针茅草原放牧衰退演替阶段的模糊聚类分析

本文利用模糊聚类分析的系统聚类法和ISODATA分类法,对短花针茅草原因过度放牧而形成的衰退演替系列的各阶段进行了分类;比较成功地在群落分类上联合使用了PCA排序与ISODATA分类。结果表明:这两种方法都将衰退演替系列分成4个阶段,它们是短花针茅群落、扁穗冰草群落、冷蓠群落和亚氏旋花群落。这与前人用其他方法分类的结果相似。本文为群落分类提供了两种合理、可行的数学分类方法。     

Mathematical Models of Retrogression of Populations under Grazing Condition in the Stipa Steppe

In the region of North-western China, there are about eight Stipa constructive species which form various communities of Stipa steppe. In this paper, the writers take Stipa breviflora + Agropyron cristatum + Artemisia frigida association as a typical example and make use of the method of mathematical analysis in an attempt to build up mathematical models which may explain the rules of succession of this type by means of mathematical language. Coverage is employed as an indication in representing the dominance of the population of species. In the moderate grazing stage, accompanying the increase in successive grazing, the dominance of the constructive species Stipa breviflora declines by degree and the curve of the population can be indicated by the equation P = 87e–0.74T. Agropyron cristatum, a subdominant in the original community, appears as a dominant species in the second stage, but after this, the 3ominance of its population drops down gradully and the curve can be expressed by the equation P=12T2.7e–0.3T2 Artemisia frigida, an accompanying species in the incipient community, gains the status as a dominant in the heavy grazing stage, and prior to this, its dominance exhibits a progressively raising curve which can be indicated by the equation P = 5.38e0.4T, yet when T > 3, the curve declines as P= 148.16–0.46e0.17T2. Convolvulus ammannii, an accidental in the first stage or an exotic species shows an slowly increase in its population before the excessive grazing stage and the equation in the section of the raising curve is expressed as P=0.745e0.45T, but as T >4, the population degrades abruptly and exhibits as the equation P = 12T2.7e–0.3T2. The community is now approaching to a secondary bare area. As a whole, the retrogressive succession of the Stipa steppe range shows a total characteristic curve of retrogression in its populations due to over grazing. The curve can be represented by the equation P = 132.9e–0.89. The incipient community entirely loses its general nature and it is said to be a heterogeneity community or disclimax. The critical straight line (curve) can be shown by the equation P = 1.1302T and under this critical situation, the total coverage of populations in the community is about 4.5%. At this point, we give the dominant (Convolvulus ammannii) of the community the name of "critical indicative species".     

Application of Numerical Classification to Study the Grazing Retrogressive Succession Stages of the Kobresia Vegetation on the Subalpine Meadow

Using the nearest-neighbour method in the course of numerical classification the four stages of the grazing retrogressive succession .of the Kobresia vegetation in Maqu Xian are divided: Ligularia virgaurea +Stipa aliena -Saussurea sp community and Leontopodium sp-Saussurea superba f. Pygmaea community belongs to the RSS (Retrogressive Succession Stages) of the grazing extremely; Anemone rivularis var fioreminore-Ligularia virgaurea-Kobresia spp community belongs to the RSS of the grazing seriously; Brachy-podium sylvaticum var gracile-Kobresia spp, Kobresia spp-Polygonum viviparum-Festuca rubra and Kobresia spp-Blysmus sinocompressus -Potentilla anserina communities belong to the RSS of the grazing moderately; Kobresia spp-Trollius farrei community belongs to the RSS of the grazing properly. Such classification method gives the same result as the traditional classificational methods of the RSS do. But it gives the numerical bases.     

黄土高原半干旱区退化草地恢复与利用过程研究

草地退化表现为土壤和植被遭到彻底破坏,草地演替过程受到强烈抑制.实验采用长期(30年)封禁措施,定位监测退化草地从次生半裸地演变为近似原生植被(进展演替)的变化过程.结果表明,随着封禁时间的变化,退化草地恢复演替经历了4个阶段,群落盖度、植株密度、物种丰富度和多样性指数、地上生物量和地下生物量在草地群落恢复过程中逐渐增加,其特征变化出现的峰值均在封禁第20年(地下生物量峰值在第15年),其中地上生物量最高达520.5 g/m2;直到封禁的第20~25年,以本氏针茅为建群种的草原群落衰败退化现象明显,而大针茅种群密度剧增;在封禁的第26年以上以大针茅为优势的群落生长较为稳定,从目前群落演替进程看,大针茅有替代本氏针茅的趋势.另外,在草原沟道两侧以斑块状聚集分布有中旱生灌木,群落的演替进入了一个新的阶段.随着封禁时间的延续,退化草地从自然封禁恢复的0~26年,通过侵入-竞争-扩散-定居的几个演替阶段,目前形成以大针茅为建群种相对稳定的"亚顶级".虽然草地生物量有一定下降,但草地质量提高,物种多样性丰富,促进草地的进展演替.草地植物群落主要由禾本科、豆科和菊科组成;多年生植物、C3和旱生物种可以作为草地演替过程和植被恢复的指示物种.长期封育对草地物种更新和生态系统稳定性有负面影响,因此,合理的封育时间是草地生态恢复中非常重要的一个因素.本研究提出,在黄土区退化草地封育10~15年后可以开始进行合理的利用,例如通过两年一次刈割和轻度放牧(2只羊/hm2).本研究可为干旱区、半干旱区相似的退化草地恢复提供理论依据.     

羊草草地放牧退化演替中种群消长模型的研究

羊草草地是东北西部及内蒙东部草原区主要的天然放牧场和割草场、具有较高的经济价值,但是由于长期过度放牧,草地已严重退化并盐碱化。本文采用数学手段,以植物种群在群落中的相对优势度为指标,用植被在放牧退化演替系列上的空间分布序列推断其在时间上演替系列的方法,研究羊草等5种植物种群的优势度随放牧退化演替消长的规律及其数学模型。羊草按D＝124.2e-0.35T衰退,寸草苔和糙隐子草分别按D＝2.13T3.3e-0.15T2和 D=1.77T3.7e-0.29T2消长,而角碱蓬和虎尾草分别按D=0.11e1.3T和D=0.38e0.94T增加。     

内蒙古锡林河流域羊草草原和大针茅草原在放牧影响下的分异和趋同

在两个具有代表性的牧压梯度上,对羊草草原和大针茅草原的群落结构与牧压的关系借助模糊聚类的方法进行分析,揭示了不同牧压下植物群落的分异和不同群落在重牧压下的趋同,其总模式是：大针茅草原—持续牧压——→冷蒿草原 羊草草原—持续牧压———→冷蒿草原 把“群落趋同”的概念广延到放牧退化演替即次生逆向演替的生态学范畴。     

Response of dominant grassland species in the temperate steppe of Inner Mongolia to different land uses at leaf and ecosystem levels

In order to study the responses of dominant species to different land uses in the semiarid temperate grassland of Inner Mongolia, we tested the physiological responses of Stipa grandis, Leymus chinensis, and Artemisia frigida to mowing, grazing exclusion, and grazing land uses at the leaf and ecosystem levels. The grazing-exclusion and mowing sites released CO₂, but the grazing site was a net carbon sink. L. chinensis and S. grandis contributed more to the ecosystem CO₂ exchange than A. frigida. At the grazing-exclusion and mowing sites, Leymus chinensis and Stipa grandis both exhibited a higher light-saturation point and higher maximum photosynthetic rate than that at the grazing site, which increased photosynthesis and growth compared to those at the grazing site. In contrast, A. frigida possessed a higher nitrogen content than the other species, and more of the light energy used for photosynthesis, particularly at the grazing site.     

典型草原退化群落不同恢复演替阶段羊草种群空间格局的比较

羊草(Leymus chinensis)为典型草原群落的主要建群种之一, 在群落中扮演着重要角色。应用摄影定位法测定处于不同恢复演替阶段的羊草种群空间格局, 通过点格局、种群空斑、种群领地及种群领地密度等方法分析发现, 羊草种群在恢复演替过程中经历了种群增长和种群衰退的过程。在此过程中, 羊草种群数量出现最高点, 此点之前, 种群拓殖大于自疏, 种群整体增长; 此点之后, 种间竞争及种内竞争致使种群衰退, 而种间竞争占主导地位, 种内竞争相对较弱。羊草种群的增衰导致种群空斑发生变化, 从而引起种群格局类型发生相应的变化, 表现为在恢复21 a的群落中, 羊草种群在10 m×10 m的取样范围内表现出两种格局分布类型: 在0~4.85 m之间呈现聚集分布, 当尺度大于4.85 m时, 则表现为随机分布; 在恢复8 a的群落中, 羊草种群在10 m×10 m的取样范围内出现3种格局分布类型: 在0~3.01 m之间呈聚集分布, 在3.01~3.37 m之间为随机分布, 当尺度大于3.37 m时则表现为均匀分布; 在严重退化群落中, 羊草种群在整个10 m×10 m测定尺度上呈现聚集分布。由此可见, 羊草种群格局在恢复演替过程中是变化的, 这种变化主要由群落剩余资源驱动下的种群拓殖及种内种间竞争所致。     

松嫩平原针茅草原的特征及其生态地理规律的探讨

 经考察,松嫩平原的针茅草原主要有4个群落类型：贝加尔针茅(Stipa baicalensis)群落、贝加尔针茅+线叶菊(Filifolium sibiricum)群落、大针茅(S．grandis)+贝加尔针茅群落和大针茅群落。通过对针茅草原各类型基本结构特征和生态地理分布规律的分析,并根据它们所反映的水土条件的差异,认为贝加尔针茅群落为该地区的地带性植被。在中国温带草原区划中的位置属于草甸草原,应与内蒙古高原典型草原分开,成为一个独立的分区     

内蒙古草原退化群落恢复演替的研究I. 退化草原的基本特征与恢复演替动力

 本项研究自1983年起在锡林河中游对放牧退化的冷蒿(Artemisia frigida)占优势的草原群落变型进行封育恢复实验与长期监测。每年在植物生长季以15天为间隔进行取样测定,即每年测定9期,每期做10或20个1m×1m的样方。测定项目包括：群落中各植物种群的地上现存生物量、密度、高度、花(果)枝数等。还采用改进的样方方差法监测植物种群空间分布格局的动态。并同时在保护良好的羊草+大针茅(Leymus chinensis+Stipa grandis)群落中进行测定取得完全对应的数据,作为对照系列。以上两种群落的土壤水分与养分动态的长期监测由本站土壤组承担。根据连续十二年监测数据的分析,对退化草原群落的性质与特征提出以下的认识,并对退化草原恢复演替的驱动因素进行厂探讨。1．草原退化演替阶段是与一定强度的放牧压力保持平衡而相对稳定的群落变形,退化阶段取决于牧压强度与持续的年代。2．当群落退化到冷蒿为主要优势种的阶段时,与原生群落的种类组成相比,只发生一定的数量消长变化,对群落的物种丰富度影响不大。3．退化群落植物种群空间格局的均匀性较高,随着恢复演替的进展,因一些种群斑块增大而使空间不均匀性增强。4．退化群落与其原生群落的种—生物量关系呈对数正态模式,其演替过渡阶段成为分割线段模式,也反映出群落资源分配格局与群落空间格局的关系。5．退化草原的显著特征是植被生产力下降,冷蒿群落的生物量下降到原生群落的30％～40％,家畜嗜食的植物种减少50％～70％总生产力不足原生群落的30％。6．退化群落在自然封育条件下能够迅速恢复的原因,可归结为植物在削除放牧干扰后的种群拓殖能力与群落资源(水分,矿质养分等)的剩余。群落资源条件是种群拓殖的物质基础,从而成为恢复演替的动力。     

不同载畜率下短花针茅分蘖数量对内源激素浓度的响应

放牧是荒漠草原最主要的利用方式之一,载畜率的变化严重影响着植物的生长发育;而内源植物激素是调节植物生长发育的开关,且植物在不同的生长发育阶段具有不同的生理要求和环境适应能力。通过测定放牧条件下短花针茅(Stipa breviflora)分蘖叶内源激素的变化,研究短花针茅分蘖生长对放牧的响应,并分析了分蘖数量受内源激素影响的机制。结果表明,(1)内源激素与载畜率之间存在显著二次相关关系,说明放牧能够显著增加内源激素的浓度(P0.05),但这种相关只存在于中、小株丛的短花针茅中。(2)其次,放牧能够在一定程度上影响短花针茅植株个体分蘖的数量(P0.05),重度放牧是增加短花针茅植株个体分蘖数量最显著的载畜率。(3)过高浓度的生长素(IAA)会抑制短花针茅的分蘖数量(P0.01)。而细胞分裂素(CTK)与短花针茅的分蘖数量之间尚未发现相关关系。     

退化草原狼毒个体年龄判定方法及其种群年龄结构的研究

详细观察了内蒙古东部退化草原糙隐子草(Cleistogenes squarosa)群落内狼毒(Stellera chamaejasme)的根颈分枝形态及其生长发育特点,研究了狼毒种群的年龄结构．结果表明,狼毒个体实际年龄为“类二叉分枝(quasi-dichotomous branching)回数加2”;根颈上茎的残茬、枝痕和环状痕是确定根颈分枝回数的重要辅助特征．重牧、过牧、极牧3个放牧演替阶段内狼毒个体最大年龄依次为15、16和19龄．8龄级个体数最多,其年龄比分别为18．71％、24．20％和19．06％．重牧阶段缺失1和2龄个体;过牧和极牧阶段均缺失1龄个体．狼毒种群年龄结构为“初始衰退型”,存活曲线接近于“凸型”或DeeveyⅠ型．老龄组(13龄以上者)个体数在重牧、过牧、极牧演替阶段分别占4．83％、2．84％和14．02％．随着放牧干扰的加剧,狼毒种群年龄结构呈现老龄化趋势．     

短花针茅叶片水分利用效率对放牧强度的响应及其影响因素

为明确植物的用水策略及适应性机制,以内蒙古四子王旗短花针茅荒漠草原为研究对象,设置对照(CK)、轻度放牧(LG)、中度放牧(MG)和重度放牧(HG)4个放牧梯度,其载畜率分别为每1 hm^(2)每年0、0.93、1.82和2.71个羊单位的放牧强度,调查建群种短花针茅的高度、盖度、密度、地上生物量以及土壤的理化性状,并且采用稳定碳同位素法和红外光合仪法对短花针茅水分利用效率进行了测定,旨在阐明短花针茅水分利用效率在不同放牧强度下的响应规律及其影响因素。结果显示:(1)放牧对短花针茅盖度、密度以及地上生物量的影响显著;随着载畜率的增大,有利于短花针茅的扩散使其分布面积增加,且在中度放牧条件下尤为明显。(2)随着放牧强度的增加,土壤水分含量较对照显著提高,土壤全氮含量呈先增加后减少的变化趋势,土壤速效钾呈现降低的变化趋势,而对土壤全碳含量和pH无显著影响,说明适度放牧能够提高土壤水分含量、促进土壤氮含量的积累,但放牧会导致土壤速效钾减少。(3)随着放牧强度的增大,短花针茅长期水分利用效率(WUE l)呈现“V”形变化趋势,而瞬时水分利用效率(WUE t)与内在水分利用效率(WUE i)总体呈降低的变化趋势。(4)相关分析显示,放牧强度与短花针茅密度、地上生物量呈显著正相关关系,土壤全氮含量与有机碳、pH、WUE i呈显著正相关关系,WUE t与WUE i呈显著正相关关系;短花针茅内在水分利用效率与土壤有机碳含量密切相关。研究表明,重度放牧导致短花针茅株丛破碎化,增加了种群的扩散面积,是短花针茅长期水分利用效率提高的直接原因;短花针茅瞬时水分利用效率随放牧强度的增加而降低可能是由其内在水分利用效率降低引起的。     

放牧退化群落中冷蒿种群生物量资源分配的变化

对放牧退化群落中冷蒿种群生物量及生物量资源分配的变化进行了研究.结果表明,在放牧干扰下,随着放牧退化程度的增加,冷蒿种群叶、茎、根的生物量及总生物量增加.其中根的重量增加幅度较大,但生殖构件(花序、果实)的生物量在轻度退化群落中增加,中度退化群落中迅速减少,重度退化群落中未发现生殖构件.随着放牧退化程度增加,冷蒿种群生物量的资源分配发生变化,对根的分配增加,对茎、叶的分配减少,根冠比增加;对无性繁殖的分配增加,对有性生殖的分配减少.在重度退化群落,冷蒿有性生殖严重受阻,繁殖格局发生变化.从资源分配的动态来看,随着放牧退化程度的增加,生长初期至盛期,冷蒿种群资源优先分配给地上部分,尤其是光合器官叶;而生长盛期至末期,资源优先分配给有性生殖或贮藏器官.繁殖格局的转变是冷蒿种群耐牧,在重度退化下成为建群种的关键.资源分配格局的时空变化,使生长、维持和繁殖等方面的分配达到和谐,是冷蒿种群在重度退化下成为建群种的物质基础.     

中温型和暖温型草原共有植物种群繁殖分配的比较研究

 1999～2000年在内蒙古草原区的中温型草原和暖温型草原两个研究站点, 分别对大针茅(Stipa grandis)、羊草(Leymus chinensis)、糙隐子草(Cleistogenes squarrosa)、达乌里胡枝子(Lespedeza dahurica)和阿尔泰狗哇花(Heteropappus altaicus) 5个共有种地上生物量、营养元素（全C、全N、全P）和能量（热值）的繁殖分配进行了初步研究。结果表明：两站点共有种各自的地上生物量、全C 和能量之间的繁殖分配较为接近,但全P、全N     

Soil drainage and phosphorus depletion contribute to retrogressive succession along a New Zealand chronosequence

Background and aims

Models of retrogressive succession have emphasised the role of phosphorus (P) depletion in driving biomass loss on surfaces of increasing geologic age, but the influence of impeded drainage on old surfaces has received much less attention. We tested whether poor drainage contributed to changes in ecosystem properties along a 291,000-year chronosequence in New Zealand (the Waitutu chronosequence).

Methods

Soil and ecosystem properties were measured at 24 evenly distributed points within each of eight 1.5 ha plots located on young, intermediate and old surfaces. Regression analyses tested whether drainage, in addition to P, affected ecosystem functioning. A complementary fertilization experiment tested whether P was indeed limiting on the most nutrient-depleted sites.

Results

Most phosphorus depletion occurred in the early stages of pedogenesis (within 24,000 years), and the older surfaces were similar in soil-P contents, whereas drainage was initially good but became increasingly impeded with surface age. In the fertilizer experiment, species showed positive responses to both nitrogen (N) and P addition on the oldest surfaces, supporting Walker and Syer’s model. However, water table depth was also found to be strongly correlated with plant species composition, forest basal area, light transmission, and litter decomposition when comparisons were made across sites, emphasising that it too has strong influences on ecosystem processes.

Conclusions

Poor drainage influences the process of retrogressive succession along the Waitutu chronosequence. We discuss the implications of our work with regard to other chronosequences, suggesting that topography is likely to have strong influences on retrogressive processes.     

Catagenesis in a series of Productus from the Liddar Valley in Kashmir

Four different species ofProductus frequently found, in the Lower and Middle Carboniferous of Kashmir show a lineage more or less in the stratigraphical succession. It starts fromProductus cora d'Orb. (the primitive member of this series) and exhibits a retrogressive accentuation of the twisting of the umbo which almost disappeares in the youngest specimens. The spiral angle varies in the four stages from 70° to 30°. The lineage is regarded as a true genetical one.     

不同放牧强度下克氏针茅(Stipa krylovii)草原的根系特征

以呼伦贝尔克氏针茅草原不同放牧强度下的演替群落为对象,开展群落及其群落建群种的地下生物量和根系形态特征研究.结果表明:从轻度放牧到重度放牧,群落种类组成和根系功能群类型趋于简单化;群落地下生物量的空间分布形态呈“T”型;不同放牧强度下草原群落的建群种出现了明显替代现象,轻度放牧样地群落建群种为密丛型根系的克氏针茅,中度放牧为疏丛型根系的糙隐子草(Cleistogenes squarrosa,重度放牧为鳞茎型根系的碱韭(Allium polyrhizum);随着放牧强度的增大,群落建群种根冠比逐渐增加,分别为0.47、1.0、4.1,并且群落建群种根系数量、根系体积、根系生物量、比根长及根长密度等各指标均发生了明显变化.另外,3种放牧强度样地群落建群种根冠比、根长密度均与土壤速效氮含量呈现显著正相关(P＜0.05).     

Examining the genetic diversity of Stipa grandis under various grazing pressures

The Stipa grandis steppe in the Inner Mongolia Autonomous Region occupies an area of 2798081 hm2. On the basis of the genetic variation, it was found that its adaptability to the environmental conditions under grazing pressure was significant. Using the Inter-Simple Sequence Repeat (ISSR) procedure, the changes to the genetic diversity of the Stipa grandis population under different grazing pressures were observed. Plant samples were collected from a series of grazing gradients of the Stipa grandis steppe in Dalinuoer National Nature Reserve in the Inner Mongolia (located at 116°38′–116°41′E and 43°25′–43°27′N.), which has the following vegetation types in abundance: Leymus chinensis is the constructive species; the dominant species include Stipa grandis, Cleistogenes squarrosa, and Artemisia frigida; the companion species is Potentilla acaulis and others. According to the grazing pressure, the following four grazing gradients were identified from the dwellings of the herdsmen to the enclosure site: (1) no grazing (CK enclosure site); (2) light grazing (LG); (3) moderate grazing (MG); (4) heavy grazing (HG). Young leaves of each Stipa grandis were collected during the growing season. The results showed that the Stipa grandis showed abundant genetic diversity despite the fact that certain polymorphic loci were lost; at the same time, new polymorphic loci emerged when grazing pressure increased; a total of 10 primers were used, and 74 bands were produced in total, of which 65 bands were polymorphic; the total percentage of polymorphism was 89%; the percentage of polymorphic loci of the Stipa grandis population decreased with the increase of grazing pressure; the percentage of polymorphic loci was 62.2% in the no-grazing (CK) population, 64.9% in the light-grazing (LG) population, 58.1% in the moderate-grazing (MG) population, and 56.8% in the heavy-grazing (HG) population; the genetic diversity of the population in the descending order using the Shannon's information index is as follows: (1) light grazing (0.3486); (2) no grazing (0.3339); (3) moderate grazing (0.3249); (4) heavy grazing (0.2735) with the same distributional pattern as the Nei's genetic diversity index. The test showed the following: As the grazing pressures increased, the change of genetic diversity decreased; the genetic differentiation coefficient among the population (Gst) was 0.1984, which showed the presence of small partial genetic diversity (19.8%) among populations; gene flow (Nm*) between primers varied from 0.9806 to 3.4463, and the mean gene flow (Nm*) was 2.0202; the UPGMA cluster figure that was constructed on the basis of the genetic distance matrix showed four populations that became genetically closer at each step: (1) The first group was the moderate-grazing (MG) population and the heavy- grazing (HG) population; (2) The second group consisted of the no-grazing (CK) population and the light-grazing (LG) population; (3) The two groups gathered together.