绵羊放牧绢蒿荒漠草地植物群落多样性及其环境解释

对天山北坡放牧条件下的绢蒿草地进行野外调查,以探讨植物群落物种组成、多样性特征及其与环境因子之间的关系。结果表明:1)绵羊放牧过程中形成了明显的放牧强度梯度,草地利用率适中。通过除趋势对应分析 (DCA)将放牧区内的植物群落划分为8个类型,各类型植物群落的物种多样性有显著差异,且群落间存在异质性;2)采用除趋势对应典范分析法(DCCA)中的前项选择,对所获取的9个环境因子进行筛选,最终土壤有机质含量、粪便量、放牧强度、凋落物生物量、海拔、坡向等6个环境因子成为决定物种分布和群落结构组成的主导因素。DCCA排序结果反映出了实际的生态意义,有机质、放牧强度、粪便量在第一排序轴有明显的梯度变化,而坡向和凋落物则在第2轴上呈现出明显梯度变化,物种和群落也沿着上述环境要素的梯度变化而依次分布,很好地解释了放牧条件下绢蒿荒漠草地物种、群落与环境条件之间的关系。     

Ecological status of species on grazing gradients on the shallow soils of the western grassland biome in South Africa

Abstract

Grasses on the shallow soils of the western grassland biome of South Africa were classified on their ecological status on the basis of their reaction to grazing. Vegetation data were gathered in such a way that those of different successional stages could be identified. An ordination technique was used to define the grazing gradient. Species abundance curves were statistically fitted to the grazing gradient and used to classify the species into decreaser and increaser categories.     

放牧干扰对伊犁绢蒿表型性状特征的影响

试验以新疆天山北坡荒漠草地建群种伊犁绢蒿(Seriphidium transiliense)为对象,研究了其单株表型性状特征对4种放牧强度:无牧(0只羊/hm~2)、轻牧(0.56只羊/hm~2)、中牧(0.95只羊/hm~2)、重牧(2.89只羊/hm~2)的响应。结果表明:放牧显著降低了伊犁绢蒿的株高、冠幅面积、短轴长、长轴长、根颈直径、茎重、地上生物量,且轻牧、中牧各性状均显著高于重牧;放牧强度与伊犁绢蒿株高、冠幅面积、短轴长、长轴长、根长、根颈直径、一级分枝、二级分枝、三级分枝、茎重、叶重、地上生物量呈极显著负相关,其中,放牧强度对株高、短轴长、长轴长、冠幅面积影响较大,且随放牧强度增加呈线性下降;伊犁绢蒿各表型性状总体变异系数为22.23%~134.95%,各放牧处理平均变异系数为20.26%~134.24%,且中牧和重牧下大部分表型性状变异程度明显大于对照。放牧干扰下伊犁绢蒿单株趋向"小型化",避免了家畜的频繁采食,利于其种群的存活。     

The quantification of rangeland condition in a semi-arid grassland of southern Africa

The degradation gradient technique was used to quantify rangeland, condition in areas ranging from poor, trampled areas close to watering points to well managed areas in a semi-arid, sweet grassland of southern Africa. Ecological values were linked to species by means of their individual positions on the degradation gradient. These species were further classified according to ecological index values. Identification of indicator species for purposes of rangeland condition assessment was done by using the correlations between the relative composition and the rangeland condition value of a species. Index values and Gaussian distribution curves were used in calculations to determine rangeland condition. The accuracy of these methods was tested and the best results were obtained by using the species curves of Themeda triandra and other species which dominate at other positions along the gradient. The advantage of this technique lies in its simplicity and ease of use. Another advantage is the fact that only the most important indicator and dominant species in the study area are used to determine rangeland condition.     

东灵山亚高山草甸的数量分析

采用双向指示种分类法(TWINSPAN)、除趋势对应分析法(DCA)和典范对应分析(CCA)相结合的方法,对东灵山亚高山草甸进行数量分类和排序,将该草甸分为7个群落类型,分别位于不同的海拔高度。分类结果很好地反映了植物群落类型与环境梯度之间的关系,并在DCA二维排序图上得到了较好的验证。DCA排序轴反映了海拔高度、坡度和垃圾数的梯度变化,表明海拔高度、水热条件和旅游干扰是影响植物群落变化的主要生态因子。CCA排序结果与DCA的排序结果基本一致。     

东祁连山高寒草地植物群落二维极点排序

利用极点排序对东祁连山高寒草地植物群落进行了分析,并通过Simpson生态优势度指标对植物群落优势度进行了测定。结果表明,(1)在不同的海拔区域内,影响植物群落分布的主要环境因子不同。根据影响植物群落分布的环境因子的变化情况,可将研究地区划分为3个地段,即较低海拔地段(2710~2930m),水分条件对植物群落的分布影响较为明显;中海拔地段(2930~2960m),植物群落的分布主要受水,热组合状况的影响;而在较高海拔地段(2960~3080m),温度条件成为限制植物群落分布的主要因素。(2)群落生态优势度与群落内植物种群数呈负相关,海拔梯度通过影响群落内的种群组成而影响群落生态优势度。不同种群生态优势度的差异则反映了群落对放牧干扰的生态响应,随退化程度的加大,种群组成由抗性弱的物种向抗性强的物种逐渐过渡。     

Quantified range condition assessment of open Camelthorn savanna along a degradation gradient

Measurements were taken at 20 different sites in a relatively homogenous area of open Camelthorn savanna in eastern Namibia. Ordination of grass species composition did not provide a good degradation gradient, due to domination by different species of annual grasses at many of the sites. However a centred PCA ordination of perennial grass species indicated a degradation gradient. This gradient was used to allocate a range condition score to each site, which was then correlated with other measurements. The range condition score did not correlate well with mulch cover, basal cover, proportion of bare soil, above-ground grass biomass, proportion of moribund grass, proportion of seedlings amongst the perennial grasses, density of woody plants lower than O.5m and canopy cover of browsable woody plants over 0.5m tall. A weak correlation (r² = 0.68, p<0.0001, n = 20) was obtained through a power trend line with woody canopy cover of only the bush thickening species. A better correlation (r² = 0.90, p<0.0001, n = 20) was obtained with mean distance from sampling point to the nearest perennial grass. This may therefore be an appropriate indicator to include in range condition score for such types of savanna.     

Grazing and Grazing Exclusion Along a Resource Gradient in Magellanic Meadows of Tierra del Fuego

Although Magellanic meadows have been subject to ungulate herbivory for a long time; they have suffered severe grazing by domestic sheep since the end of the 19th century. We hypothesized that, if protected from grazing, the present dominant dwarf forms would be replaced by taller competitive forms, mainly grasses. We then monitored floristic composition along a gradient of soils over periods of 5 to 16  on seven meadow sites under grazing and, in five, also on exclosures. Initial and final floristic samples were classified with TWINSPAN and ordinated with Detrended Correspondence Analysis (DCA). We also tracked cover changes in life-forms (grasses, dwarf sedges/rushes, rhizomatous helophytes, and cushion shrubs). At the end of the study, we assessed floristic similarity between paired grazed and exclosed treatments, and compared their life-form cover, diversity, biomass, and soil compaction with Student's t and Mann-Whitney's tests. Temporal displacements of composition in ordination space showed the effect of a long drought (DCA axis 1) and of grazing removal (DCA axis 2). Grazing exclusion had a much greater impact in wet meadows–where grasses became the dominant life-form–than in dry meadows. The effect of drought was shown in 1) the expansion of the cushion shrub Azorella trifurcata (Gaertn.) Pers. in both grazed and nongrazed treatments of the drier wetlands; 2) the decrease in Caltha sagittata Cav. in riparian meadows, and its encroachment under grazing in the wettest spring meadow; and 3) the large increase in Poa pratensis L. in exclosed wet meadows. Despite this strong response to environmental conditions, overall results supported the idea that these wetlands are equilibrium systems. Although the drier meadows have crossed an irreversible threshold, the Caltha-encroached wet meadows returned to a grass state in about 4  when protected from grazing. Their resilience suggests that they could be partly restored with rest-rotation grazing.     

贝加尔针茅草原主要植物地上生物量分配对放牧梯度的响应

通过对放牧梯度下贝加尔针茅草原主要植物不同器官(茎、叶、花或果)的生物量分配格局变化进行探索,结果表明:贝加尔针茅草原主要植物的繁殖分配随牧压梯度增加,表现出明显的规律性,中牧条件下,贝加尔针茅草原植物群落的繁殖分配与优势种羊草等较耐牧植物变化趋势一致,均较轻牧下显著增加,而优良禾草、豆科牧草等均显著减少;重牧条件下,植物群落的繁殖分配与优良禾草、豆科牧草等以及退化标志植物变化趋势一致,均较中牧下显著减少,而较耐牧植物羊草等均显著增加。     

基于冗余分析的高寒草原土壤与草地退化关系

在高寒草原退化草地设置研究样地,观测植物群落特征、采集土壤样品、分析土壤物理化学性质,依据数量生态学基本原理,探讨高寒草原退化草地与土壤因子间关系。结果表明:不同退化程度样地沿冗余分析排序图第一排序轴分布,第一排序轴反映草地退化程度的变化;草地植物群落中与第一排序轴负相关且按相关程度大小排序的指标为盖度>地上生物量>地下生物量;第一、第二排序轴能够解释97.1%的土壤因子与草地退化关系;土壤沙砾、p H与第一排序轴正相关,土壤有机碳、土壤含水量、容重、全氮、有效氮与第一排序轴负相关;第一排序轴及所有排序轴所反映的土壤因子均与草地退化之间呈极显著相关关系(P<0.01);不同土壤因子与草地退化之间相关程度不同,土壤有机碳(r=-0.890)、土壤含水量(r=-0.864)、容重(r=-0.847)、全氮(r=-0.836)、有效氮(r=-0.821)等与高寒草原退化相关程度更高且相关关系极显著(P<0.01)。利用退化草地群落特征和土壤因子数据矩阵进行冗余分析能够较好地综合反映土壤因子与草地退化之间的关系及相关程度,土壤有机碳、土壤含水量、容重、全氮、有效氮是反映高寒草原退化的重要土壤指标。     

岷江上游山地牧道对林下草本群落分布特征的影响

以岷江上游干旱河谷/山地森林交错带的林下草本层植物群落为研究对象,以牧道为切入点,通过跟踪放牧和样方调查,应用关联和典范对应分析方法探讨山地牧道与草本层群落分布特征的关系。结果表明,牧道样地草本层中耐践踏的菊科占绝对优势,禾本科和豆科植物较少,说明长期放牧下草本层植被有退化趋势。通过9个优势种种间关联分析发现,野艾蒿和老芒麦代表了人工林样地群落特征,黄花蒿、紫苜蓿等其他7种优势种代表了灌丛样地特征,各优势种均表现出环境适应的趋同性和彼此的相似性。牧道分割增加了草本层植物群落分布的异质性,牧道格局指数与草地质量指数基本呈负相关变化规律,而牧道密度与草地质量指数之间的相关性不明显,牧道密度和牧道格局具有一定的指示草地退化的作用,但相互关系复杂。通过CCA排序可知,乔灌层盖度是影响草本层植物分布的最重要因素,其次为牧道密度,坡度和坡位对其分布也有一定的影响。     

Vegetation gradients around cattleposts in the eastern mountains of Lesotho

The grasslands of the mountains in eastern Lesotho support large numbers of sheep, angora goats and other livestock during the summer, during which they are corralled nightly by herders at cattleposts. Few studies, however, have quantified the impact of grazing on the composition and structure of the mountain grasslands. Gradients of grazing and trampling intensity related to distance from 23 cattleposts in the subalpine and alpine belts (2 650–3 175 m above sea level) were examined to describe the long-term effects of livestock on unpalatable dwarf shrubs, bare area and plant species composition. The potential for shrub invasion and bare areas (low herbaceous cover) to develop was highest near cattleposts. Species composition also changed significantly along the grazing gradient, accompanied by a shift in dominants from grazing-sensitive to grazing-resistant grasses and shrubs. Species either decreased or increased monotonically along the grazing gradient or had an intermediate, unimodal response. The relative positions of species’ centroids along the grazing gradient were used to quantify their grazing sensitivity on a scale from 10 (most sensitive) to 0 (most resistant), which confirmed and contradicted previous classifications of their grazing responses. Basic ecological research on this important mountain grazing and catchment system is recommended.     

超载放牧与那曲地区高山嵩草草甸植被退化及其退化指标的探讨

对那曲地区中部高山嵩草草甸不同超载程度草地植被的调查分析结果表明,那曲地区中部高山嵩草草地超载严重,从定居点至放牧最远点,放牧压力逐渐降低,定居点附近超载高达3.73倍,超载最轻的草地也达到1.75倍;超载草地的多样性指数、植被盖度、地上现存生物量都显著低于围栏禁牧区;随超载程度的加大,莎草科植物、耐旱的杂类草、牲畜不喜食和不食的植物种有增加的趋势;综合分析超载下植被的不同特征变化并与现有的高寒草甸、草原类退化草地分类指标体系比较,初步认为,那曲地区的高山嵩草草甸都呈现退化加剧的趋势,已达到重度-中度退化程度,极重度超载区达到重度退化程度,重度和中度超载区达到中度退化程度,其比例分别达到9%和91%,远大于1996年的调查数据.     

The adventive flora of New Zealand

The ecological grouping (Decreaser and Increaser groups) of individual species was determined on two topographical units in the Highland Sourveld of the Orange Free State. For this purpose gradients were selected, giving special attention to fence‐line comparisons, vegetation at different distances from watering points and ungrazed vegetation. The ecological grouping (Decreaser and Increaser groups) of species on a grazing gradient differed not only for different topographical units, but also for sub‐habitats within a certain unit. Broad standardized groupings of species into Decreaser and Increaser groups are therefore scientifically wrong and of little practical use.     

坡度对亚高寒草甸狼毒群落植物多样性的影响

以青藏高原东北部边缘甘南亚高寒草甸草地群落为研究对象,将研究区样地坡度分为Ⅰ(0°～5°]、Ⅱ(5°～15°]、Ⅲ(15°～25°]、Ⅳ(25°～35°]及Ⅴ(>35°)5个坡度等级,采用样方调查法研究了甘南州合作市当周草原和扎油沟等亚高寒草甸区狼毒群落特征及草地生境条件.结果表明:1)研究区狼毒主要分布在土壤养分良好、水分状况适中、海拔在2900～3050 m高寒、亚高寒草甸区15°～35°的干燥阳坡地带.2)研究区植物群落组成以适应寒冷、多风的高寒环境的物种居多,坡度Ⅰ中记录有10科18属30种,坡度Ⅱ中记录有7科13属27种,坡度Ⅲ中记录有6科9属20种,坡度Ⅳ中记录有14科30属35种,坡度Ⅴ中记录有5科10属15种.3)莎草科植物重要值依次为Ⅱ>Ⅳ>Ⅰ>Ⅴ>Ⅲ,多年生根茎禾草重要值依次为Ⅴ>Ⅳ>Ⅲ>Ⅰ>Ⅱ,多年生丛生禾草重要值依次为Ⅴ>Ⅳ>Ⅰ>Ⅲ>Ⅱ,灌木与半灌木重要值依次为Ⅳ>Ⅴ>Ⅲ>Ⅱ>Ⅰ,多年生杂类草重要值依次为Ⅲ>Ⅱ>Ⅳ>Ⅴ>Ⅰ,一、二年生植物重要值依次为Ⅴ>Ⅳ>Ⅲ>Ⅱ>Ⅰ,大多数植物功能群在坡度Ⅳ和坡度Ⅴ上重要值最高,在坡度Ⅰ和坡度Ⅱ上重要值最低.4)研究区植物群落丰富度指数在不同坡度上变化幅度较大,生境结构复杂的群落其多样性指数高,物种多样性也相对丰富,坡度对狼毒群落植物多样性分布有一定的影响.     

Implications of changes to the transhumance system for conservation of the mountain catchments in eastern Lesotho

Abstract

The mountain catchments above 2 750 m a.s.l. in eastern Lesotho are a proclaimed Managed Resource Area (MRA) as a result of official concern about degradation of the grasslands of the alpine belt, and of recent parastatal interventions in the local livestock economy. However, the demarcation of the MRA may be inappropriate because it ignores recent changes in the transhumance system which threatens to cause greater degradation of the grasslands in the subalpine belt, particularly in the lower subalpine zone. In response to a variety of ecological and social factors, Basotho have modified the transhumance system by establishing winter grazing posts in this zone which lies between the summer grazing post areas in the subalpine zone and the alpine belt and the villages. The former areas are now used more intensively than the latter areas, thereby increasing the potential for greater degradation in the lower subalpine than in the upper subalpine zone and in the alpine belt. It is argued that the conservationist perspective, by which the MRA was demarcated needs to be broadened to include these lower valleys in view of these ecological dynamics.     

Influence of Livestock Grazing Strategies on Riparian Response to Wildfire in Northern Nevada

In 1999–2001 wildfires burned 1.13 million ha across northern Nevada, burning through many grazed riparian areas. With increases in wildfire frequency and extent predicted throughout the Great Basin, an understanding of the interactive effects of wildfire, livestock grazing, and natural hydrologic characteristics is critical. A comparison of pre- and postfire stream surveys provided a unique opportunity to statistically assess changes in stream survey attributes at 43 burned and 38 unburned streams. Livestock grazing variables derived from an extensive federal grazing allotment inventory were used to identify interactive effects of grazing strategies, fire, and natural stressors across 81 independent riparian areas. Differences between baseline and “postfire” stream survey attributes were evaluated for significance using the nonparametric Mann–Whitney test for paired data. Binary logistic regression models evaluated the influence of fire, grazing, and hydrologic characteristics on observed stream survey attribute changes. Grazing attributes contributed most significantly to the bankfull width increase and bank stability rating decrease models. The odds of bankfull width degradation (increase in bankfull width) decreased where there had been rest is some recent years compared to continuous grazing. As the number of days grazed during the growing season increased, the odds of bank stability degradation also increased. The occurrence of fire was not significant in any model. Variation in the riparian width model was attributed primarily to hydrologic characteristics, not grazing. For the models in which grazing variables played a role, stream survey attributes were more likely to improve over time when coupled with a history of rotational grazing and limited duration of use during the growing season. This supports long-term riparian functional recovery through application of riparian complementary grazing strategies.     

五台山亚高山草甸的人工神经网络分类与排序

人工神经网络理论是较新的数学分支学科,神经网络分类和排序是刚引入植物生态学的分析方法。本研究应用这2种方法研究了五台山亚高山高寒草甸。结果SOFM聚类将78个样方分为8个植物群落类型,基本上代表了本地区高寒草甸的群丛类型,具有明确的生态意义;SOFM排序反映了明显的生态梯度,表明海拔是影响草甸植被生长和分布的最主要因子,坡向和坡度也有一定的作用;SOFM聚类和排序方法分析应用效果好,2种方法结合使用更好;五台山草甸需要进一步加强保护。     

青藏高原冷龙岭南麓高寒小嵩草草甸植物种群物候学研究

通过对青藏高原祁连山东段冷龙岭南麓高寒小嵩草Kobrecia pygmaea草甸主要植物种群物候特性的观测研究,采用聚类分析和主分量排序法将小嵩草草甸26种植物种群划分为不同的物候类群.利用相关系数排序法指出了影响不同物候期的主要生态因子依次是温度、降水量和日照时间.研究结果对放牧管理具有指导意义.     

放牧对草甸草原植物群落结构及多样性的影响

在贝加尔针茅—羊草草甸草原的同一草地地境上,按放牧退化程度,将其划分为轻度退化区、中度退化区及重度退化区,并测定每一样地内植物群落特征及多样性指标。结果表明,随着放牧强度的增加,群落地上总生物量与中旱生植物的生物量变化保持一致,均呈降低趋势;中生植物先呈增加趋势,后下降;旱生植物呈增加趋势;群落优势种贝加尔针茅Stipa baicalensis和羊草Leymus chinensis呈降低趋势;物种丰富度指数先增加,而后降低;多样性指数和均匀度指数均呈增加趋势,优势度指数则相反。