British National Vegetation Classification Research Articles

Phytosociology informs the conservation of species-rich meadows in hydrologically dynamic habitats: an example from British floodplains in a wider European context

Nature conservation requires classification of vegetation types for site assessment and assignment. Species-rich floodplain meadows are a declining habitat in Britain and Europe yet their classification in Britain has been based on just a few samples and fails to describe community response to environmental change adequately. European classification, in opposite, has been based on samples from the wide geographical range with no environmental data/analysis supporting the choices. We propose a revised classification of the lowland meadow Alopecurus pratensis-Sanguisorba officinalis community of the British National Vegetation Classification (NVC) linked to variation in local water-table depth. Data have been collated from 58 British floodplain meadows. Based on botanical and hydrological data, four subcommunities within the Alopecurus-Sanguisorba community have been defined. Assessment of conservation sites at the subcommunity level allows temporal and spatial evaluation of the trends and suggests hydrological management towards desirable vegetation. This approach, developed on data from the British meadows, has much wider geographical applications if compared with European plant communities. Seventy-two British and European plant associations were compared via Canonical Correspondence Analysis (CCA). Species ordinations were used to study the coherence of floodplain syntaxonomic alliances across Europe from Ireland to Bulgaria. CCA confirmed the spread of the British subcommunities of the Alopecurus-Sanguisorba community along a strong hydrological gradient and highlighted their lower fertility compared to their Dutch counterparts. The hydrological gradient separating the British subcommunities should help inform site management for the conservation of the species-rich communities, especially where hydrological control is possible.

Green hay transfer for grassland restoration: species capture and establishment

Green hay transfer from species‐rich donor sites is now commonly used in Europe to restore species‐rich semi‐natural grassland, both on ex‐arable land and on former intensive grassland. However, species transfer rates are usually well below 100%, and due to lack of further colonization by additional target species after initial restoration, continued progress toward the target plant community is often very slow. We used data from a restoration experiment aiming to reestablish species‐rich grazed meadows of the MG5 grassland type according to the British National Vegetation Classification to investigate relationships between species abundance at a donor site, species capture by green hay and its seed content, and success of species establishment on experimental plots in formerly intensively managed species‐poor grassland undergoing restoration. Our results show that species with higher abundance at the donor site were more likely captured as seed in green hay, and were more likely to establish after hay application at the recipient site. Species with low abundance at the donor site that also possessed specific germination requirements that might prevent immediate establishment after green hay transfer were particularly unlikely to get established after transfer. These findings can provide guidance for additional measures aimed at ensuring establishment of a wider range of target species. Such measures could include targeted sowing of species in addition to green hay application, and management of restored grassland swards to extend or reopen an initial window of opportunity for the establishment of green hay species that might not be germinable immediately after hay transfer.

Green hay application and diverse seeding approaches to restore grazed lowland meadows: progress after 4 years and effects of a flood risk gradient

The two most common approaches to target species introduction in European meadow restoration are green‐hay transfer from species‐rich donor sites and the use of diverse seed mixtures reflecting the chosen target community. The potential of both approaches to restore species‐rich grassland has been variously reviewed, but very few studies have experimentally compared them at one and the same site. Moreover, studies involving one or both approaches have rarely taken into account environmental gradients at a site, and measured the impacts of such gradients on restoration outcomes. Such gradients do, for example, exist during grassland restoration on former arable land in river floodplains, where gradients in the occurrence of flooding, and in associated edaphic characteristics such as nutrient availability, might affect restoration outcomes. Using a randomized complete block experimental design, based on five different indicators of restoration progress, we compared the usefulness of green‐hay application and diverse seeding to restore species‐rich grazed meadows of the MG5 grassland type according to the British National Vegetation Classification, and also investigated how restoration outcomes differed after 4 years between areas within experimental plots characterized by high flood risk and areas characterized by low flood risk. Overall, both restoration approaches yielded similar results over the course of the experiment, whereas high flood risk and associated edaphic factors such as high availability of phosphorus negatively affected restoration progress particularly in terms of floristic similarity to restoration targets. These results highlight the need to take into account environmental gradients during meadow restoration.

Classifying grass-dominated habitats from remotely sensed data: The influence of spectral resolution, acquisition time and the vegetation classification system on accuracy and thematic resolution

Detailed maps of vegetation facilitate spatial conservation planning. Such information can be difficult to map from remotely sensed data with the detail (thematic resolution) required for ecological applications.For grass-dominated habitats in the South-East of the UK, it was evaluated which of the following choices improved classification accuracies at various thematic resolutions: 1) Hyperspectral data versus data with a reduced spectral resolution of eight and 13 bands, which were simulated from the hyperspectral data. 2) A vegetation classification system using a detailed description of vegetation (sub)-communities (the British National Vegetation Classification, NVC) versus clustering based on the dominant plant species (Dom-Species). 3) The month of imagery acquisition.Hyperspectral data produced the highest accuracies for vegetation away from edges using the NVC (84–87%). Simulated 13-band data performed also well (83–86% accuracy). Simulated 8-band data performed poorer at finer thematic resolutions (77–78% accuracy), but produced accuracies similar to those from simulated 13-band or hyperspectral data for coarser thematic resolutions (82–86%). Grouping vegetation by NVC (84–87% accuracy for hyperspectral data) usually achieved higher accuracies compared to Dom-Species (81–84% for hyperspectral data). Highest discrimination rates were achieved around the time vegetation was fully developed.The results suggest that using a detailed description of vegetation (sub)-communities instead of one based on the dominating species can result in more accurate mapping. The NVC may reflect differences in site conditions in addition to differences in the composition of dominant species, which may benefit vegetation classification. The results also suggest that using hyperspectral data or the 13-band multispectral data can help to achieve the fine thematic resolutions that are often required in ecological applications. Accurate vegetation maps with a high thematic resolution can benefit a range of applications, such as species and habitat conservation.

Ecohydrological studies of dune slack vegetation at Kenfig dunes, South Wales, UK

Dune slacks are important coastal sand dune habitats and seasonal changes in water levels within dune aquifers control both their formation and the specific hydrological conditions which then govern the floristic composition of their characteristic plant communities. Kenfig Dunes National Nature Reserve is one of the largest dune sites in South Wales and Southern Britain. It supports an exceptional range of dune slack communities, including most of those recognised in the British National Vegetation Classification scheme. Detailed studies of the vegetation ecology and hydrology of dune slacks reveal the important influence of hydrological variables in controlling the composition of dune slack vegetation and also valuable information on water table profile and the key factors governing the annual hydrological budget of the dune system aquifer.

Characterization of a Highly Biodiverse Floodplain Meadow Using Hyperspectral Remote Sensing within a Plant Functional Trait Framework

We assessed the potential for using optical functional types as effective markers to monitor changes in vegetation in floodplain meadows associated with changes in their local environment. Floodplain meadows are challenging ecosystems for monitoring and conservation because of their highly biodiverse nature. Our aim was to understand and explain spectral differences among key members of floodplain meadows and also characterize differences with respect to functional traits. The study was conducted on a typical floodplain meadow in UK (MG4-type, mesotrophic grassland type 4, according to British National Vegetation Classification). We compared two approaches to characterize floodplain communities using field spectroscopy. The first approach was sub-community based, in which we collected spectral signatures for species groupings indicating two distinct eco-hydrological conditions (dry and wet soil indicator species). The other approach was “species-specific”, in which we focused on the spectral reflectance of three key species found on the meadow. One herb species is a typical member of the MG4 floodplain meadow community, while the other two species, sedge and rush, represent wetland vegetation. We also monitored vegetation biophysical and functional properties as well as soil nutrients and ground water levels. We found that the vegetation classes representing meadow sub-communities could not be spectrally distinguished from each other, whereas the individual herb species was found to have a distinctly different spectral signature from the sedge and rush species. The spectral differences between these three species could be explained by their observed differences in plant biophysical parameters, as corroborated through radiative transfer model simulations. These parameters, such as leaf area index, leaf dry matter content, leaf water content, and specific leaf area, along with other functional parameters, such as maximum carboxylation capacity and leaf nitrogen content, also helped explain the species’ differences in functional dynamics. Groundwater level and soil nitrogen availability, which are important factors governing plant nutrient status, were also found to be significantly different for the herb/wetland species’ locations. The study concludes that spectrally distinguishable species, typical for a highly biodiverse site such as a floodplain meadow, could potentially be used as target species to monitor vegetation dynamics under changing environmental conditions.

Winners and losers in a long-term study of vegetation change at Moor House NNR: Effects of sheep-grazing and its removal on British upland vegetation

We analysed data collected between 1954 and 2000 from nine long-term experiments designed to assess the effects of sheep-grazing versus no-sheep-grazing at Moor House NNR, an Environmental Change Network site. The experiments were set up between 1954 and 1972 across a range of vegetation types typical of much of upland Britain. Data from this type of experiment are often difficult to analyse and we describe the procedures undertaken to prepare the data for analysis. We fitted the resultant data to the British National Vegetation Classification and used ordination techniques to assess the relative positions of the experiments to each other. Finally, we used Generalized Linear Mixed-effects Modelling within a Bayesian framework to model change of species taxonomic/physiognomic groups through time in both sheep-grazed and ungrazed treatments across all nine experiments; variables included species diversity, Shannon–Weiner index and derived data on occurrence and abundance of species groups based on taxonomy and physiognomy. Hurdle analysis was used to model the species groups; this analysis separated the change through time in both probability of occurrence (binomial distribution) and abundance (Poisson distribution).In the sheep-grazed plots (the “business-as-usual” treatment hence here designated the “control”) there was a reduction in species diversity and a decrease in abundance of vascular plants, grasses, lichens, liverworts and mosses; whereas herbs, sedges and shrubs increased. When probability of occurrence was considered, there was a reduction in number of presences of both lichens and liverworts. Thus, the status quo management of continuous sheep-grazing, even though reduced since 1972, has resulted in a marked change in species composition of these plant communities, with some winners and some losers, but overall they support the concept of biotic homogenization. It is likely that some of these changes were driven by external factors such as elevated atmospheric nutrient deposition. Removal of sheep grazing had some positive benefits; with the herbs, mosses, sedges and shrubs increasing, but faster reductions in grasses and liverworts. Sedges+rushes were stable. It suggested that future monitoring schemes might use either the probability of occurrence of liverworts and lichens, or the abundance of lichens, liverworts, grasses and mosses as sensitive indicators of change in upland Britain.Moreover, during the period that Moor House has been protected as a nature reserve some key plant species groups have declined in spite of reductions in grazing pressure. To reverse this trend requires some form of interventionist management. In order to increase the diversity of vascular plants some form of disturbance will probably be needed, but for bryophytes and lichens this remains a research question. If the results from these small-scale experiments are replicated at the landscape scale a reduction of sheep grazing pressure, for example in rewilding schemes, will have little effect on species composition over a 28–44 year period.

Are Ireland's reintroduced Pinus sylvestris forests floristically analogous to their native counterparts in oceanic north-west Europe?

Pinus sylvestris has undergone extirpation and reintroduction in several countries in north-western Europe. In Ireland, the species' native status is disputed and the conservation value of reintroduced pinewoods is unclear. To clarify the implications of this reintroduction for biodiversity conservation, we evaluated the level of floristic similarity between reintroduced and native stands. Plots recorded in reintroduced stands in Ireland and native stands in Scotland were compared using cluster analysis and Nonmetric Multidimensional Scaling. A synoptic table was prepared incorporating floristic data from native stands in south-western Norway. The reintroduced plots were classified in terms of the British National Vegetation Classification and compared with Irish fossil pinewood assemblages. Four groups were identified by cluster analysis; three were floristically similar to Irish fossil pinewood assemblages and three corresponded, to varying degrees, to extant native pinewoods in Scotland or Norway. Irish bog pinewoods corresponded to the EU Habitats Directive Annex I priority habitat bog woodland. This suggests that reintroduced P. sylvestris is an important resource for Ireland's native botanical and habitat diversity, given Ireland's low cover of native woodland. For practical conservation purposes, P. sylvestris should be retained and managed as a native species in woodland habitats in Ireland.

Biological Flora of the British Isles: Cirsium arvense (L.) Scop.

Summary 1. This account presents information on all aspects of the biology of Cirsium arvense that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, conservation and management. 2. Cirsium arvense, creeping thistle (Californian thistle, Canada thistle), one of the world’s most troublesome and persistent weeds, is native to Europe and the east northern hemisphere but introduced to North America and the southern hemisphere. Latitudinal distribution north or south is limited by low winter and summer maximum temperatures and by a long day requirement for flowering. 3. Cirsium arvense is believed to have originated in the temperate Middle East and its spread has closely followed human migration and agricultural activity. Colonization of new sites is by seed which establishes best in bare or disturbed ground, mirroring its prehistoric ecology as an opportunist pioneer of bare ground and organic residues. It is now a widespread and scheduled agricultural weed in both arable crops and pastures and also a constituent in over 70 British (National Vegetation Classification) plant communities, occurring mainly on waste neglected land, roadsides, hedgerows and disturbed areas. 4. Its presence in crops leads to yield losses and in pastures seriously interferes with utilization due to the deterrent effect of the leaf spines on grazing animals. This has led to a long history of investigation into control measures: mechanical, chemical, biological and integrated, which are summarized. Combination treatments and integrated control have achieved some success but effective control requires follow‐up procedures over a number of seasons. Climate change studies suggest C. arvense could grow better and be more difficult to control in future. 5. Success and persistence derives from an extensive, far‐creeping and deep rooting system which ensures survival and rapid vegetative spread under a wide range of soil and management conditions, and a means of escape from sub‐aerial control treatments. New adventitious buds capable of shoot development can arise at any point along the horizontal roots, even when these are cut into pieces or damaged. Root buds remain dormant until released from dormancy through damage or decay of the aerial shoots. Carbohydrate root reserves, stored in swollen cortical tissue, fall to a minimum just before flowering and are then replenished for perennation during the subsequent winter. Strategies for control aim to treat the plant when root carbohydrate reserves are at a minimum, to exhaust these reserves and to prevent replenishment for further perennation. 6. Balanced against its difficulty as a weed, C. arvense has significant conservation value as a host to numerous insects, many attracted by copious and accessible nectar and strong flower fragrance. It is however a strong competitor to low‐growing plants in natural communities. 7. Cirsium arvense is dioecious and for flowering has a 14–16 h day length requirement. Seed set is successful if male and female plants are no more than 50–90 m apart to allow insect pollination. In spite of the conspicuous wind‐borne pappus, this rarely carries a seed which normally falls near the parent plant. The flower heads and other plant parts are regularly attacked by numerous insects and less frequently by diseases. 8. Germination of seed is mainly during the high temperatures of early summer in the year following dispersal and establishment is most successful in open areas. Development of the branching root system and vegetative spread follow rapidly. 9. A combination of dioecy and vegetative reproduction has resulted in the maintenance of genotypic and genetic diversities within populations allowing efficient colonization and persistence, contributing greatly to success in the species.

Available soil phosphorus in semi-natural grasslands: Assessment methods and community tolerances

Restoration of diverse semi-natural grasslands is potentially limited by high availability of soil phosphorus (P). Successful targeting of restoration effort requires a knowledge of plant community tolerances to soil P availability. Many extraction methods for P availability have been developed but most are calibrated against the growth and P uptake of crop species grown in monoculture. To test which methods are most suitable for measuring available P in soils of mesotrophic grasslands, a bioassay experiment was undertaken to compare seven extraction methods with the growth and P uptake of grassland species. Five species were grown together on a soil treated to create a range of conditions of pH, mycorrhizal infection and P availability. Olsen P and Bray P were found to be significantly correlated with P uptake in plant growth across the range of soil treatments whilst ion exchange membrane P and resin P were significantly correlated with P uptake in plant growth in all but the calcareous soils. The acid extractions of Truog, acetic acid and EDTA–ammonium acetate were found to be less correlated with P uptake in plant growth. All extraction methods correlated more strongly with P uptake in the sterilised treatments than in those inoculated with mycorrhizal spores. The method of Olsen was therefore selected to analyse P availability in soils supporting a range of mesotrophic grassland communities from eleven sites across England. At each sampling location, the species composition of the vegetation was assessed and classified using the British National Vegetation Classification (NVC). Species-rich hay meadows across a range of alliances were found to occur on soils with low phosphorus availability. Species-poor communities, such as inundation grassland, were found to occur on soils with higher phosphorus availability. Pasture communities, of intermediate species richness, tended to occur on soils of intermediate phosphorus availability. Olsen’s method of P extraction is recommended for analysing soils of areas identified for habitat creation; values of less than 10 mg kg −1 will give the greatest potential for the restoration of species-rich mesotrophic grassland.

THE VEGETATION OF ARTIFICIAL DRAINAGE CHANNELS WITHIN GRAZING MARSHES IN THE UK: HOW DOES ITS COMPOSITION CORRESPOND WITH DESCRIBED COMMUNITIES?

Large areas of British coastal and riverine floodplains support grazing marsh, a landscape representing an intermediate stage in the reclamation of natural wetlands toward intensive agriculture. Once disregarded for nature conservation, in the late twentieth century it was realised that grazing marshes were significant for wetland birds and invertebrates, as well as the key refuge for aquatic vegetation in lowland Britain. The Centre for Ecology and Hydrology (CEH) surveyed this vegetation, focussing on drainage channels and their banks. In multivariate analysis, vegetation composition was related to channel dimensions, soil type, land use, channel management and the drainage function of the channel. CEH attempted to relate the channel vegetation assemblages to those aquatic and swamp types described within the British National Vegetation Classification and the wider literature. Although we sometimes achieved this aim channels often appeared to contain intimate concatenations of types that could not be simply separated into recognised aquatic and swamp associations. Thus, channel vegetation may be represented either as combinations of described communities or as unique multilayered associations, comparable with woodlands. The degree to which aquatic and swamp elements occur in predictable combinations is discussed. Despite being artificial habitats, drainage channels have intrinsic biodiversity value, meriting recognition within European systems for the protection of biodiversity.

The Vegetation of Artificial Drainage Channels Within Grazing Marshes in the UK: How Does its Composition Correspond with Described Communities?

Large areas of British coastal and riverine floodplains support grazing marsh, a landscape representing an intermediate stage in the reclamation of natural wetlands toward intensive agriculture. Once disregarded for nature conservation, in the late twentieth century it was realised that grazing marshes were significant for wetland birds and invertebrates, as well as the key refuge for aquatic vegetation in lowland Britain. The Centre for Ecology and Hydrology (CEH) surveyed this vegetation, focussing on drainage channels and their banks. In multivariate analysis, vegetation composition was related to channel dimensions, soil type, land use, channel management and the drainage function of the channel. CEH attempted to relate the channel vegetation assemblages to those aquatic and swamp types described within the British National Vegetation Classification and the wider literature. Although we sometimes achieved this aim channels often appeared to contain intimate concatenations of types that could not be simply separated into recognised aquatic and swamp associations. Thus, channel vegetation may be represented either as combinations of described communities or as unique multilayered associations, comparable with woodlands. The degree to which aquatic and swamp elements occur in predictable combinations is discussed. Despite being artificial habitats, drainage channels have intrinsic biodiversity value, meriting recognition within European systems for the protection of biodiversity.

Community Associations of Chalk Grassland Leafhoppers (Hemiptera: Auchenorrhyncha): Conclusions for Habitat Conservation

Due to their confinement to specific hostplants or restricted habitat types, Auchenorrhyncha have the potential to make suitable biological indicators to measure the quality of chalk grassland under different management practices for nature conservation. The Auchenorrhyncha data from a study designed to identify the factors influencing the invertebrate diversity of chalk grasslands in southern England was used to evaluate the potential use of this group of insects as biological indicators. Between 1998 and 2002 altogether 81 chalk grassland sites were sampled. Vegetation structure and composition were recorded, and Auchenorrhyncha were sampled at each site on three occasions in each of two seasons using a ‘Vortis’ suction sampler. Auchenorrhyncha assemblages were then linked to the different grassland plant communities occurring on chalk soils according to the British National Vegetation Classification (NVC). Altogether 96 Auchenorrhyncha species were recorded during the study. Using data on the frequency and dominance of species, as is commonly done for plant communities, it was possible to identify the preferential and differential species of distinct Auchenorrhyncha assemblages. Significant differences between the Auchenorrhyncha assemblages associated with the various chalk grassland plant communities of the NVC were observed down to a level of sub-communities. We conclude that data on Auchenorrhyncha assemblages can provide valuable information for the setting of conservation management priorities, where data on floristic composition alone may not be sufficient, providing additional information on aspects of vegetation structure and condition.

Influence of Seed Mixture and Hydrological Regime on the Establishment of a Diverse Grassland Sward at a Site with High Phosphorus Availability

Abstract Three experiments were undertaken to investigate the influence of seed mixture on the establishment of a target grassland community on a site with high available phosphorus. In the first experiment autumn‐ and spring‐sown commercial seed mixtures were compared with seed harvested from a nature reserve with respect to their ability to produce an inundation grassland community similar to that described by the British National Vegetation Classification (NVC) as Agrostis stolonifera–Alopecurus geniculatus grassland (MG13). In the second experiment the composition and sowing rate of a commercial seed mixture were altered to investigate whether these factors were significant in the establishment of a sward similar to MG13. Similarly, in the third experiment the composition of a commercial seed mixture designed to achieve an alternative community, Cynosurus cristatus–Caltha palustris grassland (NVC code MG8), was sown. The vegetation resulting from each of these treatments was monitored with permanent quadrats for a 3‐year period, and the hydrological regime of each quadrat location was modeled and quantified. The results showed that seed mixture, timing of sowing, and seeding rate had an initial effect on the vegetation that established. However, by the third year of monitoring there were no significant differences between these treatments, and hydrological regime had become the most important factor in determining the distribution of species. The vegetation was less diverse than predicted from germination tests and decreased in diversity over the monitoring period. It is suggested that this may be a result of the hydrological regime being unsuitable for several of the sown species or due to the extremely high available phosphorus concentration in the soil. This study highlights the need to understand the soil and hydrological conditions of a site before choosing a target community and designing a seed mixture.

The use of ground vegetation and humus type as indicators of soil nutrient regime for an ecological site classification of British forests

In many countries ground vegetation and humus type are used as indicators of forest soil quality, especially nutrient regime. This paper reports the development of such methods for use in British forests, within a new Ecological Site Classification combining climate, soil moisture regime and soil nutrient regime. To develop a field assessment method for soil nutrient regime, a study was made of soil chemistry, humus type and ground vegetation in British forests. Sites were selected in both mature plantations and semi-natural woodlands. Soil and humus profiles were described and the soil was sampled volumetrically for later chemical analysis. Vascular ground vegetation was recorded in quadrats by species cover fraction, and classified according to the existing British National Vegetation Classification. Soils were analyzed for a number of chemical variables. Vegetation data were treated by application of the species indicator values for soil reaction ( R) and soil nitrogen ( N), as proposed by Ellenberg [Vegetation Ecology of Central Europe, 4th Edition. Cambridge University Press, Cambridge]. Site mean indicator values mR and mN (weighted by species cover fraction) were then calculated. Multivariate statistical analysis techniques were applied to both the soil chemical and the vegetation sample data. Soil nutrient regime was shown to be a composite gradient of several soil chemical variables, of which the pH value and the availability of mineral (especially nitrate) nitrogen, and of calcium, were of particular importance. The species composition of the ground vegetation was related to position on this soil nutrient gradient. The vegetation: soil nutrient correlation using the site mean Ellenberg values was satisfactory ( r=0.89), but was improved by using indicator values generated from within the present data. The occurrence of the major humus types (mor, moder and mull) is broadly related to soil nutrient regime defined in this way. Both ground vegetation and humus type can therefore be used as soil nutrient indicators in British forests. A division of the soil nutrient gradient into five classes (Very Poor, Poor, Medium, Rich and Very Rich) is proposed. Future sampling work may lead to the definition of an additional class of soils with carbonate nutrient regimes. The Ecological Site Classification will provide forest managers in Great Britain with an improved basis for the selection of tree species for planting, and the adoption of silvicultural methods best suited to the site.

A test of community reassembly using the exotic communities of New Zealand roadsides in comparison to British roadsides

Summary 1 Competing theories of community assembly are very difficult to test. Four main theories exist. The Stochastic theory sees species assembly as being random. The Humpty Dumpty/Alternative Stable States (ASS) theory suggests that a community may be unable to reassemble itself from its constituent species. The Deterministic theory suggests there will be convergence to one stable state. The Pre‐adaptation theory is similar to the Deterministic theory but emphasizes that many species fit the stable state because of characters acquired elsewhere. 2 The reassembly of a flora into new communities in a different country, or its assimilation as a major component of such communities, offers a means to test these theories. The invasion of British plant species into New Zealand, and their reassembly into roadside communities there, is a good example of such a natural experiment. 3 Plant communities of NZ roadsides were compared to the communities of the British National Vegetation Classification (NVC). British roadside communities were also compared to the NVC as a control. New Zealand roadside communities provided a fit to the NVC communities of only 54.7% on average. After excluding species that are not present in NZ, and therefore could not possibly reassemble, the fit increased to 61.1%. British roadsides gave a 65.8% fit. The NZ figures are similar to the fit obtained with random data (58.7%), indicating that the NZ communities bear little relation to the ones formed by the same species in Britain. 4 Similarity between roadside communities in NZ and Britain was low, forming two almost distinct sets of communities. 5 Some of the predictions of the Stochastic, Humpty Dumpty / ASS and Deterministic models are borne out, but others are not. It is concluded that British species have reassembled into communities in NZ most of which are new, i.e. distinct from those that occur in the native range of the species in Britain. The evidence points to a process of community assembly by pre‐adaptation.

Community reassembly: a test using limestone grassland in New Zealand

To examine community reassembly, we sampled grasslands on calcareous soil (4%–24% CaCO3) in New Zealand that were largely composed of species introduced from Britain. We tested whether the British species had reassembled on New Zealand limestone into the same communities as they form on limestone in Britain. The vegetation of six New Zealand sites was sampled, each with ten 2 × 2 m quadrats that followed the standard methodology of the British National Vegetation Classification (NVC). Analysing species presence and cover using program TableFit with the full database of British species, the New Zealand species assemblages gave poor to moderate fits (40%–72%) to the communities of the NVC, and even then not to calcareous grassland, though one site did fit to a calcareous spring community. The poor fits can be partly attributed to the absence from New Zealand of many British calcareous-specialist species. On omitting from the NVC database all species not present in New Zealand, the fits increased somewhat to 48%–77%. Using this modified database, two sites fitted British calcareous grassland communities. These two sites are on thinner soil (<10 cm depth), under lower rainfall. Where fits were obtained to calcareous communities, the environment of the community in Britain matched very well that of the New Zealand site. It is concluded that environmental and perhaps biotic filtering has been strong enough in some sites to assort alien species into the same species assemblages as they form in their native range, indicating the Deterministic model of community structure. However, the absence of some species has prevented full reassembly.

Ecological gradients, subdivisions and terminology of north‐west European mires

Summary 1 The historical development of mire ecology and terminology is reviewed in relation to evolving concepts and perceptions, and the diverse schools and traditions of vegetation and habitat description and research. 2 Most ecological and floristic variation within north‐west European mire vegetation is accounted for by three ecological gradients: the acid base‐poor vs. neutral, base‐ and bicarbonate‐rich gradient; the gradient in fertility related to availability of the limiting nutrient elements N and P; and the water level gradient. Effects of salinity and the spring–flush–fen gradients are of more local significance, usually easily recognized. Land use is an important additional factor. 3 The mineral‐soil‐water limit between ombrotrophic and minerotrophically influenced sites is not sharp, and cannot be related to consistent differences in either vegetation or water chemistry. It should be abandoned as a general main division within mires. 4 The most important natural division is between ‘bog’, with pH generally &lt; 5.0, low Ca2+, and Cl– and SO42– as the main inorganic anions, typically dominated by sphagna, ericoids and calcifuge Cyperaceae, and ‘fen’, with pH generally &gt; 6.0, high Ca2+ and HCO3–, vegetation rich in dicotyledonous herbs and ‘brown mosses’. This division is reflected in a bimodal distribution of pH. 5 The terms oligotrophic, mesotrophic and eutrophic should refer only to nutrient richness (fertility, mainly N and P), not to base richness (metallic cations and pH). 6 It is recommended that ‘mire’ should embrace both wetlands on peat and related communities on mineral soils, that ‘bog’ (unqualified) should encompass both ombrotrophic and weakly minerotrophic mires, including ‘bog woodland’, and that ‘fen’ should be restricted to base‐rich mires but include both herbaceous and wooded vegetation (‘fen carr’). 7 Definitions are given for a range of broadly defined categories that should cover most vegetation types commonly encountered. The relation of these to British national vegetation classification types and to major units in European phytosociology is outlined.

Application of the British National Vegetation Classification to the communities of the Park Grass Experiment through time

The Park Grass Experiment at Rothamsted consists of a series of fertilizer treatments which have been applied to a species-rich hay meadow annually since 1856. Detailed botanical analyses of the plots between 1862 and 1992 were classified to one of the National Vegetation Classification (NVC) communities using the similarity measured by Czekanowski coefficient using computer program MATCH. Results indicated that “control” unfertilized plots were a relatively stableCynosurus cristatus-Centaurea nigra dicotyledon-rich grassland. However mineral fertilized plots moved towards a species-richArrhenatherum elatius grassland MG1e after 50–80 years and remained there. Plots receiving nitrogen fertilizer moved first to MG1e then on to aLolium perenne-Alopecurus pratensis grassland MG7D. Perhaps the most interesting plot was one which received a low rate of the soil acidifying ammonium sulphate fertilizer; the species composition changed towards a MG7D (Lolium perenne-Alopecurus pratensis) community between 1856 and 1903 but since then a liming treatment has been applied to part of the plot and the species composition on that part has recovered to a MG5 community resembling the control plots, taking 70–90 years to do so.

Aspects of the population biology ofLiparis loeselii(L.) Rich. var.ovataRidd. ex Godfery (Orchidaceae) in the dune slacks of South Wales, UK

Demographic techniques have been employed to study populations of the rare orchidLiparis loeseliivar.ovataacross a range of dune slack habitats at a South Wales site. The study has shown that very large numbers of shoots (>300) may occur within a single 1×1 m quadrat and that the vegetative production of side shoots is common. Regular population surveys over time have shown that individuals represented by a single shoot can live for 8 years. Subsequent analyses of the floristic composition of the study quadrats has revealed the presence of subtle variations in species composition and vegetation structure in relation to age and hydrology, although all of the plots still fall within the SD14Salix repens-Campylium stellatumdune slack community defined by the British National Vegetation Classification. When attributes of population flux are analysed in relation to floristic composition, one significant trend to emerge is that the appearance of new genets is most prevalent in successionally young slacks. As the natural formation of new slacks by sand blow is now a rare event in the South Wales dune field, the management ofLiparis loeseliivar.ovatais currently aimed at attempting to ensure the persistence of suitable communities through biomass reduction techniques.