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1.
North American temperate grasslands and the wildlife species they support are increasingly imperilled, largely due to habitat loss and degradation. Most remaining prairie is privately managed and supports livestock production. In Canada, voluntary stewardship is the preferred approach for protecting species at risk on private lands under the federal Species at Risk Act (SARA). However, attitudes of private land managers toward species at risk and their willingness to engage in stewardship are poorly understood. With data from interviews with 42 livestock producers in Saskatchewan, Canada, we describe producer characteristics, attitudes, and awareness of species at risk and evaluate how these factors influence willingness to protect species at risk. Younger producers with increased formal education, awareness, and positive attitudes were more willing to support conservation of species at risk. Voluntary stewardship under the SARA may be enhanced by rewarding producers for sound habitat management and improving trust between producers and government agencies.  相似文献   

2.
Grassland birds have undergone substantial population declines throughout much of their historic ranges in North America. Most of the remaining grassland bird habitat is restricted to rangelands managed for livestock production, so grazing management has strong implications for grassland bird conservation efforts. We conducted 1 830 point-count surveys at 305 sites during 2016–2017 to evaluate the relative effects of three livestock grazing systems on the abundance and community composition of grassland birds in a northern mixed-grass prairie ecosystem of eastern Montana, United States. Our objectives were to 1) evaluate effects of grazing management on abundance and community composition of grassland obligate birds, focusing specifically on grazing systems, stocking rates, and interactions with rangeland productivity; 2) evaluate the importance of local vegetation characteristics for grassland birds within grazing systems; and 3) assess the effectiveness of rest-rotation grazing to create patch-heterogeneity in rangeland vegetation through the alteration of structural components and the response of grassland birds to these treatments. Overall, we found inconsistent responses in abundances of grassland birds relative to livestock grazing systems and no discernable differences among grazing systems relative to community composition. However, local abundances were often driven by interactions between grazing system and rangeland production potential, suggesting the effects of livestock grazing management were generally mediated by rangeland productivity. In addition, associations between avian abundance and grazing management parameters (e.g., stocking rate) were species specific. Ubiquitous guidelines for livestock grazing systems may be inappropriate for grassland bird conservation efforts in the northern mixed-grass prairie, and high stocking rates may negatively impact populations of dense-grass obligate grassland birds in this region.  相似文献   

3.
Many grassland species coevolved with large herbivores and require habitats along the entire structural gradient created by grazing. Widespread declines of grassland birds, however, have prompted concerns about rangeland management. Conceptually, rest-rotation grazing functions as a conservation strategy to mimic historic disturbance regimes and create pasture-level heterogeneity in the absence of fire, but its utility for improving wildlife habitat has not been directly tested, particularly in the mesic mixed-grass prairie. We evaluated rest-rotation grazing as a conservation management technique compared with more traditional grazing systems, including summer rotation and season-long grazing, and assessed effects of different grazing systems and stocking rates on nest site selection and nest survival of sharp-tailed grouse (Tympanuchus phasianellus), an indicator species for grassland ecosystems. Both nest site selection and nest survival were directly related to vertical nesting cover, which was only weakly related to grazing management variables, including grazing system and stocking rate, at moderate stocking rates (≤ 2 animal unit month [AUM] ha 1). Cattle presence during the nesting period had a positive effect on daily nest survival, potentially through an effect by either the cows or rancher presence on predator behavior. Overall, our results suggest that rest-rotation grazing did not contribute to pasture-level vegetation heterogeneity and that both the selective foraging of cattle and inherent topographic and edaphic variability in our study area may be stronger drivers of heterogeneity at the small spatial scale required by female grouse.  相似文献   

4.
Rangelands are areas used primarily for grazing by domestic livestock; however, because they support native vegetation and fauna, their potential role in conservation should not be overlooked. Typically, “off-reserve” conservation in agricultural landscapes assumes a trade-off between maintaining the ecological processes that support biodiversity and successful food production and profitability. To evaluate this potential biodiversity trade-off in rangelands, we need to understand the effect of different livestock grazing strategies on biodiversity, in relation to their performance in terms of profitability and land condition. We monitored reptile community responses to four cattle-grazing strategies (heavy, moderate, and variable stocking rates and a rotational wet season spelling treatment) in a replicated, long-term grazing trial in north Queensland, Australia. Simultaneously, measures of profitability and land condition were collected for the different grazing strategies. Overall, reptile abundance was not negatively impacted by the more sustainably managed treatments (moderate, variable, and rotational) compared with heavy stocking, although the effect of grazing treatment alone was not significant. Profitability and land condition were also higher in these treatments compared with the heavy stocking rate treatment. As drought conditions worsened over the 3 yr, the negative impact of the heavy stocking treatment on both profitability and biodiversity became more pronounced. Heavy stocking negatively impacted reptiles and was also the least profitable grazing strategy over the long term, resulting in the worst land condition. This suggests that in this tropical savanna rangeland there was no trade-off between economic performance and reptile abundance and diversity. Grazing regimes with a moderate stocking rate or flexible management strategies were better able to buffer the effects of climate variability. The consequence was a more resilient reptile community and better economic outcomes in dry years.  相似文献   

5.
An experiment was conducted to evaluate the influence of forest fuels reduction on diet quality, botanical composition, relative preference, and foraging efficiency of beef cattle grazing at different stocking rates. A split plot factorial design was used, with whole plots (3 ha) being fuel reduced or no treatment (control), and split plots (1 ha) within whole plots were grazed to three levels of forage utilization; (low) 3 heifers · ha?1, (moderate) 6 heifers · ha?1, (high) 9 heifers · ha?1, with a 48-h grazing duration. Grazing treatments were applied in August of 2005 and 2006. Cattle diet composition and masticate samples were collected during 20-min grazing bouts using six ruminally cannulated cows in each experimental unit. Relative preference indices indicated a strong preference for grass regardless of treatment and stocking rate. Grass consumption was lower in control pastures (P < 0.05) and tended (P < 0.095) to decrease with increased stocking rates. Shrub use was higher in control pastures displaying a quadratic effect (P < 0.05) due to stocking, whereas shrub use increased with stocking rate across all treatments. Cattle grazing control pastures consumed diets higher in crude protein compared to cattle grazing treated pastures (P < 0.05). In vitro dry matter digestibility values were lower (P < 0.05) in control sites and tended (P = 0.10) to decrease with increased stocking rates. In both control and treated pastures, bites per minute and grams consumed per minute declined (P = 0.003) with increased stocking, indicating foraging efficiency of cattle decreases with increased stocking rates. Our data indicated cattle grazing late season grand fir habitat types have a strong preference for grasses regardless of treatment or stocking rate. However, as stocking rate increased in both control and treated pastures, grass consumption decreased, shrub consumption increased, and foraging efficiency decreased.  相似文献   

6.
Shrub encroachment can be explained by the abandonment of extensive livestock farming and changes to land use, and it is a common problem in the Mediterranean mountain pastures of Europe, with direct effects on biodiversity and landscape quality. In this paper, the effects of livestock exclusion vs. grazing on the dynamics of shrub and herbaceous vegetation were analyzed in a Spanish natural park located in a dry Mediterranean mountain area over a 5-yr period. Twelve 10 × 10 m exclosures were set up in six representative pasture areas of the park (with two replicates per location). Each year, the shrub number, volume, and biomass were measured in April, and the herbage height, biomass, and quality were measured in April and December (which represent the start and end of the vegetative growth season). A sustained increase of the shrub population and individual biomass was observed throughout the study, which was reflected in total shrub biomass per ha. Growth was greater in nongrazed exclosures (2 563 kg dry matter [DM] · ha?1 · yr?1), but it also happened in the grazed control areas (1 173 kg DM · ha?1 · yr?1), with different patterns depending on the location and shrub species. Herbage biomass did not change when grazing was maintained, but it did increase in places where grazing was excluded (291 kg DM · ha?1 · yr?1), mostly as a consequence of the accumulation of dead material, with a concomitant reduction in herbage quality. It was concluded that at the current stocking rates and management regimes, grazing alone is not enough to prevent the intense dynamics of shrub encroachment, and further reductions in grazing pressure should be avoided.  相似文献   

7.
Beef cattle production from rangelands in the Southern Great Plains has decreased in concert with herbaceous forage production declines in response to woody plant encroachment by honey mesquite (Prosopis glandulosa Torr.) over the past 120 yr. Combinations of livestock overstocking and fire suppression are considered to be primary drivers of these changes. This experiment evaluated cow–calf production responses over a 7-yr (1995–2001) period to ranch-scale (1 294–2 130 ha) integrated restoration strategies involving prescribed fire and grazing management. Restoration strategies tested in this year-round grazing ecosystem were 4-pasture, 1-herd rotation with fire (25% of pasture acreage burned each year; 4:1F); an 8-pasture, 1-herd rotation, with fire (8:1F); and a 4-pasture, 1-herd, with fire and aerial application of 0.28 kg · ha?1 clopyralid + 0.28 kg · ha?1 triclopyr herbicide (4:1F / H). Restoration strategies were compared to a continuous grazing strategy with no mesquite treatment. All cattle stocking rates were moderate (7.5–15 ha · animal unit?1 · year?1) and all fires were applied during late winter. Beef cattle (cow–calf) production variables measured included conception rate, weaned calf percentage, weaning weight, weight of calf per exposed cow, weight of calf per hectare, and supplement fed per cow. We observed significant differences in beef production among strategies primarily during the first 2 yr where the continuous grazing strategy exhibited better overall livestock production than the integrated restoration strategies. Differences in livestock production among strategies were minimal over the last 5 yr of the study. These livestock production results suggest livestock and management adapted to restoration strategies after the first 2 yr. Results point to the need to cautiously transition into integrated grazing and fire restoration strategies when cattle and management are changed and intensified from prior historical protocols.  相似文献   

8.
Low larkspur (Delphinium nuttallianum Pritz.) poisoning causes serious economic loss to livestock producers that graze cattle on foothill and mountain ranges in western North America. In general, all Delphinium spp. are five times less toxic to sheep than to cattle. Because low larkspurs are less toxic to sheep than cattle, grazing sheep before cattle on rangelands with dense populations of low larkspur can reduce larkspur density and risk of poisoning to grazing cattle. All previous published work on sheep and larkspur interactions has involved tall larkspurs. This series of studies was conducted to determine if sheep would consume sufficient low larkspur to reduce subsequent risk to cattle. Four summer trials were conducted in Collbran, Colorado, and Soda Springs, Idaho on pastures with dense (> 9 plants · m?2) low larkspur populations. In all trials, sheep ate very little low larkspur (< 0.5% of bites). During one final trial using high sheep density (two sheep · 0.015 ha?1 for 9 d), sheep consumed little low larkspur, but animals appeared to trample much of the low larkspur. Toxic alkaloid concentrations in low larkspur ranged from 1.1 mg · g?1 to 1.6 mg · g?1 in all trials. The use of sheep to graze low larkspurs to reduce subsequent consumption by grazing cattle does not appear to be a viable option.  相似文献   

9.
Experiments investigating grazing systems have often excluded ranch-scale decision making, which has limited our understanding of the processes and consequences of adaptive management. We conducted interviews and vegetation monitoring on 17 ranches in eastern Colorado and eastern Wyoming to investigate rancher decision-making processes and the associated ecological consequences. Management variables investigated were grazing strategy, grazing intensity, planning style, and operation type. Ecological attributes included the relative abundance of plant functional groups and categories of ground cover. We examined the environmental and management correlates of plant species and functional group composition using nonmetric multidimensional scaling and linear mixed models. After accounting for environmental variation across the study region, species composition did not differ between grazing management strategy and planning style. Operation type was significantly correlated with plant community composition. Integrated cow-calf plus yearling operations had greater annual and less key perennial cool-season grass species cover relative to cow-calf  only operations. Integrated cow-calf plus yearling ranches were able to more rapidly restock following drought compared with cow-calf operations. Differences in types of livestock operations contributed to variability in plant species composition across the landscape that may support diverse native faunal species in these rangeland ecosystems. Three broad themes emerged from the interviews: 1) long-term goals, 2) flexibility, and 3) adaptive learning. Stocking-rate decisions appear to be slow, path-dependent choices that are shaped by broader social, economic, and political dynamics. Ranchers described having greater flexibility in altering grazing strategies than ranch-level, long-term, annual stocking rates. These results reflect the complexity of the social-ecological systems ranchers navigate in their adaptive decision-making processes. Ranch decision-making process diversity within these environments precludes development of a single “best” strategy to manage livestock grazing.  相似文献   

10.
Soil properties that influence the capacity for infiltration and moisture retention are important determinants of rangeland productivity. Monitoring effects of grazing on dynamic soil properties can assist managers with stocking rate decisions, particularly if monitoring takes into account environmental variability associated with inherent soil morphological properties. On a Pacific Northwest Bunchgrass Prairie in northeast Oregon, we applied three cattle stocking rates (0.52, 1.04, and 1.56 animal unit months · ha?1) and an ungrazed control in a randomized complete block design for two 42-d grazing seasons and measured the change in four dynamic soil properties: soil penetration resistance, soil aggregate stability, bare ground, and herbaceous litter cover. To address apparent environmental heterogeneity within experimental units, we also utilized a categorical soil factor (termed Edaphic Habitat Types or EHT), determined by characterizing soil depth, texture, and rock fragment content at sample sites. Stocking rate did not affect extent of bare ground or soil aggregate stability. Stocking rate had a significant effect on penetration resistance, which was greatest at the high stocking rate (1.6 J · cm?1 ± 0.1 SE) and lowest in the control (1.1 J · cm?1 ± 0.1 SE). For litter cover, the effects of stocking rate and EHT interacted. In two rocky EHTs, litter cover was highest in the controls (60% ± 6 SE; 50% ± 3 SE) and ranged from 27% ± 3 SE to 33% ± 6 SE in the stocking rate treatments. Measures of penetration resistance, aggregate stability, and bare ground were different across EHTs regardless of stocking rate, but did not interact with stocking rate. Our study demonstrates that response of dynamic soil properties to stocking rates should be considered as a useful and accessible approach for monitoring effects of livestock management decisions on rangeland conditions.  相似文献   

11.
Complete rest or grazing deferment is a general recommendation to encourage vegetative recovery following fire in the western United States. However, effects of grazing deferments on animal performance have not been determined. Prescribed fires were individually applied to nine separate, 1.5-ha pastures each year (2006 and 2007) for a total of 18 pastures. Grazing was deferred until spring (16 May), early summer (19 June), or late summer (1 August) the growing season after fire. At the end of each deferment, a 70-d (2007) or 41-d (2008) grazing period was initiated. Stocking rates were consistent between treatments within year, but were adjusted between years to achieve the targeted residual biomass of approximately 300 kg · ha?1. Diet quality was assessed approximately every 15 d throughout each grazing period (three pastures · period?1) via collection of rumen extrusa throughout the 2-yr study. Ewe body weight was measured on and off-test for each grazing period. Diet extrusa samples for in vitro organic matter disappearance was less (P = 0.03) for late summer than early summer grazing periods and equal to the spring period (62.9, 64.6, and 61.0 ± 0.90%, respectively for spring, early summer, and late summer grazing periods). In vitro neutral detergent fiber disappearance decreased (P = 0.01) by 10.6 percentage units from early grazing to late grazing period in 2007, whereas no differences were observed in 2008. Ewe average daily gain did not differ between spring and early summer grazing periods and were greater (P = 0.03) than the negligible body weight gains of the late summer grazing period. Total gain was 10.9 kg · ha?1 greater in 2008, and a quadratic response was measured for grazing period in 2007. Results indicate that deferment until early summer may be preferable so that stocking rates can be more accurately determined and animal performance is not diminished.  相似文献   

12.
This research measured steer gains, aboveground biomass remaining at the end of the growing season, and economic returns of tallgrass prairie grazed under season-long stocking (SLS-C) and a grazing system that included a 2-yr rotation of SLS-rotated (SLS-R) and intensive early stocking (IES; 2× normal stocking rate) + late-season grazing at the normal stocking rate (IES + LSG-R). We hypothesized that even though the stocking rate on the IES + LSG-R pasture was above the recommended rate, the greater regrowth availability in the late season would result in steers gaining as well as or better than those stocked SLS at the normal rate. By rotating the IES + LSG treatment with SLS over 2 yr, we anticipated that the aboveground biomass productive capacity of the IES + LSG pasture would be restored in one growing season. Further, we hypothesized that the increased stocking rate with IES + LSG would increase net profit. Comparing traditional season-long stocking to the system, which was a combination of SLS and IES + LSG rotated sequentially over a 2-yr period, the system increased steer gains by 7 kg · hd?1 and by 30 kg · ha?1, had a consistent reduction of 429 kg · ha?1 biomass productivity, and increased net profit by $55.19 per steer and $34.28 per hectare.  相似文献   

13.
Achieving economically optimum livestock production on rangelands can conflict with conservation strategies that require lower stocking rate to maintain wildlife habitat. Combining the spatial and temporal interaction of fire and grazing (pyric–herbivory) is a conservation-based approach to management that increases rangeland biodiversity by creating heterogeneous vegetation structure and composition. However, livestock production under pyric–herbivory has not been reported. In both mixed-grass prairie and tallgrass prairie, we compared livestock production in pastures with traditional fire and grazing management (continuous grazing, with periodic fire on tallgrass prairie and without fire on mixed-grass prairie) and conservation-based management (pyric–herbivory applied through patch burning) at a moderate stocking rate. Stocker cattle weight gain, calf weight gain, and cow body condition score did not differ (P > 0.05) between traditional and conservation-based management at the tallgrass prairie site for the duration of the 8-yr study. At the mixed-grass prairie site, stocker cattle gain did not differ in the first 4 yr, but stocker cattle gained more (P ≤ 0.05) on conservation-based management and remained 27% greater for the duration of the 11-yr study. Moreover, variation among years in cattle performance was less on pastures under conservation management. Traditional management in mixed-grass prairie did not include fire, the process that likely was associated with increased stocker cattle performance under conservation management. We conclude that pyric–herbivory is a conservation-based rangeland management strategy that returns fire to the landscape without reduced stocking rate, deferment, or rest.  相似文献   

14.
牧民的减畜行为是遏制草原生态环境退化最有效的方法之一。本研究基于巴音布鲁克世界自然遗产地187户牧民的实地调查数据,运用有序Probit回归模型分析了牧民的资本禀赋与政策感知对减畜意愿的影响。研究发现:牧民的金融资本、物质资本、自然资本和人力资本对其减畜意愿的影响不显著,文化资本对牧民的减畜意愿具有正向影响,社会资本对牧民的减畜意愿具有负向影响;政策监督力度通过影响牧民对“违规成本”的心理预期来抑制超载放牧行为,补助金额能否弥补减畜带来的经济损失是影响牧民减畜意愿的关键所在。基于研究结果提出以下建议:加强草原生态保护政策的宣传和引导力度,并结合当地牧民的风俗习惯与生活特点制定合理的监管措施,充分发挥村规民约等社会规范对超载放牧行为的约束作用;积极推动牧民的生计转型,减小对草原和畜牧业的依赖程度。  相似文献   

15.
Extensive range-based livestock production has suffered a sharp decrease in Mediterranean Spain in recent decades due to two opposing trends in land use: progressive abandonment of practices in marginal rural areas and land use intensification in more productive areas. In this study, we explored the visions of key stakeholders on the current and future situation of silvopastoral systems in the Sierra Morena mountain range of southern Spain, where extensive livestock grazing is declining because of competition with other more profitable activities, such as intensive olive groves and game hunting. We performed a discourse analysis using Q methodology and evaluated the existing relationships of information exchange and conflict among local institutions such as farmer’s associations, the provincial council, and conservation organizations using social network analysis. Semistructured interviews were conducted with key stakeholders representing local formal and nonformal institutions involved in extensive livestock production. Results showed three distinct discourses among stakeholders related to profitability, conservation, and modernization. There was a strong consensus on the management strategies that should be promoted to support extensive livestock production and preserve the associated silvopastoral systems. Social networks revealed high cohesion and communication exchange and a low level of conflict among stakeholders, with few exceptions. The low influence of livestock producers on policy decision making largely hinders the development of participatory management schemes. Nevertheless, similarities among the visions and opinions of different institutions suggest that new possibilities might emerge for silvopastoral systems through the collaboration among the different socioeconomic sectors present in the area.  相似文献   

16.
Grazing plays a key role in many ecosystems worldwide and can affect the structure and composition of terrestrial plant communities. Nonetheless, how grazing management, especially grazing regime (yearlong continuous and seasonal grazing), affects the relationship between grazing and vegetation on alpine grasslands has not been extensively studied. Here, we performed a grazing experiment in Gangcha county of Qinghai province of the Qinghai-Tibetan Plateau to test the effects of different stocking rates and grazing regimes on grassland biomass and plant structure and composition. Six stocking rates (ranging from 0 to 5.62 sheep ha? 1) were used for continuous grazing, and three grazing intensities (1.72, 2.87, and 5.62 sheep ha? 1) were used for seasonal grazing (grazed only in the growing season, from June to October) at the study sites. Plant biomass and grass functional community composition were characterized in two different yr (2011 and 2012). Additionally, species richness and plant diversity indexes were estimated to quantify the impacts of grazing on plant community composition. Our results indicated that grazing intensity best explained the plant biomass decrease in low-productivity environments, and different grazing regimes also influenced these results. The shifts in plant community structure and composition in response to increased grazing intensity differed considerably between continuous grazing and seasonal grazing. Seasonal grazing maintained greater amounts of palatable plant species, and fewer undesirable species in plant communities when compared with the composition after continuous grazing. Our results emphasize the importance of grazing regime in regulating the effects of grazing on plant communities and the importance of seasonal grazing for ecosystem maintenance, especially in the Qinghai-Tibetan Plateau. This suggests that periodic resting of grasslands could be a good management strategy to keep palatable species, thereby minimizing undesirable species in the overall species composition.  相似文献   

17.
In order to evaluate the epidemiology of parasitism in farmed ruminants in the changed agricultural context in Kazakhstan, 505 cattle, sheep and goats were surveyed for gastrointestinal parasitism using coprological examination, and a further thirty sheep and four goats using post mortem extraction of helminths. The dominant helminth genera were Marshallagia, Nematodirus and Trichostrongylus. Haemonchus was also present. Faecal egg counts were low (mean abundance 0-115 eggs per gram in different groups), and there was no relationship between faecal egg density and body condition score. Eggs of Nematodirus spp. were more common in sheep less than 1 yr of age, whereas those of the Trichostrongylidae were generally more common in adult sheep. Based on faecal egg counts, sheep grazing on common land close to permanent human settlements were generally no more heavily infected than those grazing the remote open plains. This could be due to a non-linear relationship between livestock numbers and stocking density. We suggest that cessation of strategic nematode control in the region following post-Soviet agricultural reform was offset by a general reduction in stocking density, such that parasite burdens remained low. However, recovery in livestock numbers is likely to lead to increased levels of infection and production loss unless sustainable control strategies are put in place.  相似文献   

18.
Runoff from grazing pasture lands can impact water quality in receiving streams if not well managed. Management consists of conservation practices to reduce runoff and pollutants transport. Simulation models have been effectively used to design and implement these conservation practices. The Agricultural Policy Environmental Extender (APEX), a process-based hydrologic model, was used in this study to simulate the management impacts on surface runoff from three small grazed pasture watersheds located at the North Appalachian Experimental Watersheds near Coshocton, Ohio. Specific objectives of this study were to 1) calibrate the APEX model and test runoff predictions against measured runoff and 2) simulate the long-term impacts of different management scenarios on surface runoff. Results show that the APEX model simulated surface runoff reasonably well with the coefficient of determination (R2) and Nash-Sutcliffe efficiency values varying from 0.49 to 0.72 and from 0.25 to 0.60 for calibration and validation, respectively. After validation, the APEX model was run for 37 yr (1975 ? 2011) for long-term scenarios to analyze the impacts of soil properties and management on surface runoff. Data from this study indicated that keeping the watershed land use as a hay meadow instead of grazing significantly reduced cumulative runoff by 58 ? 67%. Buffer strips of perennial grasses resulted in decreased simulated runoff. To simulate the impacts of soils on runoff, the surface (0 ? 5 cm) soil properties of the toe position were applied to the entire grazed watershed. Subsequently, the increase in soil richness resulted in reduction (≤ 5%) in surface runoff. The simulation results from the present study demonstrate the benefits of hayed meadow over grazed pasture and further predict the decreased trend of runoff due to soil properties change and buffer strips.  相似文献   

19.
Targeted grazing is a promising strategy for addressing management issues in annual grasslands. We evaluated targeted cattle grazing strategies for tarweed (Hemizonia fitchii A. Gray) and vinegarweed (Trichostema lanceolatum Benth.). These native annual forbs provide biodiversity to annual grass-dominated landscapes, in addition to being important pollinator plants that discourage yellow starthistle (Centaurea solstitialis L.) invasion. However, these forbs can form dense stands that interfere with grazing. Therefore, we sought grazing strategies that promote sparse stands to maintain livestock production while supporting other ecosystem services. Treatments were 1) early grazing when dominant annual grasses were vegetative, 2) late grazing when grasses were senescing, 3) repeated grazing, and 4) a nongrazed control. These treatments were applied in 2011, 2012, and 2013. In 2012, neither tarweed nor vinegarweed were observed regardless of treatment, likely due to low water availability during their major growth period. In 2011 and 2013, grazing grasses repeatedly throughout the growing season increased tarweed to 3 ? 5 plants m? 2, compared with < 1 plants m? 2 in the control, and in 2011 repeated grazing also increased vinegarweed. Therefore, although environmental factors can prevent tarweed and vinegarweed from forming stands some years, defoliating grasses repeatedly from vegetative through senesced stages is the most reliable way to encourage these forbs in annual grasslands. However, a single period of defoliation can also encourage tarweed: In 2011 and 2013, we found a single period of grazing as annual grasses senesced and tarweed began rapid growth increased tarweed, possibly by increasing light availability. Finally, we found grazing once early in the growing season provided low tarweed and vinegarweed densities, likely because the long postgrazing period allowed annual grasses to recover and competitively suppress these forbs. Therefore, early grazing may reduce/prevent overly dense tarweed and vinegarweed stands.  相似文献   

20.
Half of the world's land base is grazed by domesticated livestock. Because of the important functional role of ants in grasslands, it is important to understand the effect of livestock grazing on ant abundance and diversity. The objectives of this study were to examine the effect of cattle grazing and site productivity on the abundance, species richness, and species diversity of ants in Lac du Bois Grasslands Provincial Park, British Columbia, Canada. We hypothesized that the measured ant variables would be lowest in grazed areas and at low site productivity. Pitfall trapping was conducted at four sites: two at each low and high site productivity levels. At each site an ungrazed (fenced exclosure) and grazed transect was sampled during May, July, and August of 2008. Captured ants were preserved in ethanol and identified. Eight genuses of ants were collected: Tapinoma, Camponotus, Formica, Lasius, Aphaenogaster, Myrmica, Solinopsis, and Temnotharox. The mean number of ants per pitfall was higher at high site productivity sites that were grazed (15.10 ±  SE) compared to high productivity sites ungrazed (3.28 ±  SE); grazing at low productivity reduced numbers of ants from 5.07 (± 0.70 SE) to 2.20 (± 0.39 SE) (F = 21.806; P [ 0.001). Tapinoma sessile and A. occidentalis had the greatest numbers in the pitfall traps. Species richness (F = 23.330, P [ 0.001) and diversity (F = 11.764, P = 0.001) followed a similar trend. Because productivity and cattle grazing affect ant diversity and abundance, and ants impact ecosystem functioning, these factors should be considered in management of grasslands.  相似文献   

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