Improving remote sensing-based net primary production estimation in the grazed land with defoliation formulation model

Remote sensing(RS) technologies provide robust techniques for quantifying net primary productivity(NPP) which is a key component of ecosystem production management. Applying RS, the confounding effects of carbon consumed by livestock grazing were neglected by previous studies, which created uncertainties and underestimation of NPP for the grazed lands. The grasslands in Xinjiang were selected as a case study to improve the RS based NPP estimation. A defoliation formulation model(DFM) based on RS is developed to evaluate the extent of underestimated NPP between 1982 and 2011. The estimates were then used to examine the spatiotemporal patterns of the calculated NPP. Results show that average annual underestimated NPP was 55.74 gC·m^(-2)yr^(-1) over the time period understudied, accounting for 29.06% of the total NPP for the Xinjiang grasslands. The spatial distribution of underestimated NPP is related to both grazing intensity and time. Data for the Xinjiang grasslands show that the average annual NPP was 179.41 gC·m^(-2)yr^(-1), the annual NPP with an increasing trend was observed at a rate of 1.04 gC·m^(-2)yr^(-1) between 1982 and 2011. The spatial distribution of NPP reveals distinct variations from high to low encompassing the geolocations of the Tianshan Mountains, northern and southern Xinjiang Province and corresponding with mid-mountain meadow, typical grassland, desert grassland, alpine meadow, and saline meadow grassland types. This study contributes to improving RS-based NPP estimations for grazed land and provides a more accurate data to support the scientific management of fragile grassland ecosystems in Xinjiang.

Effects of Non-protein Nitrogen Supplement on Growth Performance of Graze Cattle

[Objective] The experiment was conducted to investigate the growth performance of graze cattle fed on non-protein nitrogen （NPN） supplement. [ Method] The experiment was conducted in late spring and early summer before grazing. Thirty Chinese SimmentaI-Taihang taxa bulls at the age of 9-10 months weighing 150-170 kg were divided into the control group, experimental group 1 and experimental group 2, 10 in each group, Each cattle in the experimental group 1 fed on the basal diet supplemented 1.0 kg cornmeal every day. Each cattle in the experimental group 2 fed on the basal diet supplemented 1.0 kg cornmeal and 0.25 kg NPN supplement every day. Those in the control group were fed on the basal di- et. The experiment was performed for 100 d. [Result] The average daily gain of the experimental group I was 217 g larger than that of the control group, while the average daily gain of the experimental group 2 was 429 g larger than that of the control group. The differences in the average daily gain were significant between the three groups. [ Conclusion ] The growth performance of cattle grazed in northern slopes was obviously improved by supplementing a small amount of concentrate in feed. The improvement was more remarkable if a small amount of NPN supplement was also added in feed.

Effects of Feces on Spatial Distribution Patterns of Grazed Grassland Communities

Animals excrete feces during grazing. The uneven distribution of feces causes a spatial heterogeneity in grassland communities. In this study, we attempted to clarify the effects of feces on spatial distribution patterns of plant species. A field study was conducted on four grasslands each grazed by a single cow. These four grasslands were defined as Poa pratensis （Kentucky bluegrass） dominated grassland without feces （PoF-）, Poa pratensis dominated grassland with feces （PoF＋）, Zoysia japonica Steud. （Japanese lawngrass） dominated grassland without feces （ZyF-）, and Zoysia japonica Steud. dominated grassland with feces （ZyF＋）. A 50 m line that transects 100 equally spaced quadrats （L-quadrats） was drawn on each of the four grasslands. Each quadrat was 0.50 m × 0.50 m in size and consisted of four equal-area cells of 0.25 m ×0.25 m （S-quadrats）. The occurrences of all plant species were recorded in each S-quadrat. The binomial distribution （BD） and beta-binomial distribution （BBD） were used to represent the variation in spatial patterns. The BBD provided a significant description of the frequency distribution of plants per quadrat. A power law was used to calculate the spatial heterogeneity of each species together with the community heterogeneity. The results revealed that the plants on each of the four grasslands were aggregatively distributed. The ZyF＋ exhibited greater spatial heterogeneity than the ZyF-due to the uneven deposition of feces by cows grazing on the grasslands. Additionally we also found that the feces had effect on the heterogeneity inZyF＋ and did not have effect in PoF＋.

Response of understory vegetation over 10 years after thinning in an old-growth cedar and cypress plantation overgrazed by sika deer in eastern Japan

Background： Forest management strategies such as thinning have long been used to enhance ecosystem functions, especially in plantations.Thinning in plantations with high deer density, however, may not yield a desired increase in understory vegetation because deer graze on germinating plants after thinning.Here, we examine the changes in understory vegetation after thinning in plantations that have been overgrazed by sika deer to provide insight into the effects of thinning on ecosystem functions such as soil conservation and biological diversity.Methods： We conducted our survey in the Tanzawa Mountains of eastern Japan.We surveyed the change in understory vegetation within and outside of three deer exclosures on a single slope with three levels of understory vegetation cover： sparse（1%, exclosure ＂US＂）, moderate（30%, exclosure ＂MM＂）, and dense（80%, exclosure ＂LD＂） over10 years after a 30% thinning of an old-growth cedar and cypress plantation which was overgrazed by sika deer.Results： Understory vegetation cover, biomass and species richness increased within and outside the ＂US＂ and＂MM＂ exclosures after thinning, and biomass was greater within than outside the exclosures at 10 years after thinning.Unpalatable species dominated both ＂US＂ and ＂MM＂ exclosures before thinning, and trees and shrubs dominated within the exclosures over time after thinning.In contrast, unpalatable, grazing-tolerant, perennial,and annual species increased outside the ＂US＂ and ＂MM＂ exclosures.No noticeable changes were observed within and outside the ＂LD＂ exclosure when compared with the ＂US＂ and ＂MM＂ exclosures.Conclusions： Our results suggest that thinning a stand by 30% based on volume resulted in an increase in understory vegetation cover mainly composed of both unpalatable and grazing-tolerant species in a plantation forest where understory vegetation is sparse or moderate and sika deer density is high.We emphasize that establishing deer exclosures or controlling deer is essential to maintaining similar understory vegetation both within and outside exclosures.

Seed rain and soil seed bank compensatory roles on Nassella tenuis(Phil.)Barkworth seedling recruitment in ungrazed and grazed sites

In semi-arid lands,vegetation is distributed in shrub patches immersed in a less vegetated interpatch matrix.Grazing affects perennial grass seed bank through a decrease in seed rain and an increase in seed predation and soil compaction.Nevertheless,some species with anchorage mechanisms in their seeds might overcome this,such as Nassella tenuis(Phil.)Barkworth.This is an important species in grazing paddocks because it has an intermediate palatability and its relatively tolerant to grazing.These characteristics allow N.tenuis to increase its abundance in grazed sites.Our objective was to assess how grazing affects the key palatable species from seeds to seedlings:i.e.,seed rain,soil seed bank,and seedling recruitment in different microsites along a windward-leeward transect across shrub canopy.We hypothesized that:(1)the negative effects of grazing on N.tenuis fructification are reflected in its seed rain,soil seed bank,and seedling recruitment,especially in interpatches;(2)Nassella tenuis seed rain reduction,soil compaction by cattle in grazed sites,and removal of seeds by wind decrease its soil seed bank,especially in microsites exposed to the predominant wind;and(3)the decrease in N.tenuis soil seed bank and cover increase in annual species in grazed sites have negative effects on its seedling recruitment,especially in microsites exposed to predominant wind.We placed seed traps,collected soil samples,and monitored seedling recruitment in different locations around shrub canopy to address our hypotheses.Also,we established a manipulative experiment in which we sow N.tenuis seeds and followed its recruitment in different microsites.We compared the seed rain,soil seed bank,natural seedling recruitment,and sown seeds recruitment of N.tenuis between grazed and ungrazed sites.We analyzed differences between microsites along a windward-leeward transect across shrubs patches.Seed rain and soil seed bank had the same density in patches and interpatches both in ungrazed and grazed sites.But seed rain was higher,and soil seed bank was lower in ungrazed sites than in grazed sites.Almost all under-canopy microsites showed greater soil seed bank abundance and natural seedling recruitment in ungrazed sites.Sown seeds recruitment was the same between grazed and ungrazed sites,but it showed protective effects of shrubs in leeward microsites under grazed sites.As a conclusion,seed rain and soil seed bank are complementary under grazed sites.

Virally-Mediated Versus Grazer-Induced Mortality Rates in a Warm-Temperate Inverse Estuary (Spencer Gulf, South Australia)

We investigated the seasonal dynamics of flow cytometrically-defined populations of viruses, heterotrophic bacteria, and the picoeukaryotic and prokaryotic phytoplankton at three sites in the temperate oligotrophic inverse estuary of Spencer Gulf (South Australia). We consistently identified two sub-populations of viruses, three sub-populations of heterotrophic bacteria, one population of picoeukaryotic phytoplankton and two populations of prokaryotic phytoplankton (cyanobacteria Prochlorococcus and Synechococcus). Both the cytometric community composition and the abundance of viruses, heterotrophic bacteria and both prokaryotic (Synechococcus and Prochlorococcus) and eukaryotic picophytoplankton were consistent with previous observations conducted in South Australian continental shelf waters. Noticeably LDNA bacteria (i.e. inactive or dormant cells) were consistently significantly the most abundant group of heterotrophic bacteria (totaling from 29% to 68% of total bacterial abundance) and were up to 10-fold more abundant than that previously reported in South Australian continental shelf waters, including the nearby Saint Vincent Gulf. These results suggest an overall low activity of the microbial community, and are consistent with previous evidence that LDNA cells may play a greater role in heterotrophic processes than HDNA cells in oligotrophic waters. In an attempt to further assess the qualitative and quantitative nature of the mortality of these organisms, we used a specific dilution assay to assess the relative contribution of viruses and microzooplankton grazers to the mortality rates of heterotrophic bacteria, and picoeukaryotic and prokaryotic phytoplankton. We consistently reported site-specific, population specific and sea-son-specific viral lysis and grazing rates of heterotrophic bacteria and the picoeukaryotic and prokaryotic (cyanobacteria Prochlorococcus and Synechococcus) phytoplankton across sites and seasons. Specifically, both viral lysis and micro-zooplankton grazing rates of heterotrophic bacteria were consistently relatively low across sites and seasons, even though their seasonality suggested an overall dominance of grazing over viral lysis in both summer and winter. In contrast, no seasonality is found in either lysis or grazing rates of prokaryotic and eukaryotic picophytoplankton, which are comparable to previous observations conducted in oligotrophic waters, suggesting the mortality dynamics of these populations is similar to those encountered in other oligotrophic waters. The observed patterns of mortality rates of heterotrophic bacteria and both prokaryotic and eukaryotic picophytoplankton are consistent with the low chlorophyll concentration and production previously observed in the waters of the Spencer Gulf.

Grasshopper Species-Area Relationship on Ungrazed and Overgrazed Grasslands

The species richness and abundance of rangeland grasshoppers were investigated at 6 sites of ungrazed and overgrazed pastures in Inner Mongolia during the autumn of 1994.The ungrazed sites supported higher richness and density of grasshoppers than the overgrazed sites.The effects of overgrazing and ungrazing on the species-area relationships of grasshoppers were directty measured.The grasshopper assemblages from the 6 sites differed significantly in the intercept or in the slopes of their species-area regressions.The greater intercept and slope values of their species-area regression were found in grasshopper assemblages on ungrazed sites.In contrast to species-area relationship regression,the species increase rate with individual number was more rapid at overgrazed sites.Implications for conservation are discussed.

Ecosystem Services of Grazed Grasslands in the Flooding Pampa

The Flooding Pampa grasslands are the last remnant of the Rio de la Plata grasslands in Argentina.Anthropo-genic interventions have led to severe degradation and,as a result,the ecosystem services provided by the grass-lands are declining,in terms of provisioning,regulating,and supporting services.We synthesized the existing literature on the ecosystem goods and services provided by these grasslands under grazing in different conditions and conservation status.We found that plant and animal diversity and primary production are the most studied ecosystem services,while climate regulation,water supply,nutrient cycling,meat production and erosion control,in that order,are less studied.Cultural services are under-researched.Continuous grazing and glyphosate spraying are the main drivers of grassland degradation.Controlled grazing and conservative stocking rates have been shown to reverse degradation and demonstrate that livestock production is compatible with ecosystem conserva-tion by maintaining regulating and provisioning services.As these management strategies are poorly integrated,improving their implementation will require important changes in farmers’decisions and the development of policies that create the economic conditions for this to happen.Research is needed to understand the conditions that prevent the knowledge generated from being transferred to producers and translated into practices that would improve the provision of ecosystem services.

人工混播草地土壤丛枝菌根真菌对轮牧的响应

为探究轮牧对人工混播草地生态系统中植被群落及土壤丛枝菌根(arbuscular mycorrhiza,AM)真菌群落的影响机制,以宁夏盐池县人工混播草地为试验对象,采用单因素随机区组设计,设置T1(无芒雀麦+新麦草+紫羊茅+苜蓿+菊苣)、T2(垂穗披碱草+新麦草+早熟禾+苜蓿+鹰嘴紫云英)、T3(扁穗冰草+新麦草+蒙古冰草+苜蓿)3种混播组合模式,并通过Illumina高通量测序和生物信息学分析,开展轮牧影响下3种人工混播草地土壤AM真菌群落差异性研究,分析人工混播草地生态系统中植被-土壤-AM真菌群落的相互作用关系。结果表明:连续2年轮牧对植被群落生物量产生了显著影响,与轮牧第1年相比,豆科植被群落的相对重要值降低,但禾本科植被群落的相对重要值分别增加了51.16%、81.25%和33.33%。土壤AM真菌中球囊霉属和类球囊霉属为优势属;与轮牧第1年相比,连续轮牧2年后,T1处理的土壤AM真菌群落Chao 1指数较第1年显著降低了12.35%,T3处理的土壤AM真菌群落Chao 1指数、香农-维纳指数、均匀度指数和物种数较第1年分别提升了20.73%、12.80%、7.69%和31.16%(P<0.05),说明T3处理的土壤AM真菌群落对轮牧的响应更加敏感。随轮牧年限增加,T1与T2处理的土壤AM真菌群落组成相似性增加,T1与T3处理的土壤AM真菌群落组成相似性差异较大。连续轮牧2年后,土壤养分对AM真菌群落丰富度的作用强度减弱,但植被群落多样性和植被群落生物量对AM真菌群落丰富度及其组成的作用强度增强;驱动AM真菌群落变化的环境因子由土壤有效磷(p=0.006)和碱解氮(p=0.016)转变为植被群落生物量(p=0.036)。综上所述,不同类型人工混播草地植被群落和土壤AM真菌群落对轮牧表现出不同的响应特征,其中以T3混播组合处理的效果较好。

草地放牧饲养要素分析

饲养牲畜是草地放牧的目标,放牧饲养牲畜是草地饲草资源利用的最有效途径。放牧饲养要素包括草地生产率、适宜载畜率、饲草质量、牲畜生长需要和采食量及放牧方式。本文对这些要素进行了归纳分析,目的在于推进发展草地放牧饲养理论并推导草地生产和保护性利用的关键技术。本文介绍了草地生产率研究方法、适宜载畜率确定标准、划区轮牧区块数计算方法及间歇休牧期和放牧期确定方法。草地放牧饲养理论:基于土壤和气候,改善草地生产和饲草质量,制定适宜载畜率,确定合理放牧方式,满足放牧牲畜最佳生长需要,并维持草地健康,实现“双赢”或“三赢”。草地保护性利用关键技术:放牧场或割草场施肥,调整适宜的载畜率,延迟放牧及间歇休牧,确切的划区轮牧体系,放牧场和割草场等量配置,二时段饲养模式。

转入草场对牧户草场放牧强度的影响--基于自有草场和转入草场视角

【目的】探析牧户对自有草场和转入草场利用强度的差异问题,从而正确认识草场流转真实效应,推动草场流转走向规范化和促进草原生态环境改善。【方法】基于对内蒙古西乌珠穆沁旗6个苏木(镇)的实地调研数据,采用倾向得分匹配法(PSM),分析草场地块使用权属性对牧户放牧强度的影响,并在此基础上运用普通最小二乘法(OLS)进一步分析不同契约安排对牧户在转入草场放牧强度可能发挥的作用。【结果】牧户在自有草场和转入草场上的放牧强度有所差异。转入草场后,牧户会降低自有草场的放牧强度,倾向于在转入草场上放养更多的牲畜;不同契约安排对转入草场放牧强度的影响存在区别。签订书面契约和流转来源于亲戚熟人可在一定程度上约束牧户的放牧强度,而约定流转年限对牧户放牧强度未产生显著的影响。【结论】在后续草场流转的过程中,要重点关注转入草场使用程度监管、增强流转合同的约束力及对新型畜牧业经营主体的支持力度。

超声波干涉及可视化实验装置研制

为了丰富大学物理声学实验内容,研制了一种多功能超声波干涉实验装置。基于空气介质设计了双振子干涉声速测量实验和半波损失验证实验。分别采用干涉声场测量法和干涉条纹移动法进行声速测量实验,并利用示波器实现了干涉声场声压分布的可视化。分别以有机玻璃、橡胶和玻璃为反射面材料,利用干涉法验证掠入射条件下的半波损失现象,并估算出掠入射角的范围。该实验装置实验现象明显、可操作性强,获评北京市第十六届大学生物理实验竞赛一等奖。

不同放牧强度对短花针茅荒漠草原生物多样性的影响

生物多样性对维持生态系统功能与服务至关重要,结合物种、谱系及功能多样性理解群落构建十分必要。本研究以内蒙古短花针茅(Stipa breviflora)荒漠草原植物群落为对象,研究了对照、轻度、中度及重度放牧下不同维度生物多样性对不同载畜率的响应。研究结果表明:各放牧处理均显著降低物种丰富度、Simpson、Shannon-Wiener及Pielou指数。此外,中度和重度放牧处理均降低了谱系多样性。各放牧处理均显著降低了群落功能丰富度(FRic)、功能分异度(FDiv)、功能分散指数(FDis)及Rao二次熵指数(RaoQ);中度和重度放牧处理显著降低了群落功能均匀度(FEve)。总体而言,随放牧强度的增大,群落功能多样性呈现出逐渐降低的趋势。此外,物种、谱系及功能多样性之间存在显著或极显著的相关性。总之,对不同维度生物多样性的分析有利于理解植物群落构建机制,为草地合理利用及可持续性提供一定的理论基础。

放牧强度对优势种群与植物群落地上现存量关系的影响

为探究优势种对植物群落结构和功能的影响,本研究以内蒙古短花针茅草原为研究对象,整理不同降水年份(2014—2016年)和4个放牧试验区(对照,Control,CK;轻度放牧,Light grazing,LG;中度放牧,Moderate grazing,MG;重度放牧,Heavy grazing,HG)下优势种群和植物群落地上现存量数据,采用对比分析和数据包络(CCR模型)分析,发现伴随放牧强度和降水量的变化,不同优势种群地上现存量的响应存在差异。LG区下的短花针茅和无芒隐子草的地上现存量高于CK、MG和HG区。冷蒿的地上现存量对放牧响应的敏感性高于短花针茅和无芒隐子草。受放牧强度影响,植物群落地上现存量由短花针茅、无芒隐子草和冷蒿这三种优势种的调控转为主要以短花针茅调控。重牧和极端干旱年份导致优势种与植物群落地上现存量的双向协调作用丧失。

基于草本群落、牧道特征对野果林放牧干扰强度的评价

客观、综合评价野果林放牧强度对正确认识林牧矛盾,制定科学合理的放牧制度具有重要意义。目前的研究主要集中在野果林放牧对植被群落特征和物种多样性影响上,然而野果林放牧活动本身的关注以及放牧强度的量化方法等方面尚不明确。基于此以新疆野果林6个典型放牧区为试验地,分析对比各放牧区的草本群落组成结构、生长特征、物种多样性以及牧道特征,并筛选出评价放牧干扰强度的主导因子,对其放牧干扰强度进行定量评价。结果表明:(1)草本群落特征方面,杏花沟物种数最多,且以禾本科种属植物为优势种;但莫乎儿沟草本密度比杏花沟高1.26%;各放牧区物种多样性水平存在显著差异,与其他放牧区相比,莫乎儿沟Shannon-Wiener多样性、Simpson优势度指数最高,分别为1.92、0.84,而吾都布拉克沟的Pielou均匀度指数最大;(2)牧道特征方面,伊勒格代沟的牧道密度显著大于匹里青沟,分别为19.23%、14.77%,而杏花沟的牧道宽度显著大于大西沟;在牧道分布格局上,除匹里青沟外,其他放牧区皆为均匀分布;(3)相关性分析表明草本群落结构特征、物种多样性水平及牧道特征指标间均存在较好的相关关系,对其12个指标主成分分析筛选出草本群落盖度、生物量、Shannon-Wiener多样性指数、Simpson优势度指数以及牧道密度与格局指数可作为评价放牧干扰强度的主导因子,依据牧压指数判定杏花沟与莫乎儿沟为轻、中度放牧干扰,大西沟、伊勒戈代沟、吾都布拉克沟与匹里青沟为重度或极度放牧干扰。当前新疆野果林整体受到放牧重度干扰,急需优化或者制定科学的放牧制度维护野果林的可持续发展。

放牧对荒漠草原蝗虫种群动态及多样性的影响

基于2004年短花针茅(Stipa breviflora)荒漠草原建立的长期放牧试验平台,放牧牲畜为绵羊(Ovis aries),调查了放牧期不同放牧强度下蝗虫的种群动态及多度。该试验设置4个放牧梯度:不放牧(CK)、轻度放牧(LG)、中度放牧(MG)和重度放牧(HG),放牧强度分别为0、0.91、1.82和2.71羊单位/hm^(2)。结果表明:CK区优势种蝗虫为宽须蚁蝗(Myrmeleotettix palpalis)、短星翅蝗(Calliptamus abbreviatus)和毛足棒角蝗(Dasyhippus barbipes),在放牧影响下短星翅蝗的优势程度逐渐被亚洲小车蝗(Oedaleus asiaticus)取代。在4种优势种蝗虫发生的高峰期,MG和HG显著增加了宽须蚁蝗、毛足棒角蝗和亚洲小车蝗的多度,而短星翅蝗的多度则在放牧作用下显著降低(P<0.05)。蝗虫的多样性随放牧强度的增大逐渐降低,且与植物的多样性呈显著正相关(P<0.05)。研究表明荒漠草原优势种蝗虫多度对不同放牧强度响应并不一致,高放牧强度会降低蝗虫的多样性,改变蝗虫的优势种。

不同放牧管理方式对新疆山地草原植物群落特征的影响

本研究基于巴里坤县国家级山地草原监测站10 a植物群落观测数据,探究了长期不同放牧管理方式(长期禁牧M0、冬季放牧M1和全年放牧M2)对新疆山地草原植物群落特征值、植物多样性及多样性与地上生物量之间关系的影响。结果表明:M0、M1和M2对优势种沙生针茅重要值无显著影响,M1和M2提高了非优势及草地退化的指示物种芨芨草、醉马草的重要值;随着放牧强度的增加,群落高度、盖度、密度、地上生物量及其响应比显著下降;Shannon-Wiener多样性指数、Simpson优势度指数和Pielou均匀度指数在各放牧处理下均无显著差异,但Margalef丰富度指数随放牧强度显著增加;M0处理地上生物量与Simpson优势度指数、Shannon-Wiener多样性指数和Pielou均匀度指数负相关,M1处理地上生物量与Margalef丰富度指数负相关。随着处理时间的增加,长期禁牧有利于退化草地的恢复,提高了群落特征值,在一定程度上有利于草地生产力的提高和群落稳定性的维持;放牧会影响生态系统中资源的再分配,导致物种多样性的增加,但是全年放牧管理方式下草地则退化加剧。

大掠射角对海雷达导引头实测回波特性分析

大掠射角下,对海雷达导引头观测到的海杂波强度激增,舰船目标检测困难。本文结合全极化雷达导引头挂飞实测数据,分析了回波幅度和相位特性。首先,采用典型分布对回波幅度分布进行拟合,并利用拟合优度对拟合效果作出评估;然后,分析了平均相位变化量。结果表明:在大掠射角条件下,雷达导引头各极化通道海杂波幅度服从K分布;海杂波与舰船回波幅度在同极化通道服从K分布,在交叉极化通道服从对数正态分布;交叉极化通道回波信杂比高于同极化通道;海杂波与舰船回波相位平均变化量小于海杂波。

放牧家畜采食量估测方法研究进展

放牧家畜采食量是评价草地生态系统转化效率和动物生产力的主要参数,受草地植被生长情况、环境条件、放牧方式、家畜生理特征及其瘤胃内环境等因素影响。放牧家畜采食量的准确测定一直以来都是食性研究的难点和热点问题,关系到动物营养状态的评估、补饲策略的制定以及食性理论的探索。传统采食量估测方法大多基于观察法或放牧前后牧草生物量差值法,这些方法对动物的干扰较小,但是受技术本身和适用范围的限制,如未能估测单个动物的采食量,很难适用于大范围的采食量估测。链烷烃技术和近红外技术的出现为准确测定采食量提供了前所未有的机遇,不仅能克服传统测定方法的缺点,还在准确率、适用范围(圈养动物和放牧动物)等方面优势较为明显,但由于粪便回收率和数据库完整性等因素的影响,目前应用于生物多样性较高草地的放牧动物采食量估测尚有难度。在简要总结不同方法的原理和影响因素基础上,综述了差值法、内标法、链烷烃法和近红外法在放牧家畜采食量测定方面取得的最新进展及存在的问题,并建议多种方法结合可以准确测定放牧家畜采食量,以期为制定合理的草地生态系统管理策略和实现草地可持续生态服务功能提供新思路和启发。

塑性冲击振动系统的非光滑分岔

考虑塑性碰撞工况下的单自由度冲击振动系统,推导了擦边分岔和余维一滑动分岔的条件。结合二维参数和单参数分岔分析,研究了单冲击周期运动的分岔特征,揭示了冲击振动系统的穿越滑动分岔、切换滑动分岔和余维二滑动分岔等非光滑分岔以及擦边分岔和混沌激变等不连续分岔行为。非黏滞型周期运动与黏滞型周期运动经穿越滑动分岔相互转迁。在二维参数平面的低频小间隙区域,(1,1,1)周期运动与(1,2,1)周期运动交替出现。两类周期运动的临界线为切换滑动分岔线。混沌边界激变导致混沌吸引子及其吸引域突然消失。