• Can Abundant Summer Precipitation Counter Losses in Herbage Production Caused by Spring Drought?

      Heitschmidt, R. K.; Vermeire, L. T. (Society for Range Management, 2006-07-01)
      Drought is an inherent trait of most rangelands and sound management necessitates managers address two fundamental questions when facing a drought situation. The first question is, ‘‘what is the probability that a useful amount of precipitation will be received over the period of concern?’’ and the second question is, ‘‘if it does rain, what will the impact be in terms of quantity and quality of herbage produced?’’ The objective of this study was to address the second question. Our hypothesis was that herbage growth response to above normal summer precipitation (i.e., 23 in July and August) would be limited in the northern Great Plains because of a general absence of productive warm-season species. Study plots were twelve 5 X 10-m non-weighing lysimeters. Treatments were: 1) simulated (i.e., rainout shelter imposed), severe spring drought (i.e., 1 May - 1 July) followed by ambient precipitation thereafter; 2) simulated, severe spring drought followed by ambient precipitation thereafter plus summer irrigation (i.e., July and August); 3) ambient precipitation only; and 4) ambient precipitation plus summer irrigation. Results indicated substantial herbage production can be expected in this region during summer when precipitation is well above average because of the positive growth response of blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths), the dominant warm-season grass growing in this region. However, results also showed that level of production in the study situation (i.e., spring drought, wet summer) was only about 50% of that attained in a normal (i.e., wet spring/dry summer) year. Moreover, long-term weather data shows the probability of receiving 23 normal precipitation in both July and August (i.e., our irrigation treatments) is < 1%. Thus, although these rangelands possess the capacity to respond favorably to summer precipitation, the low probability of receiving substantial levels of summer precipitation ensures levels of ecological and economic risk remain high.  
    • Comparison of Comparative Yield and Stubble Height for Estimating Herbage Standing Crop in Annual Rangelands

      George, Melvin R.; Barry, Sheila J.; Larson, Stephanie R.; McDougald, Neil K.; Ward, Theresa A.; Harper, John M.; Dudley, Dennis M.; Ingram, Roger S.; Laca, Emilio A. (Society for Range Management, 2006-07-01)
      We compared calibration equations for estimating herbage standing crop (HSC) from comparative yield (CY) rank or stubble height (SH) to determine 1) if CY rank is a better estimator than SH of standing crop, 2) if addition of SH to CY rank will improve the estimation of standing crop, 3) if there is a seasonal effect on CY rank or SH, and 4) if botanical composition influences the prediction of HSC from CY. The results of this study indicate that CY is a slightly better predictor of HSC than is SH. Addition of SH to CY did not improve the prediction of HSC. Models that predict HSC from CY in summer were weaker than models for winter, early spring, and late spring. Thus the CY method can be used with confidence throughout the year. The presence of filaree (Erodium cicutarium L.) in winter and early spring resulted in steeper calibration equations than were present in nonfilaree quadrats.  
    • Consequences of Ignoring Geologic Variation in Evaluating Grazing Impacts

      Long, Jonathan W.; Medina, Alvin L. (Society for Range Management, 2006-07-01)
      The geologic diversity of landforms in the Southwest complicates efforts to evaluate impacts of land uses such as livestock grazing. We examined a research study that evaluated relationships between trout biomass and stream habitat in the White Mountains of east-central Arizona. That study interpreted results of stepwise regressions and a nonparametric test of ‘‘grazed and ungrazed meadow reaches’’ as evidence that livestock grazing was the most important factor to consider in the recovery of the Apache trout (Oncorhynchus apache Miller). That study had assumed that geologic variation was insignificant in the study area. However, lithologic and topographic differences between the felsic slopes of Mount Baldy and adjacent mafic plateaus influence many attributes of trout habitat. We tested the robustness of the earlier study by using its dataset and its method of stepwise regression, but with the addition of a variable representing geologic variation. The results suggested that geology was a highly significant predictor of trout biomass (P < 0.0001), whereas bank damage by ungulates was not a useful predictor of residual variation in trout biomass after accounting for geology (r2 = 0.015, P = 0.290). However, the associations between natural variation and land use impacts in this spatial dataset confound attempts to make inferences concerning effects of livestock grazing upon trout. Despite fundamental problems in the analysis, the results of the earlier study were repeatedly cited in scientific literature and debates about grazing management. To fairly decipher relationships between ecological production and livestock grazing in diverse landscapes requires temporal studies with reliable methodologies and proper controls for landscape variation. Ignoring geologic variation has the potential to mislead conservation policies by inappropriately implicating land use, by undervaluing inherently favorable habitats, and by inflating expectations for inherently less favorable habitats.  
    • Effect of Fire on Microarthropods in New Zealand Indigenous Grassland

      Barratt, Barbara L. P.; Tozer, Peter A.; Wiedemer, Robin L.; Ferguson, Colin M.; Johnstone, Peter D. (Society for Range Management, 2006-07-01)
      Indigenous tussock grassland in New Zealand has a history of extensive pastoralism, and burning has been used to remove litter to improve establishment of aerially oversown pasture species and to promote palatable tussock growth for livestock. In recent years, considerable areas of tussock grassland have been retired from grazing and formally protected. Conservation land managers, as well as farmers, require information on the impacts of both managed burns carried out in spring and accidental fires that usually occur in warmer, drier conditions in summer. This study investigated the impact of spring and summer tussock grassland burning on the predominant soil microarthropods, Collembola and Acari, at 2 sites in Otago, in the South Island of New Zealand. Quantitative sampling was carried out before and for up to 26 months after burning replicated 1-ha plots. Total density of microarthropods in unburnt plots covered a similar range at both sites with an average over 3 years of about 18 000- 20 000 m2 at each site. Both sites shared a dominance of Mesostigmata and Oribatida (Acari) and Isotomidae (Collembola). Burning in spring reduced densities of Oribatida after treatment at both sites for the duration of the study. However, after initial postburn reductions in density, populations of Isotomidae and Poduroidea (Collembola) recovered in the second year after burning. Prostigmata (Acari) appeared to be unaffected by fire. The effects of spring and summer grassland fires on microarthropod densities were rarely different. It was concluded that longer-term sampling would be required to observe the full recovery period for microarthropod populations after fire but that results from this study indicate rapid recovery of some microfaunal populations after fire, which is not strongly influenced by seasonal effects.  
    • Fragmentation Effects on Soil Aggregate Stability in a Patchy Arid Grassland

      Bestelmeyer, Brandon T.; Ward, Judy P.; Herrick, Jeffrey E.; Tugel, Arlene J. (Society for Range Management, 2006-07-01)
      Soil aggregate stability (AS) has been promoted as a primary indicator of soil-surface function and a key metric in state-and-transition models. There are few studies, however, that relate indices of AS to the process of grassland degradation. In a Chihuahuan Desert rangeland, we measured variation in AS across vegetated-bare patch boundaries within six plot types reflecting a hypothesized fragmentation/transition sequence. We also examined wetting front depth and pH along this sequence. We found that AS exhibited consistent and interpretable variation across the patch boundaries of the different plot types. Average AS was highest in grass patches adjacent to small to medium-sized (0.5-1.5 m) bare patches and was low in grass patches adjacent to large (> 3 m) bare patches. AS of bare ground was also lowest when bare patches in continuous grassland were large and when bare ground formed an interconnected matrix. Wetting depth after a large storm decreased and pH increased along the fragmentation sequence. The results suggest that AS has interpretable relationships with grassland fragmentation and transitions among states. Careful attention to patchiness within states and stratification, however, is important and simple classifications of strata, such as ‘‘bare interspace’’ and ‘‘plant,’’ may not be sufficient to document variation in soil function.  
    • Grazing Effects on Snow Accumulation on Rough Fescue Grasslands

      Willms, Walter D.; Chanasyk, David S. (Society for Range Management, 2006-07-01)
      Snow accumulation is an important process that defines the hydrological characteristics of grasslands and is mediated by vegetation structure. Grazing also affects those processes, but its relationship to snow accumulation is poorly understood. We conducted a study in the rough fescue grasslands in southwestern Alberta (lat 50 degrees11ʹ30 degreesN, long 113 degrees53ʹ30 degreesW) to determine the effect of grazing pressure on snow accumulation and its relationship with selected meteorological variables. Snow accumulation (mass per unit area) was measured throughout the winter from 1998 to 2004 within each of 3 watersheds that had different historical grazing pressures (high, moderate, and zero). In a second study, we examined the effect of artificially created patch sizes (0.5-, 1.0-, and 1.5-m diameter) on snow accumulation from 1998 to 2000. The yearly average of the heavily and moderately grazed watersheds was about 42% and 20%, respectively, less snow than the ungrazed watershed. Of the meteorological variables we tested, only average daily temperatures, average daily maximum temperatures, and snowfall were influenced by the watershed. Snowfall was about half as effective in predicting snow accumulation in the heavily grazed watershed as in the moderately grazed or ungrazed watersheds. Patch size was generally not effective, except at single observations in both 1998 and 1999 when the 1.0-m diameter patch captured the most snow mass per unit area. The ungrazed grassland captured a similar amount to that captured in the cut patches. The study indicates that increased grazing intensity reduces the ability of grasslands to capture snow.  
    • Individual Animal Selection Has the Potential to Improve Uniformity of Grazing on Foothill Rangeland

      Bailey, Derek W.; VanWagoner, Harv C.; Weinmeister, Robin (Society for Range Management, 2006-07-01)
      Uneven grazing distribution is a concern in rugged topography, because resources may be adversely impacted if livestock concentrate in gentle terrain near water. A study was conducted to determine if removing cattle with undesirable distribution patterns has the potential to increase uniformity of grazing. Before the study, 2 herds of cattle were observed by horseback observers during early mornings to establish terrain use patterns of individual animals. Cows were ranked on slope use and observed vertical and horizontal distance to water. Based on these rankings, cows were assigned to 1 of 2 treatments, hill climbers (observed on steeper slopes and farther from water) or bottom dwellers (used gentler slopes near water). Hill climber and bottom dweller cows grazed similar, but separate, pastures at 2 ranches during the 3-year study for a total of 8 comparisons. Based on a normalized and integrated index of terrain use from visual observations, hill climber cows used steeper and more distant areas from water (P = 0.06) than bottom dwellers. Hill climber cows tracked by global positioning system collars used steeper and more distant areas from water than bottom dwellers (P 0.09) during the first 4 weeks of the 6 weeks that pastures were grazed based on a normalized index of terrain use. Forage utilization was more uniform (P < 0.05) across slopes and varying horizontal distances to water in pastures grazed by hill climbers than by bottom dwellers. Stubble heights in riparian and coulee bottom areas were higher (P = 0.01) when grazed by hill climber cows (13.3 cm) than by bottom dwellers (8.1 cm). This study demonstrates that cattle with divergent grazing patterns when observed in the same pasture continue to use different terrain when separated, and it suggests that individual animal selection has the potential to increase uniformity of grazing. 
    • Near-Ground Remote Sensing of Green Area Index on the Shortgrass Prairie

      Przeszlowska, Agnieszka; Trlica, Milton J.; Weltz, Mark A. (Society for Range Management, 2006-07-01)
      Drought is an inherent trait of most rangelands and sound management necessitates managers address two fundamental questions when facing a drought situation. The first question is, ‘‘what is the probability that a useful amount of precipitation will be received over the period of concern?’’ and the second question is, ‘‘if it does rain, what will the impact be in terms of quantity and quality of herbage produced?’’ The objective of this study was to address the second question. Our hypothesis was that herbage growth response to above normal summer precipitation (i.e., 23 in July and August) would be limited in the northern Great Plains because of a general absence of productive warm-season species. Study plots were twelve 5 X 10-m non-weighing lysimeters. Treatments were: 1) simulated (i.e., rainout shelter imposed), severe spring drought (i.e., 1 May - 1 July) followed by ambient precipitation thereafter; 2) simulated, severe spring drought followed by ambient precipitation thereafter plus summer irrigation (i.e., July and August); 3) ambient precipitation only; and 4) ambient precipitation plus summer irrigation. Results indicated substantial herbage production can be expected in this region during summer when precipitation is well above average because of the positive growth response of blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths), the dominant warm-season grass growing in this region. However, results also showed that level of production in the study situation (i.e., spring drought, wet summer) was only about 50% of that attained in a normal (i.e., wet spring/dry summer) year. Moreover, long-term weather data shows the probability of receiving 23 normal precipitation in both July and August (i.e., our irrigation treatments) is < 1%. Thus, although these rangelands possess the capacity to respond favorably to summer precipitation, the low probability of receiving substantial levels of summer precipitation ensures levels of ecological and economic risk remain high.  
    • Removing Adult Overstory Trees Stimulates Growth and Transpiration of Conspecific Juvenile Trees

      Moore, Georanne W.; Owens, M. Keith (Society for Range Management, 2006-07-01)
      During the last century, the density of Ashe juniper (Juniperus ashei Buchholz) has greatly increased in oak savannahs of central Texas. Recently, juniper removal has been advocated as a regional water conservation tool. In this study, we investigated whether juvenile trees released from an overstory canopy after clearing exhibited accelerated growth and water consumption. We compared leaf-level transpiration (El) and carbon assimilation (Anet) rates among juvenile juniper under three different treatment scenarios: 1) in the open, 2) under an adult juniper canopy or 3) recently released by the removal of an adult juniper canopy. Released plants apparently grew faster and used more water than other juvenile trees; average Anet of released plants was 94%-162% greater (P < 0.05) than those beneath an adult canopy and 22%-44% greater than open-grown plants. Furthermore, average El of released plants was 22%-72% greater than those beneath an adult canopy and 13%-22% greater than open-grown plants. These differences persisted for at least two years after treatment. Rates of Anet were particularly elevated in released plants compared to other plants during periods of low water stress; whereas El tended to be higher in released plants compared to other plants at all levels of water availability. Our evidence suggests released plants have better access to water, because at two out of three study sites, predawn leaf water potential (Wp) was significantly more favorable for released plants than open-grown or under-canopy plants (P < 0.05). Although adult canopy removal temporarily reduced leaf area of juniper on a community level, and likely total water use, we demonstrated that released juveniles, at a minimum, partially compensated for the reduced overstory by increasing rates of water use and growth.  
    • Spatial Variation in Remnant Grasses After a Grassland-to-Shrubland State Change: Implications for Restoration

      Peters, Debra P. C.; Mariotto, Isabella; Havstad, Kris M.; Murray, Leigh W. (Society for Range Management, 2006-07-01)
      Around the world rangelands that have been degraded, such as historical desert grasslands now dominated by woody shrubs, are resistant to restoration efforts. The goal of this descriptive research was to examine the potential for black grama (Bouteloua eriopoda [Torr.] Torr.) recovery by remnant plants in a degraded area as a function of plant location across a landscape. Our objectives were 1) to document the historical dominant vegetation as a perennial grassland and determine broad-scale changes in dominance through time and 2) to examine fine-scale patterns of black grama presence and basal area with respect to microenvironmental conditions that indicate the landscape positions favorable for restoration. Historical vegetation maps starting in 1858, a field survey in 2002-2003 of the location of all individual black grama plants in a 29-ha area, and spatial data layers in a geographic information system were used to address these objectives. Upland grasses, including black grama, dominated the study site in 1858, although tarbush (Flourensia cernua DC.) was the dominant species by 1915, and creosotebush (Larrea tridentata [DC.] Cov.) is the current dominant. A total of 3 334 black grama plants were found for an average density of 0.01 plants m-2. High spatial variation was found in the occurrence and basal area of black grama plants that was related to water availability rather than livestock grazing: most plants were found in or adjacent to an arroyo (67%), at a northern aspect (47%), and outside experimental exclosures established in 1930 (43%). Largest average basal areas were found in the livestock exclosure, and in general, average basal area was not related with aspect or canopy microsite. These remnant plants can be used as propagule sources in restoration efforts, and information on microsite conditions for black grama survival can be used to improve restoration potential for similar sites. 
    • Spatio-Temporal Constraints on Moose Habitat and Carrying Capacity in Coastal Alaska: Vegetation Succession and Climate

      Stephenson, Thomas R.; Ballenberghe, Victor Van; Peek, James M.; MacCracken, James G. (Society for Range Management, 2006-07-01)
      We used a geographic information system and a Markov chain analysis to model vegetation succession on the Copper River Delta, Alaska, relative to moose (Alces alces) habitat availability and nutritional carrying capacity. Between 1959 and 1986 vegetation predominantly shifted from pioneer to later successional communities as a result of glacial retreat and earthquake uplift. Hypothesized vectors of vegetation composition in future decades indicate a trend toward an increase in late-successional communities. A decline in glacier-related disturbance has reduced the level of retrogression that maintains early successional communities in the outwash plain. In addition, landscape heterogeneity increased significantly between 1959 and 1986, particularly in the uplifted marsh. Winter severity was highly variable among years and was correlated with a shift in the location of moose wintering areas. As winter severity increased, there was increased use of the glacial outwash plain landform and its associated plant communities. Successional modeling suggests a decline in the availability of vegetation types impor- tant to moose during severe winters with deep snow. Low willow (Salix spp.) communities are expanding in the uplifted marsh, a landform used primarily during summer and mild winters. However, tall willow communities that provide winter forage are declining and are being replaced by Sitka spruce (Picea sitchensis [Bong] Carr) forest in the glacial outwash plain. Consequently, nutritional carrying capacity of moose on the outwash plain during winter will decline by 42% during 1959-2013.  
    • Using Light Attenuation to Estimate Leafy Spurge Impacts on Forage Production

      Rinella, Matthew J.; Sheley, Roger L. (Society for Range Management, 2006-07-01)
      Rangeland managers often must decide whether to suppress dicotyledonous weed populations with expensive and time-consuming management strategies. Often, the underlying goal of weed suppression efforts is to increase production of native forage plants. Many managers suppress weeds only when they feel the unwanted plants are substantially impacting their forage base. Currently, intuition and guesswork are used to determine whether weed impacts are severe enough to warrant action. We believe scientific impact assessments could be more effective than these casual approaches to decision making. Scientific approaches will necessitate data on weed abundances because the severity of a weed’s impact is highly correlated with its abundance. The need for weed abundance data poses major obstacles because gathering these data with readily available techniques is time consuming. Most managers cannot or will not spend a lot of time gathering vegetation data. In this paper, we explore a rapidly measured index (<2 minutes per sample location) that is highly correlated with weed (i.e., leafy spurge Euphorbia esula L.) abundance per unit area. This index is based on the light attenuation leafy spurge causes. After measuring light attenuation in plots planted to leafy spurge and grasses, we developed a probabilistic model that predicts leafy spurge impacts on forage production. Data from experiments where herbicides suppressed leafy spurge provided an opportunity to evaluate prediction accuracy of the model. In each case herbicide experiment data fell within the range of values (i.e., credibility intervals) the model predicted, even though the model development experiments were separated from the herbicide experiments by several hundred kilometers in space and 4 years in time. Therefore, we conclude that the model successfully accounts for spatial and temporal variation. We believe light attenuation could help natural resource managers quickly quantify some kinds of weed impacts.