There is growing evidence that plant and animal species are arranged in hierarchies of relative competitive performance. More work is needed to determine which plant traits best predict relative competitive performance. We therefore measured relative competitive performance of 63 terrestrial herbaceous plant species using Trichostema brachiatum as a reference species (that is, phytometer or target species). The neighbour species came from a wide array of terrestrial vegetation types (e.g. rock barrens, alvars, old fields), and represented a wide array of growth forms (e.g. small rosette species such as Saxifraga virginiensis and large clonal graminoids such as Agropyron repens). The experiment was repeated with two pot sizes: large (control) and small (stress treatment). Relative competitive performance in large pots (controls) was highly correlated with that in small pots (stress treatment) (r = 0.90, p < 0.001). The hierarchy of relative competitive performance in the large pots was also highly correlated with the hierarchy in the small (stressed) pots (r_s = 0.91, p < 0.001). Principal components analysis and multiple linear regression showed that plant size (measured by total biomass, above‐ground biomass, below‐ground biomass, canopy area, height and leaf area index) and leaf shape (measured as length to width ratio, length, width) were the two characteristics that best predicted relative competitive performance (large pots, r ² = 0.55; small pots, r ² = 0.48).

Nomenclature: Gleason & Cronquist (1963); Morton & Venn (1990).

Humus profiles were sampled along an altitudinal gradient in the Macot‐La‐Plagne Forest (France, northern Alps) to investigate variation occurring under carpets of Vaccinium myrtillus present within Picea abies forests. The vertical distribution of subterranean organs of V. myrtillus was compared with (1) that of P. abies roots and other accompanying vegetation and (2) other components of humus profiles, in particular humified organic matter mainly consisting of animal faeces. It was shown that V. myrtillus roots were mostly concentrated in mineral horizons, while P. abies roots and V. myrtillus rhizomes occupied litter horizons. This was interpreted in terms of competition for nutrient capture between P. abies and V. myrtillus. The effects of altitude were (1) a change in the vegetation accompanying V. myrtillus in dense V. myrtillus carpets, bryophytes at the montane level being replaced by forbs at the sub‐alpine level and (2) a decrease in the thickness of ecto‐organic horizons. This was interpreted as a shift from a moder system characterized by recalcitrant litter (moss) processed by an active faunal community (stabilized in the form of animal faeces) to a mor system characterized by low animal abundance but with litter of better quality which is easily leached in the absence of prominent faunal activity.

Nomenclature: Rameau et al. (1993) for plant species; Brêthes et al. (1995) for soil horizons.

The species pool concept has been used as a theoretical framework for understanding local community richness. A significant problem in putting the concept into practice is the lack of methods for determining the size of the species pool. We tested the hypothesis that species composition of recent forests is primarily determined by the species composition of neighbouring older forests against the null‐hypothesis that species are a random sample of the species occurring in the study area. Forest plant species composition of recently established fragments was significantly correlated with species composition in neighbouring older forests (i.e. the local species pool). When older forest within a neighbourhood of 1000m radius is considered, seed dispersal sources can be found for 91% of the flora in the recent forests. For an individual fragment, dispersal is a much more important determinant of species presence than the environment, with an average of 46% of the total pool excluded from local pools by dispersal limitation and only 8% excluded by environmental limitations. The species richness of recent forests is on average 23% of the local species pool. Several hypotheses are proposed for this low percentage, such as asymmetric competition due to the early successional state or the limited colonization period.

Nomenclature: Lambinon et al. (1998).

Abbreviations: TSP = All species occurring in the 241 inventoried forest fragments, which is the full forest resource in the study area; ESPSP = The subset of the TSP potentially occurring within the limits of the habitat hypervolume model of a specific forest fragment; DUPSP = The subset of the TSP occurring within a neighbourhood of 100, 500 and 1000 m around a specific forest fragment; LSP = Those species that belong to both, the ESPSP and the DUPSP (i.e. all species that can potentially reach and establish in a specific forest fragment); OCR = Those species which actually occur in the recent forest fragment; Relative richness = (OCR/LSP) × 100.

We investigated the effect of topography‐related environmental factors (i.e., ground‐surface stability and soil moisture) on seedling establishment of 8 deciduous tree species. A field experiment was carried out using canopy species, which were classified into 3 groups based on the spatial distribution of adult trees (ridge, slope and valley). Demographic parameters were compared among species during the early stage of seedling establishment among 3 topographic positions in combination with gap and canopy conditions. The percentage of emerging seedlings tended to be lower on the ridge irrespective of the adult topographical distribution patterns. There was no clear trend in seedling emergence among the species groups classified by their spatial distribution. Seedling survival during 2 growing seasons was significantly different among species, topographic positions and light conditions. On the ridge, seedlings of the species dominating ridge tops had greater survival than those of other species, probably due to differences in demand for soil moisture. On the slope, frequent physical damage caused by surface material movement was observed and some species showed greater adaptability to the disturbed slope habitat. Survival of all seedlings was highest in the valley plots. Light conditions were the critical factor for seedling survival in some species. The results of this study suggest that topography creates diverse habitats for the establishment of tree seedlings. In addition to soil moisture, surface material movement may be a significant factor affecting seedling establishment.

Nomenclature: Satake et al. (1981‐1982,Satake 1989) Iwatsuki (1992).

Density‐dependence in tree population dynamics has seldom been examined in dry tropical forests. Using longterm data from a large permanent plot, this study examined 16 common species in a dry tropical forest in southern India for density‐dependence. Employing quadrat‐based analyses, correlations of mortality, recruitment and population change with tree densities were examined. Mortality in 1‐10 cm diameter trees was largely negatively correlated with conspecific density, whereas mortality in > 10 cm diameter trees was positively correlated. Mortality was, however, largely unaffected by the basal area and abundance of heterospecific trees. Recruitment was poor in most species, but in Lagerstroemia microcarpa (Lythraceae ), Tectona grandis (Verbenaceae ) and Cassia fistula (Fabaceae ), species that recruited well, strong negative correlations of recruitment with conspecific basal area and abundance were found. In a few other species that could be tested, recruitment was again negatively correlated with conspecific density. In Lagerstroemia, recruitment was positively correlated with the basal area and abundance of heterospecific trees, but these correlations were non‐significant in other species. Similarly, although the rates of population change were negatively correlated with conspecific density they were positive when dry‐season ground fires occurred in the plot. Thus, the observed positive density‐dependence in large‐tree mortality and the negative density‐dependence in recruitment in many species were such that could potentially regulate tree populations. However, repeated fires influenced density‐dependence in the rates of population change in a way that could promote a few common species in the tree community.

We studied tree regeneration, a key process for the existence of urban woodlands. We hypothesized that, besides the usual biological factors, anthropogenic ones (fragmentation, wear, pollution etc.) determine the regeneration success of tree species in urban woodlands. To test this hypothesis, within an observational setting, we collected data from 30 urban woodlands in the cities of Helsinki and Vantaa, Finland. We defined the number of living saplings (30‐200cm in height) as an indicator of regeneration success and used regression analysis to test different factors as independent variables. The results showed that different tree species responded differently to urban pressure. The regeneration of Picea abies decreased with increasing fragmentation of the forest landscape, whereas for the other most common (deciduous) species, regeneration increased. Wear, measured as total path area per study site, had a negative effect on regeneration success. An a posteriori examination of the data suggested that coarse woody debris might promote regeneration. We conclude that, although tree regeneration in general is not threatened in urban woodlands in the area we studied, the species composition may gradually change. We discuss some management implications for counteracting the urban pressures on tree regeneration.

Nomenclature: Hämet‐Ahti et al. 1992.

Spatial patterns of shrub life history and Ceanothus distribution are examined in relation to topographically‐mediated differences in drought severity within 3 watersheds on the coastal and inland flank of the Santa Ynez Mountains, California. Spatially distributed fields of drought severity are simulated for the studied watersheds using high‐resolution digital terrain data and daily climate data in combination with a process‐based hydro‐ecological model (RHESSys). Field samples of species composition are spatially integrated with the distributed drought data for analysis of ecological relationships. Patterns of seedling recruitment type correspond to topographic variability in drought severity in ways that are consistent with concepts presented in the literature. Species that depend on fire for recruitment are increasingly represented with increasing drought severity, the converse also applies. Sites that experience moderate drought severity permit co‐dominance of species from both recruitment modes. Residual analysis suggests that some of the unexplained variability is related to substrate. Analyses also indicate that the distribution of 5 Ceanothus shrubs reflect differences in drought severity in ways that are consistent with their resistance to water stress‐induced xylem dysfunction. Species from the subgenus Cerastes sort in accordance with moisture availability and have unique spatial distributions. Results are evaluated and discussed with respect to studies on plant morphology, resource use and seedling establishment patterns.

Abbreviations: DEM = Digital Elevation Model; FOV = Field of View; MT‐CLIM = Mountain Microclimate Simulator; RHESSys = Regional Hydro‐Ecological Simulation System.

Nomenclature: Hickman (1993).

Statistical measures of fidelity, i.e. the concentration of species occurrences in vegetation units, are reviewed and compared. The focus is on measures suitable for categorical data which are based on observed species frequencies within a vegetation unit compared with the frequencies expected under random distribution. Particular attention is paid to Bruelheide's u value. It is shown that its original form, based on binomial distribution, is an asymmetric measure of fidelity of a species to a vegetation unit which tends to assign comparatively high fidelity values to rare species. Here, a hypergeometric form of u is introduced which is a symmetric measure of the joint fidelity of species to a vegetation unit and vice versa. It is also shown that another form of the binomial u value may be defined which measures the asymmetric fidelity of a vegetation unit to a species. These u values are compared with phi coefficient, chi‐square, G statistic and Fisher's exact test. Contrary to the other measures, phi coefficient is independent of the number of relevés in the data set, and like the hypergeometric form of u and the chi‐square it is little affected by the relative size of the vegetation unit. It is therefore particularly useful when comparing species fidelity values among differently sized data sets and vegetation units. However, unlike the other measures it does not measure any statistical significance and may produce unreliable results for small vegetation units and small data sets. The above measures, all based on the comparison of observed/expected frequencies, are compared with the categorical form of the Dufrêne‐Legendre Indicator Value Index, an index strongly underweighting the fidelity of rare species.

These fidelity measures are applied to a data set of 15 989 relevés of Czech herbaceous vegetation. In a small subset of this data set which simulates a phytosociological table, we demonstrate that traditional table analysis fails to determine diagnostic species of general validity in different habitats and large areas. On the other hand, we show that fidelity calculations used in conjunction with large data sets can replace expert knowledge in the determination of generally valid diagnostic species. Averaging positive fidelity values for all species within a vegetation unit is a useful approach to measure quality of delimination of the vegetation unit. We propose a new way of ordering species in synoptic species‐by‐relevé tables, using fidelity calculations.

Nomenclature: Ehrendorfer (1973).

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.

Nomenclature: Lambinon et al. (1992) for plants; Julve (1993) for syntaxa; Decocq (2000a) for syntaxa described after 1993 as well as for coenotaxa, sigmataxa and geosigmataxa.

Evidence is presented for the occurrence of alternative stable states in a wet calcareous dune slack on the Frisian island of Texel, The Netherlands. An early pioneer stage (0.5 kg m ^–2 total standing crop) and a more productive later successional stage (2.9 kg m ^–2 ) occur side by side, with sharp boundaries between them. The pioneer vegetation has been recorded at the site for more than 62 yr. These features indicate the occurrence of a positive‐feedback mechanism that has led to alternative stable states.

Analyses of ground and surface water composition, and decalcification depths, indicated that hydrologically the study site can be characterized as a flow‐through slack, with exfiltration of calcareous groundwater on one side and infiltration of surface water on the other side of the slack. These differences in hydrological conditions have led to distinct differences in environmental conditions within the dune slack. The occurrence of the two successional stages can, however, not be explained by differences in hydrological conditions since both stages occur side by side in the centre of the dune slack. It is, therefore, more likely that biotic interactions are the cause of the vegetation pattern. Three possible mechanisms for feedback processes are discussed: (1) enhanced nitrogen loss; (2) sulfide toxicity and (3) nutrient accumulation in internal cycle.

Nomenclature: van der Meijden (1996) for phanerogams; Schaminée et al. (1995) for syntaxa.

The effects of disturbance and microtopography on the organization and dynamics of plant communities were studied in a European salt marsh located in the Bay of Mont St. Michel, France. The existence of seed trapping mechanisms was also tested. The study took place in the lower and middle marsh plant communities dominated by the perennials Puccinellia maritima and Halimione portulacoides, respectively and associated with the annual Suaeda maritima. Three treatments were used in series of plots placed in each community: (1) vegetation removal and root destruction to a depth of 10 cm and refilling, (2) non‐remnant herbicide treatment without vegetation removal and (3) creation of depressions (20 cm deep). These treatments were compared with adjacent control plots. The first year of the experiment showed that the perennials facilitated the establishment of Suaeda by trapping its seeds. Estimation of cover, density and biomass over 5 yr following the disturbances showed that in the first 2 yr Suaeda dominated the disturbed plots. Thereafter Suaeda was gradually eliminated by competitive exclusion after ca. 3 yr in the zone originally dominated by Puccinellia maritima and after 4 yr in the zone occupied by Halimione portulacoides. Depressions constituted refuge habitats for Suaeda by limiting competition with the perennials but also led to a high risk of mortality with temporal fluctuations in density. Despite a period of investigation limited to 5 yr, our study demonstrated that natural disturbances of various types occurred and influenced the dynamics of Suaeda, Halimione and Puccinellia. We deduced that natural disturbances and microtopography are responsible for the maintenance of the habitat in a state of non‐equilibrium by favouring the establishment of both spatial and temporal environmental heterogeneity. These conditions appear to be particularly favourable for the maintenance of annual species such as Suaeda maritima.

Nomenclature: Tutin et al. (1964–1980).

Four classes of functional and morphological plant traits – established strategies (the CSR scheme sensu Grime 1979), life‐forms (sensu Raunkiaer 1934), morphology, and regenerative strategies – are used as tools for explaining vegetation gradients at summer farms in the mountains of western Norway. These farms are assembly points for free‐ranging domestic grazers, and differ floristically and ecologically from the surrounding heath or woodland vegetation. DCA and TWINSPAN are used to relate major gradients in a floristic data set from 12 summer farms to two sets of explanatory variables: (1) environmental variables representing physical factors, plot position, soils, and land use, and (2) the 4 classification schemes. The main floristic gradient parallels a spatial gradient from the centres of the farms to the surrounding vegetation. A functional interpretation based on the concurrent use of the 2 sets of explanatory variables suggests that the gradient is one of decreasing disturbance and increasing environmental stress caused by decreasing grazing and manure effects away from farms. Partial CCA is used to investigate the relationships between the 4 functional/morphological plant trait classes. The 4 classification schemes are partially redundant, and do not represent different trends of specialization within the landscape. There is no strong evidence for decoupling of the traits of the vegetative and regenerative phases within the data. The combination of general process‐based theories and specific plant attribute responses enhances the generality and interpretability of the study.

Plant nomenclature: Lid & Lid (1994).

Abbreviations: C = competitor; CEC = Cation Exchange Capacity; LOI = loss‐on‐ignition; PFT = plant funtional type; R = ruderal; S = stress‐tolerator.

Piovesan & Adams (2000) criticized the EUROFLUX network of carbon flux measurements based on the assumption that the results were ‘surprising’, as they appeared to contradict the generally accepted relationship that rates of soil and plant respiration increase with increasing temperature. The EUROFLUX studies showed an overall opposite trend, with higher rates of ecosystem respiration at the cooler, northern latitudes. In this paper the concept of ‘surprising’ results in ecology is reviewed and the original claims of Piovesan & Adams reassessed. It is concluded that results from the EUROFLUX network do not contradict the established respiration/temperature relationship for at least two reasons. First, ecosystem respiration is the net outcome of a wide range of underlying processes and a simple respiration/temperature relationship may not be observed if other nontemperature dependent processes dominate. Second, relatively higher temperatures at the northern hemisphere sites during the period over which the EUROFLUX observations were made are consistent with the hypothesis that the measured fluxes reflect a non‐equilibrium, transient loss of carbon. It is further concluded that the potential importance of inter‐year variability for determining short‐term patterns of carbon flux may provide the key to reconciling the temperature/respiration relationship highlighted by Piovesan & Adams, and the latitudinal respiration trends evident in the EUROFLUX results.