Deterministic versus Individualistic community structure: a test from invasion by Nothofagus menziesii in southern New Zealand

Abstract. The Clements' Deterministic model of plant communities implies that a change in one species, especially a change in the physiognomic dominant, would have profound effects on the remainder of the community. Gleason's Individualistic model suggests there would be little effect. These alternative models are tested by examining the forest composition on both sides of a boundary along which the tree Nothofagus menziesii is slowly invading. Classification of forest composition, excluding N. menziesii, gave little evidence of an effect of N. menziesii on the lower strata: understorey vegetation types were distributed across the boundary. Some differences were found at individual sites, but these were often inconsistent between sites. Ordination, also excluding N. menziesii, similarly showed that none of the first three understorey axes reflected any effect of N. menziesii. The fourth axis was correlated with the presence of N. menziesii, but only when canopy trees were included. It is concluded that specific composition of the canopy in these montane New Zealand evergreen forests has little effect on the understorey, supporting Gleason's Individualistic concept of the community.     

武汉钢铁公司厂区绿地绿量的定量研究

针对城市绿地结构复杂、破碎化程度高的特点,在武汉钢铁公司厂区园林绿地层片结构及其盖度调查的基础上,借助GIS对其绿量进行了定量研究.结果表明,不同生活型植物的单叶面积和叶面积指数差异较大,植物种的叶面积指数大小不仅取决于单叶面积,而且取决于树冠的冠形和枝叶的密集程度.该厂区园林绿地的平均叶面积指数为7.75,总绿量为1 694.2 hm².其中,乔-灌-草型和乔 灌型绿地的面积和绿量分别占厂区总绿地面积和总绿量的79.7%和92.3%,反映了该厂区绿化以乔木为主,乔-灌-草型和乔-灌型绿地类型占绝对优势.结构单一的纯草坪型绿地在厂区应用较少,但草本层片的绿量占总绿量的22.9%.园林绿地的绿量取决于绿地面积、绿地的层片结构、不同层片植物的叶面积指数及其盖度.城市园林绿地应在扩大绿地面积的基础上,尽量选择叶面积指数较高的树种,完善层次结构,以增加总体绿量.以层片作为基础定量单元,在各层片代表种叶面积指数测定的基础上,通过绿地群落类型的层片结构及其盖度调查,并借助遥感影像和GIS提取各类群落的面积,可较为准确地定量城市园林绿地的绿量.     

Patterns of plant species and community diversity at different organization levels in a forested riparian landscape

Abstract. Integrated synusial phytosociology combined with traditional measures of diversity is used to describe the structure of vascular vegetation diversity along the forested riparian landscape of the upper Oise valley (Belgium and France). The two dimensions (longitudinal and lateral) of the geomorphological complex are examined at four scales: synusia, phytocoenosis, tesela and catena. The results support the following hypotheses: (1) the environmental gradients observed, particularly the lateral ones, are very complex; (2) there is a clear lack of coupling between the tree, shrub and herb layers, which indicates a differential response to the underlying influence of environmental controls; (3) moderate flooding‐induced disturbance enhances herb species richness; (4) stressful environments support a low plant species diversity but a high synusial richness; (5) natural factors (substrate, climate, disturbance) are more important at the synusia and phytocoenose scales, but (6) anthropogenic disturbances, mainly through forest and river management, are more important at the landscape level. By considering plant communities as structural‐dynamic entities of ecosystems in a landscape context, integrated synusial phytosociology provides a basis for decomposing a complex system since the different hierarchical levels are both nested and thus strongly relational and process‐based.     

Numerical approaches to lake classification with special reference to macrophyte communities

Summary Various approaches to the classification of S. Swedish lakes on the basis of their macrophyte composition are discussed. A main division is made between species or life-form, and synusia or community approaches. Three steps in the classification are discussed: primary clustering of sites to arrive at a local classification, secondary classification of clusters of sites to arrive at general community types and classification of lakes according to their community composition.The estimation of species performance is discussed and a logarithmic transformation advocated. The analysis of belt transects is suggested as a satisfactory general approach.Some problems regarding synusial independence and possible synusial interactions are mentioned. A survey of boundary types in lakes is given.Examples are given of classifications based on single life-forms and life-form combinations. Helophyte community composition of lakes is effectively shown by a combination of classification and ordination. The idea of aquatic community complexes is discussed with reference to the recent sigma-syntaxon approach in phytosociology.Nomenclature follows Lid (1974).     

Grazing Dynamics of the Species Diversity in Aneurolepidium Chinese Steppe and Stipa Grandis Steppe

Aneurolepidium chinense and Stipa grandis steppes are the two main community-types in the temperate,typical steppe zone of Eastern Mongolian plateau. The changes of their species diversity under grazing influence were studied on two representative grazing gradients, situated in the Xilin River Basin, Inner Mongolia. The results showed: The species richness of the two communities is reduced with the increase of grazing intensity,while their in dices of evenness and diversity on moderately grazed sites were higher than those on both ungrazed and heavily grazed sites. The diversity changes of the steppe community on grazing gradient depended mainly on the competitive exclusion of the species and the different effects of grazing on different species. These two functions could be integratively reflected by the synusia structure in communities. So the diversity of the synusia structure in a community was a measure of the degrees of differentiation of the ecological niches in it,and could be effectively used to interprete the species diversity changes. A moderate grazing intensity prevented the competitive exclusion of the dominant synusia,and at the same time,had no restrictions to the development of other synusia, which led to a diversified synusia structure with a high species diversity. Based on the species-area curve analysis, the measurement of large nested quadrats on homogeneous habitat was suggested as a suitable method for inventory and monitoring species diversity in the steppe area.     

Stratification in a New Zealand rain forest

An undisturbed podocarp-broadleaved rain forest was sampled in eight strata (synusiae): canopy, small tree, shrub, low shrub, herb, ground, epiphyte and liane. Independent classifications of the quadrats were performed using the eight strata, and the classifications were correlated. Relations between strata were significant, but weak. Using records of plants of all ages, the relations largely reflected the presence of seedlings of woody species in the ground and herb strata. Using only records of species present as adults, the relations were quite different, and at least some seemed to reflect sociological interactions. Relations between a tree and a herb stratum was lower than in McCune & Antos' (1981) investigation, probably because of the narrow ecological range of the present study area.     

Integrated synusial phytosociology: some notes on a new,multiscalar approach to vegetation analysis

Abstract. The integrated synusial approach of the vegetation is based on the differentiation of several spatio-temporal organization levels. A phytocoenosis (community of the second level) is considered as a complex of synusiae (communities of the first level) and is characterised by a strong tendency to self-organization. At each level, a typology of the communities can be performed. Ecological indicator values as well as different diversity indices are calculated for each vegetation unit. They are useful for understanding the spatial and temporal organization of the phytocoenoses. As an example. this approach is applied to wooded meadows.     

6种人工针叶幼林下地表苔藓植物层片的物种多样性与结构特征

 为了评估人工林苔藓植物发育状况,同时为人工林生态功能评价提供依据,采用样地取样方法,调查分析了岷江上游大沟流域6种人工幼龄针叶林（川西云杉(Picea balfouriana)林、日本落叶松(Larix kaempferi)林、油松(Pinus tabulaeformis)林、华山松(Pinus armandii)林、油松-华山松混交林和川西云杉-华山松混交林）林下地表苔藓植物层片物种组成、多样性以及结构特征及其异同。6种人工林下共发现了19种苔藓,各林下组成数量在7～13种。除云杉林外,纯林下苔藓种数均小于或者等于混交林下;6种人工林下地表苔藓植物平均盖度、平均密度、平均厚度分别在0.41%±1.49%～17.79%±1.67%、(27.99±367.95)～(3 807.11±412.90)株•m-2和(1.80±1.51)～(19.89±1.69) mm之间。无论是多样性指数,还是结构参数,均以川西云杉林最高,而华山松林最低。总体说来,岷江上游人工针叶幼林下地表苔藓组成物种较少、物种多样性指数（物种丰富度指数、Shannon-Wiener指数）低、Simpson指数高、结构参数（密度、盖度、厚度）较小,说明林下地表苔藓植物组成单一、结构相当简单,发育不良。综合分析表明,具有相对较低林冠郁闭度与林木密度的云杉林是6类人工林中恢复状况相对最好的类型,暗示出疏伐、修枝等管理措施可促进人工密林下地表苔藓植物生物多样性以及地表苔藓植物层片结构的改善。     

Influence of tree cover on the diversity of herbaceous communities in subalpine wooded pastures

Abstract. The relationships between several diversity indices and tree cover in subalpine wooded pastures with Larix de-cidua were analysed at two spatial scales: phytocoenoses (2500-m² plots) and herbaceous synusia (1-m² quadrats). Diversity indices have a non-linear relationship to Larix cover; the best fit was obtained with Gaussian regressions. Species richness was influenced by Larix cover more than evenness. At the phytocoenosis level, the optimum for species and synusial richness in the herb layer was near 25 % tree cover. At the synusia level, species richness of the herb layer showed an optimum when mean distance to the four nearest Larix trees was ca. 30 m, or when the potential number of sunshine hours between April and September was close to 1250 h. Canonical Correspondence Analysis confirmed the influence of Larix cover on the composition of phytocoenoses and herbaceous synusiae, but included also the role of altitude, slope and aspect.