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The Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) alliance is the most extensive of the big sagebrush complex in the Intermountain West. This alliance provides critical habitat for many sagebrush obligate and facultative wildlife species and serves as a forage base for livestock production. There is a lack of information that describes vegetation cover values, characteristics, diversity, and heterogeneity of the Wyoming big sagebrush alliance. This study describes vegetation cover values and defines distinct associations for intact, late-seral Wyoming big sagebrush plant communities across part of its northwestern range. We sampled 107 Wyoming big sagebrush plant communities. Total herbaceous cover values were variable among sites with differences between sites exceeding 700%. Mean sagebrush cover was 12.3% with 90% of the sites producing 6% to 20% cover. Tall forb (> 18 cm) cover averaged 1.9% and 90% of the sites varied between 0.2% and 5.6% cover. Five associations delineated by dominant perennial bunchgrass species were identified: ARTRW8 (Wyoming big sagebrush)/PSSP6 (Pseudoroegneria spicata [Pursh] A. Löve, bluebunch wheatgrass), ARTRW8/ACTH7 (Achnatherum thurberianum [Piper] Barkworth, Thurber's needlegrass), ARTRW8/FEID (Festuca idahoensis Elmer, Idaho fescue), ARTRW8/HECO26 (Hesperostipa comata [Trin. & Rupr.] Barkworth, needle-and-thread), and ARTRW8/PSSP6–ACTH7 (a codominance of bluebunch wheatgrass and Thurber's needlegrass). Our results suggest when the vegetation cover values proposed for sage-grouse are applied as requirements at or above the stand level, they exceed the ecological potential of many of the sites sampled.
Predictions of forage production derived from site-specific environmental information (e.g., soil type, weather, plant community composition, and so on) could help land managers decide on appropriate stocking rates of livestock. This study assessed the applicability of the Great Plains Framework for Agricultural Resource Management (GPFARM) forage growth model for both strategic (long-term) and tactical (within-season) prediction of forage production in northern mixed-grass prairie. An improved version of the model was calibrated for conditions at the USDA–ARS High Plains Grasslands Research Station in Cheyenne, Wyoming. Long-term (1983–2001) simulations of peak standing crop (PSC) were compared to observations. Also, within-season (1983) forecasts of total aboveground biomass made for 1 March onward, 1 April onward, 1 May onward, and 1 June onward were compared to observations. The normal, driest, and wettest weather years on record (1915–1981) were used to simulate expected values, lower bounds, and upper bounds of biomass production, respectively. The forage model explained 66% of the variability in PSC from 1983 to 2001. The cumulative distribution function (CDF) derived from long-term simulated PSC overestimates cumulative probabilities for PSC > 1 500 kg·ha−1. The generated CDF could be used strategically to estimate long-term forage production at various levels of probability, with errors in cumulative probability ranging from 0.0 to 0.16. Within-season forecasts explained 77%–94% of biomass variability in 1983. It was shown that monthly updating of the forage forecast, with input of actual weather to date, improves accuracy. Further development and testing of the forage simulation model will focus on the interactions between forage growth, environmental perturbations (especially drought), and grazing.
We present a synthesis of long-term measurements of CO2 exchange in 2 US Intermountain West sagebrush-steppe ecosystems. The locations near Burns, Oregon (1995–2001), and Dubois, Idaho (1996–2001), are part of the AgriFlux Network of the Agricultural Research Service, United States Department of Agriculture. Measurements of net ecosystem CO2 exchange (Fc) during the growing season were continuously recorded at flux towers using the Bowen ratio-energy balance technique. Data were partitioned into gross primary productivity (Pg) and ecosystem respiration (Re) using the light-response function method. Wintertime fluxes were measured during 1999/2000 and 2000/2001 and used to model fluxes in other winters. Comparison of daytime respiration derived from light-response analysis with nighttime tower measurements showed close correlation, with daytime respiration being on the average higher than nighttime respiration. Maxima of Pg and Re at Burns were both 20 g CO2·m−2·d−1 in 1998. Maxima of Pg and Re at Dubois were 37 and 35 g CO2·m−2·d−1, respectively, in 1997. Mean annual gross primary production at Burns was 1 111 (range 475–1 715) g CO2·m−2·y−1 or about 30% lower than that at Dubois (1 602, range 963–2 162 g CO2·m−2·y−1). Across the years, both ecosystems were net sinks for atmospheric CO2 with a mean net ecosystem CO2 exchange of 82 g CO2·m−2·y−1 at Burns and 253 g CO2·m−2·y−1 at Dubois, but on a yearly basis either site could be a C sink or source, mostly depending on precipitation timing and amount. Total annual precipitation is not a good predictor of carbon sequestration across sites. Our results suggest that Fc should be partitioned into Pg and Re components to allow prediction of seasonal and yearly dynamics of CO2 fluxes.
Baseline information on the water balance is essential for adequately understanding ecohydrological relationships on rangelands. Unfortunately, such information is not always available, because insufficient data have been collected and/or the data do not represent relevant temporal or spatial scales. In particular, for many rangelands long-term records of runoff at the small catchment or larger scales are relatively rare. In this study, we used catchment-scale data, collected over nearly a decade, to estimate the long-term water balance for mesquite–juniper rangelands in the Rolling Plains of Texas. The data include precipitation, surface runoff, soil water, and vegetation cover; these were measured on 9 microcatchments, each about 1.4 ha in size. Soil water was determined by neutron-probe measurements to a depth of 120 cm. Surface runoff was, surprisingly, a very small component (< 1%) of the water budget and occurred only during extraordinary precipitation events. Soil-water recharge resulted mainly from winter precipitation. Evapotranspiration, which took place during the entire year, ranged from less than 1 mm·day−1 during the winter to almost 8 mm·day−1 during the summer. This study is important because it clearly documents how water is allocated on these rangelands at spatial and temporal scales that are relevant to management. The results from this study, in conjunction with other work in the Rolling Plains, suggests that there is little potential for increasing water yield via brush control in these landscapes.
Sediment and phosphorus (P) in runoff from pastures are potential non–point-source pollutants in surface waters that may be influenced by surface cover, sward height, treading damage, surface slope, soil moisture, and soil P. The objectives of the current study were to quantify sediment and total P loads in runoff produced during simulated rainfall from pastures and to evaluate their relationships with the physical and chemical characteristics of the soil and sward. Five forage management treatments—ungrazed (U), hay harvest/fall stockpile grazing (HS), continuous stocking to a sward height of 5 cm (5C), and rotational stocking to sward heights of 5 (5R) or 10 (10R) cm—were established in triplicate 0.40-ha paddocks in 3 smooth bromegrass (Bromus inermis Leyss.) pastures for 3 years. Rainfall simulations were conducted at a rainfall intensity of 7.1 cm·h−1 for 1.5 hours over a 0.5-m2 area in 3 locations at 2 slope ranges in each paddock in June, August, and October of each year and the subsequent April. Forage management did not affect mean sediment load (7.3 ± 5.0 kg·ha−1·h−1). Mean total P load was greatest from 5C treatment (0.071 ± 0.011 kg·ha−1·h−1), did not differ among the U, HS, and 10R treatments (0.019 ± 0.011 kg·ha−1·h−1), and was intermediate in the 5R treatment (0.053 ± 0.011 kg·ha−1·h−1). Of the soil and sward characteristics measured, percentage surface cover was most highly related to sediment load (R2 = 0.16) and total P load (R2 = 0.10). Surface runoff from pastures managed to maintain adequate residual forage cover did not contribute greater sediment or P to surface waters than an ungrazed grassland.
In semiarid rangelands, continuous grazing may decrease vegetation cover, accelerating soil erosion and eventually causing a transition to an alternative, degraded state. State-and-transition models invoke process-based explanations of alternative states, but there are few examples that use empirical data on key factors and processes. We used rainfall simulation to determine 1) the relationships between soil surface characteristics and interrill erosion in 3 spatially related plant communities: stable grass with scattered shrubs (GS), degraded grass with scattered shrubs (DGS), and degraded shrub steppes (DSS), and 2) the site conservation threshold (SCT) of this rangeland. We also analyzed the effect of past erosion on soil and vegetation characteristics. In the GS, sediment production and sediment concentration were significantly lower (p < 0.05) than in the DGS and the DSS. The main soil protection factors in the GS and in the DGS were perennial grass and litter cover, while in the DSS, gravel cover became the main soil protection factor. The SCT, the point at which the rate of soil erosion increases markedly, corresponded to a plant-and-litter cover close to 90% and occurred within the DGS. Although this plant community may reverse back to the conserved GS, long-term accelerated erosion may result in enough soil loss to trigger irreversible changes and prompt the transition to the DSS. The threshold underlying this transition would be reached when the A horizon is severely reduced by erosion. Under these conditions, the soil hydrological properties are affected irreversibly, preventing perennial grass establishment. While the GS represents a resource conserving plant community, desirable for both forage production and soil protection, the DSS represents a dysfunctional state with a minimum forage value. The DGS represents an unstable and transitional community that, without management intervention to halt soil erosion, will likely change into the DSS.
Fire and grazing are interactive disturbance processes that are important to the structure and function of grassland ecosystems. Studies of nitrogen (N) availability report different effects following grazing and fire. However, these studies have largely neglected the spatially controlled interaction between fire and grazing. The objective of our work was to evaluate an application of the fire–grazing interaction model on N availability in a tallgrass prairie. We compared patches within a shifting mosaic landscape where each patch varied in time since focal disturbance (fire and intense grazing disturbance). We also evaluated N availability on a burned and grazed landscape where fires and moderate grazing occurred annually and uniformly across the entire landscape. These treatments were both burned and grazed where the only difference was spatial and temporal variability in fire application and grazing disturbance. Samples were collected from upland sites in May of 2003 and 2004. Total soil inorganic N (NH4-N NO3−-N) and a growth chamber experiment with hard red winter wheat (Triticum aestivum L. cv. Jagger) were used to evaluate potential N availability. Our study produced patterns of N availability that are more similar to studies of grazing lawns where N availability is enhanced by focal grazing than from studies of fire without grazing. Overall, our study demonstrates that fire and grazing are interactive. Unburned patches have minimal grazing pressure and low N availability. Fire–grazing interaction may provide a management alternative that enables sustainable livestock production, through increased carrying capacity in focally disturbed patches, concomitant with biological diversity in tallgrass prairie.
In response to substantial economic and social dislocations in the United States, many rangeland owners are changing land use and management practices. Changes in land use can significantly affect the services rangeland ecosystems provide. Decisions associated with such changes are likely mediated by landowner views regarding individual rights, social responsibilities, and the future security of property rights. In this paper, we examine the extent to which landowners are likely to adopt, without public compensation, socially desirable land management objectives that enhance ecosystem services from rangelands. The study consisted of a mail survey of landowners with at least 40 ha: 500 in Texas, 500 in Utah, and 694 in Colorado. Adjusted response rates were 62% in Texas, 46% in Utah, and 51% in Colorado. Regression analyses showed that willingness to adopt socially desirable rangeland management objectives was positively correlated with the social responsibility dimension of respondents' property rights orientations but negatively correlated with the rights erosion dimension. Our results also suggested that landowners in private land states, such as Texas, might be less willing than landowners in states with more public land to manage their land for the maintenance of ecosystem services without being compensated. Although the scope of our study was limited, the results suggest that agencies tasked with maintaining ecosystem services on private rangelands might more successfully achieve their mission by promoting social responsibility among landowners. Including community leaders with a highly developed sense of social responsibility in programs aimed at improving land stewardship and including peer-pressure incentives in such programs might enhance social responsibility perspectives among landowners. Such programs should also be adaptable at the state-level to account for differences in property-rights orientations relative to landowner dependence on private and public land.
Housing developments are replacing ranches in the southwestern United States, with potentially significant but little-studied ecological effects. We counted grasshoppers (Orthoptera: Acrididae) and measured vegetative cover for 2 years in a grassland and mesquite/oak savanna in southeastern Arizona, on 48 transects that were grazed by livestock, embedded in low-density housing developments, or both, or neither. Grasshopper species richness was unrelated to grazing or development, but grasshopper abundance was much higher on exurban transects where homeowners kept livestock than in the other areas. Forb canopy and basal area also were highest in grazed exurban areas, perhaps because exurban grazing was relatively patchy, frequently involved horses, and created disturbances more conducive to forb establishment than did relatively uniform grazing on nearby ranches. Abundance patterns of 3 grasshopper subfamilies were generally consistent with their known habitat preferences. Counts of grass-feeding Gomphocerinae were relatively high in ungrazed and unburned areas, and positively correlated with grass cover. Numbers of forb- and mixed-feeding Melanoplinae were positively correlated with forb cover across all transects, and melanoplines dominated counts on grazed exurban properties. Band-winged grasshoppers (Oedipodinae) prefer areas of sparse vegetation, and their numbers were negatively correlated with height of ground vegetation and positively associated with the presence of livestock, in both exurban and undeveloped landscapes. Overall, our results suggest that heterogeneous landscapes in exurban areas that included small livestock pastures had higher grasshopper densities than either ungrazed areas or large cattle ranches.
Leaf traits (leaf dry matter content [LDMC], specific leaf area [SLA] and leaf life span [LLS]) previously proposed to predict plant strategies for resource use, were studied to test if they can be used to rank grasses for digestible organic matter (DOM). On 14 native grass species from natural meadows in the French Pyrenees, leaf blade chemical components (fiber, cellulose, hemi-cellulose and lignin) and DOM were estimated for two growing periods using two different methods (chemical-enzymatic and Near Infrared Reflectance Spectroscopy). The ranking of species based on LDMC, SLA and LLS was conserved. Fiber content and DOM were significantly correlated even though the data were obtained in different years (2001 and 2002), on different organs (youngest adult blades in 2001 and all the green blades of tillers in 2002) and by different analytical methods. LDMC seems to be the most suitable trait to rank native grasses according to their nutritive value because it ranks species as well as leaf traits and it is the easiest to measure. We suggest using LDMC as an indicator to rank grassland communities for herbage nutritive values.
Vegetative differences and changes were evaluated over a 6-year period (1999–2004) on adjoining conservatively grazed and grazing-excluded (22 years) shortgrass rangelands in northwestern New Mexico. Autumn total perennial grass and blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. Griffiths) standing crop did not differ on grazed and grazing-excluded areas when data were averaged across years. There were no long-term differences in vegetation basal cover or composition between the grazed and grazing-excluded areas. Plant community similarity values between the grazed and grazing-excluded areas were 80% and 93% during the first 2 years (1999–2000) and last 2 years (2003–2004) of study, respectively. Climatic conditions had more impact on vegetation composition of the 2 areas than livestock grazing. Similarity values between 1999–2000 and 2003–2004 periods were 52% and 64% for the grazed and grazing-excluded plant communities, respectively. At the beginning of our study, blue grama productivity was depressed on the grazed area compared to the exclosure, but after 3 years of conservative winter grazing, it was similar on the 2 areas. Our study indicates there is no benefit to blue grama rangelands from long-term rest from the standpoint of vegetation composition.
Hooded windmillgrass (Chloris cucullata Bisch.) and shortspike windmillgrass (C. subdolichostachya Muell.) are native perennial grasses with potential for planting on highly erodible sites and on sites where introduced species are not desired. However, in both species, seeds are dormant resulting in poor germination. The objectives of this study were to evaluate effects of lemma and palea removal and caryopsis scarification on seed germination of 8 outstanding ecotypes selected in previous studies for survival and growth characteristics. Seed treatments were 1) whole seed, 2) naked caryopsis, 3) scarified naked caryopsis (30 s), 4) scarified naked caryopsis (50 s), and 5) scarified naked caryopsis (60 s). Germination conditions were 12 h dark 20°C and 12 h light 30°C. Seed lot viability varied from 55% to 62% for shortspike windmillgrass ecotypes and from 71% to 78% for hooded windmillgrass ecotypes. Initial germination index (MIR10) of naked caryopsis for shortspike windmillgrass ecotypes ranged from 16.3 to 21.6, compared to range from 0.2 to 0.6 to whole seed; whereas hooded windmillgrass ecotypes MIR10 ranged from 30.6 to 33.0 to naked caryopsis, compared to range from 5.8 to 8.0 to whole seed. The greatest total germination (P < 0.05) was obtained with naked caryopsis for all ecotypes and the scarification treatments did not have a positive effect on this parameter. As scarification time increased the total germination decreased. Lemma and palea removal improved (P < 0.05) total germination for all studied ecotypes.
We compared the effect of applying anaerobically produced biosolids, lime-stabilized biosolids, and cattle manure on the production of blue grama (Bouteloua gracilis [HBK] Lag. ex Steud.) and black grama (B. eriopoda [Torr.] Torr.) grown in pots with moderate soil water content. We also compared the physicochemical and bacteriological composition of these 3 amendments. All amendments produced similar increases in plant growth, despite their differences in plant nutrient concentrations, as a result of limitations in soil water. Heavy metal levels in biosolids were within the US Environmental Protection agency limits for Class A and Class B biosolids, but were higher than in manure. In contrast, pathogen levels were lower in biosolids than in manure. Application of biosolids and cattle manure increased the production of both grasses and may have equivalent effects under typical climatic and soil conditions of semiarid rangelands.
Accurate estimation of one-seed juniper (Juniperus monosperma [Engelm.] Sarg.) intake by herbivores often requires harvesting, transporting, and storing plant material that is later used in pen experiments. Such manipulation could alter terpenoid profiles and modify herbivory levels significantly. We used gas chromatography mass spectrometry (GC/MS) to analyze the terpenoid profile of leaves from 10 short (0.5 m ± 0.05, mean ± SE) and 10 tall (1.14 m ± 0.06) one-seed juniper saplings subjected to 3 handling protocols: a) placed on dry ice after clipping and stored after 5 hours at −80°C for 3 weeks (Control); b) kept at ambient temperature for the first 24 hours and then frozen at −80°C for 3 weeks; or c) kept at ambient temperature for the first 24 hours, and then stored at 8°C for 3 weeks. Juniper saplings contained 51 terpenoids, 3 of which were unknown compounds. Fourteen terpenoids accounted for 95% of the total amount of volatiles. The most abundant compound was α-pinene, which accounted for 65% of total terpenoids present. Handling protocols were not associated with detectable differences in total terpenoid content (Means ± SE, Control: 21.68 ± 1.42 mg·g−1 dry matter [DM]; Frozen after 24 hours: 19.55 ± 1.08 mg·g−1 DM; Refrigerated after 24 hours: 18.80 ± 1.13 mg·g−1 DM). However, total terpenoid amount and concentration of a few major compounds tended to decrease with increasing storage temperature. Handling protocols induced detectable variations in a small number of minor terpenoids. We observed large among-plant variation in terpenoid profiles that was not fully explained on the basis of sapling size. This study suggests that the length of storage period of one-seed juniper branches should not exceed 3 weeks and that storage refrigeration temperatures should be kept below 8°C to prevent significant alterations in terpenoid profiles.
Variations in its thermal environment can influence how an animal utilizes a rangeland landscape. Mapping the spatial and temporal air temperature patterns throughout a landscape may be helpful in predicting range animal distribution and habitat use. Many sampling points are required to effectively map air temperature levels throughout extensive and topographically diverse rangelands. Self-contained air temperature data loggers are commercially available, but these require shielding from solar radiation to provide accurate measurements. Commercial shields are expensive and fragile. A low-cost, robust, and effective alternative to commercial shields is needed for air temperature mapping applications. Two types of shields, vented cylinder and inverted-U shaped, were constructed from PVC pipe. Temperature loggers protected in either of these shielding types provided more accurate air temperature measurements than unshielded loggers. Temperature measurements from loggers protected by inverted-U shields were within ±2.5°C of a reference instrument in 94.7% of 2 496 observations. About 86.2% of observations acquired by loggers within vented-cylinder shields were within ±2.5°C of the reference. Conversely, only 66.1% of the measurements from unshielded loggers were within ±2.5°C of the reference. Both shielding types were designed to be attached to a swiveling mounting system, thus avoiding damage by animals and eliminating the need for protective exclosure fencing. Materials costs for constructing either shield type, including the mounting system, were $8.00 or less. In contrast, commercially available radiation shields with mounting hardware cost $75.00 or more. Compared to the use of commercial shielding, construction and deployment of these PVC-pipe shields would reduce the cost, time, and labor required to collect accurate air temperature data at many points across an extensive landscape.