On the phytosociological status of Juncus maritimus on British saltmarshes

Summary Six noda occurring on British saltmarshes in whichJuncus maritimus is an important constituent are described. Using numerical techniques these noda are related to previously described communities. It is suggested that two noda be incorporated in theHalimionetum portulacoidis andAtriplici — Agropyretum pungentis while three others are considered to form theJuncus maritimus — Oenanthe lachenalii Ass. R. Tx. 1937 which is included within theArmerion maritimae. The status of theTriglochin — Juncus maritimus nodum remains uncertain. The affinities between northern European and MediterraneanJ. maritimus communities are discussed and it is suggested that the differences between them are not as great as might be supposed from their conventional assignment to separate classes. The variation within theJuncetum gerardii is discussed and it is considered that most of the vegetation described as theJunco — Caricetum extensae may be incorporated in theJuncetum gerardii.Nomenclature follows Hubbard (1968) forPoaceae, and Clapham, Tutin & Warburg (1962) for other British vascular plants. Bryophyte nomenclature is according to Warburg (1963).I should like to thank Dr. H. J. B. Birks for providing the necessary computer programs, I. C. Prentice for comments and criticism and Miss S. Bishop for help in preparing the figures.     

The distribution of Minuartia verna and Thlaspi alpestre in the British Isles in relation to 13 soil metals

The plant-communities from habitats of the metallophyte species Minuartia verna and Thlaspi alpestre (T. caerulescens) at sites disturbed and undisturbed by mining are described. Four communities were delineated by cluster and principal component analysis. Group 1 comprised species-poor communities on disturbed non-calcareous soils; group 2, relatively species-rich communities on disturbed calcareous soils; group 3, species-rich communities in the main on undisturbed calcareous soils. Group 4 consisted of species-rich communities with an alpine element, in damp habitats on base-rich soils derived from igneous rocks. Total and exchangeable elements As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb and Zn were determined for the soils of these sites. Levels of soil Ca, Cd, Pb and Zn accounted for most of the variation along the first axis of the PCA and soil nutrient levels were probably the main predictor along the second.Abbreviations PCA Principal Component Analysis     

Biodiversity in montane Britain: habitat variation,vegetation diversity and some objectives for conservation

The montane (low- to mid-alpine) zone in Great Britain (GB) lies above the potential tree-line (700–800 m, but descending to 200 m in the north). It is composed of moss and lichen heaths, snowbeds, blanket bog and dwarf-shrub (Ericaceae) health-covered solifluction/gelifluction terraces (38 communities/sub-communities). Approximately 3.0% of the land surface is covered by this- the most extensive predominantly near-natural terrestrial habitat in GB. Internationally distinctive features include oceanic and southern biotic outliers of arctic-alpine fellfield and mountain tundra, and plant communities that are either globally rare/localised or especially well represented in GB. The absence of extensive sub-alpineBetula spp. andSalix spp. scrub is striking.The main sources of habitat diversity are climate, regional variation in topography and geology, and regional modifications due to land-use impact. Over 50 examples are given. Five important gradients in Scottish Highland vegetation are described. Only some 15% of the sampled montane vegetation is anthropogenic; the rest is semi- or near-natural. The vegetation is divided into 5 functional groups: chionophobous (avoids snow), chionophilous (prefers snow), species-rich, mires (including springs and flushes), and anthropogenic. Chionophobous and then chionophilous communities contribute most to montane vegetation diversity (calculated here as the ShannonH diversity index).H diversity increases asymptotically with montane site area but linearly with the number of communities present. A more varied topography, geology and topo-climate gives the highestH diversity.Two examples of montane biodiversity reductions south of the Highlands are the loss of prostrateCalluna vulgaris heaths and modification ofRacomitrium lanuginosum healths. Five objectives for nature conservation are proposed, covering restoration of montaneR. lanuginosum healths, prostrate dwarf-shrub dominated heaths, sub-alpine scrub and upper treelines, and the extension of the breeding ranges of both ptarmigan (Lagopus mutus) and dotterel (Charadrius morinellus) south of the Scottish Highlands. International support for monitoring is sought.     

Markov models in the study of post-fire succession in heathland communities

Data on the presence of a number of vegetation states (defined in terms of species dominance in areas of 10×10 cm) and transition probabilities were derived from permanent quadrats in a number of recently burned heath stands. Data were taken from a species-rich community, a species-poor type and a high-level Calluna-Eriophorum bog. Simple Markovian models were constructed using these data, and the model predictions were compared with known or expected trends. Models for species-rich heath yielded poor simulations of expected trends since matrices derived from data for the first years after fire did not contain sufficient information on transitions to states important later in the developmental sequence. Model results for the simpler species-poor and bog communities were more satisfactory and simulated expected trends. In these types all species recovered quickly after fire and less rearrangement of species abundances took place. Maximum likelihood statistics carried out on the transition matrices produced inconclusive results for the species-rich and species-poor types, but indicated that the data from the Calluna-Eriophorum bog approximated a first-order time-homogeneous Markov chain. It was concluded that Markov models lack predictive ability except in relatively simple systems, but that they may be useful in illustrating variations in short-term community dynamics.Nomenclature follows Tutin et al. (1964–80) for vascular plants and Smith (1978) for mosses.I am grateful to Prof. C. H. Gimingham for help and advice during this study, which was carried out during tenure of a Natural Environment Research Council studentship. Thanks are also due to Dr M. B. Usher and an anonymous referee for their comments on the draft.     

Plant communities and landscape diversity along a Canadian Arctic river

Abstract. We analysed the structure and diversity of the vegetation along an Arctic river to determine the relationship between species richness and plant community structure. We examined whether variation in species richness along the corridor is structured as (1) an increase in the number of communities due to increasing landscape heterogeneity, (2) an increase in the floristic distinctiveness (β-diversity) of communities, or (3) an increase in within-community richness (α-diversity) as species-poor communities are replaced by species-rich communities. We described 24 community types and analysed the relationship between site vascular species richness (γ-diversity) and β-diversity, α-diversity, site environmental heterogeneity, and the number of distinct plant communities. We also measured diversity patterns of vascular, bryophyte, and lichen species within communities and examined their relationship to community-level estimates of environmental factors. We found that an increase in site species richness correlated with an increase in the number of communities (r²= 0.323, P= 0.0173) and β-diversity (r²= 0.388, P= 0.0075), rather than an increase in the α-diversity of individual communities. Moisture and pH controlled most of the differences in composition between communities. Measures of species richness and correlations with moisture and pH within communities differed among vascular, bryophyte, and lichen species. Bryophyte richness was positively correlated with moisture (r²= 0.862, P= 0.0010) and lichen richness was negatively correlated with moisture (r²= 0.809, P= 0.0031). Vascular plants had a peak in richness at pH 6.5 (r²= 0.214, P < 0.0001). We conclude that site variation in vascular richness in this region is controlled by landscape heterogeneity, and structured as variation in the number and distinctiveness of recognizable plant communities.     

EVIDENCE FOR COMPETITIVE RELEASE IN SIMPLIFIED SAXICOLOUS LICHEN COMMUNITIES

Saxicolous cryptogam communities were sampled quantitatively on two Potomac River island habitats in June of 1980. As a result of air pollution stress, the community on one island was found to be much simpler than that found on the other island. Two relatively pollution-tolerant foliose lichen species, Xanthoparmelia conspersa and Pseudoparmelia baltimorensis, were found to dominate the communities on both islands. An examination of niche breadth and position along a light intensity gradient demonstrated that P. baltimorensis was most frequent at low light intensities and X. conspersa was most frequent at high light intensities. However, X. conspersa exhibited a niche shift toward intermediate light intensities in the species-poor community, likely the result of reduced competitor diversity in this community since the intermediate light intensities supported the greatest number of species in the species-rich community. Niche overlap between the two species was found to occur at lower light intensities in the species-poor community, suggesting that X. conspersa is more likely to appropriate intermediate light intensities in this community. The significance of competition as a regulatory factor in lichen communities has not been fully appreciated. Since lichens and other cryptogams are frequently used as indicators of environmental quality, competitive processes in naturally occurring lichen communities must be thoroughly understood before changes in species distribution that apparently result from disturbance can be properly interpreted.     

Microbial assimilation of new photosynthate is altered by plant species richness and nitrogen deposition

To determine how plant species richness impacts microbial assimilation of new photosynthate, and how this may be modified by atmospheric N deposition, we analyzed the microbial assimilation of recent photosynthate in a 6-year-long field experiment in which plant species richness, atmospheric N deposition, and atmospheric CO₂ concentration were manipulated in concert. The depleted δ¹³C of fumigation CO₂ enabled us to investigate the effect of plant species richness and atmospheric N deposition on the metabolism of soil microbial communities in the elevated CO₂ treatment. To accomplish this, we determined the δ¹³C of bacterial, actinobacterial, and fungal phospholipid fatty acids (PLFAs). In the elevated CO₂ conditions of this study, the δ¹³C of bacterial PLFAs (i15:0, i16:0, 16:1ω7c, 16:1ω9c, 10Me16:0, and 10Me18:0) and the fungal PLFA 18:1ω9c was significantly lower in species-rich plant communities than in species-poor plant communities, indicating that microbial incorporation of new C increased with plant species richness. Despite an increase in plant production, total PLFA decreased under N deposition. Moreover, N deposition also decreased fungal relative abundance in species-rich plant communities. In our study, plant species richness directly increased microbial incorporation of new photosynthate, providing a mechanistic link between greater plant detritus production in species-rich plant communities and larger and more active soil microbial community.     

Distribution and importance of the lichen vegetation of the Scottish Highlands

Summary

The mountains of the Western Highlands of Scotland support a lichen vegetation that is apparently unique in Europe, and probably the world. This lichen vegetation consists mainly of microlichens and is important both intrinsically, with a number of rare and apparently endemic taxa and communities, and as a major contributor to the botanical biodiversity of the ecosystem. By contrast, the lichen vegetation of the Eastern Highlands, which consists mostly of terricolous macrolichens, is best considered a fragmented, species-poor outlier of that present in Scandinavia and is of national interest only.     

Plant communities and environmental factors in the Guayana Highlands: monitoring for conservation under future climate change

The Guayana Highlands (GH) constitute a highly diverse, but relatively poorly studied Neotropical biome, comprised of ～50 flat-topped mountain summits (called tepuis). Previous studies based on warming forecasts for the region suggested that an upward displacement of environmental conditions of 500–700 m could occur by 2100, potentially resulting in the extinction of c. 50% of its endemic flora due to total habitat loss. To assess the ecological responses of the species to climate change, and select the appropriate conservation measures, long-term monitoring of the GH plant communities will be necessary. In this study, the baseline state for future comparisons was established for the best explored tepui in terms of its flora, Roraima-tepui (2810 m), through a floristic characterization of its different vegetation types. We also identified the environmental gradients underlying the major plant communities, and assessed the effects of human activities on the chemistry of soils and water at three field camps. Our results yielded five main community types: three meadows, one shrubland, and one forest, with their corresponding diagnostic species. The herbaceous communities were mainly influenced by the presence of flat sandy soils, with varying flooding capacity. Shrublands and forests were characterized by irregular organic soils with very low pH. Finally, pH values below 3 were measured on an organic soil of a field camp, although further studies will be necessary to attribute this deviation to human activities.     

Plant community responses to Scotland's changing environment

Summary

The ecological dangers of global climatic change are frequently discussed in relation to their threat to biodiversity. Oceanic Scotland, however, differs in many respects from else- where, both in the nature of the current climatic change and the biodiversity of the flora on which it reacts. Scottish habitats, such as those in the more peripheral regions, are rarely rich in species and biodiversity may not be a relevant concept for assessing the impact of environmental change. In species-poor habitats ecosystem health may be a more useful measure of potential survival capacity than species wealth. Examination of the homeo-static properties of plant communities, and their ability to withstand environmental change, could provide a more practical method of predicting which sections of the Scottish flora are at risk from climatic change as well as indicating possible remedial action. Case histories from coastal, wetland, forest and mountain sites are discussed in terms of their present ecological robustness and future potential for surviving expected changes in the Scottish environment.     

N<Subscript>2</Subscript> fixation in three perennial <Emphasis Type="Italic">Trifolium</Emphasis> species in experimental grasslands of varied plant species richness and composition

This study is the first to investigate quantitative effects of plant community composition and diversity on N₂ fixation in legumes. N₂ fixation in three perennial Trifolium species grown in field plots with varied number of neighbouring species was evaluated with the ¹⁵N natural abundance method (two field sites, several growing seasons, no N addition) and the isotope dilution method (one site, one growing season, 5 g N m⁻²). The proportion of plant N derived from N₂ fixation, pNdfa, was generally high, but the N addition decreased pNdfa, especially in species-poor communities. Also following N addition, the presence of grasses in species-rich communities increased pNdfa in T. hybridum and T. repens L., while legume abundance had the opposite effect. In T. repens, competition for light from grasses appeared to limit growth and thereby the amount of N₂ fixed at the plant level, expressed as mg N₂ fixed per sown seed. We conclude that the occurrence of diversity effects seems to be largely context dependent, with soil N availability being a major determinant, and that species composition and functional traits are more important than species richness regarding how neighbouring plant species influence N₂ fixation in legumes.     

The lichen vegetation associated with areas of late snow-lie in the Scottish Highlands

Abstract:The lichen vegetation associated with areas of late snow-lie in the Scottish Highlands is described and three lichen-dominated communities recognized; from the tops of large boulders, from small pebbles, and from damp soil. The first of these is exclusive to this habitat throughout the Highlands, whereas the other two are restricted to areas of late snow-lie in the Eastern Highlands but are of more widespread occurrence further west. The community from damp soil has affinities with the Solorinion croceae Klement, which occupies a similar ecological niche in Central Europe, but the two other communities are apparently undescribed. The importance of the eu-oceanic climate of the Western Highlands in determining the distribution of these communities is emphasized. The new combination Micarea cinerea f. tenuispora (D. Hawksw. & Poelt) Fryday is made for the anamorph of M. cinerea (Schaer.) Hedl.     

Serpentine Soils Do Not Limit Mycorrhizal Fungal Diversity

Background

Physiologically stressful environments tend to host depauperate and specialized biological communities. Serpentine soils exemplify this phenomenon by imposing well-known constraints on plants; however, their effect on other organisms is still poorly understood.

Methodology/Principal Findings

We used a combination of field and molecular approaches to test the hypothesis that serpentine fungal communities are species-poor and specialized. We conducted surveys of ectomycorrhizal fungal diversity from adjacent serpentine and non-serpentine sites, described fungal communities using nrDNA Internal Transcribed Spacer (ITS) fragment and sequence analyses, and compared their phylogenetic community structure. Although we detected low fungal overlap across the two habitats, we found serpentine soils to support rich fungal communities that include representatives from all major fungal lineages. We failed to detect the phylogenetic signature of endemic clades that would result from specialization and adaptive radiation within this habitat.

Conclusions/Significance

Our results indicate that serpentine soils do not constitute an extreme environment for ectomycorrhizal fungi, and raise important questions about the role of symbioses in edaphic tolerance and the maintenance of biodiversity.     

Extensive Management Promotes Plant and Microbial Nitrogen Retention in Temperate Grassland

Leaching losses of nitrogen (N) from soil and atmospheric N deposition have led to widespread changes in plant community and microbial community composition, but our knowledge of the factors that determine ecosystem N retention is limited. A common feature of extensively managed, species-rich grasslands is that they have fungal-dominated microbial communities, which might reduce soil N losses and increase ecosystem N retention, which is pivotal for pollution mitigation and sustainable food production. However, the mechanisms that underpin improved N retention in extensively managed, species-rich grasslands are unclear. We combined a landscape-scale field study and glasshouse experiment to test how grassland management affects plant and soil N retention. Specifically, we hypothesised that extensively managed, species-rich grasslands of high conservation value would have lower N loss and greater N retention than intensively managed, species-poor grasslands, and that this would be due to a greater immobilisation of N by a more fungal-dominated microbial community. In the field study, we found that extensively managed, species-rich grasslands had lower N leaching losses. Soil inorganic N availability decreased with increasing abundance of fungi relative to bacteria, although the best predictor of soil N leaching was the C/N ratio of aboveground plant biomass. In the associated glasshouse experiment we found that retention of added ¹⁵N was greater in extensively than in intensively managed grasslands, which was attributed to a combination of greater root uptake and microbial immobilisation of ¹⁵N in the former, and that microbial immobilisation increased with increasing biomass and abundance of fungi. These findings show that grassland management affects mechanisms of N retention in soil through changes in root and microbial uptake of N. Moreover, they support the notion that microbial communities might be the key to improved N retention through tightening linkages between plants and microbes and reducing N availability.     

A potential habitat network for the Eurasian lynx Lynx lynx in Scotland

• 1 The severe and early destruction and fragmentation of woodland habitats due to human activities is thought to have been a leading factor in the extirpation from Britain of several large, forest‐dependent mammal species, such as the Eurasian lynx Lynx lynx. However, during the 20th century, Scotland in particular has experienced rapid, large‐scale reafforestation. In order to assess if this reafforestation has been sufficient to permit the potential restoration of extirpated forest mammal species with large spatial requirements, a Geographical Information System (GIS) analysis of potential habitat of one species, the Eurasian lynx, was performed for the Scottish mainland.
• 2 A rule‐based analysis, incorporating data and expert opinion from Switzerland, an environmentally similar area where lynx now occur, was used to identify patches of suitable lynx habitat in Scotland. A connectivity analysis was used to investigate whether and how these patches are connected to form larger interconnected networks of potential lynx habitat that would allow lynx to sufficiently interact with one another to form a single interbreeding population.
• 3 Scotland has over 20 000 km² of suitable lynx habitat split into two main networks of interconnected patches: the Highlands (c. 15 000 km²) and the Southern Uplands (c. 5000 km²). A further 800 km² of potential habitat, contiguous with the Southern Uplands lynx habitat network, lies across the border in England. Although connectivity between the Highlands and Southern Uplands networks is currently weak, the implementation of measures to mitigate the barrier effects of busy roads in central Scotland could facilitate the movement of lynx between the two areas.
• 4 Based on the availability of prey resources, Scotland could support around 400 adult and subadult lynx in the Highlands and around 50 in the Southern Uplands. A Scottish population of this size would be the fourth largest lynx population in Europe considering current population estimates.

     

Themeda australis grasslands on the Basalt Plains,Victoria: floristics and management effects

The floristic composition of remnants ofThemeda australis grasslands from basaltic areas of western Victoria was described using methods employed by the Zürich-Montpellier school of phytosociology. Most sites sampled were managed by either regular burning (rail sites) or grazing, or were not subject to any regular management practices (roadside sites). Rail sites contained relatively open, species-rich vegetation with a smaller proportion of introduced species than the other two types of site. Grazed paddock sites contained relatively open, species-poor vegetation, whilst roadside sites contained relatively dense, species-poor vegetation. Such site differences appear to be related to the effect of management practices upon the competitive ability of T. australis and to species tolerance of them.     

Biodiversity and persistence of ecological communities in variable environments

Recent analyses of climate data indicate that the intensity and frequency of different weather extremes have increased. Such increased environmental variability may lead to increased species extinction rates and hence have important consequences for the long-term persistence of ecological communities. Here we use model communities in order to investigate the relationship between species richness and community persistence in a fluctuating environment. We model two scenarios: (1) correlated species responses to environmental fluctuations and (2) uncorrelated (independent) species responses. We quantify the risk and extent of species extinctions using the so-called community viability analysis. It is shown that species-rich communities are more sensitive to environmental stochasticity than species-poor communities. Specifically, per species risk of extinction is higher in species-rich communities than in species-poor ones. Moreover, for a given species richness, communities with uncorrelated species responses to environmental variation run a considerable higher risk of losing a fixed proportion of species compared with communities with correlated species responses. We discuss the compatibility of these results with the ecological insurance hypothesis.     

Shading by Phragmites australis: a threat for species-rich fen meadows?

Abstract. Common reed (Phragmites australis Trin.) has spread in fen meadows on the Swiss Plateau during the last decades. An increased dominance of this tall grass may reduce the plant species richness and displace rare or endangered species because of the additional shade. To investigate whether this has actually happened and whether shading by Phragmites was likely to be responsible for the reduction, the plant species composition was surveyed in 241 plots (4 m²) with differing above-ground biomass of Phragmites (ABP). Species richness and the occurrence of characteristic fen species were negatively related to site productivity (total above-ground biomass), but correlations with ABP were generally weaker. The main change associated with increasing ABP within species-rich fens (alliances Molinion and Caricion davallianae) was an increase of species characteristic of the more species-poor alliance Filipendulion. Thus, Phragmites did apparently not play a disproportionate role in the reduction of species richness in the plant communities studied. Selective clipping experiments and light measurements also indicated that shading by Phragmites does not have a strong effect upon the performance of other species in the community, at least in the short term. The reason appeared to lie in the later seasonal growth of Phragmites compared with the other species. These results suggest that the direct impact of shading by Phragmites on the species richness of fen meadows is probably lower than has been assumed. However, possible long-term or indirect effects still need to be investigated.     

The halophilous vegetation of the Po Delta (northern Italy)

The halophilous vegetation in the Po Delta region (north Adriatic) has been studied with the Braun-Blanquet method. Vegetation types have been defined by numerical classification of vegetation data. Their ecology has been studied by indirect gradient analysis. The following three main groups of phytocoena have been recognized. (1) Perennial halophytic vegetation (class Puccinellio-Salicornietea) including 7 associations: Spartinetum maritimae, Puccinellietum palustris, Salicornietum radicantis, Salicornietum fruticosae, Agropyro-Inuletum crithmoidis, Halimionetum portulacoidis, are quoted according to an approximate gradient of decreasing soil moisture. The Juncetum maritimi is conditioned by soil erosion. (2) Therophytic vegetation settled on soils subject to natural or artificial disturbance (class Thero-Salicornietea), including 3 associations: Suaedo-Kochietum hirsutae, Salicornietum herbaceae s.1. and the Aster tripolium-Suaeda maritima community. (3) Halotolerant vegetation (class Artemisietea vulgaris), including only the Atripliceto-Elytrigietum pungentis settled on soils with a low salt content.Nomenclature of species follows Pignatti (1982).The research was supported by a grant of the Istituto per i Beni Artistici, Culturali e Naturali, Regione Emilia-Romagna (Italy) and by a grant of the Italian C.N.R. (Research Group for Naturalistic Biology).