焚烧对芨芨草滩地草场土壤生态条件的影响

本文研究了焚烧对芨芨草滩地草场上壤生态条件的影响。结果表明，焚烧可使土壤温度升高，地表可升温3．2～10．8℃，地表以下土层也有所升温，但其数值随深度增加而递减。焚烧后土壤含水量在0～40cm土层内可增加2．42～4．58％，土壤含盐量和土壤含磷量均有增加，但土壤含氮量则有所下降。     

芨芨草的自然—经济特性及其利用与培育

简述了芨芨草的形态特征，地理分布，概述了芨芨草草甸在我国的分布及其群落特征，详述了芨芨草饲用特性及其利用与培育措施。     

氢氧化钙尿素复合处理芨芨草的效果研究

分别用4％尿素、4％尿素 4％氢氧化钙处理芨芨草，试验结果表明：氢氧化钙尿素复合处理剂可极显著(P＜O．01)提高芨芨草粗蛋白含量，比对照组提高142．61％，增加5．79个百分点。NDF舍量比对照组降低11．51％(P＜0．01)。钙含量比对照组提高1．92倍(P＜0．01)。4％尿素处理芨芨草后．芨芨草DM中CP含量比对照组增加145．81％(P＜0．01)。氢氧化钙尿素复合处理芨芨草后．可分别提高芨芨草DM、OM、NDF有效降解率55．08％、62．04％、28．89oA(P＜0．01)。4％尿素可分别提高芨芨草DM、0M、NDF有效降解率46．61％、50．87％、18．80％(P＜0．01)。     

内蒙古芨芨草盐化草甸的资源、特性和对策的研究

本文从芨芨草盐化草甸的资源着手，指出芨芨草为建群的草场，总面积为２５０万ｈｍ２，内蒙古占全国此类面积的７３．２８％，共有１０个群落，分为二大类，以芨芨草＋羊草＋杂类草为主要群落。本文又从芨芨草本身的特性以及在不同利用条件下的变化提出今后应采取的对策进行探讨。     

围栏封育对青海湖地区芨芨草草原群落特征的影响

选择青海湖地区围栏内封育和围栏外自由放牧的芨芨草草地为研究对象，用样线和样方相结合的方法进行群落调查，分析了围栏内外芨芨草草地的群落特征和地上生物量特点。结果表明：多年围栏封育使围栏内外群落类型发生了变化，围栏内为芨芨草＋裸花碱茅群落，围栏外为芨芨草＋赖草群落，且每个小样方中的物种数围栏内大于围栏外。围栏内外芨芨草群落的相似性系数达0．743。围栏外自由放牧区域的芨芨草种群优势地位有所加强，其重要值也大于围栏内的芨芨草。物种丰富度指数围栏外大于围栏内，多样性指数中Shannon-winner指数、Hill指数和丰富度指数具有同样的趋势，而均匀度指数和Simpson指数则是围栏内大于围栏外。围栏封育后群落地上生物量发生变化，地上总生物量和禾草类生物量均为围栏内〉围栏外，而杂类草和豆类毒杂草则是围栏内〈围栏外。     

当前(1970—2000)与未来气候变化情境下中国醉马芨芨草潜在分布预测

醉马芨芨草(Achnatherum inebrians)是我国西北、华北地区严重危害草地畜牧业和生态安全的主要毒害草之一，但其在药用、造纸、脱毒后饲用等方面有一定利用价值。本研究利用优化的MaxEnt模型预测了当前(1970—2000年)条件下和未来(2050 s和2070 s)4种气候变化情景下的醉马芨芨草潜在分布。结果显示：影响当前醉马芨芨草分布的关键环境变量与其适生阈值为12月平均最高气温(—7.5~7.9℃)、海拔(1 053.8~4 590.9 m)、最冷季降水量(1.6~24.6 mm)和降水量变异系数(25.5~111.5)；当前醉马芨芨草主要分布于新疆、西藏、四川、青海、甘肃、内蒙古、宁夏、陕西和山西等省区；在未来4种气候情景下，醉马芨芨草适生区面积均会增加，并向高纬度和高海拔地区迁移。研究为醉马芨芨草的防治和资源利用、草地生态学研究和草地放牧管理提供了理论依据和参考。     

盐胁迫对芨芨草苗期质膜H+-ATP酶活性及5''-核苷酸酶活性的影响

以芨芨草（Achnatherum splendens）为试验材料,在不同浓度NaCl和Na2SO4胁迫下,对芨芨草叶片与根系的质膜H＋-ATPase和5′-AMPase的活性进行测定。结果表明：在NaCl和Na2SO4胁迫下,芨芨草根系的质膜H＋-ATPase活性呈＂先升后降＂的趋势,当浓度小于300mmol/L时,根系的质膜H＋-ATPase和5′-AMPase活性均高于对照。同一盐胁迫下,芨芨草根系中质膜H＋-ATPase活性和5′-核苷酸酶活性均显著高于叶片。在Na2SO4胁迫下,芨芨草根系和叶片的质膜H＋-ATPase和5′-AMPase活性分别显著高于相同浓度的NaCl胁迫组,芨芨草在Na2SO4胁迫下有更强的抗性。     

盐胁迫对芨芨草苗期质膜H~+-ATP酶活性及5′-核苷酸酶活性的影响

以芨芨草(Achnatherum splendens)为试验材料,在不同浓度NaCl和Na2SO4胁迫下,对芨芨草叶片与根系的质膜H+-ATPase和5′-AMPase的活性进行测定。结果表明:在NaCl和Na2SO4胁迫下,芨芨草根系的质膜H+-ATPase活性呈"先升后降"的趋势,当浓度小于300mmol/L时,根系的质膜H+-ATPase和5′-AMPase活性均高于对照。同一盐胁迫下,芨芨草根系中质膜H+-ATPase活性和5′-核苷酸酶活性均显著高于叶片。在Na2SO4胁迫下,芨芨草根系和叶片的质膜H+-ATPase和5′-AMPase活性分别显著高于相同浓度的NaCl胁迫组,芨芨草在Na2SO4胁迫下有更强的抗性。     

用过硫酸铵、过硫酸钾处理芨芨草提高其营养价值的研究

分别用0.5%过硫酸铵(B)、1%过硫酸铵(C)、2%过硫酸铵(D)、0.5%过硫酸钾(E)、1%过硫酸钾(F)、2%过硫酸钾(G)、4%尿素(H)处理芨芨草,A组为对照,水分调至45%,密封保存20天,然后利用瘤胃尼龙袋法测定芨芨草有效降解率,分析相关营养指标。试验结果表明:B、C、D可极显著(p<0.01)提高芨芨草DM中CP含量,分别提高CP8.62%、16.01%、30.30%;过硫酸铵可显著降低(p<0.05)NDF含量,B、C、D分别比对照组A降低2.14%、5.04%、9.09%。过硫酸钾可显著降低(p<0.05)NDF含量,E、F、G三个处理组分别比对照组A降低3.53%、6.74%、10.43%;4%尿素处理芨芨草后,芨芨草DM中CP含量极显著(p<0.01)提高(145.81%),NDF含量略有降低(2.5%),差异不显著(p>0.05)。用过硫酸铵、过硫酸钾处理芨芨草后,可极显著地(p<0.01)提高芨芨草DM、OM、NDF有效降解率,以0.5%过硫酸铵处理芨芨草效果最好,可分别提高芨芨草DM、OM、NDF有效降解率48.70%、53.43%、38.13%;4%尿素可极显著地(p<0.01)提高芨芨草DM、OM、NDF有效降解率,分别提高46.61%、50.87%、18.80%;0.5%过硫酸铵与4%尿素处理芨芨草的效果相当,但在提高NDF降解率方面,0.5%过硫酸铵优于4%尿素处理芨芨草的效果。     

芨芨草的利用与研究现状

简述了芨芨草的地理分布、形态特征和生物学特性，概述芨芨草的利用及其生态、饲用等方面的研究现状。     

松嫩草原不同时间火烧后环境因子变化分析

松嫩草原火烧后，土壤表层硬度增加，早烧地硬度异质性程度增高，晚烧地降低。晚烧地土壤０￣５ｃｍ范围内窝重降低，早烧地与未烧地比无差异。火烧地土壤０￣３０ｃｍ范围内含水率降低，早烧地更低，表面差别最大，火烧地土壤含水率在春季严重亏缺。火烧地土壤温度在生长季内恒高于未烧地，平均温度亦高。群落平均温度低于未烧地，但白天火烧地群落温度高于未烧地，夜间群落温度低于未烧地，土壤表层温度波动幅度较大，火烧与未烧边     

Soil Seed Banks of the Exotic Annual Grass Bromus rubens on a Burned Desert Landscape

Red brome (Bromus rubens), an exotic annual grass, can dominate soil seed banks and poses serious threats to mature native plant communities in the Mojave Desert by competing with native species and providing fine fuels that facilitate widespread wildfire. By exploring how seed bank density and composition in burned areas change over time since fire (TSF), we can improve our understanding of how the seed banks are affected by fire. Samples of the 5-cm-deep soil seed bank were collected from two microsites (under shrubs, in open interspaces) within paired burned and unburned areas on 12 fires ranging from 5–31 yr TSF. Seed bank samples were assayed using the emergence method and seed densities were compared among TSFs, burn status (burned, unburned), and microsites for the species that emerged. Red brome soil seed bank density was spatially variable and TSF rarely predicted abundance. Overall, undershrub seed densities did not differ between burned and unburned areas. However, at some fire sites, seed densities in interspaces were greater in burned than unburned areas. Although native seed densities were low overall, they did not appear to differ according to burn status. Studies have shown that red brome plant and seed bank densities can be greatly reduced immediately after fire. Management efforts that focus on this initial colonization window may be able to take advantage of diminished red brome seed densities to limit its reestablishment while facilitating the establishment of native species. However, this window is brief, as our findings indicate that once reestablished, red brome soil seed densities in burned areas can be similar to those in unburned areas within 5 yr.     

Burning and Climate Interactions Determine Impacts of Grazing on Tallgrass Prairie Systems

Tallgrass prairie may respond differently to prescribed burning and subsequent preferential grazing, termed pyric herbivory, under variable climate conditions. This 6-yr study (2011−2016) compared tallgrass prairie pastures that were subjected to burned and unburned conditions while exposed to grazing under differing climate conditions in the Southern Great Plains of the United States. The study area consisted of six pastures, three burned and three unburned. Each burned pasture was further divided into three patches and subjected to a 3-yr rotational burning cycle. The Enhanced Vegetation Index (EVI) derived from Landsat 7/8 (EVI_LS) and Moderate Resolution Imaging Spectroradiometer (MODIS, EVI_MOD) was used to indicate vegetation production depending on size of pastures. On the basis of EVI_LS, most burned patches (11 of 18) had lesser production (overall difference of 3%) than unburned patches within the same pasture. The differences were larger (13%) in a drought yr (2011) compared with normal (3% in 2013) and wet (<1% in 2015) yrs. The distribution of precipitation controlled EVI_LS for periods during and after grazing. The burned patches tended to have lower EVI_LS during grazing periods than the unburned patches within the same pasture, probably because of selective grazing of newly grown grass in recently burned patches. In contrast, the differences in EVI_LS between during and after grazing periods were mostly (78%) smaller in burned than unburned patches. However, more variations in EVI_LS existed among pasture comparisons due to landscape heterogeneity. Similar results were observed with EVI_MOD. Overall, results demonstrated that pyric herbivory management and climate determine the impacts of grazing on tallgrass prairie systems. The contrasting seasonal forage availabilities in burned and unburned patches, indicated by different seasonality of EVI, also suggests that patch burning might better balance the quantity and quality of the grass available for cattle grazing.     

Herbaceous Biomass Response to Prescribed Fire in Juniper-Encroached Sagebrush Steppe

Western juniper (Juniperus occidentalis Hook.) has expanded into sagebrush steppe plant communities the past 130 ? 150 yr in the northern Great Basin. The increase in juniper reduces herbage and browse for livestock and big game. Information on herbaceous yield response to juniper control with fire is limited. We measured herbaceous standing crop and yield by life form in two mountain big sagebrush communities (MTN1, MTN2) and a Wyoming/basin big sagebrush (WYOBAS) community for 6 yrs following prescribed fire treatments to control western juniper. MTN1 and WYOBAS communities were early-successional (phase 1) and MTN2 communities were midsuccessional (phase 2) woodlands before treatment. Prescribed fires killed all juniper and sagebrush in the burn units. Total herbaceous and perennial bunchgrass yields increased 2 to 2.5-fold in burn treatments compared with unburned controls. Total perennial forb yield did not differ between burns and controls in all three plant communities. However, tall perennial forb yield was 1.6- and 2.5-fold greater in the WYOBAS and MTN2 burned sites than controls. Mat-forming perennial forb yields declined by 80 ? 90% after burning compared with controls. Cheatgrass yield increased in burned WYOBAS and MTN2 communities and at the end of the study represented 10% and 22% of total yield, respectively. Annual forbs increased with burning and were mainly composed of native species in MTN1 and MTN2 communities and non-natives in WYOBAS communities. Forage availability for livestock and wild ungulates more than doubled after burning. The additional forage provided on burned areas affords managers greater flexibility to rest and treat additional sagebrush steppe where juniper is expanding, as well as rest or defer critical seasonal habitat for wildlife.     

Postfire Succession in Big Sagebrush Steppe With Livestock Grazing

Prescribed fire in rangeland ecosystems is applied for a variety of management objectives, including enhancing productivity of forage species for domestic livestock. In the big sagebrush (Artemisia tridentata Nutt.) steppe of the western United States, fire has been a natural and prescribed disturbance, temporarily shifting vegetation from shrub–grass codominance to grass dominance. There is limited information on the impacts of grazing to community dynamics following fire in big sagebrush steppe. This study evaluated cattle grazing impacts over four growing seasons after prescribed fire on Wyoming big sagebrush (Artemisia tridentata subsp. Wyomingensis [Beetle & Young] Welsh) steppe in eastern Oregon. Treatments included no grazing on burned and unburned sagebrush steppe, two summer-grazing applications after fire, and two spring-grazing applications after fire. Treatment plots were burned in fall 2002. Grazing trials were applied from 2003 to 2005. Vegetation dynamics in the treatments were evaluated by quantifying herbaceous canopy cover, density, annual yield, and perennial grass seed yield. Seed production was greater in the ungrazed burn treatments than in all burn–grazed treatments; however, these differences did not affect community recovery after fire. Other herbaceous response variables (cover, density, composition, and annual yield), bare ground, and soil surface litter did not differ among grazed and ungrazed burn treatments. All burn treatments (grazed and ungrazed) had greater herbaceous cover, herbaceous standing crop, herbaceous annual yield, and grass seed production than the unburned treatment by the second or third year after fire. The results demonstrated that properly applied livestock grazing after low-severity, prescribed fire will not hinder the recovery of herbaceous plant communities in Wyoming big sagebrush steppe.     

Short-Term Response of Two Beneficial Invertebrate Groups to Wildfire in an Arid Grassland System,United States

Rangeland invertebrates contribute greatly to biodiversity and provide important services including pollination, pest control, and nutrient cycling. As wildfire frequency increases across these areas of the United States, it is imperative to understand how these disturbances affect beneficial invertebrate communities. We examined bee (Hymenoptera), spider (Araneae), and vegetative communities 1 yr before and 1 yr after a large wildfire swept across an intact grassland in eastern Oregon. Several sites were left unburned after the fire, and a before-after-control-impact study design was used to assess changes within the communities. Fire had no effect on bee or spider abundance, or spider diversity or richness; however, fire significantly increased native bee diversity and richness. In addition, composition of both native bee and spider communities differed significantly between burned and unburned areas 1 yr after the fire. Sheet web spiders (Linyphiidae) and several bee species (primarily large, generalist species) were associated with burned sites. Invasive annual grass and biological soil crust cover decreased significantly in burned sites, but maximum vegetation height and litter cover did not differ significantly among treatments. Forb abundance increased in burned sites; however, species richness of forbs in burned and unburned sites did not differ significantly 1 yr after the fire. Several forbs were indicative of burned areas including non-native species, such as Douglas’ knotweed (Polygonum douglasii) and Russian thistle (Salsola tragus), and native species such as Canadian horseweed (Conyza canadensis), hoary tansyaster (Machaeranthera canescens), and tall willowherb (Epilobium brachycarpum). This study demonstrates that both invertebrate and plant communities show strong short-term responses to wildfire, and our results can be used to inform management of rare habitat and biodiversity in rangelands impacted by wildfire in arid grasslands.     

Postfire Invasion Potential of Rush Skeletonweed (Chondrilla Juncea)

North American sagebrush steppe communities have been transformed by the introduction of invasive annual grasses and subsequent increase in fire size and frequency. We examined the effects of wildfires and environmental conditions on the ability of rush skeletonweed (Chondrilla juncea L.), a perennial Eurasian composite, to invade degraded sagebrush steppe communities, largely dominated by cheatgrass (Bromus tectorum L.). Recruitment of rush skeletonweed from seed and root buds was investigated on 11 burned and unburned plot pairs on Idaho's Snake River Plain following summer 2003 wildfires. Emergence from soil seedbanks was similar on burned and unburned plots in 2003 and 2004 (P = 0.37). Soils from recently burned plots (P = 0.05) and sterilized field soil (P &spilt; 0.01) supported greater emergence than did unburned field soils when rush skeletonweed seeds were mixed into the soils in the laboratory. These decreases may indicate susceptibility of this exotic invasive to soil pathogens present in field soils. Seeds in bags placed on field soil in late October 2003 reached peak germination by mid-January 2004 during a wet period; 1% remained viable by August 2004. Seedling emergence from sown plots or the native seedbank and establishment of new rosettes from root sprouts in 2003–2005 indicate that seed germination of rush skeletonweed on the Snake River Plain may be facultative, occurring in fall or spring if soil moisture is adequate, although many germinants may not survive. Stand development results primarily from root sprouting. Establishment from seed is episodic but provides for dispersal, with increasing fire frequency and size expanding the areas of disturbance available for new invasions.     

Sheep and Goat Grazing Effects on Three Atlantic Heathland Types

Heathlands in the northwest of Spain have been traditionally used by domestic herbivores as a food resource. However, their abandonment in the past decades has promoted a high incidence of wildfires, threatening biodiversity. Sheep and goats exhibit different grazing behavior, affecting rangelands dynamics in a different way, but the botanical and structural composition may also affect such dynamics. The aim of this article was to compare the grazing effects of sheep and goats on three different heathland types: previously burned grass- or gorse (Ulex gallii Planchon)-dominated and unburned heather (Erica spp.)-dominated shrublands. Two grazing treatments (sheep or goats) were applied in each vegetation type in a factorial design with two replicates (12 experimental plots). A small fenced area was excluded from grazing in each plot (control treatment). The experiment was carried out from 2003 to 2006, and the grazing season extended from May to October–November. Plant cover, canopy height, and phytomass amount and composition were assessed in each plot. Results showed that goats controlled shrub encroachment, phytomass accumulation, and canopy height more than sheep in either burned grass– and gorse– and unburned heather–dominated shrublands. It was accompanied by a higher increase of herbaceous species under goat grazing. Nevertheless, plant dynamics showed different trends between the three vegetation types studied. Grazing effects were more important in previously burned grass-dominated heathlands than in unburned heather-dominated shrublands. At the end of the experiment (May 2006), shrub cover, height, and woody phytomass were significantly higher in the ungrazed enclosures than in the grazed plots. Small ruminant grazing, especially with goats, is proposed as an efficient tool to reduce shrub encroachment and woody phytomass accumulation in heathlands, thus reducing fire hazard, although these grazing effects depend on heathland composition.     

Influence of Fire on Black-tailed Prairie Dog Colony Expansion in Shortgrass Steppe

Factors influencing the distribution and abundance of black-tailed prairie dog (Cynomys ludovicianus) colonies are of interest to rangeland managers because of the significant influence prairie dogs can exert on both livestock and biodiversity. We examined the influence of 4 prescribed burns and one wildfire on the rate and direction of prairie dog colony expansion in shortgrass steppe of southeastern Colorado. Our study was conducted during 2 years with below-average precipitation, when prairie dog colonies were expanding throughout the study area. Under these dry conditions, the rate of black-tailed prairie dog colony expansion into burned grassland (X ¯ = 2.6 ha · 100-m perimeter^-1 · y^-1; range = 0.8–5.9 ha · 100-m perimeter^-1 · y^-1; N = 5 colonies) was marginally greater than the expansion rate into unburned grassland (X ¯ = 1.3 ha · 100-m perimeter^-1 · y^-1; range = 0.2–4.9 ha · 100-m perimeter^-1 · y^-1; N = 23 colonies; P = 0.066). For 3 colonies that were burned on only a portion of their perimeter, we documented consistently high rates of expansion into the adjacent burned grassland (38%–42% of available burned habitat colonized) but variable expansion rates into the adjacent unburned grassland (2%–39% of available unburned habitat colonized). While our results provide evidence that burning can increase colony expansion rate even under conditions of low vegetative structure, this effect was minor at the scale of the overall colony complex because some unburned colonies were also able to expand at high rates. This result highlights the need to evaluate effects of fire on colony expansion during above-average rainfall years, when expansion into unburned grassland may be considerably lower.