Question: What are the impacts of factors controlling patterns of change in woodland field-layer vegetation, through time?

Location: Wytham Woods, Oxford, UK (51°41′ N, 1°19′ W).

Methods: Species occurrence was monitored in 163 permanent plots three times between 1973 and 2002 and related to management compartment and history. The dataset was analysed using a combination of ordination methods, univariate and multivariate analysis of variance and HOF modelling.

Results: The two key findings of this paper are: (1) that the species composition of ancient woodlands (often cited as a conservation goal), may be moving along an ‘undesirable’ trajectory, from a conservation viewpoint; and (2) that the impact of a synergistic effect of changing canopy dynamics, nitrogen deposition and a rising deer population has resulted in an increase in grass species, at the expense of woodland herbs. These findings have significant implications for the practical conservation of similar habitats across Europe.

Conclusions: The analytical methodology presented here allowed detailed assessment of the potential roles of a range of environmental factors controlling change. The methodology may be applicable to other long-term studies of vegetation, and is particularly appropriate for identification of cross-site drivers, such as pollutant load and climate change.

Nomenclature: Stace (1997).

Questions: Is plant diversity in mesic grassland ecosystems vulnerable in the short-term to extreme climate change events? How rapidly can responses in vegetation composition occur in perennial grasslands? Are the expected compositional changes related to rare species losses or to shifts in the relative abundance of the dominants?

Location: Subalpine mesic grasslands on limestone in the Pyrenees.

Methods: Transplanting turves from the upland, with cold-temperate climate, to a lowland location, with continental Mediterranean climate.

Results: Transplanting led to decreased biodiversity and strong shifts in vegetation composition. Results from both permutation tests and traditional multivariate analysis suggested different trajectories of vegetation depending on the initial species pool. Vegetation showed a tendency to converge in composition in the lowland over time, independently of initial differences. Estimated changes in relative biomass of the five most abundant species between the upland and the lowland ranged from −89 to 96 %. The ensemble of all other species was reduced by 80%. The most dominant species in the upland, Festuca nigrescens, reduced its abundance in the lowland, shifting from having mainly positive to mainly negative associations with other species.

Conclusions: Mesic grassland ecosystems in the Pyrenees showed strong shifts in plant diversity and composition after a short period of warming and drought, as a consequence of acute vulnerability of some dominant grasses, losses of rare species, and aggregate and trigger effects of originally uncommon forb species.

Nomenclature: Tutin et al. (1964–1980); Bolòs et al. (1993).

Questions: What are the long-term effects of climate change on the plant species composition and carbon sequestration in peat bogs?

Methods: We developed a bog ecosystem model that includes vegetation, carbon, nitrogen and water dynamics. Two groups of vascular plant species and three groups of Sphagnum species compete with each other for light and nitrogen. The model was tested by comparing the outcome with long-term historic vegetation changes in peat cores from Denmark and England. A climate scenario was used to analyse the future effects of atmospheric CO₂, temperature and precipitation.

Results: The main changes in the species composition since 1766 were simulated by the model. Simulations for a future warmer, and slightly wetter, climate with doubling CO₂ concentration suggest that little will change in species composition, due to the contrasting effects of increasing temperatures (favouring vascular plants) and CO₂ (favouring Sphagnum). Further analysis of the effects of temperature showed that simulated carbon sequestration is negatively related to vascular plant expansion. Model results show that increasing temperatures may still increase carbon accumulation at cool, low N deposition sites, but decrease carbon accumulation at high N deposition sites.

Conclusions: Our results show that the effects of temperature, precipitation, N-deposition and atmospheric CO₂ are not straightforward, but interactions between these components of global change exist. These interactions are the result of changes in vegetation composition. When analysing long-term effects of global change, vegetation changes should be taken into account and predictions should not be based on temperature increase alone.

Question: What floras are typically associated with domestic gardens in cities?

Location: The urban areas of the cities of Belfast, Cardiff, Edinburgh, Leicester and Oxford, UK.

Methods: The composition and diversity of plant species in 267 urban domestic gardens in the five cities was recorded by complete census and quadrat sampling.

Results: The entire garden flora consisted of 1056 species, of which 30% were native and 70% alien. 34% of the 50 most frequently recorded species in gardens were native, a number of them being weeds. Although plant species richness in individual gardens varied with garden area, the above breakdowns held true when the cities were considered individually. The only exception was Belfast where, overall, plant species richness was slightly lower than in any of the other cities.

Comparing quadrat samples, species richness was found to be greater in the garden habitats of each of the cities than in a number of other habitats, with species accumulation curves showing no sign of reaching saturation at 120 quadrats. This is due to the high proportion of alien species found in gardens, and in particular those surviving at low densities as a result of human intervention.

Conclusion: There was surprisingly little difference in plant species richness, diversity or composition between the cities, despite the variation in geographical and climatic factors. This suggests that human factors such as plant availability, garden management and social/economic status of individual householders had an overriding influence.

Question: How do broad-leaved ravine forests in SE Europe differentiate phytogeographically? Do they differ from analogous European forests? What is their distribution pattern?

Location: southeastern Europe, Apennine-Balkan province.

Methods: The initial data set of 2189 relevés was stratified geographically and phytosociologically; 614 relevés remaining after stratification were classified with a TWINSPAN and cluster analysis, wich resulted in four clusters and eight subclusters. Average Pignatti indicator values for relevés of each subcluster were subjected to PCA to show ecological relationships among the clusters. The spectra of geoelements and sociological species groups of individual subclusters were calculated to show phytogeographical and sociological relationships between them. The diagnostic species combination was calculated by a fidelity measure (φ-coefficient) and presented in a synoptic table.

Results: Broad-leaved ravine forests in southeastern Europe form a separate group within the European broad-leaved ravine forests. They are well differentiated by the species with a southeast European distribution, as well as by many other species that reflect their different ecological affinities.

Conclusions: The phytosociological and phytogeographical relationships between the Apennines and the Balkan peninsula that have already been recognized for other vegetation types have been confirmed for broad-leaved ravine forests. According to the numerical analysis, two suballiances of broad-leaved ravine forests in southeastern Europe are proposed, both belonging to the alliance Tilio-Acerion: an amphi-Adriatic xerothermophilous suballiance Ostryo-Tilienion platyphylli suball. nova and a mesophilous suballiance Lamio orvalae-Acerenion suball. nova, the latter appearing only on the Balkan Peninsula.

Nomenclature: Tutin et al. (1964–1980); except Stellaria montana Pierrat and Dryopteris affinis (Lowe) Fraser-Jenkins. Fagus moesiaca is included in Fagus sylvatica; syntaxonomy follows Mucina et al. (1993), except for the syntaxa under consideration. New names are based on the nomenclature rules in Weber et al. (2000).

Question: What is the effect of nutrient addition on primary production, phytodiversity and succession of a very unproductive plant community (ca. 100 g.m⁻².a⁻¹)?

Location: A nutrient-poor, calcareous inland sand ecosystem in the northern upper Rhine valley, Germany.

Methods: Within a five-fold replicated randomized block design, 10-m² plots were given six single or combined applications of nitrogen, phosphorus, potassium and other essential nutrients for four years. An organic carbon treatment was included as a measure to immobilize soil nitrogen. Data were analysed by mixed linear models.

Results: Productivity of above-ground vascular plant species doubled after nitrogen addition. Additional nutrient elements did not increase productivity further. The cover of ten species and the height of 15 (out of 19 examined) species were significantly enhanced by nutrient addition. Centaurea stoebe is nitrogen-limited and exhibits a decisive impact on total above-ground vascular species productivity. Nutrients did not affect phytodiversity. Low-dosage nitrogen addition (25 kg.ha⁻¹a⁻¹) and organic carbon treatment had no significant impact. However, long-term effects cannot be excluded.

Conclusions: The productivity of the examined plant community is responsive to nutrient addition. Although the response is actually more pronounced than in plant communities with higher initial productivity, productivity remained at a low level. Nutrient limitation (mostly phosphorus nitrogen co-limitation) of many individual species across all life forms is shown. Total above-ground vascular plant productivity is nitrogen-limited. No species were suppressed completely, nor has there yet been an encroachment of new species. However, high-dosage nitrogen addition resulted in accelerated succession.

Nomenclature: Wisskirchen & Haeupler (1998) for vascular plants; Koperski et al. (2000) for bryophytes.

Question: Relevés in large phytosociological databases used for analysing long-term changes in plant communities are biased towards easily accessible places and species-rich stands. How does this bias influence trend analysis of floristic composition within a priori determined vegetation types and how can this bias be reduced by resampling methods?

Location: The Netherlands.

Methods: Basis for the analysis was the Dutch national phytosociological database, consisting of more than 460 000 relevés. For the Cirsio dissecti-Molinietum, Genisto anglicae-Callunetum and the Stellario-Carpinetum betuli, we analysed differences in floristic composition (species frequencies) before and after 1970, using χ²-statistics. We resampled the original dataset, using different types of stratification. The results of the trend analysis with the resampled datasets were compared with the results using the original dataset.

Results: In the resampled datasets a much smaller number of plant species showed a significant trend over both periods, compared to the results form the original dataset. Differences could be related to the smaller size of datasets after resampling, but also to avoiding over-representation of certain geographical localities in the datasets. The influence of stratification was different for the three plant communities, due to the different distribution of relevés in time and space.

Conclusions: Analysis of long-term changes in plant communities is strongly affected by the uneven spatiotemporal distribution of relevés in different research periods. These effects are reduced by geographical stratified resampling. The results of the trend analysis after stratified resampling are expected to give a more reliable representation of true changes, than the results after using the original data. The scale of stratification is dependent on the structure of the data.

Question: How will warming and increased nutrient availability affect individual alpine plant species abundances (non-vascular and vascular) and community composition?

Location: Dryas octopetala heath at alpine Finse, southern Norway.

Methods: Four years with experimental warming (open top chambers) and nutrient addition. Detrended Correspondence Analysis and Redundancy Analysis were used to examine changes in community composition. GLM-ANOVA was used to examine treatment effects on individual species.

Results: Warming alone decreased the abundance of some Carex and bryophyte species, but did not affect community composition. Nutrient addition and warming combined with nutrient addition increased the abundance of high stature species, such as grasses (Festuca spp., Poa alpina) and some forbs (e.g. Cerastium alpinum, Potentilla crantzii). Low stature forbs (e.g. Tofieldia pusilla), a lycophyte (Selaginella selaginoides) and most bryophytes and lichens decreased in abundance. After four years of warming combined with nutrient addition 57% of the mosses, 57% of the liverworts and 44% of the lichens had completely disappeared. Community composition changed significantly, with the largest shift when warming and nutrient addition was combined.

Conclusions: Tall species may expand at the expense of low stature species in the alpine region if temperature and soil nutrient content increase. Contrasting responses between grasses and sedges, and species-specific responses within forbs, sedges and shrubs, within and across alpine and arctic sites, suggest that the use of functional types in environmental change research may mask important information on individual species responses. The response of one species within a functional type cannot predict the response of another.

Nomenclature: Lid & Lid (1994) for vascular species; Hallingbäck & Holmåsen (1995) for bryophytes; Krog et al. (1994) for lichens.

Questions: 1. Does flood pulsing drive metacommunity dynamics and provide insurance against catastrophic flooding in desert southwestern riparian ecosystems? 2. Do upland and wetland species in the floodplain differ in their dynamics?

Location: Southwestern USA.

Methods: We sampled vegetation and propagule banks in four communities along a floodplain hydrogradient. Plant species were classified as wetland or upland and community wetland indicator scores were calculated. ANOVA tested for differences between data categories amongst communities (extant vegetation and propagule banks) and soil depths. Sørensen's similarity coefficient was calculated to determine compositional similarity between vegetation and propagule banks.

Results: Community propagule banks had high similarity indicating broad dispersal by flood waters. Wetland propagules were present in soils from channel bars to floodplain edges, despite declines in wetland vegetation with distance from channel. Wetland communities in propagule banks were dissimilar from those in vegetation except on channel bars. Upland species (vegetation and propagule banks) increased with distance from channel. Propagules of upland species were most abundant in the litter, and were compositionally similar to upland species in most communities.

Conclusions: Flood pulsing is one mechanism that drives spatiotemporal metacommunity dynamics in dynamic desert riparian ecosystems. The homogenized regional propagule bank created by flood pulsing provides wetland species with a mechanism to escape local extinction by allowing for recolonization after flooding creates suitable establishment conditions. Upland species are able to germinate from in-situ sources after small-scale flooding or rainfall moistens soil. In fluctuating environments, these dynamics sustain biodiversity in the face of ongoing environmental change.

Nomenclature: Kearney & Peebles (1960).

Question: What is the main ecological process determining species assemblage in roadside herbaceous plant communities?

Location: Roadside slopes (roadcuts and embankments) in the south (Málaga, mesic Mediterranean) and east (Valencia, dry and continental) of the Iberian Peninsula.

Methods: We identified 417 plant species, from which we selected the 331 most abundant (within the 70th abundance percentile) at each site. We compiled information on 28 functional traits and on the biogeographic range of each of these 331 species. We quantified the phylogenetic signal of each trait for the species of each community and determined the number of functional convergences or divergences over the phylogenetic tree for each of the four situations (roadcuts and embankments in the two sites).

Results: There was a significant phylogenetic signal in many traits, being positive in Valencia embankments and negative in Valencia roadcuts with almost no signal in any type of slope in Málaga. Each trait was significantly correlated with 20% – 35% of all other traits but correlation coefficients were low. No significant phylogenetic signal was found for the species' distribution range in any of the four communities studied, which might be the consequence of the complex mixture of biogeographic origins of the species found in these communities.

Conclusion: The lack of a phylogenetic signal in most traits in Málaga, a climatically favourable locality, suggests that competitive exclusion was the main process involved in the assemblage of these communities. The significant and either positive or negative phylogenetic signal (in embankments and roadcuts respectively), the latter coupled with a significant number of functionally convergent nodes in the phylogenetic tree, suggests that environmental filtering is the most likely process involved in the harsh locality of Valencia.

Questions: Sand storms from east Inner Mongolia are a major threat to the ecological safety of North China and actions are desirable to control further desertification. Small patches of relict Pinus tabulaeformis could play a major role in this. The climate signal recorded in the tree-ring widths and the dates of past regeneration episodes of these trees growing at the northern border of their natural distribution are considered here.

Location: Ortindag Sand Land in North China.

Methods: We collected increment cores from relict P. tabulaeformis trees at five sites, built a standard tree-ring chronology for each site and a regional tree-ring chronology from the three longest site chronologies, analysed the tree growth/climate relationships and determined the germination years of the trees to recognize past regeneration dynamics.

Results: Monthly precipitation and relative air humidity in the previous and current growing seasons are the major limiting factors for the radial growth of P. tabulaeformis. Years with a high frequency of absent tree rings are characterized by particularly extreme dry conditions. These results are supported by negative correlations between radial growth and monthly maximum temperature and evaporation during the growing season. In a 163-year time series of precipitation from previous July to current June reconstructed from the tree rings, cycles with wave lengths of 2-3, 17.4 and 20.5 years are significant.

Conclusion: P. tabulaeformis trees are reliable recorders of high and low frequency variations of dry/wet environmental conditions in the Ortindag Sand Land. Their age structures within the forest patches prove that they regenerate preferen-tially in less dry periods.

Question: We studied the patterns of plant species co-occurrence on three, nested, spatial scales in semi-natural grassland communities and explored the possible ecological processes underlying the patterns.

Location: Dry, semi-natural grasslands in a 4.5 km × 4.5 km area on the Baltic Island of Öland (Sweden).

Methods: The study used replicated samples on three, nested, spatial scales: 50 cm × 50 cm plots (N = 516), grassland patches (N = 109) and the whole landscape (N = 6). We used a null model approach to study species co-occurrence patterns and compared the ecological amplitudes of the pairs of species contributing most to the patterns. We used linear models to search for associations between species segregation and environmental and landscape factors.

Results and Conclusions: Our results support the prediction that patterns of species co-occurrence are likely to be influenced by different mechanisms on different spatial scales. On the plot scale, we interpreted the species segregation in terms of species interactions. The degree of species segregation was significantly associated with the plots' positions within the grassland patches (edge effects) and with management intensity of the grasslands – both variables can be assumed to influence species interactions. On the grassland patch scale, we interpreted the species segregation in terms of within-patch environmental heterogeneity. The degree of segregation was significantly associated with the area of the grassland patches and with management intensity – both variables that are likely to be related to environmental heterogeneity within the grasslands. Species segregation on the landscape scale was interpreted in terms of environmental heterogeneity among grassland patches and was significantly associated with land-use history.

Nomenclature: Karlsson (1998).

Questions: What factors influence tree species diversity of mangrove forests, an example of species-poor systems? What are the respective importance and interactions of these factors? Is the intermediate disturbance hypothesis applicable to such systems?

Methods: We used the spatially explicit individual-based model KiWi to investigate the effects on species diversity of perturbation frequency and intensity, different abiotic conditions, and interspecific competition simulated at the individual level. The simulation system considered the three dominant Caribbean mangrove species: Rhizophora mangle, Avicennia germinans and Laguncularia racemosa, applying species-specific growth and mortality characteristics. Firstly, effects on species dominance of the abiotic conditions nutrient availability and porewater salinity were tested with two competition scenarios. Secondly, the effect of perturbation frequency and intensity were investigated with selected abiotic conditions.

Results: Abiotic conditions influenced species dominance and, in extreme cases, excluded one or two species. Abiotic and competition settings controlled the successional dynamics and the response of species dominance to perturbation regimes. A response consistent with the intermediate disturbance hypothesis was observed only with a configuration of plant interaction in which one species behaved as a pioneer so that succession occurred by competitive exclusion.

Conclusions: We suggest that successional dynamics interact with the intensity and timing of perturbations and determine whether or not mangrove tree diversity conforms to predictions of the intermediate disturbance hypothesis. For mangroves, these successional dynamics are site-specific depending on abiotic conditions and species configurations.

Questions: What is the structure of the anthropogenic upper forest-grassland ecotone and are there differences in the spatial relationships between the tree species involved?

Location: Valfurva Valley, Italian central Alps.

Methods: We conducted a spatial distribution and structure analysis in three 1-ha permanent plots along an altitudinal gradient, from the treeline to the sub-alpine forest. We reconstructed the age structure from cores from each individual with diameter > 4 cm at 50 cm height.

Results: All tree species and age classes examined had a clumped structure. The cluster tendency was more evident at the treeline where the environmental conditions are more severe. In the sub-alpine forest there was a repulsion between Pinus cembra and Pinus mugo but at the treeline P. cembra was frequently found downslope from P. mugo.

Conclusions: Although human influence has been the main driving force in shaping the present forest structure, in the last few decades natural dynamics have become the predominant force acting on forest structure and processes, showing a higher magnitude as altitude increases. Our results emphasize the existence of facilitating and interfering mechanisms between different species. P. cembra seems to be favoured compared to the other tree species.