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1.
This study quantified herbaceous biomass responses to increases in honey mesquite (Prosopis glandulosa Torr.) cover on two soils from 1995 to 2001 in north central Texas. Vegetation was sampled randomly with levels of mesquite ranging from 0% to 100%. With no mesquite covering the silt loam soils of bottomland sites, peak herbaceous biomass averaged (±SE) 3 300 ± 210 kg · ha−1 vs. 2 560 ± 190 kg · ha−1 on clay loam soils of upland sites (P = 0.001). A linear decline of 14 ± 2.5 kg · ha−1 in herbaceous biomass occurred for each percent increase in mesquite cover (P = 0.001). The slope of this decline was similar between soils (P = 0.135). Herbaceous biomass with increasing mesquite cover varied between years (P = 0.001) as did the slope of decline (P = 0.001). Warm-season herbaceous biomass decreased linearly with increasing mesquite cover averaging a 73 ± 15% reduction at 100% mesquite cover (P = 0.001) compared to 0% mesquite cover. Cool-season herbaceous biomass was similar between soils with no mesquite, 1 070 ± 144 kg · ha−1 for silt loam vs. 930 ± 140 kg · ha−1 for clay loam soils, but averaged 340 ± 174 kg · ha−1 more on silt loam than on clay loam soils at 100% mesquite cover (P = 0.004). Multiple regression analysis indicated that each centimeter of precipitation received from the previous October through the current September produced herbaceous biomass of 51 kg · ha−1 on silt loam and 41 kg · ha−1 on clay loam soils. Herbaceous biomass decreased proportionally with increasing mesquite cover up to 29 kg · ha−1 at 100% mesquite cover for each centimeter of precipitation received from January through September. Increasing mesquite cover reduces livestock forage productivity and intensifies drought effects by increasing annual herbaceous biomass variability. From a forage production perspective there is little advantage to having mesquite present.  相似文献   

2.
Supplement placement can be used to manipulate livestock grazing patterns. The objective of this case study was to compare the effect of low-moisture blocks (LMB) and range cake (barley-based cylindrical cubes, 2 cm in diameter, and 2 to 8 cm long) supplementation on cattle grazing patterns in Montana foothill rangeland. One group of nonlactating cows (n = 79) was fed cake 3 times per week (1.8 kg · cow−1 · feeding−1), and the other group (n = 81) had continuous access to LMB in separate pastures using a crossover design. Movement patterns of cows were recorded with global positioning system collars during four periods (2 wk · period−1) during autumn. Range cake was fed on accessible areas, and LMB were placed in higher and steeper terrain. Intake of LMB averaged (mean ± SE) 318 ± 50 g · d−1. Cows fed LMB (8.07° ± 0.20°) were observed on steeper slopes (P = 0.08) than cows fed range cake (6.96° ± 0.19°). Forage utilization decreased as slope increased to a greater degree when range cake was fed than when LMB was fed (P = 0.001). Cows spent more time (P = 0.05) within 100 m of LMB (274 ± 23 min · d−1) than at range cake feeding sites (67 ± 24 min · d−1). Strategic placement of LMB on high, steep terrain appears to be a more practical and effective approach than traditional hand-feeding range cake on intermediate terrain to improve uniformity of cattle grazing on rugged rangeland.  相似文献   

3.
The objective of this study was to evaluate the effect of different levels of rough agave (Agave scabra Ortega) flowers on dry matter intake (DMI), average daily gain (ADG), volatile fatty acid (VFA) production in the rumen, and particular serum metabolites and minerals of native × dairy growing goats (Capra hircus L.). Forty female goats with an initial weight of 11.1 ±  kg (mean ± SD) were used in a completely randomized design experiment that lasted for 84 d. Goats were fed a completely mixed ration (30% roughage, 70% ground corn [Zea mays L.] and soybean [Glycine max {L.} Merr] meal). Treatments consisted of offering goats (4 pens · group−1, 2 goats · pen−1) air-dry rough agave flowers, which replaced alfalfa (Medicago sativa L.) hay at 0% (control; T0), 25% (T25), 50% (T50), 75% (T75), and 100% (T100) of the of the roughage portion of the diet. Values of nutritional parameters for rough agave flowers were in vitro organic matter digestibility, 493 g · kg−1; crude protein, 115 g · kg−1; and metabolizable energy, 6.29 MJ · kg−1 DMI. There were differences (P < 0.05) in ADG (range, 108–155 g · d−1) between diets. Goats fed T0 had higher (P < 0.05) gains than goats fed T50 and T100. DMI was not affected by dietary treatments (range, 3.4% to 3.6% of body weight). Feed conversion ratio (FCR, defined as DMI/ADG) increased (P < 0.05) 27% with total substitution of alfalfa by rough agave flowers, in comparison with T0. Lower (P < 0.05) values of total VFA were obtained with T100, in comparison with all other dietary treatments. These results demonstrated that totally replacing alfalfa with rough agave flowers in diets did not affect DMI but decreased AGD and compromised FCR. Thus, rough agave flowers have the potential to partially replace alfalfa in diets for growing goats.  相似文献   

4.
Redberry juniper (Juniperus pinchotii Sudworth) is an invasive, evergreen tree that is rapidly expanding throughout western and central Texas. Goats will consume some juniper on rangelands; however, intake is limited. The objective of our research was to determine how the age and body condition of goats influence their consumption of juniper and an artificial feed containing 4 monoterpenes. Two separate experiments were conducted. Experiment 1 examined the intake of redberry juniper foliage and used 39 goats either young (2 yr) or mature (> 6 yr). One-half of each age group was fed appropriate basal rations to reach either a high (HBC) or low body condition (LBC). Goats in LBC ate more (P < 0.01, 8.6 g · kg−1 body weight [BW] ± 0.7 SE) juniper than those in HBC (2.3 g · kg−1 BW ± 0.3 SE), and young animals consumed more (P < 0.05, 7.2 g · kg−1 BW ± 0.7 SE) juniper than mature goats (3.9 g · kg−1 BW ± 0.5 SE) across body condition treatments. In experiment 2, 36 goats, either young (2 yr) or mature (> 6 yr) and in either HBC or LBC, were offered a synthetic ration treated with 20.8 g · kg−1 of 4 monoterpenes found in redberry juniper. Goats in LBC ate more (P < 0.01, 25.3 g · kg−1 BW ± 1.0 SE) of the terpene-treated feed than those in HBC (17.5 g · kg−1 BW ± 0.7 SE), and young animals ate more (P < 0.05, 22.5 g · kg−1 BW ± 0.8 SE) than mature goats (20.3 g · kg−1 BW ± 0.8 SE) across body condition treatments. Total intake as a proportion of body weight was also affected by body condition. Age and body condition are important factors that influence intake of chemically defended plants. A better understanding of how these attributes affect diet selection will aid livestock producers in improving grazing management.  相似文献   

5.
Questions have been raised about whether herbaceous productivity declines linearly with grazing or whether low levels of grazing can increase productivity. This paper reports the response of forage production to cattle grazing on prairie dominated by Kentucky bluegrass (Poa pratensis L.) in south-central North Dakota through the growing season at 5 grazing intensities: no grazing, light grazing (1.3 ±  animal unit months [AUM] · ha-1), moderate grazing (2.7 ±  AUM · ha-1), heavy grazing (4.4 ±  AUM · ha-1), and extreme grazing (6.9 ±  AUM · ha-1; mean ± SD). Annual herbage production data were collected on silty and overflow range sites from 1989 to 2005. Precipitation and sod temperature were used as covariates in the analysis. On silty range sites, the light treatment produced the most herbage (3 410 kg · ha-1), and production was reduced as the grazing intensity increased. Average total production for the season was 545 kg · ha-1 less on the ungrazed treatment and 909 kg · ha-1 less on the extreme treatment than on the light treatment. On overflow range sites, there were no significant differences between the light (4 131 kg · ha-1), moderate (4 360 kg · ha-1), and heavy treatments (4 362 kg · ha-1; P &spigt; 0.05). Total production on overflow range sites interacted with precipitation, and production on the grazed treatments was greater than on the ungrazed treatment when precipitation (from the end of the growing season in the previous year to the end of the grazing season in the current year) was greater than 267.0, 248.4, 262.4, or 531.5 mm on the light, moderate, heavy, and extreme treatments, respectively. However, production on the extreme treatment was less than on the ungrazed treatment if precipitation was less than 315.2 mm. We conclude that low to moderate levels of grazing can increase production over no grazing, but that the level of grazing that maximizes production depends upon the growing conditions of the current year.  相似文献   

6.
Grasslands and agroecosystems occupy one-third of the terrestrial area, but their contribution to the global carbon cycle remains uncertain. We used a set of 316 site-years of CO2 exchange measurements to quantify gross primary productivity, respiration, and light-response parameters of grasslands, shrublands/savanna, wetlands, and cropland ecosystems worldwide. We analyzed data from 72 global flux-tower sites partitioned into gross photosynthesis and ecosystem respiration with the use of the light-response method (Gilmanov, T. G., D. A. Johnson, and N. Z. Saliendra. 2003. Growing season CO2 fluxes in a sagebrush-steppe ecosystem in Idaho: Bowen ratio/energy balance measurements and modeling. Basic and Applied Ecology 4:167–183) from the RANGEFLUX and WORLDGRASSAGRIFLUX data sets supplemented by 46 sites from the FLUXNET La Thuile data set partitioned with the use of the temperature-response method (Reichstein, M., E. Falge, D. Baldocchi, D. Papale, R. Valentini, M. Aubinet, P. Berbigier, C. Bernhofer, N. Buchmann, M. Falk, T. Gilmanov, A. Granier, T. Grünwald, K. Havránková, D. Janous, A. Knohl, T. Laurela, A. Lohila, D. Loustau, G. Matteucci, T. Meyers, F. Miglietta, J. M. Ourcival, D. Perrin, J. Pumpanen, S. Rambal, E. Rotenberg, M. Sanz, J. Tenhunen, G. Seufert, F. Vaccari, T. Vesala, and D. Yakir. 2005. On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm. Global Change Biology 11:1424–1439). Maximum values of the quantum yield (α=75 mmol · mol?1), photosynthetic capacity (Amax=3.4 mg CO2 · m?2 · s?1), gross photosynthesis (Pg,max=116 g CO2 · m?2 · d?1), and ecological light-use efficiency (εecol=59 mmol · mol?1) of managed grasslands and high-production croplands exceeded those of most forest ecosystems, indicating the potential of nonforest ecosystems for uptake of atmospheric CO2. Maximum values of gross primary production (8 600 g CO2 · m?2 · yr?1), total ecosystem respiration (7 900 g CO2 · m?2 · yr?1), and net CO2 exchange (2 400 g CO2 · m?2 · yr?1) were observed for intensively managed grasslands and high-yield crops, and are comparable to or higher than those for forest ecosystems, excluding some tropical forests. On average, 80% of the nonforest sites were apparent sinks for atmospheric CO2, with mean net uptake of 700 g CO2 · m?2 · yr?1 for intensive grasslands and 933 g CO2 · m?2 · d?1 for croplands. However, part of these apparent sinks is accumulated in crops and forage, which are carbon pools that are harvested, transported, and decomposed off site. Therefore, although agricultural fields may be predominantly sinks for atmospheric CO2, this does not imply that they are necessarily increasing their carbon stock.  相似文献   

7.
Kenaf (Hibiscus cannibinus) var. “India”, lablab (Lablab purpureus) variety “Tecomate,” combine and iron-clay cowpeas (Vigna unguiculata), and sunflowers (Helianthus annuus) S682 and S573 were planted at the Stephenville Research and Extension Center in the spring seasons of 1998 and 1999. Dairy compost was incorporated into half the plots prior to seeding both years at 11.2 t DM ha−1. Average days to maturity and number of harvests per season varied from 66 to 84 d and 1 to 3 harvests, respectively. Average yields were highest for kenaf (13,762 kg DM ha−1 yr−1) followed by lablab (7,925 kg DM ha−1 yr−1). Acid detergent fiber and lignin DM concentrations were lowest in kenaf (average 26.9 and 3.57%, respectively) and cowpeas (average 25.9 and 4.39%, respectively). Crude protein and phosphorus (P) concentrations were high in the iron-clay cowpea (22.3 and 0.269, respectively), combine cowpea (18.3 and 0.276%, respectively), lablab (16.8 and 0.268%, respectively), and kenaf (14.9 and 0.204%, respectively) and relatively low in the sunflower (9.7 and 0.174%, respectively). Compost increased forage yields 21.6% and forage P concentration 18.8% following the second year’s application. Compost was applied to supply 130 kg P ha−1 yr−1; on average, forages removed only 34.2 kg P ha−1 yr−1. As a result, soil P was 2.4 times higher in plots with compost (26.9 ppm) by the end of the 2-yr trial. Kenaf had the highest P uptake, averaging 56.6 kg P ha−1 over 2 yr, accounting for 43% of the P applied.  相似文献   

8.
A comparison of animal gains and vegetation trends was made from 2002–2008 between a continuous season-long stocking (SLS) system and a modified intensive–early stocking system (IES) with late-season grazing (IES 1.6× + 1; 1.6 times the number of animals of the SLS system from May 1 to July 15, and 1 times the number of animals of SLS from July 15 to October 1) on shortgrass native rangeland of western Kansas. The continuous season-long stocked system placed animals at a density of 1.37 ha · steer?1 from May through October, or 2.63 animal unit months (AUM) · ha?1, whereas the intensive–early stocked system with late-season grazing (3.33 AUM · ha?1) stocked pastures at 0.85 ha · steer?1 from May through the middle of July, and then stocked pastures at 1.37 ha · steer?1 for the remainder of the grazing season by removing the heaviest animals mid-July each yr. Average daily gains (0.78 vs. 0.70 kg · d?1, P = 0.039) and total animal gain (58 vs. 52 kg, P = 0.042) were different between the continuous season-long stocked and the intensive–early stocked animals during the first half of the grazing season. No difference was found between average daily gain (0.61 vs. 0.62 kg · d?1, P = 0.726) and total animal gain (48 vs. 49 kg, P = 0.711) for the continuous season-long stocked and intensive–early stocked with late-season grazing animals during the last half of the season. Total individual animal gain (106 vs. 101 kg, P = 0.154) and average daily gain (0.70 vs. 0.66 kg · d?1, P = 0.152) was not different between the continuous season-long stocked and the intensive–early stocked system animals that were on pasture the entire grazing season. Total beef gain on a land-area basis (96 vs. 77 kg · ha?1, P = 0.008) was greater for the modified intensive–early stocked system with late-season grazing with greater animal densities. Changes in residual biomass and most key vegetation components at the end of the grazing season were not different between the two systems.  相似文献   

9.
Prescribed burning of aboveground biomass in tallgrass prairie is common and may influence dynamics and magnitudes of carbon (C) movement between the surface and atmosphere. Carbon dioxide (CO2) fluxes were measured for 2 yr using conditional sampling systems on two adjacent watersheds in an ungrazed tallgrass prairie near Manhattan, Kansas. One watershed was burned annually (BA) and the other biennially (BB). Leaf and soil CO2 fluxes were measured in the source area. Net ecosystem exchange (NEE) of CO2 reached a maximum daily gain of 26.4 g CO2·m?2·d?1 (flux toward surface is positive) in July 1998 (year when both sites were burned and precipitation was above normal); gains were similar between sites in 1998. The maximum daily NEE loss of CO2 was ?21.8 g CO2·m?2·d?1 from BA in September 1997 (year when only BA was burned and precipitation was below normal). When data were integrated over the two years, both sites were net sources of atmospheric CO2; NEE was ?389 g C·m?2·2 yr?1 on BA and ?195 g C·m?2·2 yr?1 on BB. Burning increased canopy size and photosynthesis, but the greater photosynthesis was offset by corresponding increases in respiration (from canopy and soil). Carbon losses from fire represented 6–10% of annual CO2 emissions (bulk came from soil and canopy respiration). Data suggest that annual burning promotes C loss compared to less-frequently burned tallgrass prairie where prairie is not grazed by ungulates. Greater precipitation in 1998 caused large increases in biomass and a more positive growing season NEE, indicating that C sequestration appears more likely when precipitation is high. Because C inputs (photosynthesis) and losses (canopy and soil respiration) were large, small measurement or modeling errors could confound attempts to determine if the ecosystems are long-term CO2 sources or sinks.  相似文献   

10.
Nitrogen (N) availability can strongly influence forage quality and the capacity for semiarid rangelands to respond to increasing atmospheric CO2. Although many pathways of nitrogen input and loss from rangelands have been carefully quantified, cattle-mediated N losses are often poorly understood. We used measurements of cattle N consumption rate, weight gains, and spatial distribution in shortgrass rangeland of northeastern Colorado to evaluate the influence of cattle on rangeland N balance. Specifically, we estimated annual rates of N loss via cattle weight gains and spatial redistribution of N into pasture corners and areas near water tanks, and used previous studies to calculate ammonia volatilization from urine patches. Using measurements of plant biomass and N content inside and outside grazing cages over 13 yr, we estimate that cattle stocked at 0.65 animal unit months (AUM) · ha?1 consumed 3.34 kg N · ha?1 · yr?1. Using an independent animal-based method, we estimate that cattle consumed 3.58 kg N · ha?1 · yr?1 for the same stocking rate and years. A global positioning system tracking study revealed that cattle spent an average of 27% of their time in pasture corners or adjacent to water tanks, even though these areas represented only 2.5% of pasture area. Based on these measurements, we estimate that cattle stocked at 0.65 AUM · ha?1 during the summer can remove 0.60 kg N · ha?1 in cattle biomass gain and spatially redistribute 0.73 kg N · ha?1 to areas near corners and water tanks. An additional 0.17 kg N · ha?1 can be lost as NH3 volatilization from urine patches. Cumulatively, these cattle-mediated pathways (1.50 kg N · ha?1) may explain the imbalance between current estimates of atmospheric inputs and trace gas losses. While NOx emission remains the largest pathway of N loss, spatial N redistribution by cattle and N removed in cattle biomass are the second and third largest losses, respectively. Management of cattle-mediated N fluxes should be recognized as one means to influence long-term sustainability of semiarid rangelands.  相似文献   

11.
Management practices are often needed to ensure that riparian areas are not heavily grazed by livestock. A study was conducted in Montana during midsummer to evaluate the efficacy of low-stress herding and supplement placement to manage cattle grazing in riparian areas. Three treatments were evaluated in three pastures over a 3-yr period in a Latin-square design (n = 9). Each year, naïve 2-yr-old cows with calves were randomly assigned to the three treatments: 1) free-roaming control, 2) herding from perennial streams to upland target areas, and 3) herding to upland sites with low-moisture block supplements. Stubble heights along the focal stream were higher (P = 0.07) in pastures when cattle were herded (mean ± SE, 23 ± 2 cm) than in controls (15 ± 3 cm). Global positioning system telemetry data showed that herding reduced the time cows spent near (< 100 m) perennial streams (P = 0.01) and increased the use of higher elevations (P = 0.07) compared with controls. Evening visual observations provided some evidence that free-roaming cows (44% ± 19%) were in riparian areas more frequently (P = 0.11) than herded cows (23% ± 6%). Fecal abundance along the focal stream was less (P = 0.07) with herding (61.9 ±  kg · ha−1) than in controls (113.2 ±  kg · ha−1). Forage utilization within 600 m of supplement sites was greater (P = 0.06) when cows were herded to low-moisture blocks (18% ± 6%) compared with controls and herding alone (8% ± 2%). Moving cattle to uplands at midday using low-stress herding is an effective tool to reduce use of riparian areas. Herding cattle to low-moisture blocks can increase grazing of nearby upland forage but may not provide additional reduction in cattle use of riparian areas compared with herding alone.  相似文献   

12.
Postfire succession in mountain big sagebrush (Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle) ecosystems results in a gradual shift from herbaceous dominance to dominance by shrubs. Determining the quality, quantity, and distribution of carbon (C) in rangelands at all stages of succession provides critical baseline data for improving predictions about how C cycling will change at all stages of succession under altered climate conditions. This study quantified the mass and distribution of above- and belowground (to 1.8-m depth) biomass at four successional stages (2, 6, 20, and 39 yr since fire) in Wyoming to estimate rates of C pool accumulation and to quantify changes in ecosystem carbon to nitrogen (C∶N) ratios of the pools during recovery after fire. We hypothesized that biomass C pools would increase over time after fire and that C∶N ratios would vary more between pools than during succession. Aboveground and live coarse roots (CR) biomass increased to 310 and 17 g C · m?2, but live fine roots (FR) mass was static at about 225 g C · m?2. Fine litter (≤ 1-cm diameter) accounted for about 70% of ecosystem C accumulation rate, suggesting that sagebrush leaves decompose slowly and contribute to a substantial soil organic carbon (SOC) pool that did not change during the 40 yr studied. Total ecosystem C (not including SOC) increased 16 g · m?2 · yr?1 over 39 yr to a maximum of 1 100 g · m?2; the fastest accumulation occurred during the first 20 yr. C∶N ratios ranged from 11 for forb leaves to 110 for large sagebrush wood and from 85 for live CR to 12 for bulk soil and were constant across growth stages. These systems may be resilient to grazing after fire because of vigorous regrowth of persistent bunchgrasses and stable pools of live FR and SOC.  相似文献   

13.
Evapotranspiration (ET) is a key component limiting groundwater recharge past the root zone in semiarid regions. Vegetation management may alter groundwater recharge if ET is altered due to changes in vegetation type or cover. This study quantifies changes in groundwater recharge following vegetation cover change from native woodland to pasture in a semiarid region of southwest Texas. The Carrizo–Wilcox aquifer is a valuable groundwater resource in this area, where overuse by dependent farming practices has lowered aquifer levels significantly in the last 85 yr. Combining data from short-term (30 mo) monitoring of the changes in soil moisture and long-term (5–30 yr) changes in total soil chloride indicated deep drainage increased slightly where land had been cleared of vegetation. Annual recharge rates below rooting depths (standardized to 155 cm) averaged only 0.72 ±  mm · yr-1 (mean ± SE) in areas not cleared of woody vegetation, as estimated by chloride mass balance. Upon clearing, 72% of the total chloride naturally occurring in the soil profile was flushed away within 30 yr, leading to an estimated 2.59 ±  mm · yr-1 additional recharge. Deep soil moisture in recently cleared land increased by up to 17% during the growing season of wet years (double the average rainfall) but did not increase in dry or normal precipitation years, providing supporting evidence that more water penetrated below the roots under certain environmental conditions. These results demonstrate that brush management can increase recharge by modest, but measurable, amounts depending on site-specific soil characteristics and degree of reduction in vegetation.  相似文献   

14.
Artemisiaordosica Krasch. is a semishrub native to the Ordos Plateau of Inner Mongolia, northern China, and forms a unique and dominant vegetation type in the sandland of the region. To determine the variation of productivity in A. ordosica rangeland, we investigated net primary production (NPP), fine root turnover, soil microbial C (Cmic), and soil organic carbon density (SOCd) on sand dunes differing in mobility (i.e., fixed, semifixed, and shifting sand dunes) in Mu Us sandland. We found that, on an area basis, the NPP, SOCd, Cmic, and fine root turnover rates all increased with increasing vegetation cover. However, the ratios of root NPP to total NPP (RMRN) increased with declining vegetation cover. Total NPP varied markedly among habitats and ranged from 18.3 g · m-2 · yr-1 for communities on the shifting sand dunes to 293.8 g · m-2 · yr-1 for communities on the fixed sand dunes; whereas the rates of fine root turnover varied from 0.16 · yr-1 to 0.54 · yr-1. Our study demonstrated that habitat change in sandland has significant impacts on ecosystem productivity by affecting many related aspects of NPP. From the perspective of biomass production, protection of the semifixed dunes from degradation should be taken as a higher priority than trying to convert shifting sand dunes to semifixed sand dunes; whereas conversion of semifixed sand dunes to fixed sand dunes would appear to be a much easier task than restoring shifting sand dunes.  相似文献   

15.
Fuel loading information is important for prescribed fire planning, evaluating wildfire risk, and understanding fire effects in grassland. Yet fuel loads in grasslands often go unmeasured because of the time required to clip plots and process samples, as well as limited access or proximity to a drying oven. We tested the digital photography biomass estimation technique for measuring fuel load in grasslands in two national parks in the eastern Great Plains. The method consists of using percentage image obstruction, as determined by digital photography, to estimate vegetation biomass based on a linear transformation (i.e., regressing dry clipped weights against percent digital obstruction). We used the technique with some modification and measured digital obstruction at two sites at Wilson’s Creek National Battlefield, Missouri (WICR), and three sites at Tallgrass Prairie National Preserve, Kansas (TAPR). The method did not result in strong correlations at either of the two sites at WICR (Site 1: r2=0.02; Site 2: r2=0.32), but performed relatively well at TAPR (Site 1 [<1 yr since burn]: r2=0.82; Site 2 [2 yr since burn]: r2=0.57; Site 3 [1 yr since burn]: r2=0.88). Linear regressions for the three sites at TAPR did not differ in slope (P>0.05). In general, the denser the vegetation, the weaker the relationship between the vegetation biomass of clip plots and the percentage image obstruction of digital images. The digital photography technique may not be useful for estimating fuel loads in grasslands with relatively high biomass (>80 g · 0.1 m?2) or digital image obstruction >50%. Large amounts of litter may also potentially reduce the accuracy of the technique.  相似文献   

16.
Small ponds are often the main source of drinking water for grazing livestock. The hydrology of these ponds must be understood so impoundments can be located, designed, and managed to avoid water shortages during dry weather. A study was conducted to measure the water balance of a stock-watering pond in the Flint Hills region of east-central Kansas from June 2005 to October 2006. The 0.35-ha pond supplied water to 250-kg yearling steers in a 65-ha pasture of native tallgrass prairie. Evaporation, depth change, and cattle consumption were measured continuously using meteorological sensors, depth recorders, and water meters. Seepage, transpiration, and inflow were measured periodically or modeled. Evaporation was also predicted from weather data using forms of the Penman and Priestley-Taylor models. Evaporation accounted for 64% of the total water loss annually, while seepage, cattle consumption, and transpiration accounted for 31%, 3%, and 2%, respectively. The greatest water loss was observed in July, with total monthly losses over 358 mm and peak daily losses sometimes exceeding 18 mm · d−1. Cattle consumption averaged 30 L · day−1 · animal−1with peak usage of 46 L · day−1 · animal−1. On average, the Priestley-Taylor and Penman evaporation models estimated monthly evaporation to 3% and 5%, respectively. Thus, evaporation, the main form of loss, can be predicted with simple models using data from weather station networks. Inflows from runoff proved difficult to predict and were highly dependent on antecedent soil water content. Results showed that losses from ponds can be measured or predicted with reasonable accuracy. These data could be incorporated into catchment-scale hydrology models to provide site-specific designs for stock-watering ponds and livestock-watering strategies.  相似文献   

17.
The Northern Great Plains grasslands respond differently under various climatic conditions; however, there have been no detailed studies investigating the interannual variability in carbon exchange across the entire Northern Great Plains grassland ecosystem. We developed a piecewise regression model to integrate flux tower data with remotely sensed data and mapped the 8-d and 500-m net ecosystem exchange (NEE) for the years from 2000 to 2006. We studied the interannual variability of NEE, characterized the interannual NEE difference in climatically different years, and identified the drought impact on NEE. The results showed that NEE was highly variable in space and time across the 7 yr. Specifically, NEE was consistently low (?35 to 322 g C·m?2·yr?1) with an average annual NEE of ?2 ± 242 g C·m?2·yr?1 and a cumulative flux of ?152 g C·m?2. The Northern Great Plains grassland was a weak source for carbon during 2000–2006 because of frequent droughts, which strongly affected the carbon balance, especially in the Western High Plains and Northwestern Great Plains. Comparison of the NEE map with a drought monitor map confirmed a substantial correlation between drought and carbon dynamics. If drought severity or frequency increases in the future, the Northern Great Plains grasslands may become an even greater carbon source.  相似文献   

18.
The importance of sexual reproduction in tussock grasses that regenerate through vegetative growth is unclear. Festuca gracillima Hook. f. was studied as a model because it is a perennial tussock-forming grass that produces abundant seed but rarely regenerates through seedlings. The Study area was the Magellanic Steppe, Patagonia, Argentina (182 mm rainfall), managed with sheep-grazing regimes of 0.65 (high), 0.21 (low), and 0 (exclosure) ewe equivalents · ha?1 · yr?1. Tussock size and spikelet production of 358 individuals were recorded over 5 yr. Yearly models of reproductive effort in relation to plant size were tested using a maximum likelihood procedure. Seed was collected and soil cores were tested for germination and viability. Survival and growth of cohorts of seedlings sown in nylon bags were recorded. Eighteen experimental plots were cleared, and seed establishment under protected and grazed conditions was registered. Reproductive effort varied with years and plant size, with a mean of 2.41%. Florets were produced at mean density of 544 ± 217 · m?2. Predispersal losses reduced viable seed production to 187 ± 48 seeds · m?2. Seed weighed 2–2.5 mg, with 65–95% germination. Postdispersal losses reduced the seed bank in spring to 33 ± 1.3 seeds · m?2. Seedling survival curves were negatively exponential, with 95% mortality in the first year. Up to 5% of resources were used for sexual reproduction in favorable years and a recruitment of 1–3 new seedlings · m?2 · yr?1 was expected. These new plants were not observed in undisturbed plots, but established naturally in cleared plots and reached a density of 1 plant · m?2 after 10 yr, together with 44 plants · m?2 of other species. Competition might block the final establishment in these grasslands. Grazing does not appear to interfere in any stage of seed reproduction. Seed production may not maintain population numbers but could enhance genetic variation in these clonal plant populations and enable dispersal and recolonization of disturbed areas.  相似文献   

19.
Cheatgrass (Bromus tectorum L.) is an invasive annual grass that creates near-homogenous stands in areas throughout the Intermountain sagebrush steppe and challenges successful native plant restoration in these areas. A clipping experiment carried out at two cheatgrass-dominated sites in eastern Oregon (Lincoln Bench and Succor Creek) evaluated defoliation as a potential control method for cheatgrass and a seeding preparation method for native plant reseeding projects. Treatments involved clipping plants at two heights (tall = 7.6 cm, and short = 2.5 cm), two phenological stages (boot and purple), and two frequencies (once and twice), although purple-stage treatments were clipped only once. Treatments at each site were replicated in a randomized complete block design that included a control with no defoliation. End-of-season seed density (seeds · m−2) was estimated by sampling viable seeds from plants, litter, and soil of each treatment. Unclipped control plants produced an average of approximately 13 000 and 20 000 seeds · m−2 at Lincoln Bench and Succor Creek, respectively. Plants clipped short at the boot stage and again 2 wk later had among the lowest mean seed densities at both sites, and were considered the most successful treatments (Lincoln Bench: F6,45 = 47.07, P < 0.0001; Succor Creek: F6,40 = 19.60, P < 0.0001). The 95% confidence intervals for seed densities were 123–324 seeds · m−2 from the Lincoln Bench treatment, and 769–2 256 seeds · m−2 from the Succor Creek treatment. Literature suggests a maximum acceptable cheatgrass seed density of approximately 330 seeds · m−2 for successful native plant restoration through reseeding. Thus, although this study helped pinpoint optimal defoliation parameters for cheatgrass control, it also called into question the potential for livestock grazing to be an effective seed-bed preparation technique in native plant reseeding projects in cheatgrass-dominated areas.  相似文献   

20.
The pharmacokinetics of orphenadrine (ORPH) following a single intravenous (i.v.) dose was investigated in six camels (Camelus dormedarius). Orphenadrine was extracted from the plasma using a simple sensitive liquid–liquid extraction method and determined by gas chromatography/mass spectrometry (GC/MS). Following i.v. administration plasma concentrations of ORPH decline bi-exponentially with distribution half-life (t1/2α) of 0.50 ± 0.07 h, elimination half-life (t1/2β) of 3.57 ± 0.55 h, area under the time concentration curve (AUC) of 1.03 ± 0.10 g/h l−1. The volume of distribution at steady state (Vdss) 1.92 ± 0.22 l kg−1, volume of the central compartment of the two compartment pharmacokinetic model (Vc) 0.87 ± 0.09 l kg−1, and total body clearance (ClT) of 0.60 ± 0.09 l/h kg−1. Three orphenadrine metabolites were identified in urine samples of camels. The first metabolite N-desmethyl-orphenadrine resulted from N-dealkylation of ORPH with molecular ion m/z 255. The second N,N-didesmethyl-orphenadrine, resulted from N-didesmethylation with molecular ion m/z 241. The third metabolite, hydroxyl-orphenadrine, resulted from the hydroxylation of ORPH with molecular ion m/z 285. ORPH and its metabolites in camel were extensively eliminated in conjugated form. ORPH remains detectable in camel urine for three days after i.v. administration of a single dose of 350 mg orphenadrine aspartate.  相似文献   

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