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We investigated relationships between richness patterns of rare and common grassland species and environmental factors, focussing on comparing the degree to which the richness patterns of rare and common species are determined by simple environmental variables. Using data collected in the Machair grassland of the Outer Hebrides of Scotland, we fitted spatial regression models using a suite of grazing, soil physicochemical and microtopographic covariates, to nested sub‐assemblages of vascular and non‐vascular species ranked according to rarity. As expected, we found that common species drive richness patterns, but rare vascular species had significantly stronger affinity for high richness areas. After correcting for the prevalence of individual species distributions, we found differences between common and rare species in 1) the amount of variation explained: richness patterns of common species were better summarised by simple environmental variables, 2) the associations of environmental variables with richness showed systematic trends between common and rare species with coefficient sign reversal for several factors, and 3) richness associations with rare environments: richness patterns of rare vascular species significantly matched rare environments but those of non‐vascular species did not. Richness patterns of rare species, at least in this system, may be intrinsically less predictable than those of common species.

The article highlights a comparatively neglected area of biogeographical research - seed banks and the distribution of seeds in the soil. The article reviews some of the relevant literature on seed banks and the methods for their study. Attention is focused on aspects of seed banks of particular relevance to biogeographers, with detailed examples drawn from seed bank studies in both temperate and tropical environments. In the review of the seed bank literature, the topics covered include the seed banks of successional communities and the size of seed banks in different vegetation types. The species composition of seed banks in different plant communities is discussed, particularly the degree of correlation between the species composition of seed banks and associated ground flora. The relationships between seed persistence, depth of burial in the soil and soil properties, such as moisture and pH, are explored. Seed bank heterogeneity is examined and a number of studies which have attempted to describe and measure the spatial variability of seed banks are summarized. Ways of classifying seed banks in terms of seed bank strategies are explained. The role of seed banks in conservation is discussed, for example in restoration projects, where preferred species have been lost from the vegetation but survive in the seed bank. The relevance of seed banks for the conservation of rare species and in landscape management is considered. Lastly, the contribution of seed banks to the recovery of vegetation following disturbance in various plant communities is discussed. In the review of seed bank sampling techniques, the subjects considered include methods of sample collection, the sampling intensity required for reliable estimates of seed density, a consideration of the relative merits of random and systematic sample distribution, as well as the importance of the timing of sampling. Various methods for the estimation of seed numbers in samples are appraised; these either involve extraction of seeds from the soil, followed by seed identification or enumeration by germination and seedling identification. Problems of analysing seed bank data are considered and several useful techniques for data analysis are suggested. Finally, the article draws attention to areas of future seed bank research for biogeographers and plant ecologists.

The increasing relevance and importance of the subject of landscape ecology to bio geography are introduced. Research into landscape and plant community boundaries, never theless, remains comparatively neglected. In particular, the nature of those boundaries in terms of the patterns of floristic change and related ecosystem properties constitutes a potentially signifi cant new area of research for biogeographers. The term 'ecotone' has traditionally been used to describe boundaries between plant communities and ecosystems at a range of scales. Various definitions are presented and the often confusing terminology surrounding the word 'ecotone' is reviewed. Boundary types range from sharp, clearly defined boundaries (ecotones) between more highly modified plant communities and anthropogenically created land-use types at one extreme, to more gradual and diffuse boundaries (ecoclines) between natural and semi-natural plant communities at the other. It is proposed that the term 'transitional area' is used to describe all types of vegetation boundary when working at the local/community scale. There is little literature of direct significance to the subject of transitional areas. The concept can only be meaningfully discussed in the context of recent developments in the conceptualization of the plant community and these are summarized. The importance of mosaics within plant communities is described and the need to understand and recognize mosaics when studying transitional areas between plant communities is emphasized. The range of research methods available to describe and analyse variations in patterns of floristics and associated environmental variables across transitional areas is then critically reviewed. The potential relevance of remote sensing and geographical information systems, net work analysis and fractals is demonstrated. Ideas on possible adaptations of sampling strategies for the description of floristics and environmental/biotic factors to cater for boundary/transitional area situations are presented and the concept of a rectangular sampling area as an alternative to the more normal linear transect is introduced. The traditional approach to the description of vegetation change across boundaries using transects and similarity coefficients has now been superseded by new developments, notably moving-window analysis, the Mantel test, pattern analysis, semi-variograms, spectral analysis and analysis for spatial autocorrelation, and the scope of these methods is summarized. Finally, the dynamics of plant communities and their boundaries are considered and the implications of research into transitional areas for vegetation management and biological conserv ation are assessed. The importance of this whole subject as a possible new focus for biogeography and spatial ecology is then reiterated.