青海三江源区果洛藏族自治州草地退化成因分析

本文利用长期历史资料,通过分析气候变化和人类放牧活动对草地生产力的影响,探讨1960s以来青海三江源区果洛藏族自治州草地退化主要原因,结果显示：研究区是全球变暖的敏感地区,1961-2010年研究区气温升高、年降水略有下降、湿润程度下降,Miami模型、Thornthwaite Memorial模型和综合自然植被净第一性生产力模型（综合模型）模拟的该区植被净初级生产力（NPP）均具有上升趋势,近50年来研究区气候变化总体上有利于该区草地生产力改善;研究区家畜年末存栏数60年代剧烈上升,至70年代达到顶峰,家畜年末存栏数与植被NDVI呈极显著负相关关系(P<0.01),草地实际载畜量过大造成牲畜对草地过度啃食,导致草地退化。研究区退化草地恢复治理的重点应放在减轻载畜压力、控制草地现实载畜量方面。     

Quantitative assessment of the individual contribution of climate and human factors to desertification in northwest China using net primary productivity as an indicator

An accurate quantitative assessment of the relative roles of climate change and human activities in desertification is significant to understand the driving mechanisms deeply and control desertification development. In this study, we selected net primary productivity (NPP) as an indicator to discriminate the relative roles of climate and human factors in desertification during 2001–2010 in northwest China. The potential NPP and the difference between potential and actual NPPs were used to represent the impacts of climate change and human activities on desertification. Desertification expanded on 55.8% of the study area, within which 70.3% of the desertification expansion was caused by human activities compared with only 21.7% induced by climate change. On the contrary, 42.1% of desertification reversion was caused by human activities and 48.4% resulted from climate changes. The NPP variation also could be calculated to assess the relative roles and showed that 69% of NPP decrease was caused by human impacts compared with 15.2% induced by climate change. By contrast, 23.9% of NPP increase was caused by climate change, whereas 54% resulted from human activities. In addition, the relative roles of two factors possessed great spatial heterogeneity in six provinces. We developed three propositions. First, the desertification expansion was dominated by human activities, whereas desertification reversion was dominated by climate change, as typified by Xinjiang, Qinghai, and Gansu. Second, both desertification expansion and reversion were induced by human activities, as typified by the west of Inner Mongolia and Shaanxi. Third, climate change dominated the desertification expansion in Ningxia province.     

黄河源区玛多县草地退化成因分析

对黄河区玛多县草地退化的自然和人为因素作了深入分析。结果表明,过度放牧是导致玛多县草地退化的主要原因,自20世纪80年代末期以来,玛多县温度和降水较历史平均水平均有较大幅度的提高,其中温度增加表现为明显的暖冬现象,降水增加集中在春夏两季,水热条件的变化是向着利于草地恢复的方向发展的,由于玛多县是一个纯牧业县,扩大畜群数量是经济增长的必然选择,加上人口压力和当地藏族居民的传统价值观,驱使牧畜数量不断扩大,并在70年代末达到最大值,此后长期维持过牧状态,造成草地持续退化,过牧在导致草地退化的同时,也为鼠类的侵入创造了条件,从而加强了退化过程。     

藏北那曲地区草地退化动态评价

利用1982—2000年NOAA/AVHRR 第1通道、第2通道和NDVI的旬资料反演得到的藏北那曲地区历年植被覆盖度、年最大牧草鲜质量和6—9月平均改进型土壤调节植被指数,分析了近20年来那曲地区草地荒漠化的动态变化规律.结果表明：以草地荒漠化评价“基准”和5年滑动平均的方法,得到那曲地区近20年平均草地退化面积占土地总面积的43.1%,草地退化面积总体呈减少趋势,其中前10年呈减少趋势,后10年呈增加趋势,西部地区的退化面积大于其它地区.在气温、降水、潜在蒸散、水汽压、风速、日照时数、降水蒸散比和温度降水比8个气候因子中,潜在蒸散量对草地退化面积的影响最显著.     

我国三北地区植被变化的动因分析

地表植被变化是气候变化、人类活动等多种因素共同作的结果。然而,以往的研究要么集中在与气候变化有关的气象因素,要么集中在与人类活动有关的人为因素,鲜有基于长期数据监测下对自然与社会因素之间相互作用的定量评估。因此,气候变化和人为因素对地表植被变化的相互作用并不明确,各个因素对植被变化影响的量化贡献仍然不确定。为了评价生态修复项目对荒漠化防治的效果、以及在土地荒漠化防治中自然与社会因素对我国植被变化的影响、及其复杂的相互作用机理,该研究应用卫星遥感影像资料,通过面板数据混合回归模型大数据分析方法,计算了1983年至2012年气候变化和人类活动对我国北方地区植被变化的贡献率。结果表明,气候变化和人类活动对NDVI变化均有重要作用,其中人类活动对植被覆盖度变化的影响占58.2%—90.4%、气候变化占9.6%—41.8%;不同地区表现出不同的地理分异特征,并存在时滞效应。由此可见,荒漠化防治必须充分考虑不同因素的综合作用和地域特征,才能取得事半功倍的效果。研究结果较好地体现了卫星遥感影像资料在大尺度(省域尺度)下与社会经济统计指标的融合,为进一步中尺度(县域尺度)研究提供了方法借鉴。     

利用草场健康指数监测典型草原的植被退化

利用表征群落总量、放牧退化的主成份和草场健康指数(Grassland Health Index,GHI)与样方光谱反射率之间的相关性,建立了GHI与可见光、红外光因子的回归模型。应用此模型结合TM卫星遥感数据计算GHI,并与同一TM影像的计算出的NDVI作对比研究。研究发现GHI在反映放牧等人为干扰因素对草原植被的影响效应方面比NDVI有明显的优点。此外,GHI对植被分布格局,特别是斑块结构有更好的显示效果。应用GHI到历史TM数据,对所研究地域的植被覆盖变化、农牧业的变迁模式等进行了定性研究。研究发现,有较长放牧史的过度放牧区的植被类型没有沿牧压梯度的规律性分布,而是呈随机斑块模式分布。     

人工草地在退化草地恢复中的作用及其研究现状

分析了草地类型生态系统退化的现状、原因及其恢复途径,提出人工草地的建立是恢复退化天然草地的有效途径;综述了人工草地的研究进展。提出高效型人工草地的建立是缓解草原压力、促进牧区可持续发展的良策;从高效角度出发。种植饲用玉米可以作为建立人工草地的一个有益尝试．     

青藏高原植被退化对高原及周边地区大气环流的影响

利用耦合了陆面模式的大气环流模式,结合青藏高原植被退化的范围和程度,通过在模式中修改高原地区(27°—40°N,75°—100°E)的叶面积指数的方法,探讨了植被退化以后对高原及其附近地区上空大气环流的影响。结果表明,该模式对高原地表温度场具有很强的模拟能力,并且能够很好地模拟出青藏高原及附近地区夏季位势高度场的平均特征及南亚高压的位置和强度,但南亚高压中心强度偏大且略微西退。在青藏高原植被出现退化以后,高原整体地表土壤温度和地表2 m空气温度升高,感热通量增加、潜热通量减小,进而改变了高原地区的波文比。地表感热增加导致高原及附近地区500 h Pa高度场降低和200 h Pa高度场升高,并在200 h Pa上存在强大的反气旋性环流异常,导致南亚高压增强和北扩东伸。植被退化造成的青藏高原感热增加导致了高原南部上升运动增强和北部上升运动减弱,同时又引起高原以北地区下沉气流的影响范围扩大,而下沉气流的强度减弱,其结果有助于高原以北的干旱范围扩大,而干旱程度却得到缓解。     

Long‐term dynamics of the hemiparasite Rhinanthus angustifolius and its relationship with vegetation structure

Questions: 1. How are the long‐term dynamics of the root hemiparasite Rhinanthus angustifolius related to vegetation structure, grassland management and climate? 2. Does R. angustifolius have a long‐term impact on standing crop and community composition? Location : A formerly fertilized grassland, part of a larger brook valley system in the nature reserve ‘Drentsche Aa’, near Groningen, The Netherlands. Methods : Vegetation development has been monitored since 1973 in 54 permanent plots in nine management regimes without fertilizer application. Results : 1. The hemiparasite established when standing crop was less than 600 g.m^?2 and performed best under annual haymaking using machinery. Since its appearance, the population fluctuated stochastically, with two peaks. Coinciding collapses in six adjacent grasslands and comparison with an integrated climatic index suggest that the population collapses are induced by spring drought. 2. We did not find a relationship between total standing crop and R. angustifolius cover. Cover of grasses was negatively related to the abundance of the hemiparasite in the same and the previous year. Forb cover tended to increase with the parasite. Conclusions : R. angustifolius shows stochastic population fluctuations, mainly determined by spring drought, to which this species is probably highly vulnerable because of its parasitic and annual life style without a persistent seed bank. The hemiparasite also shows long‐term relationships with grass cover (negative) and forb cover (positive), but it seems to have no lasting impact on standing crop.     

Non-stomatal limitations of photosynthesis in grassland species under artificial drought in the field

As drought stress is expected to occur more frequently in future climate in central Europe, survival and productivity of grassland species are an important issue. Non-stomatal limitation processes related to the drought-stress inhibition of photosynthesis of selected grassland species were analysed at three locations using leaf gas exchange and chlorophyll fluorescence. The effect of an artificial drought on the non-stomatal limitations differed considerably between species present in the same grassland plot. The maximum efficiency of photosystem II (F_v/F_m), indicator for the intactness of the photosynthetic electron transport, showed only small differences under drought. On the other hand, more pronounced effects were observed for the carboxylation velocity of Rubisco (V_c,max). V_c,max was in Phleum pratense about 20% lower under drought than in control plants, while other species in the same plot were far less affected. The carboxylation velocity of Rubisco is highly sensitive to water deficit and might represent a tool to evaluate the drought response of various species in order to address the performance of grasslands.     

我国北方草原沙漠化过程中土壤碳、氮变化规律研究

对内蒙古锡林郭勒盟多伦县境内75个样点土壤质地、全碳、全氮的测定和地上植被状况分析结果表明,草原沙漠化过程不同阶段的变化体现在土壤氮、碳、粘粒含量的有规律变化,土壤氮、碳含量减少、质地变粗;土壤氮、碳含量与粘粒含量间呈显著相关性,氮含量与粘粒含量间的相关系数(0．901)分别大于碳、氮含量间的相关系数(0．627)和碳含量与粘粒含量间的相关系数(0．642)．土壤中粘粒含量显著减少．土壤中氮元素的衰减比碳元素明显;沙质草原沙漠化不同阶段的C／N比呈现增加的趋势．     

Effects of grassland degradation and precipitation on carbon storage distributions in a semi-arid temperate grassland of Inner Mongolia,China

Environmental degradation influences carbon (C) cycling and storage in grassland ecosystems by altering vegetation productivity. However, the impacts of different degradation intensities on vegetation–soil C distributions in grasslands have not been well documented. We measured C storage in soil, roots, and plants under light, moderate, and severe degradation levels in a typical steppe region of Xilinhot, Inner Mongolia, China in 2011 and 2012. Grassland C storage was highest in soil, followed by roots, and then aboveground plant biomass. Grassland degradation and precipitation significantly influenced C storage distributions. During the dry year (2011), total C storage in vegetation and soil was highest under light degradation. Carbon storage in aboveground plant biomass and roots increased with degradation intensity. During the wet year (2012), C storage was highest in aboveground plant biomass and roots under light degradation. Root biomass tended to be concentrated in the soil surface during the wet year.     

地表水热要素在青藏高原草地退化中的作用

在全球气候变暖和频繁的人类活动影响下,青藏高原草地生态系统发生了生产力下降、生物多样性减少及生态功能退化等一系列现象。与传统观测技术相比,遥感技术具有大范围、快速和连续监测等优点,因此被广泛用于区域尺度的草地植被长时间序列监测。以往对青藏高原草原植被影响因子的研究多集中在气温与降水,而相比较于气温和降水,地表温度和土壤湿度直接作用于植物的根部,对植物种子的萌芽和植株的生长也都有着重要影响,所以地表温度和土壤湿度与植被生长的关系更加紧密。基于遥感技术,利用青藏高原草地区域的MODIS和AVHRR数据,选择草地植被覆盖度作为草地退化的遥感监测指标,建立了青藏高原草地退化遥感监测和评价指标体系,并对青藏高原2001-2017年的草地退化状况进行了遥感监测和评价。同时,利用遥感数据获取青藏高原区域尺度的地表温度和温度植被干旱指数数据,用于指示地表水热状况,最后基于回归方法分析了地表水热要素在青藏高原草地退化中的作用。结果表明：从2001-2017年,青藏高原植被退化程度空间差异明显,柴达木盆地和青海湖附近退化较为严重,喜马拉雅山脉北部、昆仑山脉南部、冈底斯山脉北部交汇的地区退化也较严重。在2001-2017年间,青藏高原草地未退化面积从50.60%上升到59.00%,说明青藏高原草地整体上在朝着改善的方向发展。2001-2017年内,青藏高原草地整体上大部分时间处于轻度退化状态,但是2001年和2015年这两个年份青藏高原草地退化整体上达到中等退化水平。通过回归分析发现,土壤湿度主导的对青藏高原草地的影响面积达到14.04%。地表温度主导的影响面积达到草地总面积的约36.61%。但地表温度与植被之间相互影响,且主要呈现负相关关系。其中,在温性草甸地区,当植被覆盖度较低时,地表温度正向影响植被生长。     

青藏高原典型草地植被退化与土壤退化研究

采用野外样方调查和室内分析法,探讨了青藏高原不同退化程度高寒草原和高寒草甸植被群落结构、植物多样性、地上-地下生物量、根系分配及土壤理化特性差异。研究表明:(1)随着退化程度加剧,高寒草原禾草优势地位未改变,高寒草甸优势种莎草逐渐被杂类草取代。(2)随着退化程度加剧,高寒草原地上生物量显著降低(P<0.05),高寒草甸地上生物量先保持稳定再下降。高寒草甸地下生物量较高寒草原地下生物量对退化响应更敏感。(3)高寒草原退化过程中,莎草地上物生量变化不明显(P>0.05),禾草地上生物量贡献率由88.12%减少至53.54%,杂类草地上生物量贡献率由0.08%增加至42.81%;高寒草甸退化过程中,禾草和杂类草地上生物量先增加后减小,莎草地上生物量占比由69.15%减少至0.04%,杂类草地上生物量占比由12.56%增加至92.61%。(4)随着退化程度加剧,高寒草原根系向浅层迁移,高寒草甸根系向深层迁移。(5)退化对高寒草甸土壤含水量(θ)、土壤有机碳(SOC)、总氮(TN)及土壤容重(BD)影响均比高寒草原更强烈。本研究对青藏高原退化草地恢复治理具有重要的参考价值。     

IPBES土地退化和恢复专题评估报告及其潜在影响

随着国际社会对生物多样性保护和人类福祉关注度的提升, 土地退化作为全球面临的重要问题逐渐成为国际公约和进程关注的热点问题。生物多样性和生态系统服务政府间科学政策平台(Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, IPBES)将“土地退化和恢复”列入2014-2018年工作方案, 开展评估。2018年3月, 该评估报告在IPBES第六次全体会议上获得通过。本文概述了评估报告的主要内容和结论, 探讨了对其他国际进程的可能影响。评估报告在IPBES概念框架的基础上, 厘清了土地退化的概念与内涵, 全面梳理了土地退化对人类生活质量的影响, 阐明了土地退化的现状和进程, 分析了直接和间接驱动因素与土地退化的作用, 揭示了土地退化与人类福祉的关系, 提出了土地退化和恢复的对策建议。该项评估将为各国决策者制定政策工具提供最有效的技术支撑, 为相关国际进程谈判提供重要的科学参考。中国作为生物多样性大国, 应重视IPBES的评估机制并积极参与, 加强促进生物多样性和生态系统服务领域的科学成果转化, 适时针对国内关键问题启动相关评估, 促进我国生态文明建设和山水林田湖草系统治理, 实现美丽中国的建设目标。     

Micro-patterns in grassland vegetation created and sustained by sheep-grazing

An initially uniform Holcus lanatus-dominated sward came partly under hay-making and partly under sheep-grazing. Preferential grazing by sheep resulted in grazing at different intensities giving rise to a macro-pattern of various plant communities. Besides this macro-pattern a micro-pattern developed in the grazed area, which was absent under hay-making. In the micro-pattern short, heavily grazed areas alternated with taller, lightly grazed patches, both having the same species composition. The heavily grazed area was characterized by equal amounts of monocots and dicots. The lightly grazed patches were dominated by Agrostis tenuis, and had a large amount of litter which probably causes the absence of mosses. The protein percentage of green material is higher in the heavily grazed areas than in the lightly grazed patches.Sequential charting indicated that the micro-pattern was more or less stable. An interaction between the vegetation micro-pattern and grazing patterns is suggested. Heavy grazing results in forage with a high protein content and hence attracts animals. Light grazing results in forage with a relatively low protein content, animals avoid the area and litter accumulates.Nomenclature follows Heukels & van Ooststroom (1977) Flora van Nederland.Mrs J. O'Brien corrected the English text     

The elevation history of the Tibetan Plateau and its implications for the Asian monsoon

The determination of the evolving palaeoaltitude of the Tibetan Plateau since the India-Eurasia collision underpins our understanding of how orography in central Asia affects the intensity of the monsoon and hence global climate change. Palaeoaltitudes, however, cannot be measured directly and need to be inferred from proxy observations that are usually model-dependent. Differing tectonic models for the behaviour of the lithosphere during continental collision have contrasting implications for the elevation of the plateau. However, two techniques recently employed for determining palaeo-elevation are independent of tectonic models, the first involving the variation with altitude of oxygen isotopes in precipitation and the second involving the change of leaf morphology with moist static energy of the atmosphere.Elevation studies have focused on southern Tibet, largely due to the relative ease of access to the region. There is a remarkable unanimity amongst the diverse techniques applied that the altitude of the southern plateau has not significantly changed since at least the mid Miocene (ca. 15 Ma) arguing for an onset of the monsoon system during or before the early Miocene. A range of tectonic studies suggest that the northern and eastern parts of the plateau are younger geomorphological features, but there are few quantitative constraints of the timing of elevation from these regions of Tibet. Since both the elevation and the surface area of the plateau impact on atmospheric circulation, palaeoaltitude studies need to be extended to chart the increasing areas of elevated land surface through time.     

21世纪初我国草地生态学研究展望

草地退化是我国天然草地面临的突出问题,在21世纪初期,我国的草地生态学将围绕解决草地退化这一核心问题展开深入的研究。其热点领域应在草地恢复生态学,草地界面生态学,草地放牧生态学,草地的健康诊断和草地的价值评估等5个方面。其中草地恢复生态学是治理退化草地的基础;草地界面生态学是剖析退化草地的切入点;草地放牧生态学是调控退化草地的手段;草地健康诊断有助于对草地退化进行客观评价;草地的价值评估则是对草地生态系统效益和服务的估算。     

青藏高原草地退化特征及其与气候因子的关系

了解草地退化的分布、特征、变化趋势及持续性,揭示草地退化机理,可为有效管理和保护草地提供重要的科学依据。本研究选择草地覆盖度作为草地退化的遥感监测指标,建立了草地退化遥感监测和评价指标体系,对青藏高原草地退化现状(2016—2020年)进行了评价,利用线性回归和Hurst指数分析了长时间序列尺度上(1982—2020年)草地覆盖度变化的趋势及持续性,并且基于草地覆盖度与气候因子的偏相关分析,研究了气候因子对草地退化的影响。结果表明: 2016—2020年,平均草地退化面积达24.3%,主要表现为轻度退化和中度退化,主要分布在低海拔和高植被覆盖地区。1982—2020年,草地覆盖度在青藏高原北部、西部和西南部地区呈增加趋势,在东部和中部地区呈减少趋势。98.1%的地区草地覆盖度的Hurst指数小于0.5,草地覆盖度变化表现出反持续性。草地覆盖度与降水量的偏相关系数(0.096)整体高于其与温度的偏相关系数(-0.033),温度占主导地位的面积占比为16.0%,主要分布在青藏高原的中部和东南部,降水量占主导地位的面积占比为12.2%,主要分布在青藏高原东北部和西部。     

植被退化对滇西北高寒草地土壤微生物群落的影响

【目的】在同尺度下比较我国滇西北高寒草地土壤(GS)及其退化土壤(DGS)中细菌和真菌群落,研究植被退化对高寒草地土壤微生物群落的影响,并探索其环境驱动因子。【方法】分别以16SrRNA基因和ITS基因作为细菌和真菌分子生态学分析的靶标基因,采用定量PCR法测定基因数量来表征微生物群落丰度,采用Illumina Hiseq测序及生物信息学分析研究土壤微生物群落组成和群落结构。【结果】草地退化后,土壤pH值显著上升0.65个单位,土壤水分、总有机碳、可溶性氮含量和C/N比分别显著下降了18.4%、67.5%、47.2%和71.2%;草地退化显著降低了土壤细菌和真菌群落丰度,降低幅度分别为92.4%和94.9%;草地退化没有影响土壤细菌和真菌群落α-多样性,但显著改变了细菌和真菌群落β-多样性(群落结构);草地退化改变了土壤细菌和真菌在OTU水平上的物种组成,土壤真菌OTU种类变化更为显著;草地退化没有影响土壤细菌在门水平上的群落组成,但改变了细菌在纲水平上的群落组成(如Acidimicrobiia、Betaproteobacteria、Chloroplast等);草地退化没有影响土壤真菌在门水平和纲水平上的群落组成。【结论】本研究发现植被退化后滇西北高寒草地土壤质量显著降低,寄居在土壤中的微生物群落丰度也显著降低、微生物群落结构明显改变。