空间粒度变化对景观格局分析的影响

认识空间异质性的多尺度依赖性和景观格局特征对尺度效应关系的影响是进行空间尺度推绎的基础。以2种真实景观(中国广东粤北植被景观与美国凤凰城城市景观)和SIMMAP景观中性模型产生的27种模拟景观为对象。利用景观格局分析软件FRAGSTATS对18种常用景观指数的尺度效应进行了系统的分析。根据这些指数对空间粒度变化的响应曲线和尺度效应关系,18种景观指数可分为3类。第1类指数随空间粒度的增大单调减小。具有比较明确的尺度效应关系(幂函数下降),尺度效应关系受景观空间格局特征的影响较小;这类指数包括缀块数、缀块密度、边界总长、边界密度、景观形状指数、缀块面积变异系数、面积加权平均缀块形状指数、平均缀块分维数和面积加权平均缀块分维数。第2类指数随空间粒度的增大将最终下降。但不是单调下降的;尺度效应关系比较多样,可表现为幂函数下降、直线下降或阶梯形下降。主要受缀块空间分布方式和缀块类优势度的交互影响;这类指数有5种：平均缀块形状指数、双对数回归分维数、缀块丰度、缀块丰度密度和Shannon多样性指数。第3类指数随空间粒度的变粗而增加。随缀块类优势度均等性的增加。尺度效应关系由阶梯形增加、对数函数增加、直线增加向幂函数增加过渡。尺度效应关系主要受缀块类优势度的影响;此类指数包括平均缀块面积、缀块面积标准差、最大缀块指数与聚集度。景观指数随空间粒度变化是一种1临界现象,当粒度大于或小于1临界值时,景观指数对空间粒度变化非常敏感。变化速率非常大。绝大部分情况下。真实景观粒度效应关系和曲线形状与模拟景观所得分析结果相似。说明模拟景观具有很好的代表性。文中也讨论了本研究结果与前人研究的异同。分析了造成差异的原因。景观指数的粒度效应关系与指数本身所反映的景观格局信息有一定关系,总体上来说。随粒度增加。缀块数、边界长度、缀块形状的复杂性、多样性将减小,而平均缀块面积和聚集度将增加。一系列的尺度效应图和不同景观指数的尺度效应关系可作为景观格局分析时指数选择、分析结果的解释和进行空间尺度推绎的参考。     

基于不同零模型的三江平原沼泽湿地主要物种小尺度点格局分析

在三江平原沼泽湿地,基于不同零模型的点格局方法,研究了常年积水环境条件下沼泽湿地主要优势种毛苔草、漂筏苔草、狭叶甜茅以及小叶章种群的空间分布格局特征。结果表明:在0—200cm尺度范围内4种物种基本都偏离完全随机模型,表现为聚集分布,但偏离的程度不同;除了数量最少的小叶章种群外,其他3种物种都在一定尺度上偏离了泊松聚块模型;毛苔草和狭叶甜茅种群在极小尺度上偏离嵌套双聚块模型,但不显著,而漂筏苔草种群在所有尺度上符合嵌套双聚块模型。种群的实测值偏离完全随机模型的程度越大,越有可能符合符合泊松聚块模型,偏离泊松聚块模型的程度越大,越有可能符合嵌套双聚块模型。4种物种在0—200cm尺度范围内形成的聚块是由营养繁殖引起的,多个分株系统组成大聚块,而每个分株系统形成一个小聚块,聚块的形成加剧了种内竞争,使得种群的聚集强度降低。     

草地贪夜蛾幼虫在苗期玉米田的空间分布格局及其抽样技术

草地贪夜蛾Spodoptera frugiperda(Smith)是2019年1月新入侵我国的重要害虫,研究并明确空间格局对确定该虫田间抽样技术、调查虫情具有指导意义。本研究调查获得了玉米苗期喇叭口初期、大喇叭口期草地贪夜蛾幼虫空间分布数据,应用多个聚集指标、Iwao m~*-m模型、Taylor幂法则等方法分析明确了该虫幼虫空间格局,发现苗期整体上幼虫个体群为聚集分布,喇叭口初期为聚集分布而大喇叭口期为均匀分布;苗期整体上及大喇叭口期幼虫聚集度对密度不具依赖性,而喇叭口初期幼虫聚集度对密度具依赖性;同一幼虫密度和误差条件下不同苗期抽样数量显著不同,玉米生育期越早则抽样数量越大。     

云南兰坪云南红豆杉种群年龄结构与空间分布格局分析

利用点格局分析法对滇西北兰坪县4个云南红豆杉(Taxus yunnanensis)种群的年龄结构、不同生长阶段空间分布格局及其关联性进行分析。结果表明:(1)林窗与人为干扰影响4个云南红豆杉种群的龄级结构,小林窗的种群呈稳定型;较大林窗的种群呈进展型;群落结构完整未出现林窗和有较大人为干扰的种群年龄结构均呈衰退型,幼苗、幼树与小树个体缺乏,种群存在一定程度的更新困难,林窗的大小是种群更新的重要因素。(2)人为干扰、自然生境与本身生物学特性影响4个种群空间分布格局,种群1整体及其不同生长阶段个体均呈聚集分布;种群2和种群4在小尺度呈聚集分布,而在大尺度上呈随机分布;种群3随着空间尺度增大分布格局表现为聚集→随机→聚集趋势。(3)种群2中幼苗、小树和中树在小尺度下表现为聚集分布,其他尺度下表现为随机分布;种群3的小树阶段聚集分布和随机分布皆有出现,中树与大树在不同尺度上表现为聚集分布;种群4聚集分布的强度随生长阶段的增加在减弱。(4)4个种群各发育阶段间皆呈或接近显著正相关,种内竞争弱,有利于种群维持。     

湖南省阳明山山顶苔藓矮林优势种空间分布格局

山顶苔藓矮林是亚热带山地常绿阔叶林区在极端气候与环境条件下发育的一种群落变型,通过研究优势植物的分布格局与规模,可以有效地指导植被保护与管理活动。在湖南阳明山国家级自然保护区的山顶苔藓矮林区设置3个样地,应用相邻格子法对优势种云锦杜鹃(Rhododendron fortunei)进行每木调查,在不同取样尺度(面积)上采用方差/均值比率法(v/m)、负二项参数(k)、丛生指数(I)、平均拥挤度(m~*)、聚块性指数(m~*/m)、聚集指数(C_a)和格林指数(GI)等聚集强度指数对云锦杜鹃种群分布格局进行分析。结果表明:阳明山山顶苔藓矮林优势种云锦杜鹃种群在北、南、东三个方位上的空间分布格局总体上为聚集分布,随着取样尺度的增大,聚集格局强度和规模依次减弱;而山顶苔藓矮林优势种群不同年龄阶段的空间分布特征为随着种群年龄的增大,其空间分布格局呈聚集强向聚集弱、以至于向随机分布发展;阳明山山顶苔藓矮林优势种群及其分布格局形成的主要原因是云锦杜鹃种群本身的种子繁殖及传播方式和类营养繁殖等生物学特性及方位、坡向等环境因子影响所致。     

山东省滨海湿地柽柳种群的空间分布格局及其关联性

柽柳(Tamarix chinensis)是暖温带滨海盐碱湿地的先锋灌木物种, 在滨海湿地植物群落演替和防止沿海地区海水入侵中发挥着重要的作用。研究柽柳种群的空间分布格局和不同径级柽柳个体之间的空间关联性, 揭示种群发展规律, 可以为盐碱地柽柳种群的保护提供指导, 并为滨海湿地生态系统的演替和生态管理提供依据。该研究在昌邑国家海洋生态特别保护区核心区内沿平行海岸线方向设置两条间隔800 m左右的样带, 每条样带上设置3个50 m × 50 m的样地, 共设置6块样地进行每木调查, 绘制柽柳种群空间位置分布图, 并将调查的柽柳按照其基径大小分为≤4 cm、4-8 cm、>8 cm 3个不同径级。利用Programita软件对柽柳种群的分布格局以及不同径级间的空间关联性进行分析。结果显示: (1) 6块样地共调查柽柳个体374株; (2)不同样地间柽柳植株密度差别较大, 说明柽柳在区域尺度上的分布并不均匀; (3)柽柳种群在小尺度(小于5 m)上表现为聚集分布, 在大尺度(大于15 m)上表现为随机分布, 总体表现为随空间尺度的增大柽柳种群呈现由聚集分布过渡到随机分布的趋势; (4) 3个径级两两之间在小尺度上表现为正关联, 在大尺度上表现为无关联, 但在15 m尺度上径级II与径级III因为竞争而呈空间负相关关系。     

大兴安岭次生林空间分布格局及其尺度效应

研究大兴安岭落叶松林、白桦林和落叶松+白桦混交林3种次生林中,不同树种(落叶松、白桦和其他)和不同大小级(Ⅰ～Ⅴ级)树木的空间分布格局及其尺度效应。结果表明:3个林型中,仅落叶松林的更新数量达到良好状态,其余2种林型均为更新不良;各林型中,更新层幼苗、幼树的数量组成均与乔木层存在显著差异,且各林型中树木的直径(落叶松林和落叶松+白桦混交林除外)和树高分布也不够合理,3个林型均属于不稳定群落。各林型内林木空间分布整体以聚集分布为主,但方差/均值比率、负二项指数、Green指数、平均拥挤度和Morisita指数5个判别指数随尺度的变化显著不同,并以线性递增(40%)、幂函数递增(22%)和负二次多项式(20%)趋势为主。Ⅰ～Ⅲ级的更新层林木在不同尺度上以聚集分布为主,而乔木层(Ⅳ～Ⅴ级)在多种分布格局间波动,其对尺度的响应同样以线性递增(44%)、幂函数递增(15%)和负二次多项式(12%)为主。同一林型和取样尺度下,林木空间聚集程度整体随着林木大小级的增加呈线性下降趋势。各林型中,非优势树种的种群格局规模往往大于优势树种,而更新层林木空间格局规模大于乔木层。     

祁连山金露梅灌丛草甸群落结构及主要种群的点格局分析

金露梅灌丛草甸是青藏高原高寒草地生态系统的重要组分之一,采用Ripley的K(t)函数分析方法,对放牧和封育条件下主要种群的分布格局和种间关系及金露梅灌丛群落动态变化进行了研究.结果表明:(1)经过6年的围栏封育,金露梅灌丛草甸主要种群的空间分布格局表现出从均匀或随机分布向随机或聚集分布转变的趋势,聚集强度随围封尺度增大而增加,随放牧的干扰而降低,聚集分布有利于种群发挥功能群整体效应.(2)围栏内不同功能群之间主要呈显著正关联;围栏外的禾草与杂类草、莎草与杂类草之间均呈显著负关联,出现种间资源竞争,且随着尺度的增大负关联逐渐增强,不同物种的生态位差异明显.(3)围栏内外种群点格局分布都具有明显的尺度依赖性,植物间相互作用和外界放牧干扰是影响物种不同尺度下空间格局变化的主要原因,点格局的变化驱动了群落结构的变化.可见,长期夏季放牧抑制了高寒金露梅灌丛草甸禾草和莎草植物的分株和生长,促进了杂类草的生长,金露梅灌丛草甸呈现出退化的趋势,围栏封育有利于草地生态系统的恢复演替.     

基于Ripley K函数的武汉市景观格局特征及其变化

基于1987、1996和2007年武汉市TM遥感影像,应用点格局分析方法之一的RipleyK函数,分析了武汉市市域景观格局的特征及其变化.结果表明:1987—2007年间,耕地是武汉市的景观基质,而林地、水体、草地、城乡建设用地和其他未利用地则以斑块或廊道的形式镶嵌其中;林地、水体、草地和城乡建设用地在所有研究尺度下均呈现出显著的聚集空间格局,且林地、草地和城乡建设用地的空间聚集性强于水体;耕地在小尺度下呈现出聚集的空间格局,随着尺度的增大,逐渐变为随机、均匀的空间格局.研究期间,武汉市林地、城乡建设用地面积逐次增大,水体、草地和耕地面积逐次减少;各景观类型的空间格局特征也发生了改变,总体表现为林地和城乡建设用地空间聚集度降低,分布的均匀程度增加,而草地、水体和耕地的空间分布变得更加不均匀,聚集程度增加.与样方法、样线(带)法相比,利用样点分析景观格局具有简单、准确、易用等优点.Ripley K函数是多尺度景观格局分析的有效手段,是景观指数法的支持和补充.     

四川卧龙自然保护区珙桐种群的空间分布格局

采用扩散系数的t检验、Poisson分布的x^2拟合检验及Morisita指数的F检验来研究珙桐种群的空间分布格局类型,用负二项参数（K）、Green指数（GI）和Lloyd的平均拥挤度（m^＊）与聚块性指标（PAI）来研究珙桐的聚集强度。同时利用上述指数研究取样尺度、海拔及克隆繁殖对珙桐种群分布格局和聚集强度的影响。结果表明,总体上珙桐种群的分布格局类型为集群分布,具一定的聚集强度。取样尺度、海拔对其分布格局和聚集强度均有不同程度的影响。基株种群和分株种群的分布格局和聚集强度在不同取样尺度和海拔下出现不同的变化。最后对珙桐种群格局在各种因素影响下的变化原因进行了讨论,认为珙桐种群格局呈集群分布的最主要原因是由其本身的繁殖特性决定的。     

放牧对松嫩平原农牧交错区防护林下草地的影响

针对当前防护林草地已成为松嫩平原农牧交错区牲畜主要放牧场的实际情况,分析了不同放牧强度对防护林草地的影响．结果表明,未放牧防护林草地严重退化,与极度放牧防护林草地最为相似．未放牧和极度放牧均抑制了防护林草地的生长,轻度放牧和中度放牧却促进了防护林草地的生长,草地产量和质量均明显提高,并合理地利用了杨树叶资源．未放牧防护林草地质量指数仅为15．51。属严重退化草地范畴;轻度放牧草地质量指数为86．4,随着放牧强度的增加,草地质量逐渐下降．因此,应提倡轻度放牧、中度放牧,防止未放牧和极度放牧现象出现,促进防护林草地生长,并充分利用杨树叶资源增加畜牧业牧草的来源．     

放牧对黄河低阶地盐化草场土壤水盐空间异质性的影响

选定黄河低阶地地形大致相近的放牧草场与封育草场,按实地情况分别设置长770m（放牧）、370m（放牧）和240m（封育）3条样线,采用校正后的便携式WET Sensor以10m为间隔进行土壤水盐的分层（0～10cm,10～20cm）测定,并对其进行地统计学分析.结果表明：黄河低阶地盐化草场表层土壤水盐的变异系数和相关性高于下层,土壤水分的变异系数低于土壤盐分且层间的相关性较高;放牧使土壤水盐之间的相关程度增大,变异降低,且使土壤水分存在一定的冗余.所研究草场的土壤水盐表现为中等或强烈空间自相关,封育盐化草场水盐空间相关尺度的差异较小,而放牧草场则相反.持续放牧已经成为一种稳定影响盐化草场水盐空间分布的结构性因素,使盐化草场的水盐空间异质性减弱.盐生植物在草场内随机分布且不受放牧干扰,是封育盐化草场随机作用较强的最可能原因;而放牧草场内牲畜的啃食和践踏对盐生植物和土壤结构改变所形成的反馈作用大大降低了这些植物对水分特别是盐分的再分配,进而导致放牧草场水盐的含量趋于增大且分布格局趋于简单.     

Configuration of daily grazing and searching of growing beef cattle in grassland: observational study

Many of the studies in Campos grasslands focus on management aspects such as the control of herbage allowance, and application of nutrients and/or overseeding with legumes. However, there is little literature on how the Campos grassland resource is utilised, especially regarding the grazing pattern and the relationship between pasture quantity and quality on daily grazing activities. The study of the ingestive behaviour in species-rich and heterogeneous native grasslands during daylight hours, and understanding how animals prioritise quality or quantity of intake in relation to pasture attributes, are important to comprehend the ingestive-digestive processes modulating the energy intake of animals and to achieve a better grazing management. Therefore, the objective was to describe and quantify the daily grazing behaviour of growing cattle grazing native pasture with different structures as a result of different management practices, and study the relationship of pasture attributes and intake through multivariate analysis. The study was carried out at the Faculty of Agronomy, Paysandú, Uruguay. Treatments were native grassland, overseeding with Trifolium pratense and Lotus tenuis + phosphorus, and native pasture + nitrogen-phosphorus. Grazing activities were discriminated into grazing, searching (defined when animals take 1–2 bites in one feeding station and then change to another feeding station and so on), ruminating and idling. The probability of time allocated to each activity was continuously measured during daylight hours (0700–1930) and was related to pasture structure and forage quality using regression tree models, while the bite rate was determined every 2 h. The diurnal pattern of growing cattle showed grazing and searching sessions, followed by ruminating and idling sessions. The length of sessions (as the probability of time allocated to each activity) varied throughout the day. The grazing probability was greater during afternoon than morning and midday (0.74 vs 0.45 vs 0.46, respectively), and it was associated with higher bite rate (34.2 bites/min). Regression tree models showed different grazing, searching and ruminating strategies according to pasture attributes. During the morning, animals modified grazing, searching, ruminating and idling strategies according to bite rate, crude protein in diet and herbage allowance. At midday, they only adjusted ruminating and idling, while during afternoon sessions, grazing activities were modified by pasture quantity attributes such as herbage mass and herbage allowance. By controlling the herbage allowance, herbage mass and pasture height, animals prioritise quality in the morning and quantity in the afternoon, integrating and modifying the grazing-searching and ruminating-idling pattern.     

From plant neighbourhood to landscape scales: how grazing modifies native and exotic plant species richness in grassland

The interactive effect of grazing and soil resources on plant species richness and coexistence has been predicted to vary across spatial scales. When resources are not limiting, grazing should reduce competitive effects and increase colonisation and richness at fine scales. However, at broad scales richness is predicted to decline due to loss of grazing intolerant species. We examined these hypotheses in grasslands of southern Australia that varied in resources and ungulate grazing intensity since farming commenced 170 years ago. Fine-scale species richness was slightly greater in more intensively grazed upper slope sites with high nutrients but low water supply compared to those that were moderately grazed, largely due to a greater abundance of exotic species. At broader scales, exotic species richness declined with increasing grazing intensity whether nutrients or water supply were low or high. Native species richness declined at all scales in response to increasing grazing intensity and greater resource supply. Grazing also reduced fine-scale heterogeneity in native species richness and although exotics were also characterised by greater heterogeneity at fine scales, grazing effects varied across scales. In these grasslands patterns of plant species richness did not match predictions at all scales and this is likely to be due to differing responses of native and exotic species and their relative abundance in the regional species pool. Over the past 170 years intolerant native species have been eliminated from areas that are continually and heavily grazed, whereas transient, light grazing increases richness of both exotics and natives. The results support the observation that the processes and scales at which they operate differ between coevolved ungulate—grassland systems and those in transition due to recent invasion of herbivores and associated plant species.     

放牧制度对草地产流产沙及氮磷流失的影响

研究不同放牧制度草场水土流失过程,对草原生态环境保护和治理具有重要的理论意义。以内蒙古呼伦贝尔草原不同放牧草场为研究对象,设置选取三种放牧制度草场(自由放牧、轮牧、休牧),采用人工模拟降雨的方法进行0.74mm/min和1.5mm/min雨强的降雨模拟试验,测定径流量,含沙量,径流和泥沙中总氮,总磷浓度,并探讨植被截留对径流的影响规律。结果表明:植被截留对减少降雨径流具有明显的作用,休牧草场径流系数减小最多,自由放牧草场减小最少,产沙量显示为自由放牧草场轮牧草场休牧草场。降雨强度对径流中的氮磷浓度影响显著,自由放牧草场总氮浓度和休牧草场总磷浓度受雨强影响最大,氮磷流失过程浓度变化曲线更符合幂函数分布。休牧草场泥沙氮含量和泥沙磷含量均为最高,自由放牧草场与休牧草场的总氮富集率基本相等且均大于轮牧草场,总磷富集率为自由放牧休牧轮牧,三种放牧草场氮磷和泥沙流失主要影响因素为径流量和含沙量。因此,适当的将呼伦贝尔草原自由放牧草场向休牧和轮牧草场转变,将有利于减少草场水土营养元素流失及草原生态可持续发展。     

草地植物生产力主要影响因素研究综述

草地是全球分布面积最大的陆地生态系统,植物初级生产力是反映草地功能的重要指标。从植物种多样性、资源有效性、放牧、退化草地恢复和气候变化等方面较系统综述了影响草地植物生产力的关键要素和驱动力。大量研究表明,植物多样性与生产力的关系尚未有一致的结论,依据试验地点、起始状态甚至度量指标不同而不同;特别是资源有效性调节着生产力水平并对植物多样性和生产力关系产生显著影响;放牧改变了植物群落特征和养分有效性进而影响生产力的形成过程,也改变了资源有效性-植物多样性-生产力之间的关系;对于退化生态系统,在退化草地恢复过程中植物与土壤资源有效性的互作效应对植物生产力的变化起着关键作用;而在未来气候变化特别是增温对植物生产力的影响因地点和生态系统的不同而异,但多数研究结果显示增温提高了草地植物生产力。与国外其它草地分布区相比,国内的相关研究不仅在数量上明显不足,更重要是欠缺机理上的深入研究。在放牧和未来气候变化背景下如何维持和提高草地生产力,如何加速退化草地生态系统的恢复,进而实现生态安全建设和经济社会协调发展,是我国当前急需解决的理论和实践问题。     

Low intensity, mixed livestock grazing improves the breeding abundance of a common insectivorous passerine

Livestock grazing is a major driver of ecosystem change and has been associated with significant declines in various bird species in Britain and worldwide. However, there is little experimental evidence to show how grazing affects bird populations. We manipulated livestock densities in a replicated field experiment and found that mixed sheep and cattle grazing, at low intensity, improved the breeding abundance of a common upland passerine, the meadow pipit Anthus pratensis, after two years. Plots stocked with sheep alone (at high or low density) or not stocked at all held fewer pipit territories. Despite a year-on-year decline in pairs of meadow pipits in intensively grazed plots, we found no effect of sheep number on breeding abundance. Our results support the hypothesis that mixed species of herbivores generate greater heterogeneity in vegetation structure, which modifies prey availability, resulting in a greater abundance of birds. The results of our study should inform the management of grassland areas and enhance the abundance of some bird species, particularly in areas that have seen significant shifts from mixed livestock grazing to grazing dominated by single species of animals.     

Ungulate preference for burned patches reveals strength of fire-grazing interaction

The interactions between fire and grazing are widespread throughout fire-dependent landscapes. The utilization of burned areas by grazing animals establishes the fire-grazing interaction, but the preference for recently burned areas relative to other influences (water, topography, etc.) is unknown. In this study, we determine the strength of the fire-grazing interaction by quantifying the influence of fire on ungulate site selection. We compare the preference for recently burned patches relative to the influence of other environmental factors that contribute to site selection; compare that preference between native and introduced ungulates; test relationships between area burned and herbivore preference; and determine forage quality and quantity as mechanisms of site selection. We used two large ungulate species at two grassland locations within the southern Great Plains, USA. At each location, spatially distinct patches were burned within larger areas through time, allowing animals to select among burned and unburned areas. Using fine scale ungulate location data, we estimated resource selection functions to examine environmental factors in site selection. Ungulates preferred recently burned areas and avoided areas with greater time since fire, regardless of the size of landscape, herbivore species, or proportion of area burned. Forage quality was inversely related to time since fire, while forage quantity was positively related. We show that fire is an important component of large ungulate behavior with a strong influence on site selection that drives the fire-grazing interaction. This interaction is an ecosystem process that supersedes fire and grazing as separate factors, shaping grassland landscapes. Inclusion of the fire-grazing interaction into ecological studies and conservation practices of fire-prone systems will aid in better understanding and managing these systems.     

Reversed effects of grazing on plant diversity: the role of below‐ground competition and size symmetry

Grazing is known as one of the key factors for diversity and community composition in grassland ecosystems, but the response of plant communities towards grazing varies remarkably between sites with different environmental conditions. It is generally accepted that grazing increases plant diversity in productive environments, while it tends to reduce diversity in unproductive habitats (grazing reversal hypothesis). Despite empirical evidence for this pattern the mechanistic link between modes of plant–plant competition and grazing response at the community level still remains poorly understood. Root‐competition in particular has rarely been included in theoretical studies, although it has been hypothesized that variations in productivity and grazing regime can alter the relative importance of shoot‐ and root‐competition. We therefore developed an individual‐based model based on plant functional traits to investigate the response of a grassland community towards grazing. Models of different complexity, either incorporating only shoot competition or with distinct shoot‐ and root‐competition, were used to study the interactive effects of grazing, resource availability, and the mode of competition (size‐symmetric or asymmetric). The pattern predicted by the grazing reversal hypothesis (GRH) can only be explained by our model if shoot‐ and root‐competition are explicitly considered and if size asymmetry of above‐ and symmetry of below‐ground competition is assumed. For this scenario, the model additionally reproduced empirically observed plant trait responses: erect and large plant functional types (PFTs) dominated without grazing, while frequent grazing favoured small PFTs with a rosette growth form. We conclude that interactions between shoot‐ and root‐competition and size symmetry/asymmetry of plant–plant interactions are crucial in order to understand grazing response under different habitat productivities. Our results suggest that future empirical trait surveys in grassland communities should include root traits, which have been largely ignored in previous studies, in order to improve predictions of plants’ responses to grazing.     

高寒草地不同径级根形态对围封年限的响应

以根径级表征根系形态结构，可以反映植物资源利用和生物量分配状况。研究高寒草地不同径级根形态，对了解地下碳分配、水分和养分吸收及生产力具有重要意义。围封被认为是防治草地退化的最有效措施之一，但目前有关围封年限对不同径级根形态影响的研究还极度缺乏，以致无法确定有利于根生态效益，即资源吸收利用能力最大化的围封年限。以位于青海省海北台站围封5、13、22、39 a的高寒草地为研究对象，季节性放牧草地为对照，探讨围封年限对不同径级根形态(包括根长、根表面积和根尖数)的影响。结果表明：在0—15 cm土层中，径级小于0.5 mm时，围封13 a的根尖数显著高于围封5 a的草地，其对应的生物量也最大；径级小于0.6 mm时，围封13 a的根长和根表面积均显著高于围封5 a和放牧草地，且其对应的生物量也达最大；径级大于0.5 mm时，各草地之间的根尖数均无差异；径级大于0.6 mm时，围封39 a的根长和根表面积均显著高于放牧草地，且其对应的生物量最大。在15—30 cm土层中，各径级下，围封5 a的根长、根表面积和根尖数均显著大于围封39 a和放牧草地，但其对应的生物量在围封13 a时达最大。土壤硝...