• Fingerprint composition of seedling root exudates of selected grasses

      Dormaar, J. F.; Tovell, B. C.; Willms, W. D. (Society for Range Management, 2002-07-01)
      The competitiveness of plants within a community is dictated to some extent by their association with microorganisms in the soil. That association is affected by root exudates and possibly by their quality. The competitiveness of species under various grazing regimes has been defined by their response to grazing as decreaser, increaser, or invader. To test the hypothesis that there are recognisable differences in the chemical fingerprints of the root exudates of decreasers, increasers and invaders, seeds of 8 grasses, representing these 3 designations, were germinated and grown for 2 weeks in a root exudate trapping system in the laboratory. Tentative identification of the suite of compounds recovered from the root exudates by a solvent extraction technique was done with the help of gas chromatography/mass spectrometry and authentic samples. Eleven identified compounds, present in all exudates as major peaks, but absent in the blanks, were selected for semi-quantitatively comparing the 3 grazing response groups. For all 11 compounds, there was always at least 1 of the grazing response groups that had the highest percentages. That is to say, they were qualitatively, based on the 11 compounds selected, but not quantitatively similar.
    • Large ungulate habitat preference in Chobe National Park, Botswana

      Omphile, U. J.; Powell, J. (Society for Range Management, 2002-07-01)
      Both large ungulates and wildlife tourists tend to concentrate along the Chobe River in Chobe National Park, Botswana, during the dry season causing concern for wildlife habitat and the recreational experience for wildlife viewers. Therefore, ground reconnaissance inventory data of 5 most common large ungulates were collected during the early morning and late afternoon hours along tourist routes in 5 different habitat types every second month for a period of 24 months in Chobe National Park to determine their relative, seasonal habitat preference and availability for viewing by vehicular tourists. A total of 909 herds: greater kudu (Tragelaphus strepsiceros), 285; impala (Aepyceros melampus), 209; elephant (Loxodonta africana), 200; giraffe (Giraffa camelopardalis), 138; and buffalo (Syncerus caffra), 77 were observed during the 760 observation periods. The average frequency of observation of a herd of 1 or more of these 5 ungulates per habitat type was alkali flats, 3.42; floodplain grassland, 2.67; shrub savanna, 2.29; tree savanna, 1.04; and woodland, 0.30. This order of frequency of observation is highly correlated with nearness to the Chobe River, the major water source during the dry season. Elephant and giraffe were more wide-ranging than buffalo, impala, and kudu. During the dry season, all animals were seen more often on the floodplain grassland in the afternoon than in the morning. Giraffe were never seen in any habitat type in December, and impala were never seen in the woodland in any month. Our data confirm that tour operators interested primarily in providing their guests with a view of the greatest numbers of animals in a limited period of time are justified in congregating along the Chobe River during the dry season. However, as in most public wildlife reserves, Chobe National Park management is faced with the decision of how best to optimize the biological needs of Park animals and their habitat with the economic and recreational desires of Park users.
    • Long-term impacts of livestock grazing on Chihuahuan Desert rangelands

      Navarro, J. M.; Galt, D.; Holechek, J.; McCormick, J.; Molinar, F. (Society for Range Management, 2002-07-01)
      Rangeland ecological condition was monitored over a 48 year period on 41 sites on Bureau of Land Management rangelands scattered across 6 counties in southwestern New Mexico. All sites were grazed by livestock during the study period. Sampling occurred in 1952, 1962, 1982, 1992, 1997, 1998, and 1999. A modified Parker 3 step method in conjunction with Dyksterhuis quantitative climax procedures were used to determine rangeland ecological condition. At the end of the 48 year study period (1952-1999), the average rangeland ecological condition score across study sites was the same (P > 0.05) as the beginning of the study (39% versus 41% remaining climax vegetation, respectively). Major changes (P > 0.05) in rangeland condition occurred within the study period due to annual fluctuations in precipitation. Ecological condition scores increased in the 1980s and early 1990s due to above average precipitation. However, drought in the early to mid 1950's and again in the mid to late 1990's caused rangeland condition scores to decline. At the end of the study (1997-1999), 38% of the sites were in late seral ecological condition, compared to an average of 25% in the 1952 to 1982 period. The amount of rangeland in late seral ecological condition increased while the amount of rangeland in mid seral and early seral condition decreased in the 1990s compared to the 1952-1962 period. The average percent cover of black grama (Bouteloua eriopoda Torr.) and tobosa (Hilaria mutica Buckley), the primary forage grasses in the Chihuahuan Desert, were the same (P > 0.05) in 1952 and 1999. Over the 48 year study period, the average cover of shrubs including honey mesquite (Prosopis glandulosa Torr.) showed no change (P > 0.05). However major increases in honey mesquite basal cover occurred on 1 site and creosote-bush (Larria tridentata [Pursh] Nutt.) increased on another. Grazing intensity was evaluated during the last 3 years of study (1997, 1998, 1999). Overall grazing use of forage across sites and years averaged 34% or conservative. Our research shows controlled livestock grazing is sustainable on Chihuahuan Desert rangelands receiving from 26-35 cm annual precipitation.
    • Monitoring a half-century of change in a hardwood rangeland

      Heise, K. L.; Merenlender, A. M. (Society for Range Management, 2002-07-01)
      Changes in rangeland species composition can effect forage quality, ecosystem function, and biological diversity. Unfortunately, documenting species compositional change is difficult due to a lack of accurate historic records. We took advantage of herbarium records dating from the early 1950's to reconstruct the past flora of a 2,168 ha hardwood rangeland in Mendocino County, California, and then compared this to the current flora of the site. An inventory of vascular plants conducted from 1996 to 2001 added 44 native and 15 non-native species bringing the total number of species and infraspecific taxa at the study site to 671. Of the original 612 species recorded prior to this study, 34 native and 1 non-native species could not be relocated. The percentage of non-native species increased from 19% in 1952 to 23% in 2001. Based on estimates from the early 1950's, mid 1980's, and 1996 to 2001, at least 13 non-native species have increased in abundance, while some native species have decreased. Livestock grazing, competition with invasive species, conversions to different vegetation types, and transportation of propagules into the site by vehicles and livestock, combined with the difficulty of relocating rare species, are posed as the most likely causes for the documented changes.
    • Plains larkspur (Delphinium geyeri) grazing by cattle in Wyoming

      Pfister, J. A.; Gardner, D. R.; Stegelmeier, B. L.; Knight, A. P.; Waggoner, J. W.; Hall, J. O. (Society for Range Management, 2002-07-01)
      Plains larkspur (Delphinium geyeri Greene) is a major cause of cattle deaths in the northern Great Plains of Wyoming and Colorado. We examined the amount and timing of larkspur ingestion by grazing cattle in relation to larkspur phenology, nutrient concentrations, and weather conditions. Four summer grazing trials were conducted near Cheyenne (1996 and 1997) and Laramie, Wyo. (1998 and 1999). All trials began when plains larkspur was vegetative or in the early bud stage. In the first 2 studies, 6 yearling heifers grazed from 3 May to 4 August 1996; the same animals plus 5 cow-calf pairs grazed from 13 May to 10 August 1997. During both 1996 and 1997, cattle ate 0.5 to 1% of bites as larkspur during May, then consumption decreased to nearly 0 during the remainder of both summers. When eaten, larkspur was typically consumed during cool, foggy weather conditions. In the last 2 studies, 6 cow-calf pairs grazed near Laramie, Wyo., from 13 May to 30 June 1998, and 6 different cow-calf pairs grazed from 2 June to 20 July 1999. Cattle ate substantial amounts of plains larkspur (herd average approximately 3%) during the vegetative and bud stages from mid-May into early June, 1998. Cattle may have eaten more larkspur during 1998 because drought reduced spring availability of green grass. Consumption of larkspur was negatively related (r2 = 0.43) to daily temperature in 1998, but not during 1999. During 1999 cattle ate essentially no plains larkspur during the vegetative and bud stages, but ate larkspur (herd average approximately 5%) during the flower and pod stages when larkspur plants were beginning to desiccate and ambient temperatures were above average. This series of trials indicates that it will be difficult to predict plains larkspur consumption based on larkspur growth patterns or weather. Although cattle sometimes increase plains larkspur consumption when temperatures are cooler than normal, this pattern is not consistent enough to serve as a basis for management recommendations.
    • Population cycles of broom snakeweed in the Colorado Plateau and Snake River Plains

      Ralphs, M. H.; Sanders, K. D. (Society for Range Management, 2002-07-01)
      Broom snakeweed (Gutierrezia sarothrae (Pursh) Britt. Rusby) is one of the most widespread range weeds in North America. The objective of this study was to monitor broom snakeweed populations in the salt-desert shrub community of the Colorado Plateau and in crested wheatgrass (Agropyron desertorum (Link) Schultes) seedings typical of the Snake River Plains and Great Basin, and determine if its population cycles are related to precipitation patterns. Foliar cover of broom snakeweed and associated plant species was measured along 7.6 or 33 m transects by the line intercept technique. Density of snakeweed age classes (seedling, juvenile, mature) was counted in 1 m2 quadrats at the beginning and end of each transect. Correlations were made between snakeweed cover and density, and seasonal precipitation. The snakeweed population at the Colorado Plateau site completed 2 cycles over the 13 year study period, dying out in the drought of 1989-90 and again in 2001. There were positive correlations between density of snakeweed classes and seasonal precipitation: seedlings with spring precipitation (r = 0.63); juveniles with winter precipitation (r = 0.69); and mature plants with previous fall precipitation (r = 0.62). Only 1 cycle occurred at the Snake River Plains site. Following the snakeweed invasion into crested wheatgrass seedings in the mid 1980's, the population was at the top of its population cycle when the study began in 1990, dropped back and fluctuated between 6-10% cover from 1992 to 1999, and died out in 2001. Although density of mature plants did not change much during the middle part of the study, the change in snakeweed cover was correlated with spring (r = 0.81) and total precipitation (r = 0.60), reflecting increase and decrease in size of plants in response to precipitation.
    • Prior feeding practices do not influence locoweed consumption

      Ralphs, M. H.; Greathouse, G.; Knight, A. P.; Doherty, D.; Graham, J. D.; Stegelmeier, B. L.; James, L. F. (Society for Range Management, 2002-07-01)
      Anecdotal evidence suggests that cattle fed alfalfa hay during the winter are inclined to graze locoweed on spring range. Two studies were conducted to compare the influence of feeding alfalfa hay vs grass hay during the winter on subsequent consumption of white locoweed (Oxytropis sericea Nutt. ex TG) in the spring. Eight cows were daily fed alfalfa hay (15.2% CP in 1998, 17.1% CP in 2000) and 8 cows were daily fed grass hay (10.7% CP in 1998, 12.1% CP in 2000) plus 20% protein molasses block during the January-April winter feeding period. Treatment groups grazed in separate pastures (8 ha) on white locoweed-infested range in May and June in northern Colorado in 1998 and in northeast New Mexico in 2000. Diets were estimated by bite count. There was no difference in locoweed consumption between the 2 groups (P > 0.22). Cattle grazed locoweed for 5% of diets in Colorado and 10% of diets in New Mexico. Feeding alfalfa hay over winter did not predispose cattle to graze locoweed in the spring. Previous research showed other feeding practices or supplements do not affect locoweed consumption or poisoning. Prevention of locoweed poisoning requires denying access to locoweed when it is relatively more palatable than associated forages.
    • Sediment movement and filtration in a riparian meadow following cattle use

      Mceldowney, R. R.; Flenniken, M.; Frasier, G. W.; Trlica, M. J.; Leininger, W. C. (Society for Range Management, 2002-07-01)
      Improper livestock grazing practices in western U.S. riparian areas may reduce the nutrient and pollutant removal function of riparian communities, resulting in degradation of surface water quality. Short duration-high intensity cattle use in 3 x 10 m plots was evaluated in a montane riparian meadow in northern Colorado to quantify livestock effects on sediment movement and filtration under simulated rainfall (approximately equal to 100 mm hour(-1)) plus overland flow (approximately equal to 25 mm hour(-1)) conditions. Four treatments: 1) control, 2) mowed to 10 cm stubble height, 3) trampled by cattle, and 4) cattle grazed plus trampled (grazed) were evaluated. Sixty kg of sediment was introduced to overland flow in each plot. Sediment movement was evaluated using sediment traps positioned in microchannels and on vegetation islands at 5 distances downslope from the upper end of the plots and by sediment front advancement. Most sediment deposition occurred within the first meter downslope from application. About 90% of the applied sediment was filtered from runoff within 10 m in the control and mowed treatments, while approximately 84 and 77% of the applied sediment was trapped in the trampled and grazed treatment plots, respectively. The primary variables that influenced sediment filtration were stem density and surface random roughness. Stem density was the most influential variable that affected sediment filtration. Cattle grazing reduced the stem density by 40%. Monitoring of stem density should aid land managers in regulating cattle use of riparian communities and facilitate the protection of surface water quality from sediment in overland flow.
    • Short-term monitoring of rangeland forage conditions with AVHRR imagery

      Thoma, D. P.; Bailey, D. W.; Long, D. S.; Nielsen, G. A.; Henry, M. P.; Breneman, M. C.; Montagne, C. (Society for Range Management, 2002-07-01)
      A study was conducted to determine the potential of using Advanced Very High Resolution Radiometer (AVHRR) imagery to monitor short-term changes in rangeland forage conditions on a regional scale. Forage biomass and nitrogen concentration were estimated at 6 study sites throughout a typical grazing season (April to October). Study sites were located in northern and southern Montana in areas classified as foothills grassland and shortgrass prairie. Normalized Difference Vegetation Index (NDVI) values from AVHRR imagery (1 km pixels) were used to predict live biomass, dead standing biomass, total biomass, nitrogen (N) concentration and standing N. Values of the NDVI were correlated (r < 0.4, P < 0.01) to live, dead, and total biomass estimates and standing N, but were not correlated to N concentration (r = 0.04, P = 0.8). Relationships between NDVI and vegetative attributes were similar (P > 0.05) for all 6 study sites, which indicates that NDVI could be used to predict forage abundance at multiple locations and at variable dates. Using simple linear regression, NDVI accounted for 63% of the variation in live and total biomass, 18% of the variation in dead biomass, 66% of the variation in standing N, but < 1% of the variation in N concentration. The NDVI obtained from AVHRR imagery was a good predictor of forage abundance as measured by live, dead and total biomass as well as standing N, but it was not related to forage quality as measured by N or crude protein concentration. On a regional basis, land managers could use AVHRR-NDVI values to identify areas with high or low levels of forage abundance that may result from factors such as drought, variable precipitation patterns, or uneven grazing.
    • Shrub control and streamflow on rangelands: A process based viewpoint

      Wilcox, B. P. (Society for Range Management, 2002-07-01)
      In this paper, the linkage between streamflow and shrub cover on rangelands is examined, with a focus on the extensive Texas rangelands dominated by mesquite and juniper. The conclusions drawn are consistent with results from field studies and with our understanding of runoff processes from rangelands. Whether and how shrub control will affect streamflow depends on shrub characteristics, precipitation, soils, and geology. Precipitation is perhaps the most fundamental of these factors: there is little if any real potential for increasing streamflow where annual precipitation is below about 500 mm. For areas in which precipitation is sufficient, a crucial indicator that there is potential for increasing streamflow through shrub control is the presence of springs or groundwater flow to streams. These conditions often occur at locations where soils are shallow and underlain by fractured parent material. Under such conditions, reducing shrub cover may increase streamflows because water that would otherwise be lost through interception by the canopy instead moves into the soil and quickly travels beyond the root zone. If, on the other hand, there is no obvious subsurface connection between the hillslope and the stream channel and when runoff occurs it occurs as overland flow, shrub control will have little if any influence on streamflow. In assessing the potential for shrub control to increase streamflow, the runoff generation process should be explicitly identified. An improved understanding of the linkages between shrubs and streamflow on rangelands will require additional research on (1) hillslope hydrologic processes and how these are altered by shrub cover (2) groundwater-surface water interactions and (3) hydrologic scale relationships from the patch to the hillslope to the landscape levels.