Species Ordination Research Articles

Vegetation response on a forest slope cleared for a skirun with special reference to the Herb Alstroemeria aurea graham (Alstroemeriaceae), Argentina

The vegetation structure and composition of an area of Nothofagus pumilio forest clear-felled for skiing (Mt Catedral, Argentina) have been studied, with special reference to the development of Alstroemeria aurea shoots and seedlings. The recovery of this species after cutting to ground level was also evaluated. Eight trasects were set up in three areas with shrub-cutting activities and different intensities of disturbance by footpaths after the ski-run development. Ordinations of sampling areas and species were obtained. Understorey clonal species dominate all sampling areas, although patches of exotic species and native ruderals were to be found in more disturbed areas. Alstroemeria aurea recovered after vegetative-shoot cutting by producing new vegetative shoots and curtailing the development of reproductive shoots. The closure of some footpaths and the restriction of maintenance activities to the end of the growing season could prevent further invasions by ruderals.

Distribution of Microlaena stipoides and Its Association With Introduced Perennial Grasses in a Permanent Pasture on the Northern Tablelands of New South Wales

The distribution of Microlaena stipoides (Labill.) R.Br. and its association with introduced perennial grasses was studied in a 10.2-ha permanent pasture on the Northern Tablelands of New South Wales. There were 105 systematically arranged plots (2m × 2m quadrats) located in the field, and at each sampling location composition by basal cover of the perennial herbaceous species encountered was recorded using 100 points. Dominant perennial grasses identified in the field were the native M. stipoides and the introduced Lolium perenne L., Dactylis glomerata L. and Poa pratensis L. Trifolium repens L., sown in the field in 1961, was also widespread. M. stipoides was abundant throughout the paddock, although higher composition by basal cover was observed under tree canopies. Discriminant function analysis and hierarchical classification showed a tendency towards aggregation of plots dominated by M. stipoides, L. perenne and T. repens, which may indicate the stability of this combination of species. T. repens was present in almost all plots and had a similar distribution to M. stipoides; both species were quite close in the species ordination analysis and were found associated with other perennial grasses at different locations in the paddock. These species associations are probably stable and appear to be common in permanent pastures in the eastern parts of the Northern Tablelands.

Environmental correlates of species distributions in a saxicolous lichen community

Abstract. The importance of abiotic environmental factors in determining species distributions in a saxicolous lichen community at Jonas Rockslide, Jasper National Park, Alberta is assessed using Canonical Correspondence Analysis. This technique allows ordination of species on axes determined by measured environmental variables. The suitability of this technique for handling data which may not be normally distributed is confirmed by comparison with the results obtained using a non‐parametric correlation coefficient. The variables found to be most highly correlated with species distributions are altitude on the rockslide and inclination from horizontal of the rockface (slope). These variables are thought to determine temperature and water availability at the rock surface. Using the first two ordination axes, species can be divided into groups, based on shared responses to the measured environmental variables.

Demersal Fish Assemblages on the Scotian Shelf, Northwest Atlantic: Spatial Distribution and Persistence

This study is based on 18 surveys, 12 in summer, and three each in spring and fall, with bottom trawls over the Scotian Shelf and Bay of Fundy. The data analysis sequence was: temporal and spatial aggregation of trawl sets; estimation of interspecies and intersite distance indices; clustering and ordination of sites and species, and discrimination of site groups using environmental variables. Nine species-groups, and 10 site-groups were defined, and displayed in a two-way table. Depth and temperature were the environmental variables most strongly associated with differences in assemblage structure among site-groups. Changes in assemblage structure from one area to another were distinct but apparently gradual, with no sharp assemblage boundaries. This pattern is expected if species are distributed independently on environmental gradients, rather than if assemblages consist of highly co-evolved, interdependent species. The observed spatial patterns were highly persistent through time. There are regions which are relatively homogeneous with regard to species composition and which can therefore be useful in dealing with bycatch problems. However, this study does not indicate the existence of discrete assemblages which might be appropriate as ecologically based fishery management units.

Vegetation patterns in James Bay coastal marshes. III. Salinity and elevation as factors influencing plant zonations

Plant zonations and selected environmental variables were studied in a subarctic coastal marsh at Ekwan Point, James Bay, Ont. Eight distinct community types were identified using two-way indicator species analysis classification (TWINSPAN). These were interpreted as a primary successional sequence. The eight communities were found to conform closely to the classical marsh zonations based on elevation and tidal influence: (1) lower salt marsh, (2) middle salt marsh, (3) upper salt marsh, (4) saline meadow, (5) freshwater meadow, and (6) freshwater fen. Environmental data collected along the vegetation transects indicated that changes in elevation and soil-water salinity probably influence species distributions. A species ordination using detrended correspondence analysis (DECORANA) revealed several trends in plant distribution patterns. Consideration of the environmental affinities of species separated along three ordination axes suggested that salinity and elevation, water content, and soil texture were probably important factors influencing successional processes in the marsh during at least the last century. An inverse salinity gradient, which has been reported at many sites along the west coast of Hudson and James bays, was not found at Ekwan Point.

The Influence of Habitat Structure on Fish Assemblage Composition in Southeastern Blackwater Streams

-We quantitatively sampled fish assemblages and measured habitat structure in upper coastal plain streams of the central Savannah River drainage, South Carolina. Fish species abundances ordinated in principal component space based on 15 habitat variables were arrayed along gradients of velocity and stream size (depth and width) and their covariates such as substrate and cover. The majority of species' centroids oriented toward slower, deeper habitats with depositional substrates and cover. Size classes within some species were well separated, indicating change in habitat use with age, whereas others clustered closely, indicating consistent habitat use through ontogeny. In an ordination based on species distributions and abundances (detrended correspondence analysis) species again oriented along velocity and stream size gradients. Although taxonomically related species had distinct optima, most genera and families clumped into similar regions, indicating a phylogenetic component to assemblage composition. A Mantel comparison of species ordinations on PCA and DCA axes resulted in high and significant concordance, indicating that these independent techniques produce the same conclusion regarding response of fishes to habitat parameters. Much site-to-site variation in composition of coastal plain fish assemblages can be attributed to variation in habitat structure, primarily current velocity and

Le peuplement de Mammifères Insectivores des forêts du Nord-Est du Gabon

Le peuplement de Mammifères Insectivores des forêts du Nord-Est du Gabon

An Application of Detrended Correspondence Analysis and Non-Metric Multidimensional Scaling to the Identification and Analysis of Environmental Factor Complexes and Vegetation Structures

(1) A four-stage computational procedure is proposed for the analysis of complex vegetation-environment systems. This consists of: (i) an initial ordination by Detrended Correspondence Analysis (DCA), summarizing the structure in a vegetation data set; (ii) simple 2 x 2 correlation (using Kendall's rank-order correlation coefficient) of a matrix of environmental data and DCA sample scores; (iii) environmental plexus construction by means of the application of Non-metric Multidimensional Scaling (NMDS), using the environmental correlation matrix as data; and finally (iv) construction of an integrated plexus, incorporating both environmental variables and DCA ( vegetation) gradients. (2) The procedure was tested on data from the Storbreen glacier foreland, Jotunheimen, Norway, as part of a wider study of this successional system. On the basis of the NMDS plexus diagrams, two principal structures were identified: (i) a 'terrain-age factor complex', principally comprising measures of soil development and site disturbance and (ii) an 'exposure-moisture regime-snowmelt factor complex'. Clear links were suggested between these complexes and two DCA axes. These relationships were found to be compatible with the trends displayed in the species ordination. (3) The analytical sequence, which involves an extension of previous applications of both DCA and NMDS, provides a comprehensive framework for the examination of vegetation-environment interactions. The most novel feature of this sequence is the representation of the relationships in interpretable plexus diagrams. The approach is recommended for the generation of ecological hypotheses which interrelate complex gradients in environmental factors and vegetational composition.

FLORISTIC PATTERNS ON AVALANCHE PATHS IN THE NORTHERN ROCKY MOUNTAINS, USA

Avalanche paths in the northern Rocky Mountains have transverse zones of plant physiognomic types representing major exogenous environmental gradients related to topography. Species composition was analyzed among these transverse zones. Forty plots on two paths in Montana, USA, were ordinated by detrended correspondence analysis, giving ordination axes for both plots and species. The results of the ordination of the plots did not correspond to their differentation in physiognomic zones. Dominant species of similar physiognomy were widely separated in the ordination of species. Endogenous spatial processes are suggested to explain the more complex floristic pattern. (Keywords: avalanche, floristic patterns, Rocky Mountains, vegetation)

Structure and dynamics of jack pine stands near Elk Lake, Ontario: a multivariate approach

Multivariate techniques were utilized to examine even-aged jack pine stands on upland sandy sites at the southern edge of the boreal forest near Elk Lake, Ontario. Cluster analysis of 180 stands led to the recognition of 10 vegetation types, each showing a unique combination of floristics, physiognomy, and environmental components. Classification of common species led to the recognition of five ecological groupings, which show varying degrees of association with the vegetation types. Nonmetric multidimensional scaling of the stands suggested a vegetational continuum in response to overall moisture availability. A corresponding ordination of common species indicated the development of interspecific associations related to soil moisture conditions. It is suggested that the vegetational composition of upland jack pine forests is determined by both probabilistic and deterministic effects, and this is discussed in the context of vegetation structure and dynamics.

Veld compositional response to fertilization in the tall grassveld of Natal

The plant species compositional response of veld at Ukulinga to application, over 30 years, of nitrogen, phosphate and lime is reported. Two types of nitrogen fertilizer were applied at four levels with and without phosphate, lime and lime + phosphate. Each treatment was replicated three times. Data on veld composition were obtained using a Levy bridge and observing 100 points per plot. The response of the veld to fertilization was examined using detrended correspondence analysis, providing simultaneously a samples and species ordination. The amount, but not the form, of nitrogen fertilizer strongly affected veld composition. Phosphate and lime had a lesser effect on veld compositon, but the presence of phosphate enhanced the effect of nitrogen on some grasses. S. Afr. J. Plant Soil 1986, 3: 1–10

Use of detrended correspondence analysis to evaluate factors controlling spatial distribution of benthic insects

Detrended correspondence analysis (DCA) was evaluated for its effectiveness in displaying factors controlling the spatial distribution of benthic insects in an oligotrophic stream where an experimental gradient (copper) that selectively affects population abundances was imposed. DCA proved to be highly sensitive to differences among samples and consistently provided ecologically meaningful species ordinations.

Ordinations of species and fuel arrays and their use in fire management

Fuel arrays were sampled on 40 plots on avalanche paths in Montana, U.S.A. Two measures of fire intensity were calculated for each plot: total heat release (kWh m −2) and Byram's Index (kW m −1). The biomass of species was ordinated using Detrended Correspondence Analysis (DCA). The fuel arrays, under three assumptions, were ordinated using DCA and Principal Component Analysis (PCA). The axes for the floristic and fuel load ordinations are not well correlated. Stepwise regressions of the fire intensity measures on the ordination axes show that PCA represents the relationship between fuel and fire better than DCA. Similar regressions on the sampled fuel arrays produce equivalent predictors. Ordinations of vegetation and fuel may provide information for use in fire behavior calculations, but of themselves cannot be used to predict fire.

Structure in temperate predaceous diving beetle communities (Coleoptera: Dytiscidae)

Collection records of adult dytiscid beetles (Coleoptera, Dytiscidae) from 312 sites within the province of Alberta, Canada, were analyzed for patterns of similarity in species distribution. Sites compared on the basis of species occurrence (Jaccard coefficient of similarity and group average cluster analysis) separated into 12 principal clusters, interpreted as communities. However, cluster inclusion occurred at very low levels of similarity and 30% of sites were unclustered outliers. Ecological charade us tics of sites that were recognized as varying between dusters were salinity, productivity, stability, water temperature, substrate type, flow and vegetation. An index relating these qualitatively defined variables to species numbers is presented.An analysis of co‐occurrence patterns of species was conducted as an alternative approach to definition of multispecies associations. Each possible combination of co‐occurrence between pairs of species occurring in more than 5 collections each was tested for significance (p = 0.005) by means of Yates corrected χ2 tests. Results of tests were expressed in binary terms, blank – no significance, x ‐ significant. Species were then clustered on the basis of patterns of significant co‐occurrences as above. This analysis was used as the basis for ordination of species in a symmetrical matrix with species ordered so as to maximize density of points of significant co‐occurrence (x) around the principal diagonal. Areas in the matrix showing high densities of co‐occurrence were interpreted as representing communities.The cluster analysis of species produced a better cluster pattern than obtained for sites but while generally similar, the species clustering pattern was less fine. The principal species groups consisted of those of saline water, alpine/subalpine lotic sites, other lotic habitats, and lentic habitats with two subgroups, species in forest areas and grassland species. The ordination, while reflecting this grouping of species, demonstrated that each group graded into others through loss of certain species and acquisition of others and thus showed the continuum nature of these communities. Restricting ordination to congeneric species indicated that these do not usually show identical patterns of co‐occurrence but neither are patterns coincident with mutual exclusion. Within genera, considerable overlap in occurrence between species is the norm but species tend to occupy slightly different positions relative to one another along qualitatively defined ecological gradients. Relative position of species in these ordinations shows good correlation with patterns of geographical distribution lending support to the interpretation of ordination patterns reflecting relative ecological segregation. The dytiscid beetle fauna of north temperate regions is especially rich. Also, the large number of significant co‐occurrences observed between species shows that species packing in many habitats of this region is dense. It is speculated that this species richness is possible because of the seasonality of habitats at these latitudes which reduces competition and predation from other groups and produces seasonal pulses of high productivity permitting a species rich fauna to develop because of abundant resources. It is likely that factors other than interspecific competition for resources are important in shaping dytiscid communities in habitats with strong nutrient pulses.

STRUCTURAL PATTERN IN ALPINE TUNDRA VEGETATION

Several aspects of the spatial pattern of plants were investigated in six very different stands in the alpine tundra of the Colorado Front Range. Pattern was related to the internal structure of the stands, to interactions among the species, and to microhabitats within the stands.Evidence from species‐species associations and species ordinations clearly divided the stands into two groups. The first was characterized by thin, coarse, unstable soils, low plant cover, and nurse‐plant establishment. The second group was characterized by deeper, more mature, and more stable soils, higher plant cover, and more competition between species.Pattern evidence allowed some species to be categorized as competitors, ruderals, or stress‐tolerators in the context of the alpine vegetation. The two groups of stands also differed in the relative importance of species with these “strategies.”

Species Ordination of Upper Slope Oak-Hickory Stands of Southeastern Ohio

MCCARTHY, B. C., T. I. VIERHELLER, AND W. A. WISTENDAHL (Dept. Bot., Ohio Univ., Athens, Ohio, 45701). Species ordination of upper slope oak-hickory stands of southeastern Ohio. Bull. Torrey Bot. Club 111: 56-60. 1984.-Detrended correspondence analysis was used to analyze the variations in the distribution of tree species with respect to aspect in an upper slope oak-hickory community of the mixed mesophytic forest of southeastern Ohio. Intensive sampling within this restricted slope position minimized the heterogeneity of soil parent materials while maximizing aspect variation between stands. Aspect proved to be of predictive value in estimating species distribution patterns. Quercus spp. and Carya glabra were more abundant on south-facing slopes. Carya ovata appeared to be more closely associated with the mesic species of north-facing slopes. Carya tomentosa, however, exhibited a distribution pattern apparently independent of aspect.

Principal Components Biplots and Alpha and Beta Diversity

Attention is drawn to some useful but not generally known properties of principal components analysis (PCA). Noncentered PCA of proportion data gives site ordinations that display approximate alpha diversities of sites and beta diversities of groups of sites, as measured by the Simpson index and mean squared Euclidean distance, respectively. Species centering allows a better approximation to beta diversities. Alpha diversities can still be visualized after centering if the true origin is projected into the plane of the ordination. The approximate species composition of each site can also be visualized if the site ordination is combined with a species ordination. The resulting plot of site scores and species loadings is called a PCA biplot. Finally, in a PCA biplot that displays both species composition and diversity, diversity values can be explained in terms of the main species contributing to diversity. In such a biplot the sum of squares of the species loadings must be scaled to unity, while the site scores must be scaled to a sum of squares equal to the corresponding eigenvalue. This type of biplot is termed a "distance biplot." For a simple illustration noncentered and species—centered distance biplots were produced for some diatom samples taken from Dutch moorland pools in the 1920s and 1978. The distance biplot is concluded to be among the most powerful analytical tools for species—composition data and derives some of its power from properties not possessed by, for example, reciprocal averaging. One problem is that it attaches little weight to rare species, but this problem can be solved by various possible data transformations based on the theory of diversity indices.

CONTROL OF VEGETATION ON CONTRASTING SUBSTRATES: HERB PATTERNS ON SERPENTINE AND SANDSTONE

Binary discriminant analysis (BDA) reveals relationships between species distributions and environmental variables. In this study, BDA was applied to transects on serpentine and sandstone in the Wenatchee Mountains, Washington. Species presence and states of ten habitat variables were recorded in each quadrat. Species response patterns significantly different from a random expectation suggested that distributions are controlled by soil moisture far more strongly on serpentine than they are on sandstone, where light and its correlates are more important. Environmental patterns were explored with direct principal components analysis (PCA) of standardized environmental variables and indirectly by PCA of the significant D‐values. The latter is biased towards variables to which species respond strongly. The results emphasize the environmental and floristic contrasts between substrates. On serpentine, direct PCA indicates that effective moisture, soil fertility, and insolation control the first three axes, while on sandstone, insolation, fertility, and effective moisture control the first three axes, respectively. The PCA of D‐values (Q‐mode) is similarly interpreted: moisture is strongly correlated with the first component on the serpentine transect, while insolation and fertility are correlated with the first component on sandstone. Species ordinations also result from Q‐mode analysis. They reflect species responses to the identified gradients and indicate mutual species‐environment interactions. These analyses conform to the hypothesis that mineral conditions of serpentine select against intolerant species and that survivors respond primarily to moisture conditions that are a result of low productivity, attributable to adverse nutrient conditions. On sandstone, the moisture gradient is less pronounced, and direct canopy effects that create variable light conditions predominate. BDA is a useful tool in ecological survey and pattern analysis. Species responses to environmental factors may be estimated quickly and directly. This method will help to focus subsequent research, improve experimental design, and generate explicit and testable hypotheses about species‐habitat interactions.

A rapid sampling technique suitable for expedition use, with reference to the vegetation of the Faroe islands

A stratified random procedure was adopted for sampling the vegetation of two islands in the Faroe group, as a basis for the estimation of the proportional areas occupied by the principal vegetation types. The plot data were classified using Indicator Species Analysis and the 12 plot groups generated by this technique were used as a basis for extrapolation to cover the total land area. Interpretation of the groups was fascilitated by ordination of both plots and species. The factors influencing the vegetation were primarily edaphic and secondarily altitudinal. The particular advantages of this method of survey for use by expeditions to remote areas are discussed.

An indirect gradient analysis of the ecological relationships between ancient and recent reiverine woodlands to the south of Bruges (Flanders, Belgium)

Riverine forests to the south of Bruges were sampled according to the principles of the Braun-Blanquet approach. Cartographic data allowed a distinction between old (pre-1775) and recent (planted after 1775) woodland. Using a chi-square criterion and/or a Fisher exact probability test, the association of species with the two historical types of woodland was tested. Corylus avellana, Lamium galeobdolon, Primula elatior, Anemone nemorosa, Deschampsia cespitosa and Thamnium alopecurum are confined to ancient woodland. Glechoma hederacea, Prunus padus, Lysimachia nummularia, Ribes rubrum and Lychnis floscuculi have a significant affinity for recent woods. R-type prineipal components analysis produced an effective ordination of species and releves. Interpretation of the scatter diagrams was performed using indicator values for the species and some environmental parameters for the releves. Two major gradients were detected: the first one is the coenocline from wet, basic clay soils towards drier, more acidic, sandy soils. Anthropogenic dynamics, through the general management which effects the micro-climate in the wood, particularly the relative light intensity, has been recognized as the second ecological parameter. The potential natural vegetation of the valleys is thus determined primarily by soil texture and soil moisture, and secondarily by former land use (and age). It takes at least 200 years before old woodland species start to colonize recent woodland. We are much indebted to Prof. Dr. P. Van der Veken for his criticism of the manuscipt and to B. Kuziel en G. Dujardin for reviewing the English text.