A seriation method for summarizing vegetation-environment relationships

A computer program is described for producing site-species tables termed seriation arrays. Sites can be ordered according to sequences in direct habitat gradients, indirect site ordination axes, and trends oblique to the axes of an indirect site ordination. A ² technique is used to filter species for restriction to segments of each site sequence, retaining only accepted species in the construction of arrays.     

On non-metric multidimensional scaling ordination and interpretation of the matorral vegetation in lowland Murcía

The plant-environment relationships in a range of matorral communities, having different rainfall conditions in semi-arid lowland habitats in Murcía, S.E. Spain, were examined using the non-metric multidimensional scaling ordination technique. Hypotheses on floristic variations were derived based on an interpretative strategy which involved a site configuration rotation, followed by stepwise multiple regression analysis. An environmental data set was used to isolate variables associated with site co-ordinate trends. Results showed that floristic variation in these communities was mainly determined by aspect induced radiation receipt. Besides, most environmental trends in the study areas were found to be oblique to original site ordination axes and configuration rotation seemed to be a prerequisite in quantitative interpretation. The interpretative strategy introduced in this study was effective. It enhanced straightforward, quantitative and objective interpretation whereby inductive inferences on environmental trends could be readily formulated.Abbreviations ARAD radiation receipt surrogate - DEPTH soil depth - DISTURB disturbance index - NMDS non-metric multidimensional scaling - NUT nutrient scalar - SLOPE slope angle - TEXTIN texture index     

Variability and ecology of the alpine dwarf shrub community Loiseleurio-Cetrarietum

Summary Variation in the dwarf shrub community Loiseleurio-Cetrarietum from Mt. Patscherkofel, Austria, was investigated using polar ordination, principal component analysis, hierarchical cluster analysis, and multiple correlation analysis. Comparison was made with existing data (relevé tables) from the Alps. In addition to phytosociological methods the canopy structure and the morphological variability of the dominant species Loiseleuria procumbens were studied. The result of the namerical phytosociological analyses yield 3 clusters representing: 1) A dense Loiseleuria carpet, 2) a Loiseleuria carpet damaged by erosion and 3) an open Loiseleuria community on skeletal soils. The first two communities can be combined as one type because of their canopy structure in the form of dense intertwined individual plants and because of the morphological uniformity of Loiseleuria, although in the second group there are species growing on erosion gaps and showing close floristic connections to the third group. The comparison of 140 relevés from the Alps proves that the Loiseleurio-Cetrarietum is characterized only by the dominance of Loiseleuria procumbens while the abundantly occurring lichens change in their species composition along the gradient of wind, and elevation. The open Loiseleuria community at the most extreme habitats (cluster 3) is regarded as a new association. Not only floristic but also physiognomical, morphological and ecophysiological evidence led to this conclusion. The name Gymnomitrio-Loiseleurietum (ass. prov.) is proposed. This plant community shows floristic and ecological correlations to the Diapensia-Loiseleuria-Cesiolichen community known from Scandinavia.Nomenclature of species follows Ehrendorfer (1973) (vascular plants), Poelt (1974) (lichens) and Gams (1973) (mosses).For PCA, hierarchical cluster analysis, and multiple correlation analysis, computer programs from the data bank system (AFO-data) of the Alpine Forschungsstelle Obergurgl, Austria were used. I am indebted to Dr. S. Pamer and P. Moser for their invaluable help. For polar ordination a separate program was developed (language: Simula, author: Dr. G. Knecht). I am also indebted to Dr. H. Hilscher for the translation of the text.     

Revealing biogeographical patterns by nonlinear ordinations and derived anisotropic spatial filters

Aim Spatial floristic and faunistic data bases promote the investigation of biogeographical gradients in relation to environmental determinants on regional to continental scales. Our aim was to extract major gradients in the distribution of vascular plant species from a grid‐based inventory (the German FLORKART data base) and relate them to long‐term precipitation and temperature records as well as soil conditions. We present an ordination technique capable of coping with this complex data array. The goal was also to sort out the influence of spatial autocorrelation, assuming floristic autocorrelation is anisotropic. Location Germany, at a spatial resolution of 6′ × 10′. Methods Isometric feature mapping (Isomap) was applied as a nonlinear ordination method. Isomap was coupled to ‘eigenvector‐based filters’ for generating spatial reference models representing spatial autocorrelation. What is novel here is that the derived filters are not based on the assumption of equidirectional autocorrelation. Instead, the so‐called ‘principal coordinates of anisotropic neighbour matrices’ build filters to test the influence of geographical vicinity in directions of high similarity among observations. Results The Isomap ordination of floristic data explained more than 95% of the data variance in six dimensions. The leading two dimensions (representing about 80% of the FLORKART data variance) revealed clear spatial gradients that could be related to independent effects of temperature, precipitation and soil observations. By contrast, the third and higher FLORKART dimensions were dominated by an antagonism of anisotropic spatial autocorrelation and soil conditions. A subsequent cluster analysis of the floristic Isomap coordinates educed the spatial organization of the floristic survey, indicating a considerable sampling bias. Conclusions We showed that Isomap provides a consistent methodical framework for both ordination and derived spatial filters. The technique is useful for tracing the often nonlinear features of species occurrence data to environmental drivers, taking into account anisotropic spatial autocorrelation. We also showed that sampling biases are a conspicuous source of variance in a frequently used floristic data base.     

Stand characteristics,understorey associates and environmental correlates ofEucalyptus tetrodonta F. Muell. forests on Gunn Point,northern Australia

An ordination study of 20Eucalyptus tetrodonta forest stands growing on deep earths in monsoonal Australia revealed two major gradients in understorey vegetation type. The first axis reflected both floristic and structural understorey variation, where litter and shrub cover were inversely related to grass cover. This axis is thought to reflect a complex fire-vegetation type interaction, where vegetation is primarily determined by the saturation of the soil profile in the wet season, as measured by the colour of the iron rich soils. On the second axis of the ordination, floristic composition but not vegetation structure, and stand height were found to vary with the intercorrelated measures of soil gravel and moisture supply.E. tetrodonta is able to regenerate in the absence of fire, but firing appears to stimulate regeneration. All stands contained some advance growth, which occurs in distinct clumps, probably reflecting these plants clonal origin. Sapling presence in the stands is variable and the recruitment of advance growth into this size class appears to be related to over-wood competition. The size class distribution of trees was found to be similar amongst the stands, therefore stand structure appeared to be independent of understorey type. In comparison to general models of temperate eucalypt regeneration processes the tropical eucalypts have evolved different regeneration strategies, possibly in response to the severe annual drought.Nomenclature: Chippendale (1971), unless otherwise indicated. Structural classification: Specht (1970).I acknowledge the help of Mr. Clyde Dunlop who identified plant specimens and provided stimulating discussion, and Dr. Peter Minchin for permission to use the computer package ECOPACK to prepare and handle the floristic data, and his invaluable assistance with the ordination analysis. Mr. Lee Belbin and CSIRO Division of Water and Land Resources kindly gave their permission to use the Numerical Taxonomy Package (NTP).     

Using past and present habitat to predict the current distribution and abundance of a rare cryptic lizard,Delma impar (Pygopodidae)

We present logistic regression models predicting the distribution and abundance of a threatened cryptic lizard, Delma impar (Pygopodidae), in the Australian Capital Territory (ACT). The models incorporate current habitat and historical land use and habitat change (woodland clearance, ploughing, grazing, fertilizer application). Information on historical land use was acquired from land survey maps, aerial photographs and from floristic indices of land management. Floristic indices were developed from a survey of local agronomists who scored individual plant species, responses to grazing, ploughing and fertilizer application. Floristic indicies proved to be more informative than floristic ordination analyses. It emerged that historical factors were of key importance for predicting the distribution and abundance of D. impar. Since European settlement, D. impar has apparently spread from primary (naturally treeless grasslands) into secondary grasslands (grassland formerly with an overstorey of trees) and has been locally excluded by some farming activities such as ploughing. We conclude that a combination of current habitat and past changes in habitat may be necessary to understand the current distributions of plant and animal species that have limited dispersal ability and that are susceptible to local temporary habitat destruction. Active conservation strategies involving, for example, assisted dispersal, may be important for these species.     

Interspecific relationships of the glacial relics Swertia perennis L. and Pedicularis sceptrum-carolinum L. in a Rumanian fen

In a eutrophic peat bog impregnated with mineral springs in the Carpathians, where the glacial relics Swertia perennis and Pedicularis sceptrum-carolinum have earlier been shown to occupy different microhabitats, an analysis of the relationships of these species with accompanying species has been made on the basis of numerous quadrats and a correlation method. The closest floristic associates of the two species are quite different, and the results of this analysis are broadly in agreement with subjective assignments made earlier by phytosociologists.Nomenclature follows T. G. Tutin & V. H. Heywood (eds.), Flora Europaea, Vols. I–V. Cambridge Univ. Press, Cambridge, 1964, 1968, 1972, 1976, 1980 for Cormophyta and R. van der Wijk (ed.), Index Muscorum, Vols. I, II. Utrecht, 1959, 1962 for Bryophyta.     

Recognition of successional pathways in forest communities using size-class ordination

Certain of the problems associated with the use of size-class ordinations to identify successional pathways are explored. Examples of such ordinations, where it was attempted to minimize a number of the interpretational dangers noted by Austin (1977), are presented for two tropical rainforest types from Papua New Guinea. By limiting the analysis to groups of sites which show a high degree of homogeneity, and by using the non-linear ordination method Continuity Analysis (Noy-Meir 1974) a simple successional interpretation of the species-in-size-class data was possible. As heterogeneity increases so does the number of possible interpretations of the resultant size-class-in-space pattern.Nomenclature follows Paijmans, K. (ed.) 1976. New Guinea Vegetation. A.N.U. Press, Canberra.I would like to thank Dr. T. Meredith and Dr. J. Ogden for reading and commenting on a draft of this paper. The research was conducted whilst the author was a Ph.D. scholar in the Department of Biogeography and Geomorphology, R.S.Pac.S., Australian National University, Canberra, Australia.     

Habitat structure is more important than vegetation composition for local‐level management of native terrestrial reptile and small mammal species living in urban remnants: A case study from Brisbane,Australia

Abstract As urban areas continue to expand and replace natural and agricultural landscapes, the ability to manage and conserve native wildlife within urban environments is becoming increasingly important. To do so we first need to understand species' responses to local‐level habitat attributes in order to inform the decision‐making process and on‐ground conservation actions. Patterns in the occurrence of native terrestrial reptile and small mammal species in 59 sites located in remnant urban habitat fragments of Brisbane City were assessed against local‐level environmental characteristics of each site. Cluster analysis, multidimensional scaling ordination, and principal axis correlation were used to investigate relationships between species' occurrences and environmental characteristics. Native reptiles were most strongly associated with the presence of termite mounds, a high amount of fallen woody material, and a moderate amount of weed cover. Native small mammals were most strongly associated with the presence of grass trees (Xanthorrhoea spp.), and both reptiles and small mammals were negatively influenced by increased soil compaction. Significant floristic characteristics were considered to be important as structural, rather than compositional, habitat elements. Therefore, habitat structure, rather than vegetation composition, appears to be most important for determining native, terrestrial reptile and small mammal species assemblages in urban forest fragments. We discuss the management implications in relation to human disturbances and local‐level management of urban remnants.     

Vegetation changes along a precipitation gradient in Central Argentina

Changes in vegetation along a precipitation gradient in Central Argentina were studied. Floristic samples were taken along an east-west transect of about 300 km. Correlation analysis between precipitation and ordination axes was used to provide an environmental interpretation of vegetation variability.Floristic analysis produced an ordination of plant communities from evergreen forests (precipitation >500 mm) to desert shrublands and therophyte communities (precipitation <200 mm). Results showed a trend of floristic and structural impoverishment towards the west. There is a replacement of species along the transect and a shift in dominant growth forms. The first ordination axis is significantly, negatively correlated with annual precipitation.     

Fluctuations in a coastal dune grassland due to fluctuations in rainfall: Experimental evidence

Experiments with rainfall on a dune grassland near Oostvoorne, the Netherlands with Festuco-Galietum as the main syntaxon are described. Both increase in rain through additional watering and decrease in rain through catchment are presented to plots belonging to the xerosere and the mesosere. Clear changes in the floristic composition are the result, even after only two years. Typical Festuco-Galietum species are promoted by high rainfall, species of open habitat such as Corynephorus canescens are promoted by drought. The results are discussed against the background of long term permanent plot observations in the area and a relation with rabbit grazing intensity is supposed.Nomenclature of vascular plants follows Heukels-van Ooststroom (1975) Flora van Nederland 18 ed., Woiters-Noordhoff, Groningen; Nomenclature of syntaxa follows Westhoff & den Held (1969). Plantengemeenschappen in Nederland, Thieme, Zutphen.Field work in 1978 was carried out with Frans Bongers and Marc de Lyon, in 1979 with Marc de Lyon, Picter Meeuwissen and Guiljo van Nuland, all then MSc. students at the Division of Geobotany. Their help and the advice of Dr. Peter van der Aart, Institute of Ecological Research, Oostvoorne, are acknowledged.     

The bootstrapped ordination re-examined

Abstract. A method is described to determine the number of significant dimensions in metric ordination of a sample. The method is probabilistic, based on bootstrap resampling. An iterative algorithm takes bootstrap samples with replacement from the sample. It finds in each bootstrap sample ordination coordinates and computes, after Procrustean adjustments, the correlation between observed and bootstrap ordination scores. It compares this correlation to the same parameter generated in a parallel bootstrapped ordination of randomly permuted data, which upon many iterations will generate a probability. The method is assessed in principal coordinates analysis of simulated data sets that have varying number of variables and correlation levels, uniform or patterned correlation structure. The results suggest the method is more reliable than other available methods in recovering the true intrinsic dimensionality. Examples with grassland data illustrate utility.     

Classification of macroinvertebrate communities across drainage basins in Victoria, Australia: consequences of sampling on a broad spatial scale for predictive modelling

1. Spatial scale may influence the interpretation of environmental gradients that underlie classification and ordination analyses of lotic macroinvertebrate communities. This could have important consequences for the spatial scale over which predictive models derived from these multivariate analyses can be applied. 2. Macroinvertebrate community data (identified to genus or species) from edge and main-channel habitats were obtained for sites on rivers from 25 of the 29 drainage basins in Victoria. Trends in community similarity were analysed by carrying out separate multivariate analyses on data from the edge habitats (199 sites) and the main-channel habitats (163 sites). 3. Hierarchical classification (UPGMA) showed that the edge data could be placed into 11 site groups and the main-channel data into 12 site groups. 4. Ordination analysis (hybrid multidimensional scaling) showed no sharp disjunctions between site groups in either habitat; overlap was frequent. Correlation of the ordination patterns with environmental variables showed that edge communities varied longitudinally within a drainage basin and from the east to the west of Victoria. These two trends were superimposed on one another to form a single gradient on the ordination. The taxon richness of edge communities was also related to the species richness of macrophytes at a site. Main-channel communities also displayed a longitudinal and a geographic gradient, but these two gradients were uncorrelated on the ordination. 5. Community similarity only weakly reflected geographic proximity in either habitat. A preliminary subdivision of Victoria into a series of biogeographic regions did not match the pattern of distribution of site groups for the edge habitat, illustrating the difficulties of applying to lotic communities a priori regionalizations based on terrestrial features of the landscape. 6. The longitudinal gradients in the two data sets were commonly observed in data gathered at smaller spatial scales in Victoria. The other gradients (geographic, macrophyte), however, were either not consistently repeated or not evident at smaller spatial scales. At small spatial scales (i.e. within a single drainage basin) gradients were related to variables that varied over restricted ranges, e.g. mean particle size of the substratum. 7. Species richness was very variable when plotted against river slope or distance of site from source; both of these are measures of position on the longitudinal gradients. In contrast to suggestions in the literature, species richness did not show a unimodal trend on these gradients, or any other trend. 8. Environmental gradients (apart from longitudinal gradients) that underlie predictive models of macroinvertebrate distribution are reflections of the spatial scale on which the model has been constructed and cannot be extrapolated to different scales. Models must be suited to the spatial scale over which predictions are required.     

The significance of littoral and shoreline habitat integrity to the conservation of lacustrine damselflies (Odonata)

Human development of pond and lake shorelines may significantly impact native lacustrine biota including a variety of aquatic macroinvertebrate groups. In an effort to better understand the habitat associations and sensitivities of lacustrine damselflies (Odonata: Zygoptera), we sampled adults in littoral macrophyte habitat during two flight periods at 35 randomly selected pond and lake sites in southern Maine during 2000 and 2001. Data were also collected to help characterize water body, shoreline disturbance, and aquatic vegetation at each study site. Nonmetric multidimensional scaling was used for ordination of damselfly assemblages, and coordinates from the most stable solution were related to site variables using forward stepwise multiple regression. Our results suggest that the diversity and composition of damselfly assemblages is related to the abundance and richness of littoral zone macrophytes, extent of riparian disturbance, benthic substrate granularity, and lake productivity; all variables subject to anthropogenic degradation on excessively developed waterbodies. Additionally, we developed a Habitat Tolerance Index useful for distinguishing between relative habitat specialists and generalists from among a diverse assemblage of 19 lacustrine species. Finally, species-specific damselfly associations with multiple genera of floating and emergent macrophytes were assessed using both nonparametric correlation and multiplicative regression yielding significant relationships for 17 species, including two damselflies of global conservation concern (Enallagma laterale and E. pictum). We conclude that the protection of littoral and shoreline habitat integrity, with special emphasis on emergent and floating macrophytes, is critical to the conservation of lacustrine biodiversity.     

Theoretical habitat templets, species traits, and species richness: Trichoptera in the Upper Rhône River and its floodplain

• 1 For Trichoptera occurring in two sites of the Upper Rhône River (France) we examine: (i) relationships among species traits; (ii) habitat utilization of Trichoptera species; (iii) the relationship between species traits and habitat utilization; (iv) trends of species traits in the framework of spatial–temporal habitat variability to test predictions of the habitat templet concept; and (v) trends of species richness in the framework of spatial–temporal habitat variability to test predictions of the patch dynamics concept.
• 2 Of the sixteen species traits selected, twelve have high correlation ratios for the seventy-five species used in this analysis; these traits are related to behavioural, morphological, or physiological aspects. Traits related to reproduction or life cycle have lower correlation ratios.
• 3 An ordination by species traits separates the five main families into three groups: (i) Hydropsychidae and Polycentropodidae; (ii) Hydroptilidae; and (iii) Leptoceridae and Limnephilidae. An ordination of the habitat utilization of the species in ten habitats indicates that the Hydropsychidae occur preferentially in the main channel, Hydroptilidae, Polycentropodidae, and Limnephilidae occur in backwaters or oxbow lakes, and the Leptoceridae are ubiquitous.
• 4 The Hydropsychidae exhibit a relationship between species traits and habitat utilization, i.e. they use similar habitat types with similar species traits. The species traits of the other four families are similar but their habitat utilization is quite different.
• 5 The Hydropsychidae occur in lowest spatial–temporal variability habitats and Limnephilidae in the highest. Therefore, net spinners and filterers are characteristic of habitats with a low spatial–temporal variability, whereas shredders and case makers using plant material are characteristic of habitats with high spatial–temporal variability. The trends in species traits show little agreement with trends predicted from the river habitat templet.
• 6 Trends of species richness in the framework of spatial and temporal variability do not follow the predictions of the patch dynamics concept because richness is similar in all superficial habitats. This implies that each habitat, in spite of large differences in their spatial and temporal variability, offers Trichoptera a similar but limited number of ecological niches.

     

Plant species richness and spatial organization at different small scales in western Mediterranean landscapes

The relationship between plant species richness and the space organization of the community at different small scales was studied. The study was based on 51 sites distributed along a belt from Central Spain to Portugal. Each site was analyzed with a transect cutting across the boundary between two neighboring patches of shrubland and grassland. Local spatial organization of vegetation was analyzed at different levels of detail and each transect was divided into successively smaller portions. The first division coincides with a physiognomic perception of the site in two patches (shrubland and grassland). The average spatial niche width of the species was used to calculate the spatial organization of the vegetation of each division in each site. The correlation between species richness and spatial organization depended on the block size under consideration. A physiognomic criterion, sectorizing the sites into patches of shrubland and grassland, determines noteworthy floristic changes but does not enable us to express satisfactorily the variability in plant richness. In order to account for this variation, other factors must be taken into account which act at a more detailed small-scale and which determine the internal variability of these patches. In the case studied, the species richness of the sites increases along with an increase in the percentage of species whose occupation of the space is relatively restricted within the site. Many of these species are, however, frequent within the whole of the territory studied. The results highlight the importance of the level of local scale at which the factors influencing occupation of the space, and consequentially, plant richness, preferentially act. This circumstance ought to be taken into consideration in strategies for the conservation of biological diversity, and based on the delimitation of protected spaces with criteria frequently linked to the physiognomy of the vegetation.Nomenclature: Follows T.G. Tutin et al. 1964-1980. Flora Europaea. Cambridge University Press, Cambridge     

Importance of soil nutrients in the distribution of forest communities on a large geographical scale

Aim Soil nutrient content plays a key role in plant growth through mineral nutrition and toxicity. Its impact on plant species and community distribution is studied on a large geographical scale through surrogates like topography or geology. We investigated the importance of soil pH and C:N ratio, as direct nutritional gradients, to determine, with climatic factors, the spatial distribution of plant communities over large territories. Location We studied the distribution of six beech habitats of the NATURA 2000 network throughout France (550,000 km²). Methods Models were calibrated with 2108 floristic plots classified in the NATURA 2000 system and including climatic and topographic variables and soil nutritional measurements carried out in a laboratory. Logistic regression was used to model habitat distribution according to environmental variables. Climatic layers, a digital elevation model and maps of soil pH and nitrogen content, created using plant indicator values and large floristic databases, were used to map the sites suitable for beech communities. Distribution models were evaluated with an independent set of 2091 phytosociological plots. Results pH and nitrogen supply were the key distribution drivers for four of the six beech communities on a national scale. Their use in the distribution models distinguished within homogeneous climatic territories a gradient of nutritional conditions from acidic areas, suitable for nutrient‐poor beech communities, to calcareous areas suitable for nutrient‐rich ones. Predicted maps of beech habitats fit the spatial distribution of validation plots. Main conclusions Soil pH and nitrogen supply strongly improve predictions of forest community distribution carried out with climatic variables on a broad geographical scale. They allow delineation of areas with nutritional conditions suitable for each community, as well as the realization of predictive high‐resolution maps over large areas useful for sustainable and conservation management. Nomenclature Tutin & Heywood (2001 ) Flora Europaea. Cambridge University Press, Cambridge.     

A soil nutrient gradient in Magellanic Empetrum heathlands

The relationship of environmental and soil-nutrient variables with the floristic composition of Empetrum rubrum heathlands and related communities from northern Tierra del Fuego were studied by means of ordination techniques. A floristic gradient was found which had its axis of major variation closely related to a gradient in soil trophic status. Increases in the densities of Empetrum and other cushion plants (Bolax gummifera, Azorella lycopodioides, Pernettya pumila) along the floristic gradient were: (a) associated with a lower number of species and total cover, and greater soil erosion; (b) positively correlated with the C/N ratio and aluminium content in the soil; and (c) negatively correlated with pH, calcium content and base saturation.Climate, lithology, habitat exposure, and the history of human activity would be key factors in developing the oligotrophic conditions that favoured the establishment of different Empetrum heathlands.     

Fine‐scale determinants of butterfly species richness and composition in a mountain region

Aim Global patterns of species richness are often considered to depend primarily on climate. We aimed to determine how topography and land cover affect species richness and composition at finer scales. Location Sierra de Guadarrama (central Iberian Peninsula). Methods We sampled the butterfly fauna of 180 locations (89 in 2004, 91 in 2005) at 600–2300 m elevation in a region of 10800 km². We recorded environmental variables at 100‐m resolution using GIS, and derived generalized linear models for species density (number of species per unit area) and expected richness (number of species standardized to number of individuals) based on variables of topoclimate (elevation and insolation) or land cover (vegetation type, geology and hydrology), or both (combined). We evaluated the models against independent data from the alternative study year. We also tested for differences in species composition among sites and years using constrained ordination (canonical correspondence analysis), and used variation partitioning analyses to quantify the independent and combined roles of topoclimate and land cover. Results Topoclimatic, land cover and combined models were significantly related to observed species density and expected richness. Topoclimatic and combined models outperformed models based on land cover variables, showing a humped elevational diversity gradient. Both topoclimate and land cover made significant contributions to models of species composition. Main conclusions Topoclimatic factors may dominate species richness patterns in regions with pronounced elevational gradients, as long as large areas of natural habitat remain. In contrast, both topoclimate and land cover may have important effects on species composition. Biodiversity conservation in mountainous regions therefore requires protection and management of natural habitats over a wide range of topoclimatic conditions, which may assist in facilitating range shifts and alleviating declines in species richness related to climate change.     

Geographical and ecological differentiation in Greek Fagus forest vegetation

Question: Which are the gradients of floristic differentiation in Greek beech (Fagus sylvatica) forests? Which is the role of geographical and ecological factors in this differentiation? Location: Beech forests of the plant geographical regions Northeast, North Central and East Central Greece. Methods: A total of 1404 published and unpublished phytoso‐ciological relevés were used in the analyses. TWINSPAN and DCA were applied to classify and ordinate the relevés. Altitude, Indicator Values of relevés and their X and Y coordinates were used in a posteriori interpretation of the ordination axes. Kendall's correlation coefficients were calculated between DCA relevé scores and explanatory variables. Multiple linear regression was used to partition the variation explained by the first two DCA axes, between the geographical and the ecological variables. Results: Classification resulted in 14 vegetation units defined by species composition. Two types of gradients, ecological and geographical, were revealed by the DCA of all releves. The partition of the variation accounted for by the first and second DCA axis was attributed mainly to ecological and geographical variables, respectively. Conclusions: Beech forests of northeast and Central Greece show phytogeographical differences, while ecologically similar vegetation units occur in both regions. A west‐east gradient is revealed in Greek beech forest vegetation. The extent of the study area, its position along regional gradients and the comprehensiveness of the data set that is analysed determine the types of the gradients which can be revealed in a vegetation study.