Differences in habitat quality explain nestedness in a land snail meta-community

We set up two alternative hypotheses on how environmental variables could foster nestedness; one of “nested habitats” and another of “nested habitat quality”. The former hypothesis refers to situations where the nestedness of species depends on a nestedness of discrete habitats. The latter considers situations where all species in an assemblage increase in abundance along the same environmental gradient, but differ in specialisation or tolerance. We tested whether litter‐dwelling land snails (terrestrial gastropods) in boreal riparian forest exhibited a nested community structure, whether such a pattern was related to differences in environmental variables among sites, and which of the two hypotheses that best could account for the found pattern. We sampled litter from 100 m² plots in 29 mature riparian forest sites along small streams in the boreal zone of Sweden. The number of snail species varied between 3 and 14 per site. Ranking the species‐by‐site matrix by PCA scores of the first ordination axis revealed a similarly significant nested pattern as when the matrix was sorted by number of species, showing that the species composition in this meta‐community can be properly described as nested. Several environmental variables, most notably pH index, were correlated with the first PCA axis. All but two species had positive eigenvectors in the PCA ordination and the abundance increased considerably along the gradient for most of the species implying that the hypothesis of “nested habitats” was rejected in favour of the “nested habitat quality” hypothesis. Analyses of nestedness have seldom been performed on equal sized plots, and our study shows the importance of understanding that variation in environmental variables among sites can result in nested communities. The conservation implications are different depending on which of our two hypotheses is supported; a conservation focus on species “hotspots” is more appropriate if the communities are nested because of “nested habitat quality”.     

Plant composition associated with environmental gradients in tropical montane forests (Cueva de Los Guacharos National Park,Huila, Colombia)

Niche differentiation among tropical forest plants can generate species turnover along gradients of soil, topography, climate, and land use history. In this study we explore the relative importance of these variables as drivers of floristic composition in Cueva de Los Guacharos National Park. We established twenty 0.1‐ha plots, within which trees, lianas, and shrubs (diameter ≥ 2.5 cm) were censused. We selected plot locations in primary and disturbed forests, and we measured topography and soil variables. Despite their structural similarity, primary and disturbed forests differed floristically, and also differed in environmental variables measured. A NMDS ordination showed that variation in the floristic composition across plots is highly correlated to the exchangeable acidity, elevation, temperature, and magnesium availability. Variance partitioning analysis shows that together spatial and environmental variables explain 24.2 percent of the variation in species composition. ‘Pure environmental’ variables were more important in explaining compositional variability than ‘pure spatial’ processes (9.8% and 1.4%, respectively). Residual variance may be attributed to stochastic process or non‐measured biotic effects.     

Are cloud forest tree structure and environment related in the Venezuelan Andes?

Cloud forest vegetation structure and composition were studied in the Venezuelan Andes at three sites in Mérida State. Although the sites are within 10 to 30 km of each other, climatic, geologic and topographic differences are remarkable. The main purpose of the study was to determine the relationship of specific environmental variables to forest vegetation characteristics, including basal area, tree height, density and diversity, and leaf area index (LAI). At 51 plots, all trees' diameter at breast height >10 cm were recorded and identified. Although the environment at the three sites is distinctive, the tree species composition of the most abundant species was very similar. None of the measured environment variables were significantly correlated with the measured vegetation structure variables, except LAI, which was correlated with slope orientation; LAI showed higher values at south‐facing plots. Tree height was relatively uniform, while basal area was highly variable and reached very high values. Stem densities were in the range reported elsewhere in cloud forests. Multivariate analysis using structure or composition data shows segregation of the plots by site. Principal component analyses by site indicate a minor impact of environmental factors on forest variables. At each site, a particular group of species are correlated with the ordination axes. We conclude that species pools and forest dynamics add to the complexity of the structure of the studied cloud forests.     

Measuring ecological niche overlap from occurrence and spatial environmental data

Aim Concerns over how global change will influence species distributions, in conjunction with increased emphasis on understanding niche dynamics in evolutionary and community contexts, highlight the growing need for robust methods to quantify niche differences between or within taxa. We propose a statistical framework to describe and compare environmental niches from occurrence and spatial environmental data. Location Europe, North America and South America. Methods The framework applies kernel smoothers to densities of species occurrence in gridded environmental space to calculate metrics of niche overlap and test hypotheses regarding niche conservatism. We use this framework and simulated species with pre‐defined distributions and amounts of niche overlap to evaluate several ordination and species distribution modelling techniques for quantifying niche overlap. We illustrate the approach with data on two well‐studied invasive species. Results We show that niche overlap can be accurately detected with the framework when variables driving the distributions are known. The method is robust to known and previously undocumented biases related to the dependence of species occurrences on the frequency of environmental conditions that occur across geographical space. The use of a kernel smoother makes the process of moving from geographical space to multivariate environmental space independent of both sampling effort and arbitrary choice of resolution in environmental space. However, the use of ordination and species distribution model techniques for selecting, combining and weighting variables on which niche overlap is calculated provide contrasting results. Main conclusions The framework meets the increasing need for robust methods to quantify niche differences. It is appropriate for studying niche differences between species, subspecies or intra‐specific lineages that differ in their geographical distributions. Alternatively, it can be used to measure the degree to which the environmental niche of a species or intra‐specific lineage has changed over time.     

山西太岳山脱皮榆群落的生态梯度分析及环境解释

为了解释山西太岳山脱皮榆(Ulmus lamellosa)群落中物种的分布情况与该群落环境因子之间的相互关系,采用TWINSPAN数量分类和典范对应分析(CCA)与环境因子的变量分离进行讨论。结果表明,TWINSPAN将60个调查样方划分为7种群丛类型,体现了该脱皮榆群落主要以乔木脱皮榆和草本披针叶苔草(Carex lanceolata)为优势种。7种群丛类型与CCA排序结果一致,CCA排序第1轴主要体现了坡位和海拔;坡向与第2排序轴存在显著相关性。Monte Carlo检验结果表明,影响脱皮榆群落物种分布最主要的环境因子是海拔。在环境分离变量解释方面,环境因子解释了39.60%,空间因子解释了7.95%,空间因子与环境因子交互作用解释部分占10.89%。而其中不能解释的部分占41.56%。在该研究区,海拔对植物的分布有较好的解释力,其次是坡位和坡向。     

上海地区早春非耕地杂草分布与环境因子关系的统计生态学研究

野外调查发现上海地区早春非耕地杂草共106种,隶属于29科88属．计测了261个样地1305个样方中杂草的生态重要值和6种主要环境因子,应用典范对应分析作出了反映106种杂草与6种环境因子关系的二维排序图,应用双向指示种分析对106种杂草进行了有生态学意义的定量分类．根据6种环境因子与前两个排序轴相关系数的大小,发现土壤水分、土壤翻耕程度、人迹出没程度、交通影响程度是影响上海地区早春非耕地杂草分布的主要环境因素;根据双向指示种分析,结合典范对应分析的结果,可以从106种早春中分出五个生态类群,即类群Ⅰ：湿生淤泥海边滩涂杂草类群,类群Ⅱ：相对干燥海边滩涂杂草类群,类群Ⅲ：干扰相对较小的人工林地杂草类群;类群Ⅳ：干旱、开阔、干扰较重环境中的杂草类群;类群Ⅴ：湿润、开阔、干扰较重的弃耕农田环境中的杂草类群．     

Effects of plot size on the ordination of vegetation samples

Questions: Do ordination patterns differ when based on vegetation samples recorded in plots of different size? If so, how large is the effect of plot size relative to the effects of data set heterogeneity and of using presence/absence or cover‐abundance data? Can we combine plots of different size in a single ordination? Methods: Two homogeneous and two heterogeneous data sets were sampled in Czech forests and grasslands. Cover‐abundances of plant species were recorded in series of five or six nested quadrats of increasing size (forest 49‐961 m2; grassland 1‐49 m²). Separate ordinations were computed for plots of each size for each data set, using either species presences/absences or cover‐abundances recorded on an ordinal scale. Ordination patterns were compared with Procrustean analysis. Also, ordinations of data sets jointly containing plots of different size were calculated; effects of plot size were evaluated using a Monte Carlo test in constrained ordination. Results: The results were consistent between forest and grassland data sets. In homogeneous data sets, the effect of presence/absence vs. cover‐abundance was similar to, or larger than, the effect of plot size; for presence/absence data the differences between ordinations of differently sized plots were smaller than for cover‐abundance data. In heterogeneous data sets, the effect of plot size was larger than the effect of presence‐absence vs. cover‐abundance. The plots of smaller size (= 100 m2 in forests, = 4 m² in grasslands) yielded the most deviating ordination patterns. Joint ordinations of differently sized plots mostly did not yield patterns that would be artifacts of different plot size, except for plots from the homogeneous data sets that differed in size by a factor of four or higher. Conclusions: Variation in plot size does influence ordination patterns. Smaller plots tend to produce less stable ordination patterns, especially in data sets with low ß‐diversity and species cover‐abundances. Data sets containing samples from plots of different sizes can be used for ordination if they represent vegetation with large ß‐diversity. However, if data sets are homogeneous, i.e. with low ß‐diversity, the differences in plot sizes should not be very large, in order to avoid the danger of plot size differences distorting the real vegetation differentiation in ordination patterns.     

Understorey vegetation development in North Finnish Picea forests after disturbance: re‐analysis of Sirén's data

Abstract. Sirén (1955) studied understorey species composition, tree stand properties and humus‐layer thickness in 64 unlogged forest stands on topographically and pedologically comparable sites. The stands were of even age (6 – 300 yr), stocked with the first or second tree generation after wildfire. The view of Sirén and several authors after him, that the vegetation of old‐growth boreal Picea forests is homogeneous on a broad scale, was examined by applying, in parallel, the partial variants of two ordination methods (DCA and PCA) to Sirén's vegetation data. Two main vegetation gradients were found: a major gradient running from recently burnt plots with prominence of pioneer species to plots with stand age > 100 yr, a well stocked tree layer and a thick humus layer, dominance of feather‐mosses and ample occurrence of shade‐tolerant as well as light‐preferring vascular plant species, and a second gradient along which first‐ and second‐generation plots segregate. The more prominent element of Betula trees in first‐ than in second‐generation stands < 100 yr contributed to the latter. A minor third gradient related to humus‐layer thickness was recovered by partial DCA only. The main vegetation gradient reappeared in separate ordinations of data from 47 mature forest stands (> 100 yr), but without being correlated with forest age. Variation among mature‐forest stands in the importance of pioneer species is considered mainly to be brought about by fine‐scale disturbance processes such as tree uprooting. Increasing importance of factors operating on within‐stand scales [development of a varied gap structure and stronger gradients in tree influence (radiation at ground level), soil moisture, soil depth and nutrient availability] with time is also reflected in the second and third mature‐forest ordination axes. Possible implications of the results for conservation of biological diversity and monitoring of changes in boreal forests are discussed.     

Interactions between alien plant species traits and habitat characteristics in agricultural landscapes in Finland

The survival and success of alien plant species is determined by species traits (i.e., invasiveness) and the characteristics of the habitats in the region of introduction (i.e., invasibility). However, little is known about species traits as related to habitat characteristics. We assessed the characteristics of successful invaders and the interaction of environmental factors and life-history traits for alien plant species. The vascular plants were recorded from 52 agricultural landscapes in Finland. We compared the traits of native and alien plant species with Fisher’s exact test and used a three table ordination analysis, RLQ analysis, to relate species traits to environmental conditions. Species were clustered according to their position on the RLQ axes, and the clusters were tested for phylogenetic independence. The successful alien plant species were associated with life form and preferences for moisture and nitrogen, but the trait composition varied according to the habitat type. Two RLQ axes explained 80.5% of the variation, and the species traits were significantly associated with environmental variables. The clustering showed that the occurrence of alien plant species in agricultural habitats was driven by invasion history, traits related to dispersal (dispersal type, seed mass) and habitat preferences, as well as environmental features, such as geographical location, temperature and the quality and disturbance regime of the habitats. All clusters were phylogenetically non-independent. Thus, the clusters of alien species comprised species of diverse taxonomic affinities, although, they shared the traits explaining their occurrence in particular habitats. This information is useful for understanding the link between species traits and the environmental conditions of the habitats, and complexity of the invasion process.     

Do vine species in neotropical forests see the forest or the trees?

Questions: Is the occurrence of vine species in neotropical rain forests primarily determined by properties of the forest (environmental factors), by properties of the trees (tree species or tree size) or are vines randomly distributed? Location: Maya Biosphere Reserve, Guatemala. Methods: In five 1‐ha plots that span variation from unlogged forest to forest impacted by recurrent human disturbance we recorded the presence of all climbing vine species on every tree. The presence of all free standing vine species and 11 environmental variables were recorded in 100‐m² subplots. The relationship of host tree diameter and host tree identity on single tree vine species richness was investigated by GLM modelling. Partial redundancy analyses were used to partition the variation in vine species composition on two sources: environmental factors and tree species identity. Results: Single tree vine richness increased with increasing host tree DBH and differed significantly among host species. For climbing vines, the ratio of variation in subplot presence explained by tree species and by environmental variables was ca. 4:1 (in the most disturbed logged plots slightly lower), for free standing vines this ratio varied from 1:2 in the most disturbed logged plots to 9:1 in reserve plots, while a ratio of ca. 1:1 was found for all plots analysed together. Conclusion: Different tree species have different probabilities of being infested by vines. Vines see both the forest and the trees; the environment is more important in earlier developmental stages, properties of individual trees become more important from the time vines start to climb.     

Land‐use legacies in a central Appalachian forest: differential response of trees and herbs to historic agricultural practices

Question: Are contemporary herb and tree patterns explained by historic land use practices? If so, are observed vegetation patterns associated with life‐history characteristics, soil properties, or other environmental variables? Location: Southeastern Ohio, USA. Methods: Using archival records, currently forested sites were identified with distinct land use histories: cultivated, pasture (but not plowed), and reference sites which appear to have never been cleared. Trees were recorded by size and species on twenty 20 m × 20 m plots; percent cover was estimated for each herb species in nested 10 m × 10 m plots. Environmental characteristics were noted, and soil samples analysed for nutrient availability and organic matter. Nonmetric multidimensional scaling ordination was performed separately on both tree and herb datasets to graphically characterize community composition among plots. Life‐history traits were investigated to explain observed compositional differences. Results: Vegetation patterns were explained by current environmental gradients, especially by land‐use history. Cultivated and pasture sites had similar tree composition, distinct from reference sites. Herb composition of pasture and reference sites was similar and distinct from cultivated sites, suggesting the ‘tenacity’ of some forest herbs on formerly cleared sites. Tilling removes rhizomatous species, and disfavors species with unassisted dispersal. These life‐history traits were underrepresented on cultivated sites, although ant‐dispersed species were not. Conclusions: Historic land‐use practices accounted for as much variation in species composition as environmental gradients. Furthermore, trees and herbs responded differently to past land‐use practices. Life‐history traits of individual species interact with the nature of disturbance to influence community composition.     

Spatial variation in insect community and species responses to habitat loss and plant community composition

Several experimental studies have examined species responses to manipulations of habitat area and spatial arrangement, but plant composition and spatial variation in species distributions also affect animal responses to habitat alteration. We used an experimental approach to study the combined effects of habitat area, edge, and plant community composition on the spatial structure of insect species richness and composition. The abundance of three guilds (herbivores, predators and parasitoids) and individual species were also analyzed. Habitat patches were created that differed in area and edge by selectively mowing portions of 15 m×15 m plots in a 1.7-ha old field. Spatial and environmental variables were used to predict insect responses in separate multiple regression and ordination models. The variation in species responses due to spatial and environmental variables was then partitioned by combining these variables into an overall regression or ordination. Spatial and environmental variables contributed similar percentages to the total variance in insect species richness, abundance or composition. No significant effects of habitat area were observed in any response variable. Herbivore abundance showed positive responses to legume or grass cover, as well as spatial variation that was unrelated to environmental variables. Predators and parasitoids had greater effects of plant species richness and habitat edge, and less unexplained spatial variation. Individual species differed in their responses to plant variables, depending on host specialization or intraspecific aggregation. Our study highlights the importance of plant community composition and spatial variation apart from environmental variables. Spatial variation stems both from species responses to environmental features as well as species differences in habitat specialization and intraspecific aggregation.     

Scale‐dependence of vegetation‐environment relationships in semi‐natural grasslands

Questions: Which environmental and management factors determine plant species composition in semi‐natural grasslands within a local study area? Are vegetation and explanatory factors scale‐dependent? Location: Semi‐natural grasslands in Lærdal, Sognog Fjordane County, western Norway. Methods: We recorded plant species composition and explanatory variables in six grassland sites using a hierarchically nested sampling design with three levels: plots randomly placed within blocks selected within sites. We evaluated vegetation‐environment relationships at all three levels by means of DCA ordination and split‐plot GLM analyses. Results: The most important complex gradient determining variation in grassland species composition showed a broad‐scale relationship with management. Soil moisture conditions were related to vegetation variation on block scale, whereas element concentrations in the soil were significantly related to variation in species composition on all spatial scales. Our results show that vegetation‐environment relationships are dependent on the scale of observation. We suggest that scale‐related (and therefore methodological) issues may explain the wide range of vegetation‐environment relationships reported in the literature, for semi‐natural grassland in particular but also for other ecosystems. Conclusions: Interpretation of the variation in species composition of semi‐natural grasslands requires consideration of the spatial scales on which important environmental variables vary.     

稀有种处理对RDA排序结果影响的比较研究

为了解稀有种对RDA排序结果的影响,该研究以北京东灵山华北落叶松林调查数据为例,在RDA排序的基础上,对比分析了未处理稀有种RDA与剔除频度5%、盖度5%的稀有种后RDA排序结果的差异,并用蒙特-卡罗拟合检验分析了二者物种变量和环境变量之间的相关关系,以及用Spearman秩相关系数检验了对应排序轴的相关性。结果表明:(1)蒙特-卡罗拟合检验结果显示未处理稀有种RDA与剔除稀有种RDA各自对应的物种变量和环境变量之间均呈极显著相关关系;(2)从排序轴特征值对物种数据方差以及物种—环境关系解释量来看,剔除稀有种RDA前两排序轴与前四排序轴均有较高的物种-环境关系累积解释量;(3)剔除稀有种前后对应排序轴的Spearman秩相关分析结果表明,尽管未处理稀有种RDA和剔除稀有种RDA在第三轴和第四轴间存在一定的交叉,但二者对应的前四排序轴均呈极显著的一一对应关系(P0.001),相似性极高。总之,结合物种-环境关系的累积解释量及对应排序轴的相关性可知,在环境因子个数较少、研究尺度较小时,使用RDA排序揭示植物种、植物群落和环境因子之间相互作用的生态关系时,剔除稀有种前后RDA排序具有较高吻合性,只是对环境因子的解释趋势稍有差异。     

Gradient analysis of dry grassland vegetation in Denmark

Abstract. We present a gradient analysis of 620 vegetation samples covering most of the floristic and environmental variation in semi‐natural grassland vegetation on well‐drained soils in Denmark. Vegetation was sampled using frequency in subplots. Explanatory variables were surface inclination, aspect, pH, geographical co‐ordinates together with indications of soil type. Detrended Correspondence Analysis revealed four floristic gradients that could be interpreted in ecological terms by measured variables supplemented with site calibrations based on weighted averaging of Ellenberg's indicator values. All four axes were interpreted using rank correlation statistics, and linear and non‐linear multiple regression of sample scores on explanatory variables. The first gradient was from dry calcareous to humid acidic grasslands; the second reflected an underlying gradient in fertility; the third reflected regional differentiation and the fourth was associated with variation in intensity of competition as indicated by association with calibrated Grime‐CSR values for the plots. We applied subset ordination to the data as a supplement to traditional permutation and correlation statistics to assess the consistency of ordination results. DCA axes 1 and 2 were consistent in space and time. This gradient analysis is discussed in a context of plant strategy theory and species diversity models. Ecocline patterns lend support to the view that grazing not only favours the ruderal strategy but also the stress‐tolerant strategy. The low rank of competition as an explanatory variable for the floristical gradients supports the notion that competitive effects play a subordinate role for species composition compared to microclimate and soil conditions in infertile semi‐natural grasslands.     

The influence of multi‐scale environmental variables on the distribution of terricolous lichens in a fog desert

Question: How do environmental variables in a hyper‐arid fog desert influence the distribution patterns of terricolous lichens on both macro‐ and micro‐scales? Location: Namib Desert, Namibia. Methods: Sites with varying lichen species cover were sampled for environmental variables on a macro‐scale (elevation, slope degree, aspect, proximity to river channels, and fog deposition) and on a micro‐scale (soil structure and chemistry). Macro‐scale and micro‐scale variables were analysed separately for associations with lichen species cover using constrained ordination (DCCA) and unconstrained ordination (DCA). Explanatory variables that dominated the first two axes of the constrained ordinations were tested against a lichen cover gradient. Results: Elevation and proximity to river channels were the most significant drivers of lichen species cover in the macro‐scale DCCA, but results of the DCA suggest that a considerable percentage of variation in lichen species cover is unexplained by these variables. On a micro‐scale, sediment particle size explained a majority of lichen community variations, followed by soil pH. When both macro and micro‐scale variables were tested along a lichen cover gradient, soil pH was the only variable to show a significant relationship to lichen cover. Conclusion: The findings suggest that landscape variables contribute to variations in lichen species cover, but that stronger links occur between lichen growth and small‐scale variations in soil characteristics, supporting the need for multi‐scale approaches in the management of threatened biological soil crust communities and related ecosystem functions.     

Early succession on plots with the upper soil horizon removed

Abstract. Succession was studied on plots with the upper soil horizon removed in an area affected by acidic air pollution in the Kru?né Hory Mts., Czech Republic. 10 permanent 1‐m² plots were marked and vegetation recorded annually using a grid of 100 subplots from 1989 to 1995. Constrained ordination analyses showed that soil texture is the most important environmental factor influencing the course of succession. Its effect on species composition increases with successional age of the plant community. On fine‐grained soils species‐poor communities dominated by grasses (Calamagrostis villosa, Deschampsiaflexuosa) and on coarse‐grained soils species‐rich communities dominated by heather (Calluna vulgaris) developed. Succession proceeded from communities where species composition was determined by diaspore availability towards communities where species composition depended on environmental conditions. Successional communities after 10 yr are more dependent on soil characteristics and consequently environmental determination increases over the course of succession and causes the communities to diverge.     

山西灵空山小蛇沟林下草本层植物群落梯度分析及环境解释

通过对山西灵空山小蛇沟集水区的林下草本层植物群落进行调查和多元分析——TWINSPAN分类、典范对应分析(CCA)与生境、生物因素变量分离, 探讨林分水平上草本层物种分布与环境因子之间的关系。结果如下: 1) TWINSPAN将26个调查样方划分为6种群落类型: 以辽东栎(Quercus wutaishanica)为主的辽东栎-油松(Pinus tabulaeformis)林型、辽东栎杂木林型、辽东栎林型、华北落叶松(Larix principis-rupprechtii)林型、油松林和阔叶油松林型、油松-辽东栎均匀混交林型, 体现了该地区地带性植被类型为暖温带森林的特点。2)群落类型的划分与CCA的结果相吻合, 主要反映了CCA排序第一、二轴的环境梯度, CCA排序轴第一轴突出反映了林分类型与土壤养分梯度, 第二排序轴与坡度、坡位显著相关。Monte Carlo检验结果表明, 林分类型、土壤养分和坡度是影响小蛇沟集水区内林下草本物种分异的最主要的环境因子。3)生境因子与生物因子解释了物种格局变化的42.9%, 其中生境因子占31.8%, 生物因子占7.9%, 生境因子与生物因子交互作用解释部分占3.2%。良好的环境解释反映了调查取样和环境因子选取的合理性。对于50%以上未能被解释的变异部分, 可能归咎于未被选取的因子如干扰或者随机过程。4)在海拔梯度较小的山区, 坡向等小地形因子能较好地指示局部生境的小气候条件, 对林下植物的分布有较好的解释力。     

Studies of a vegetation transect through brigalow (Acacia harpophylla) forest in central Queensland

Vegetation and environmental data were collected in 182 contiguous plots along a belt transect, 3.7 km long, in central Queensland through a relatively undisturbed forest dominated by brigalow (Acacia harpophylla). A subset of eighty-nine plots using percentage cover of 128 species was classified using a polythetic agglomerative approach. Dual stand and species ordinations by principal component analysis and reciprocal averaging were also undertaken. The cluster analysis and ordination of unstandardized cover data, grouped stands on the basis of abundance of the predominant canopy species, but only where these species were true dominants such as Macropteranthes leichhardtii did these same groupings appear in the ordination of standardized data. The latter ordination was ecologically more satisfying, but the complementary species ordination was unsatisfactory. The vegetation-species complex was best explained by dual species and stand ordinations using presence-absence data. Reciprocal averaging appeared to produce a marginally better ordination than principal component analysis. An ordination of eleven environmental factors indicated soil profile and presence of gilgai were the most important environmental variables. The ordination was enhanced by varimax rotation which focused on a more homogeneous environmental gradient and coincided more closely with the vegetation ordinations. An ordination using both species and environmental factors substantiated the explanation of the vegetation-environmental complex derived from separate ordinations. The main gradient revealed from the ordinations appeared to be a mesic-xeric gradient stretching from Macropteranthes leichhardtii semi-evergreen vine thicket at the mesic end diverging through various A. harpophylla - dominant communities to A. harpophylla - Eucalyptus melanophloia woodland on duplex soils and Dichanthium affine grassland on clay soils. Six plant communities are defined and described and each related to a particular set of environmental conditions. These communities are bonewood (Macropteranthes leichhardtii) - semi-evergreen vine thicket, brigalow (Acacia harpophylla) - semi-evergreen vine thicket, brigalow (A. harpophylla) continuum (clay soils), Dichanthium affine grassland, brigalow (A. harpophylla) continuum (duplex soils) and brigalow (A. harpophylla) - silver-leaved ironbark (Eucalyptus melanophloia) woodland.