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刈割对羊草叶面积指数的影响   总被引:2,自引:0,他引:2  
对经过17年不同刈割处理的内蒙古羊草草原羊草种群的叶面积指数进行了比较研究,结果表明:连年刈割使羊草叶面积指数迅速下降,轮休则能减弱下降趋势;隔几年刈割一次会促进羊草种群的生长,增加其叶面积指数;结实期和结实后期刈割,叶面积指数下降最大,开花期刈割次之,果后营养期刈割下降最小;羊草叶面积指数的变化主要由刈割后种群密度的变化引起,平均单叶面积对其影响较小;分株叶片数的变化对叶面积指数无显著影响;羊草叶面积指数的变化与羊草营养枝高度、干重、密度和种群相对生物量之间呈显著相关关系,与生殖枝高度和群落总生物量相关不显著.  相似文献   

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We investigated bird abundance in response to western juniper (Juniperus occidentalis) removal using a short-term chronosequence approach and generated estimates of density and responses to management for the most abundant species. Stands targeted for tree removal were primarily in the middle stages of juniper encroachment (Phase II, 7 851 ha). Trees were removed using hand felling combined with either lop and scatter, single tree burning, or jackpot burning, which were carried out to minimize loss of shrub cover. Brewer’s sparrow (Spizella breweri) density was greater at treated versus untreated portions of the study area. At sites in the third year following tree removal, Brewer’s sparrow density was 23.6 (95% confidence interval [CI]: 19.4–27.8) territories per km2 higher than locations that had not yet been treated. This equates to a net increase of 1 212 ? 1 737 nesting pairs within the project area. Green-tailed towhee increased by 4.6 (95% CI: 3.1–6.1) territories per km2 for an estimated project-wide increase of 194–381 nesting pairs, and vesper sparrow (Poocetes gramineus) increased by 6.5 (95% CI: 4.6–8.4) territories per km2 corresponding to an estimated increase of 460–559 nesting pairs within the project area. Density of gray flycatcher (Empidonax wrighti) was lower in cut areas, and over the entire project area we estimate a net loss of 183–486 nesting pairs as a result of juniper tree removal. This study demonstrates that conifer removal projects designed to retain shrub cover and structure can have benefits to multiple species of ground and shrub nesting birds, including several species of conservation concern.  相似文献   

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Stable bunchgrass populations are essential to resilience and restoration of sagebrush steppe rangelands, yet few studies have assessed long-term variation in plant abundance from a known starting point. We capitalized on a previous paddock study by reestablishing in 2011 nine replicate blocks consisting of 29 × 29 grid of cells, each planted in 1998 with a single individual of one of eight sagebrush steppe bunchgrasses, including the widely planted exotic, crested wheatgrass (Agropyron cristatum). Plant species and numbers were determined in 2011 for each cell, which were classified as holds or cedes, with ceded cells used to determine species-specific gains. We hypothesized the competitive crested wheatgrass would proportionally occur more in gained cells compared with native grasses. While crested wheatgrass did proportionally hold and gain the greatest number of cells, the relative number of plants within holds and gains was constant across all species, with most plants (80 ? 87%) occurring outside cells originally planted with them. Crested wheatgrass had greater proportions of holds and gains where it was the only species within the cell and showed even presence across all cells planted with other grass species in 1998. Native grasses were underrepresented in 1998 crested wheatgrass cells and sometimes overrepresented in other native species cells. The ratio of total crested wheatgrass to native bunchgrass plants followed a sigmoidal step increase with increasing crested wheatgrass density. These results show population changes in sagebrush steppe bunchgrasses are determined by seed production and emergent seedling survival, both of which are stronger in the exotic bunchgrass. This study also showed that native grasses can maintain presence via seed in areas depending on crested wheatgrass density. This information could help shape management strategies capitalizing on the utility of crested wheatgrass and sustaining desirable levels of native grass productivity and diversity.  相似文献   

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Stocking density, both current and past, is a major determinant of the nature and condition of rangelands. Despite this fact, there have been few detailed examinations of historical trends in stocking density. We used data from the U.S. Census of Agriculture to track the density of domestic livestock from the early 1900s to the present, for six rangeland regions in the State of Texas: (1) the Edwards Plateau; (2) the Trans-Pecos; (3) the Lampasas Cut Plain; (4) the South Texas Plains; (5) the Rolling Plains; and (6) the High Plains. We find that stocking densities have declined across the state—ranging from a decline of about 40% in some regions to as much as 75% in the Trans-Pecos and Edwards Plateau regions. The period of sharpest decline, which began in the middle of the last century, reflects important, but not fully understood, socioeconomic changes. These most likely include changing land ownership, fragmentation of land holdings, and increasing emphasis on wildlife conservation. Other factors potentially contributing to the destocking of Texas rangelands include woody plant encroachment and a rise in predation. We argue that the dramatic reduction in stocking densities documented here has profound socioeconomic, ecological, and hydrological implications that need to be better understood.  相似文献   

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Although indirect methods for estimating intra-abdominal pressure (IAP) have been extensively studied in humans, mainly for identification of IAP increments in critical care unit patients (life-threatening condition), little work has been performed in veterinary medicine, especially in horses. The standard method of acquisition of intrabladder pressure (IBP) in human subjects (fluid-filled system with no balloon distention) has been previously evaluated in horses with an unfavorable outcome. Therefore, we reexamined the previously performed method of IBP investigation in horses by using an air-filled intrabladder manometry system in female horses. Intrabladder pressure was estimated by air-filled balloon manometry in seven healthy adult mares. The results were compared with two sets of directly acquired IAP values obtained by right paralumbar puncture using an 8-G needle in seven horses. Direct IAP values were obtained at times unrelated to IBP measurement acquisitions, and three of the seven horses used (for direct IAP measurement) were different animals from the mares used for assessment of IBP. Both sets of IAP measurements yielded subatmospheric values (IAP1 = −10.5 ± 2.2 mm Hg; IAP2 = −11.6 ± 2.0 mm Hg). Slightly subatmospheric IBP values were also recorded in some mares, but the mean (±SD) IBP was 1.4 ± 2.0 mm Hg. There was no correlation between IBP and IAP. These results suggest that this indirect (IBP) method for estimating IAP is not applicable for female horses.  相似文献   

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Western juniper expansion is one of the largest threats to conserving sagebrush steppe ecosystems in the northwestern United States. Juniper expansion has degraded the sagebrush steppe by altering fire regimes and outcompeting shrubs and herbaceous vegetation for limited resources. We characterized the effect of juniper removal in a severely degraded sagebrush steppe habitat for 3 yr following juniper cutting. In addition, we measured the effect of low-intensity seasonal grazing on plant community recovery through cattle exclusion treatments. We monitored plant community composition (exotic annual grasses, preferred grasses, preferred forbs, and shrubs); fuel loads; and juniper recruitment in a factorial design of juniper removal and grazing exclusion. We found that although there were significant differences between cut and uncut juniper treatments, there were no consistent trends across all 3 yr. Our results suggest that other factors, such as timing of precipitation, may also have strong short-term effects on plant community composition. We detected no significant grazing effects during the study period, suggesting the current grazing regime is appropriate for the area. The cutting of juniper increased total fuel loads and herbaceous fuel loads. Compared with open interspace, a twofold increase in juniper seedlings and saplings was detected beneath juniper piles, which will act as sources for future juniper encroachment.  相似文献   

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Western Juniper (Juniperus occidentalis Hook.) has greatly expanded in the past 150 + years and now dominates over 3.6 million ha of rangeland in the Intermountain Western United States. The impacts of juniper encroachment on critical ecohydrological relationships among snow distribution, water budgets, plant community transitions, and habitat requirements for wildlife, such as the greater sage grouse (Centrocercus urophasianus), remain poorly understood. The goal of this study is to better understand how juniper encroachment affects water availability for ecohydrologic processes and associated wildlife habitat in snow-dominated sagebrush (Artemisia spp.) steppe ecosystems. A 6-yr combined measurement and modeling study is conducted to explore differences in snow distribution, water availability, and annual water balances between juniper-dominated and sagebrush-dominated catchments. Although there is large interannual variability in both measured weather data and modeled hydrologic fluxes during the study, results indicate that juniper-dominated catchments have greater peak accumulations of snow water equivalent, earlier snow melt, and less streamflow relative to sagebrush-dominated catchments. Water delivery is delayed by an average of 9 days in the sagebrush-dominated scenario compared with the juniper-dominated scenario as a result of increased water storage in snow drifts. The delayed water input to sagebrush-dominated ecosystems in typical water years has wide-ranging implications for available surface water, soil water, and vegetation dynamics associated with wildlife habitat for sagebrush obligates such as sage grouse. Results from this study imply that the retention of high-elevation, sagebrush-dominated landscapes may become crucial for sage grouse habitat management if mid- and low-elevation precipitation continues to transition from snow to rain dominated.  相似文献   

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Current paradigm suggests that spatial and temporal competition for resources limit an exotic invader, cheatgrass (Bromus tectorum L.), which once established, alters fire regimes and can result in annual grass dominance in sagebrush steppe. Prescribed fire and fire surrogate treatments (mowing, tebuthiuron, and imazapic) are used to reduce woody fuels and increase resistance to exotic annuals, but may alter resource availability and inadvertently favor invasive species. We used four study sites within the Sagebrush Steppe Treatment Evaluation Project (SageSTEP) to evaluate 1) how vegetation and soil resources were affected by treatment, and 2) how soil resources influenced native herbaceous perennial and exotic annual grass cover before and following treatment. Treatments increased resin exchangeable NH4+, NO3-, H2PO4-, and K+, with the largest increases caused by prescribed fire and prolonged by application of imazapic. Burning with imazapic application also increased the number of wet growing degree days. Tebuthiuron and imazapic reduced exotic annual grass cover, but imazapic also reduced herbaceous perennial cover when used with prescribed fire. Native perennial herbaceous species cover was higher where mean annual precipitation and soil water resources were relatively high. Exotic annual grass cover was higher where resin exchangeable H2PO4- was high and gaps between perennial plants were large. Prescribed fire, mowing, and tebuthiuron were successful at increasing perennial herbaceous cover, but the results were often ephemeral and inconsistent among sites. Locations with sandy soil, low mean annual precipitation, or low soil water holding capacity were more likely to experience increased exotic annual grass cover after treatment, and treatments that result in slow release of resources are needed on these sites. This is one of few studies that correlate abiotic variables to native and exotic species cover across a broad geographic setting, and that demonstrates how soil resources potentially influence the outcome of management treatments.  相似文献   

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Concerns over climate change have increased interest in carbon sequestration in agricultural lands. While the per-hectare carbon capture potential of rangelands is less than either cropland or forests, existing research suggests modest changes in carbon storage on rangelands can potentially alter the global carbon cycle. This paper examines the potential firm-level revenues from voluntary carbon offset programs, such as the Chicago Climate Exchange (CCX) Rangeland Soil Carbon Offset program. We estimate revenues for short-term voluntary offsets given historical prices and prices projected with potential cap-and-trade legislation. We also estimate revenues assuming 100-yr offsets are required to meet international sequestration standards. Simulation results indicate a relatively wide range of modest revenues from recent CCX contracts and carbon prices. The analysis suggests that recent carbon prices or low-end projected prices from cap-and-trade legislation are not likely to encourage producer participation. Medium and high carbon price projections for cap-and-trade legislation may make carbon sequestration a more attractive option for rangeland managers, but given potential requirements for projects to meet international guidelines for greenhouse gas offset projects, many issues remain before range managers may be interested in carbon sequestration as an enterprise.  相似文献   

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Balancing the number of grazing animals with the level of plant resources is a core issue in grazing management. Complete, full-coverage vegetation surveys are often used for this purpose, but these are expensive undertakings. We have presented a method to downscale information from regional sampling surveys by poststratification using a land cover map derived from satellite-based measures of reflectance values. This approach opens new prospects for landscape-level evaluation of productivity. We applied this method to eight grazing districts (19–245 km2) in Setesdal Vesthei, Norway, in 2006. Sheep densities in three of eight grazing districts of Setesdal Vesthei fluctuated above the estimated grazing capacity. We fitted 43 sheep with Global Positioning System collars in two contrasting grazing districts in 2007–2008 to assess their selection of the land cover productivity classes in the map used for poststratification. In the area with high vegetation coverage, sheep selection increased in areas with an overall higher productivity, supporting the main basis of the approach. However, in the grazing districts with lower vegetation coverage, selection was higher for areas of overall low vegetation productivity. The likely explanation is the presence of small areas of snow bed vegetation with high-quality forage in areas with a generally rocky surface. Our study provides a first step toward a grazing capacity evaluation to achieve a sustainable management of sheep on alpine ranges of Scandinavia, and our approach is likely applicable to other open alpine ranges in the northern hemisphere.  相似文献   

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Successful postfire reseeding efforts can aid rangeland ecosystem recovery by rapidly establishing a desired plant community and thereby reducing the likelihood of infestation by invasive plants. Although the success of postfire remediation is critical, few efforts have been made to leverage existing geospatial technologies to develop methodologies to assess reseeding success following a fire. In this study, Terra Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data were used to improve the capacity to assess postfire reseeding rehabilitation efforts, with particular emphasis on the semiarid rangelands of Idaho. Analysis of MODIS data demonstrated a positive effect of reseeding on rangeland ecosystem recovery, as well as differences in vegetation between reseeded areas and burned areas where no reseeding had occurred (P < 0.05). We conclude that MODIS provides useful data to assess the success of postfire reseeding.  相似文献   

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兴义市退化天然草地改良试验初报   总被引:1,自引:1,他引:1  
研究结果表明,退化天然草地通过补播,鲜草产量每公顷提高68%,经t检验差异显著(p<001)。施肥试验组与对照比较,各处理差异极显著(p<001),其中每公顷施1875kg尿素效果最佳。刈割试验与对照比较差异极显著(p<001),鲜草产量每公顷提高611%。  相似文献   

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通过研究表明,硅对紫花苜蓿的分枝数在现蕾期是增加的,特别在盛花期差异显著(P〈0.05),0.100g/kg的硅处理增加效果最为明显;施硅对紫花苜蓿初花期、盛花期的花序数差异是极显著的(P〈0.01),0.100g/kg的硅处理花序数和结荚数最多,分别为10.9个/株和16.0个/株;高硅水平会减小苜蓿中部叶的叶夹角,施硅对紫花苜蓿在分枝期的叶面积影响不大,但0.100g/kg的施硅处理对盛花期的叶面积有增加作用。  相似文献   

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1990~1993年在柴达盆地尕海地区弃耕地进行土壤可溶性盐分测定,测定结果,该地区土壤盐分组成为氯化物-硫酸盐和硫酸盐-氯化物,大部分地区耕层盐分含量小于10g.kg^-1,少部分盐荒地表层含盐量高达70g.kg^-1,牧草生长季节中,土壤盐分含量最低期在6月份。  相似文献   

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