respectively. There were no differences among stocking rates for total production or for the production of any individual grass species (P > 0.05). Forb production was also not affected by stocking rate, averaging 200, 140, and 120 kg ha-1 for stocking rates of 43, 57, and 85 AUD ha-1 y-1 (P > 0.05). Differences in production among years were much greater than differences among stocking rates for all vegetation components. Little bluestem [Schizachyrium scoparium (Michx.) Nash] and sand lovegrass [Eragrostis trichodes (Nutt.) Wood] showed the greatest responses to favorable precipitation. Herbaceous production of this sand sagebrush-grassland was little affected by 20 years of differential stocking rates.