Hans Henrik K. Bruun

Abstract: Aim Habitat fragmentation is a major driver of biodiversity loss but it is insufficiently known how much its effects vary among species with different life-history traits; especially in plant communities, the understanding of the role of traits related to species persistence and dispersal in determining dynamics of species communities in fragmented landscapes is still limited. The primary aim of this study was to test how plant traits related to persistence and dispersal and their interactions modify plant species vulnerability to decreasing habitat area and increasing isolation. Location Five regions distributed over four countries in Central and Northern Europe. Methods Our dataset was composed of primary data from studies on the distribution of plant communities in 300 grassland fragments in five regions. The regional datasets were consolidated by standardizing nomenclature and species life-history traits and by recalculating standardized landscape measures from the original geographical data. We assessed the responses of plant species richness to habitat area, connectivity, plant life-history traits and their interactions using linear mixed models. Results We found that the negative effect of habitat loss on plant species richness was pervasive across different regions, whereas the effect of habitat isolation on species richness was not evident. This area effect was, however, not equal for all the species, and life-history traits related to both species persistence and dispersal modified plant sensitivity to habitat loss, indicating that both landscape and local processes determined large-scale dynamics of plant communities. High competitive ability for light, annual life cycle and animal dispersal emerged as traits enabling species to cope with habitat loss. Main conclusions In highly fragmented rural landscapes in NW Europe, mitigating the spatial isolation of remaining grasslands should be accompanied by restoration measures aimed at improving habitat quality for low competitors, abiotically dispersed and perennial, clonal species.

Abstract: The inclusion of environmental variation in studies of recruitment is a prerequisite for realistic predictions of the responses of vegetation to a changing environment. We investigated how seedling recruitment is affected by seed availability and microsite quality along a steep environmental gradient in dry tundra. A survey of natural seed rain and seedling density in vegetation was combined with observations of the establishment of 14 species after sowing into intact or disturbed vegetation. Although seed rain density was closely correlated with natural seedling establishment, the experimental seed addition showed that the microsite environment was even more important. For all species, seedling emergence peaked at the productive end of the gradient, irrespective of the adult niches realized. Disturbance promoted recruitment at all positions along the environmental gradient, not just at high productivity. Early seedling emergence constituted the main temporal bottleneck in recruitment for all species. Surprisingly, winter mortality was highest at what appeared to be the most benign end of the gradient. The results highlight that seedling recruitment patterns are largely determined by the earliest stages in seedling emergence, which again are closely linked to microsite quality. A fuller understanding of microsite effects on recruitment with implications for plant community assembly and vegetation change is provided.

Abstract: We report the first documented records of the gall midge Dasineura odoratae Stelter, based on adults reared from galls on the single host plant of the species, Viola odorata. We also report Aphanogmus abdominalis (Thomson) (Hymenoptera: Ceraphronidae) as a parasitoid of this gall midge. In addition, we report some recent Danish finds of the rare gall midge Mayetiola hellwigi (Rübsamen).

Abstract: The herbaceous understory forms the richest stratum in temperate broadleaved forests in terms of plant diversity. Understanding the process of understory succession is thus of critical importance for the development of management guidelines for biodiversity restoration in post-agricultural plantation forests. We studied effects of stand age, forest fragmentation, and soil and canopy conditions on species richness and abundance of four species groups in the understory of post-arable oak plantations in southern Sweden: herbaceous forest specialists, habitat generalists and open land species, and woody species. The group of forest specialists may approach the richness of continuously forested sites after 60-80 years in non-fragmented plantations, but many forest species were sensitive to habitat fragmentation. Open-land species richness decreased during succession, while the richness of woody species and of generalists remained stable, and were not affected by fragmentation. Abundance of generalists gradually decreased in non-fragmented plantations, probably due to competition from colonizing forest specialists. Soil pH in post-arable stands remained consistently higher than in continuously forested stands, which maintained differences in species composition. The development of a shrub layer seemed to imply a competitive advantage for forest specialists compared to generalist species. For successful recovery of a rich understory, we suggest that post-arable plantations should be established on loamy soils of intermediate to high pH proximate to older forest with source populations, and that a continuous overstory canopy cover of 70-80% is maintained by regular light thinnings and promotion of a shrub layer.

Abstract: The regeneration niche has been little investigated in studies of community assembly and plant distribution. We examined adaptive associations between seedling traits and habitat specialization. Two habitat contrasts were investigated across several evolutionary lineages of angiosperms: species specialized to forest vs. open habitats and to dry vs. wet habitats. We also tested whether effects of shade and drought vary independently or, alternatively, if shade may amplify effects on drought-stressed plants. Seedling response in terms of growth rate, height, slenderness, specific leaf area (SLA) and degree of elongation (longest internode; petiole or leaf-sheath depending on species' morphology) to light and watering treatments was assessed. We used a factorial design involving three light regimes and two watering frequencies. The open-shaded habitat contrast and the dry-wet habitat contrast were investigated using six and five pairs of congeneric species, respectively. The congeneric species pair design controlled for confounding effects of evolutionary history prior to divergence in habitat specialization. Seedling growth rate generally decreased with shade and reduced watering frequency. Plant height was generally largest at intermediate light. Specialization to shaded habitats was associated with a more conservative growth strategy, i.e. showing a more modest growth response to increasing light. Species from all habitats showed the highest relative elongation at intermediate light, except for the moist-habitat species, for which elongation increased with shade. Contrary to our expectations, species from dry habitats grew bigger than species from moist habitats in all treatments. SLA responded to the light treatment, but not to watering regime. The contrasting light and moisture conditions across habitats appear to not have selected for differences in SLA. We conclude that seedling phase strategies of resource allocation in temperate herbs contribute to their habitat specialization. Habitat-specific seedling strategies and trade-offs in response to resource availability and environmental conditions may be important to adaptive specialization.

Abstract: Reforestation of ex-arable land in temperate regions increases the area of potential habitat for forest plants. However, the herbaceous plant layer of these plantations contains fewer forest species than comparable plantations at continuously forested sites. One of the reasons for this might be differences in recruitment. The present study addresses post-dispersal seed predation, mainly of woody plants, as the factor limiting the recolonization of young oak plantations in southern Sweden. Our objectives were to investigate differences in dispersal and post-dispersal seed predation between first-generation forest plantations on ex-arable land and re-planted clear-cuts on continuously forested land. There was no recruitment following the experimental sowing of six commonwoody species (Alnus glutinosa, Betula pendula, Frangula alnus, Sambucus nigra, Sorbus aucuparia and Sorbus intermedia). Thus, the colonization of forest plantations by native shrubs and trees appears to be habitat-limited; the only exception being Rhamnus catharticus, for which poor dispersal ability may be more important. Post-dispersal seed predation of forest shrubs and trees was marked, especially in relatively small and isolated plantations on ex-arable land. There was a high seed predation of Crataegus monogyna, Sorbus aucuparia and Viburnum opulus on ex-arable land, while that of Frangula alnus and Sambucus racemosa was not associated with site placement and land-use history. Seed predation is probably a more important factor limiting restoration of near-natural forests than previously thought.

Abstract: Background: Climate warming in arctic and alpine regions is expected to result in the altitudinal migration of plant species, but current predictions neglect differences between species' regeneration niche and established niche. Aims: To examine potential recruitment of Vaccinium myrtillus, V. uliginosum and V. vitis-idaea on a mountain slope in northern Sweden in relation to current adult occurrence. Methods: We combined a seed-sowing experiment in seven community types with adult occurrence observations and species distribution mapping. Results: Emergence of V. myrtillus and V. vitis-idaea seedlings was significantly related to community type, while V. uliginosum was indifferent, but exhibited the highest average emergence. Adult occurrence was related to community, and ontogenetic niche shifts were observed for all three study species. Vaccinium myrtillus was shown to have the highest potential recruitment in habitats at altitudes above its current populations. Conclusions: The potential for migration exists, but incongruence between regenerative and established niches presents a challenge for colonisers, as well as for plant migration modelling.

Abstract: Questions: (1) Does soil acidification in calcareous sandy grasslands lead to loss of plant diversity? (2) What is the relationship between the soil content of lime and the plant availability of mineral nitrogen (N) and phosphorus (P) in sandy grasslands? Location: Sandy glaciofluvial deposits in south-eastern Sweden covered by xeric sand calcareous grasslands (EU habitat directive 6120). Methods: Soil and vegetation were investigated in most of the xeric sand calcareous grasslands in the Scania region (136 sample plots distributed over four or five major areas and about 25 different sites). Environmental variables were recorded at each plot, and soil samples were analysed for exchangeable P and N, as well as limestone content and pH. Data were analysed with regression analysis and canonical correspondence analysis. Results: Plant species richness was highest on weakly acid to slightly alkaline soil; a number of nationally red-listed species showed a similar pattern. Plant species diversity and number of red-listed species increased with slope. Where the topsoil had been acidified, limestone was rarely present above a depth of 30 cm. The presence of limestone restricts the availability of soil P, placing a major constraint on primary productivity in sandy soils. Conclusions: Acidification of sandy grasslands leads to reduced abundance of desirable species, although the overall effect is rather weak between pH 5 and pH 9. Slopes are important for high diversity in sandy grasslands. Calcareous soils cannot be restored through shallow ploughing, but deep perturbation could increase the limestone content of the topsoil and favour of target species.

Abstract: Large seeds are assumed to have higher probability of successful recruitment than small seeds. This is because larger seeds give rise to larger seedlings and larger seedlings better withstand environmental hazards like deep shade and drought. Biotic and abiotic limitations to seedling growth and survival, and conversely availability of safe sites for recruitment, vary along environmental gradients and between habitat types. Thus, the value to plant species of possessing large seeds may differ between plant communities. We analyzed the relationship between seed mass and per-seed recruitment success (seedlings established per number of seeds produced) along an environmental gradient from open grassland to closed-canopy forest using data collected by Uuno Perttula in southern Finland in 1934. We found that larger seeds have greater recruitment success relative to smaller seeds in all investigated communities. However, the recruitment success of large seeds relative to small seeds strongly increased from grassland and open forest to closed-canopy forest. Of the measured environmental variables, canopy closure most strongly explained this increase. This indicates a strong direct effect of deep shade on seedling survival in natural plant communities. Additional explanatory power was associated with soil moisture. Litter cover, moss cover, and soil pH did not contribute to explaining the variation in relative recruitment success of larger seeds. Thus, the advantage of large seeds in recruitment success is pronounced in deeply shaded forest but may be insignificant in open vegetation.

Abstract: The potential contribution of vertebrate-mediated seed rain to the maintenance of plant community richness in a High Arctic ecosystem was investigated. We analysed viable seed content in dung of the four numerically most important terrestrial vertebrates in Northeast Greenland, viz. muskox (Ovibos moschatus), barnacle goose (Branta leucopsis), arctic fox (Alopex lagopus) and arctic hare (Lepus arcticus). High numbers of plant propagules were found in the dung of muskox and barnacle goose. Seeds of many plant species were found in the faeces of one vertebrate species only. Propagule composition in barnacle goose droppings was relatively uniform over samples, with high abundance of the nutritious bulbils of Polygonum viviparum (Bistorta vivipara), suggesting that geese have narrow habitat preference and feed selectively. Propagule composition in muskox dung was diverse and heterogeneous among samples, suggesting generalist food selection and haphazard ingestion of plant propagules with foliage. Species composition of plant propagules in dung samples was different from species composition of the receiving plant communities (in terms of Sørensen and Czekanowski dissimilarity indices) and dung deposition, especially by muskox, often brought new species to the receiving community. The results suggest that endozoochorous propagule dispersal in the Arctic has a great potential in the generation and maintenance of local species richness, albeit being little specialized. It is further suggested that endozoochory is an important means of long-distance dispersal, and hence plant migration in response to climate change.

Abstract: Stands of pedunculate oak (Quercus robur) planted 50-80 years ago on two types of land (previously forested land and former arable fields) were compared regarding vegetation and soil. Former arable soils were characterized by a higher pH, higher nitrate concentration and higher soil density, but had lower organic matter content and lower ammonium concentration in the topsoil (0-5 cm). These differences, however, decreased with soil depth. Phosphorus concentration was consistently higher in former fields throughout the soil profile (0-45 cm). Nitrogen mineralization, determined by in situ incubation, showed a strong seasonal pattern with peak values in spring. Non-metric multidimensional scaling ordination revealed marked compositional differences in the vegetation between the two land-use categories, and also compositional turnover along gradients in soil pH and nitrogen availability. Differences in soil pH between land-use categories occurred in a range critical for the establishment of many typical forest herb layer species. Plant indicator species were identified for the two land-use categories. The results showed that acid-sensitive forest herbs may benefit from the higher pH soils in new woodlands, in contrast to ancient forest soils with little buffer capacity towards natural and anthropogenic acidification. In conclusion, former arable use has long-lasting effects on soil properties and vegetation composition in broadleaved forests. New woodlands on former fields can thus offer relatively persistent new habitats for acid-sensitive species that have suffered from reduction in habitat area during historic periods of deforestation and cultivation.

Abstract: The relative importance of seed, habitat and microhabitat limitation has rarely been investigated for invasive non-native species, although this is critical for their effective management and for predicting future range expansion. Rosa rugosa is an abundant non-native shrub in coastal habitats of NW Europe; it is common along the Baltic coast but more scarce in exposed dunes of the North Sea. To investigate whether invasion of exposed dunes is limited by seed, habitat and microhabitat limitation, seedling emergence and establishment were examined in a factorial sowing, transplant and disturbance experiment. Twenty plots were randomly placed in each of five dune habitats (white dune, Empetrum dune, grey dune, outer dune heath, inner dune heath), and studied over two years. Seedling emergence in control subplots was zero in all habitats, whereas 96% and 98% of the undisturbed and disturbed seeded subplots produced seedlings. Disturbance had a positive effect on emergence and subsequent survival in white dune, outer and inner dune heath. Seedling survival and growth, and growth of transplanted seedlings, were markedly lower in grey dune. These findings indicate that establishment of R. rugosa is seed-limited in coastal dune habitats, and that the species is able to establish in both active and fixed dunes once seed have arrived. Although differential seedling emergence and growth indicate that habitats differ in their degree of invasion susceptibility by R. rugosa, the positive influence of small-scale disturbance suggests microhabitat limitation in some dune habitats as well. Dune management should aim to reduce seed production and dispersal of R. rugosa in near-natural sites, and anthropogenic changes of habitat dynamics should be prevented.

Abstract: Allozyme markers were used to fingerprint clones of the grassland plant Hieracium pilosella and, by inference, to estimate the relative importance of sexual and vegetative reproduction in a population. Field studies in populations of clonal plant species have often reported negligible or absent recruitment from seed. In contrast, studies of genetic markers have found substantial clonal diversity in populations, suggesting recruitment of new genets into established populations. Our results showed that H. pilosella regenerates from seed both within and between dense clonal patches. Two sites differing in environmental conditions were sampled in order to investigate how the balance between seed-derived and stolon-derived recruitment changes with biotic and abiotic stress. In a relatively drought-prone site on a south-facing slope, the balance was shifted towards recruitment from seed, compared to a mesic site in which vegetative regeneration was more important.

Abstract: The vegetation databank established by our working group covers the classes Festuco-Brometea, Koelerio-Corynephoretea, and Trifolio-Geranietea sanguinei in the Nordic and Baltic region, i.e. NE Germany, Denmark, Norway, Sweden, Finland, N Poland, Lithuania, Latvia, Estonia, and NW Russia. We aim to use these data to develop a consistent supra-national phytosociological classification of these xerothermic vegetation types in the study area and to analyse their biodiversity patterns. Up to now, we located some 12,500 relevés meeting our criteria, and more than 3,500 of them have already been included in the databank. We give an overview of the properties of these relevés as regards coverage of syntaxa and countries, source types, plot sizes, and cryptogam treatment. We also present first analyses for the basiphilous semi-dry grasslands (Brachypodietalia pinnati) within the Festuco-Brometea. For this group of communities, many different and incompatible classification schemes have been proposed. We give an overview of the alliance and association names that have been in use for them in the study area, accompanied by a nomenclatural assessment. The relevés presently included in the databank have been tentatively assigned to those vegetation classes whose diagnostic taxa were prevailing. Accordingly, more than 2,000 relevés have been placed in the Festuco-Brometea. These show considerable floristic differences compared to stands of the southern temperate Brachypodietalia pinnati alliances Bromion erecti, Cirsio-Brachypodion pinnati, and Agrostion vinealis. The presence degrees of Avenula pratensis and Homalothecium lutescens, for instance, are significantly increased in the study area, and those of Festuca rupicola and Euphorbia cyparissias decreased. An analysis of the species-area relationship yielded a power function with z = 0.09 which is considerably lower than increments determined by nested-plot analyses of this commu-nity type, indicating the probable incompleteness of the species lists for many of the larger plots. Finally, we give an outlook on the future objectives of the working group.

Abstract: It is hard to defend the view that biotic communities represent a simple and predictable response to the abiotic environment. Biota and abiotic environment interact and the environment of an individual certainly includes its neighbors and visitors in the community. The complexity of community assembly calls forth a quest for general principles, yet current results and theories on assembly rules differ widely. Using grassland microcosm as a model system, we manipulated fertility, disturbance by defoliation, soil/microclimate and arrival order of species belonging to two groups differing in functional attributes. We analyzed the outcome of community assembly dynamics in terms of species richness, invasibility and species composition. The analyses revealed strong environmental control over species richness and invasibility. Species composition was mainly determined by the arrival order of species, indicating that historical contingency may change the outcome of community assembly. The probability for multiple equilibria appeared to increase with productivity and environmental stability. The importance of arrival order offers an explanation of the difficulties in predicting local occurrences of specific species in the field. In our experiment, variation in fertility and disturbance was controlling colonization with predictable effects on emergent community properties such as species richness. The key mechanism is suggested to be asymmetric competition and our results show that this mechanism is relatively insensitive to the species it works through. While our analyses indicate a positive and significant correlation between richness and invasibility, the significance disappears after accounting for the effect of the environment. The importance of arrival order (historical contingency) and environmental control supports the assumption of the unified neutral theory that different species within a trophic level can be considered functionally equivalent when it comes to community assembly. However, our results indicate that variation in asymmetric competition is the key factor determining the richness of the resulting communities, and this is far from neutral.

Abstract: The biota of herbivorous arthropods and pathogenic microorganisms associated with Rosa rugosa in its native and exotic ranges is reviewed. This is done as an initial step towards the identification of potential agents for biological control of this plant species invasive in Europe and North America. It is shown that more insect (but apparently not fungal) species attack R. rugosa in its native range than in its exotic range, and that most of the specialized insect and fungal enemies are confined to its native range. Among the close relatives of R. rugosa in its exotic ranges are many native species, as well as economically important crop plants. Few organisms appear to be narrowly specialized to R. rugosa, but true host specificity can only be indentified through experimental testing. Based on the literature, the most promising candidates for biocontrol seem to be the aphids Myzus japonensis and Amphorophora amurensis, the leaf hopper Empoasca ussurica, the tortricid moth Notocelia longispina, the cynipid gall-wasp Diplolepis fukudae, and the rust fungi Phragmidium rosae-rugosae and P. yezoense. A screening programme is suggested, investigating the impact of these organisms on R. rugosa performance, their host specificity and the risk of undesired indirect effects in the ecosystem where agents are released. In addition, demographic studies of the target plant should be integrated to provide guidance for the stage in the life cycle most sensitive to control and, thus, enable selection of the most efficient and safe biocontrol agents.

Abstract: In this study, we examined the relationship between seed size, seed rain and seed bank in a species-rich perennial grassland in Sweden. The seed rain was monitored by 100 seed traps placed in a 10 x 10 m area during one year. The seed bank was sampled by taking 100 soil samples, each in close vicinity to a seed trap. Abundance of reproductive ramets in the area was estimated since this is likely to affect the proportion of hit seed traps and seed bank samples. When abundance of reproductive ramets was accounted for, we found a negative relationship between seed size and proportion of hit seed bank samples, but we found no relationship between seed size and proportion of hit seed traps. We found strong positive relationships between the abundance of reproductive ramets and proportion of hit seed traps and seed bank samples. We also found strong positive relationships between abundance of reproductive ramets and abundance of seeds in the seed rain and the seed bank, but no relationship between seed size and abundance of seeds in the seed rain or the seed bank. We discuss these results in the context of theory suggesting that large-seeded and small-seeded species may coexist due to a trade-off between colonisation and competitive abilities, where smaller-seeded species are able to reach more sites than seeds of larger-seeded species, because they are more numerous and/or better dispersed.

Abstract: A near-natural coastal dune system in NW Jutland, Denmark was investigated. The area contains a gradient in natural soil mobility with the highest values in dynamic white dunes dominated by Ammophila arenaria and low mobility in fixed decalcified dune heath with Empetrum nigrum and Calluna vulgaris. A total of 267 plots was investigated and presence of mosses and rooted vascular plants recorded. Cluster analysis identified five communities: white dune, grey dune, outer dune heath, inner dune heath and humid dune heath. These communities were ordered along two main axes in a Detrended Correspondence Analysis (DCA). The relationship between DCA axes and several environmental variables, including soil characteristics and Ellenberg indicator values, were investigated by correlation. Two major complex gradients underlying compositional variation were identified; one short coenocline with an underlying steep gradient in habitat maturity, soil stability and nutrient-limited productivity, and one longer gradient in water-limited productivity and peat accumulation only applying to the older successional stages. Distance from the coast was an important correlate of several of the measured variables. Microclimatic indices, i.e. heat index and wind index, had limited value as descriptors of community patterns as they were not correlated with the DCA axes or with other environmental variables. However, within communities the microclimatic indices correlated with several explanatory variables.

Abstract:

Abstract: Long-distance dispersal of seeds is an important process in metapopulation dynamics and in plant migrations, but at the same time extremely difficult to observe or quantify directly. If seed dispersal ability were related to attributes of seeds or motherplants, long-distance seed dispersal would be predictable by indirect approximation using easy-to-measure traits. Seed size has been suggested to be such a key trait in seed dispersal ability. However, having smaller seeds also implies having more numerous seeds per plant individual (given equal reproductive effort), and consequently increases the probability of seeds being ingested accidentally. The question is whether small-seeded species are more abundant in herbivore dung because smaller seed size increases survival rate during gut passage or because they are produced (and ingested) in greater numbers than larger seeds. We investigated endozoochorous seed dispersal via cattle grazing a meadow, and related seed abundance in dung samples to seed attributes. We found that seeds were ingested and passed through the bovine intestinal tract in proportion to the numbers produced per unit area in the grazed vegetation. In contrast, no relationship could be found between endozoochorous dispersal potential (measured as abundance of seeds in dung samples corrected for seed output in the grazed vegetation) and seed attributes such as seed mass, seed shape (roundness), and thickness of the seed coat. This finding underlines the importance of seed number in plant dispersal ability. In addition, it shows that grazing mammals may constitute an important dispersal vector for many plant species conventionally classified as �unspecialised�.

Abstract: We propose a conceptual model to explain the variation in species richness in local communities and in build-up of regional species pools over time. The idea is that the opportunity for new species to enter a community (its invasibility) determines the present richness of that community as well as the long-term build-up of a species pool by speciation and migration. We propose that a community�s invasibility is determined by the turnover rate of reproductive genets in the community, which we call the �community-level birth rate�. The faster the turn-over, the more species will accumulate per unit time and per unit community size (number of genets), given equal per-birth rates of immigration and speciation. Spatially discrete communities inhabiting similar environments sum up to metacommunities, whose inhabitant species constitute the regional species pool. We propose that the size of a regional species pool is determined by the aggregate community-level birth-rate, the size of the metacommunity through time and age of the metacommunity. Thus, the novel contribution is our proposal of a direct effect of local environment on the build-up rate of species pools. The relative importance of immigrating species and neospecies originating locally will change with the temporal and spatial scale under consideration. We propose that the diversification rate specific to evolutionary lineages and the build-up rate of species pools are two sides of the same coin, and that they are both depending on mean generation time. The proposed model offers a reconciliation of two contrasting paradigms in current community ecology, viz. one focussing on present-time ecological processes and one focussing on historical events governing the size of species pools which in turn determines local richness.

Abstract: Question: What is the relationship between species richness of vascular plants, bryophytes and macrolichens, and two important gradients in the alpine environment, altitude and local topography? Location: Northernmost Fennoscandia, 250-1525 m a.s.l. corresponding to the range between timberline and mountaintop. Methods: The vegetation was sampled on six mountain areas. For each 25 vertical metres, the local topographic gradient from wind-blown ridge to snowbed was sampled in quadrats of 0.8 � 0.8 m. Patterns in species richness were explored using Poisson regression (Generalized Linear Models). Functional groups of species, i.e. evergreen and deciduous dwarf-shrubs, forbs, graminoids, mosses, hepatics and lichens were investigated separately. Results: Functional groups exhibited markedly different patterns with respect to both altitude and topography. Species richness of all vascular plants showed a unimodal relationship with altitude. The same was true for graminoids, forbs and lichens analysed separately, but forb richness peaked at much higher altitudes than total richness. The richness of dwarf-shrubs decreased monotonically with altitude, whereas richness of mosses and liverworts showed an increasing trend. Significant interactions between altitude and local topography were present for several groups. The unimodal pattern for total plant species richness was interpreted in terms of local productivity, physical disturbance, trophic interactions, and in terms of species pool effects. Conclusions: Patterns in local species richness result from the action of two opposing forces: declining species pool and decreasing intensity of competition with altitude.

Abstract:

Abstract: The arctic fox (Alopex lagopus) excavates its dens in gravely ridges and hillocks, and creates a local environment quite distinct from the surrounding tundra or heath landscape. In northern Sweden, the vegetation of 18 dens of the arctic fox was investigated, as well as reference areas off the dens but in geologically and topographically similar locations. The species composition showed considerable differences between den and reference areas, with grasses and forbs occurring more abundantly on the dens, and evergreen dwarf-shrubs occurring more in reference areas. The effect of the foxes� activities is thought to be either through mechanical soil disturbance, or through nutrient enrichment via scats, urine, and carcasses. This was expected to result in differences in plant traits with key functional roles in resource acquisition and regeneration, when comparing dens with reference areas. We hypothesised that the community mean of specific leaf area (SLA) would differ if nutrient enrichment was the more important effect, and that seed weight, inversely proportional to seed number per ramet and hence dispersal ability, would differ if soil disturbance was the more important effect. Specific leaf area showed a significant difference, indicating nutrient enrichment to be the most important effect of the arctic fox on the vegetation on its dens. Arctic foxes act as ecosystems engineers on a small scale, maintaining niches for relatively short-lived nutrient demanding species on their dens in spite of the dominance of long-lived ericaceous dwarf-shrubs in the landscape matrix. Thus, foxes contribute to the maintenance of species richness on the landscape level.

Abstract: The population sizes of five perennial vascular plant species confined to old unimproved dry grasslands were assessed, viz. Anthericum ramosum, Filipendula vulgaris, Silene nutans, Thymus pulegioides, and Thymus serpyllum. All populations within the region were included. Only for Filipendula vulgaris and Thymus serpyllum, significant relationships between habitat area and population size were found. Thus, apparently perennial vascular plants have a limited ability to respond to large habitat areas by forming large populations. This puts a question mark to the use of incidence function models for the study of plant metapopulations, because these models are based on an assumed positive relationship between habitat area and population size.

Abstract: This paper describes the use of supervised methods for the classification of vegetation. The difference between supervised classification and clustering is outlined, with reference to their current use in vegetation science. In the paper we describe the classification of Danish grasslands according to the Habitats Directive of the European Union, and demonstrate how supervised classification can be used to achieve a standardised and statistical interpretation within a local flora. We thereby offer a statistical solution to the legal problem of protection of certain selected habitat types. The Habitats Directive protects three types of Danish grassland habitats, whereas two remaining types fall outside protection. A classification model is developed, using available Danish grassland data, for the discrimination of these five types based on their species composition. This new Habitats Directive classification is compared to a previously published unsupervised classification of Danish grassland vegetation. An indicator species analysis is used to find significant indicator species for the three protected habitat types in Denmark, and these are compared to the characteristic species mentioned in the interpretation manual of the Habitats Directive. Eventually, we discuss the pros and cons of supervised and unsupervised classification and conclude that supervised methods deserve more attention in vegetation science.

Abstract: Arctic foxes are evaluated as seed dispersal vectors for Greenlandic plant species through a feeding experiment with subsequent scat analysis and germination test. Seeds of 22 common species with different morphology were tested. Passage time ranged between 4 and 48 hours. No significant differences was detected in passage time for seeds with different morphology. Cerastium alpinum and Stellaria longipes had higher germination after passage through the fox� digestive tract as compared to controls. Sibbaldia procumbens, Oxyria digyna and Silene acaulis were favoured by passage when shorter than 10 hours. Salix glauca ssp. callicarpaea, Veronica alpina, Gnaphalium norvegicum, Papaver radicatum, Ranunculus hyperboreus, Chamaenerion latifolium, Luzula parviflora and bulbils of Polygonum viviparum and Saxifraga cernua were inhibited by passage, whereas the remaining species had too low germination percentage to allow for evaluation. Species with adaptations to wind dispersal seemed particularly vulnerable to gut pasage. Arctic foxes are able to provide long-distances dispersal of seeds lacking morphological adaptations to dispersal, but for most species seeds need to be defecated within 12 hours to remain viable.

Abstract: Aim This paper seeks to investigate whether alpine floras on isolated mountains in boreal forest show nestedness, and, if that is the case, to determine whether selective extinction or colonization is the likely cause of the observed patterns. Location Isolated mountains in the boreal coniferous forests of northern Sweden (province of Norrbotten, c. 66°N; 18°E). The timberline in the region probably has been 300-400 m above the present some thousands of years before present, potentially covering these mountains. Methods A data matrix of twenty-seven alpine plant species on twenty-seven isolated mountains was subjected to nested subsets analysis. Extinction probability was assumed to increase with decreasing area, and colonization probability was assumed to decrease with increasing isolation. By sorting the data matrix by these factors and sequentially computing the degree of nestedness, we were able to determine whether the alpine floras were structured mainly by selective extinction or mainly by differential colonization. Results When ordered by decreasing area the data matrix was significantly more nested than random, but that was not the case when ordered by decreasing isolation. Ordering by maximum altitude also produced significant nestedness. Main conclusions Contrary to the conventional view that isolated mountains were completely covered with boreal forest some thousands of years ago, the nestedness patterns of alpine plants indicate that many of them survived the forest period on the isolated mountains, probably on cliffs and slopes too steep for the formation of closed forest.

Abstract: We investigated the species richness of vascular plants at the scale of 5´5 km in the Swedish province of Härjedalen, and the relationship between richness and environment. Environmental variables included geographical, altitudinal, topographical, bedrock, soil type, and land cover descriptors. The species richness was subdivided into groups of species with similar life-form, i.e. trees, dwarf shrubs, hydro- and helophytes, vascular cryptogams, forbs, graminoids, and mountain plants. The data were split at random into two equal subsets. Explanatory models were built by multiple linear regression on the first subset, and the models were validated on the second subset. The total species richness of vascular plants could be explained by sandy and clayey soil, the heterogeneity in bedrock types and the area of acid volcanic bedrock. The model could explain about 46% of the variation in species richness. The richness of trees and hydrophytes tended to decrease with altitude, whereas that was not the case for mountain plants. That group occurred frequently at low elevation, but then predominantly along streams and rivers. Clayey soils, sandy soils, and basic volcanic bedrock were the variables most frequently included in the regression models.

Abstract: Plant species associated with the traditional agricultural landscape in northern Europe and Scandinavia are subjected to a drastic habitat fragmentation. In this paper we discuss the species response to this fragmentation, against a background of vegetation and land-use history. Recent evidence suggests that grassland-forest mosaics have been prevalent even long before the onset of human agriculture. We suggest that the creation of infield meadows and outland grazing (during the Iron Age) increased the amount and spatial predictability of grasslands, resulting in the development of plant communities with high species densities. Thus, the distribution patterns of plant species in the present-day landscape is likely to reflect historical landuse. This holds also for areas where the traditional management has ceased to exist, due to an inertia in plant response to abandonment and fragmentation. The distribution patterns are not in equilibrium with the present habitat distribution. We suggest that fragmentation influences remaining semi-natural grasslands such that the species density is likely to decline as a result of local extinctions and invasion by habitat generalists. Remnant populations and, perhaps, small local populations of plants associated with traditional grasslands are likely to remain even in the modern landscape. Conservation should focus not only on "hot-spots" with high species richness, but also consider the species dynamics in a landscape context.

Abstract: The recent decline in species richness in (semi)-natural habitats in northern Europe has largely been attributable to habitat destruction, and to subsequent limitation in seed dispersal among fragments. However, some habitat types were probably split up already in the historical landscape, but the segregated parts were probably not isolated to the present degree. This paper seeks evidence for livestock as vectors for propagules at 3 spatial scales in the past cultural landscape. Three main scales at which livestock acted as seed dispersers are important: free movement in the landscape (1-10 km), driving animals to mast feeding or to manors (10-50 km), and the export of living animals (hundreds of km). The emerging picture is for most plant species a dramatically decreased chance of dispersal in the modern landscape. The consequence is probably decreasing species richness in (semi)-natural plant communities, such as pasture, meadow, and heathland.

Abstract: Island biogeographical theory predict species richness to increase with habitat area and to decrease with isolation from colonisation sources. This theory has been applied to habitat fragments, and the predictions tested and found valid in empirical studies on fragments of deciduous woodland in northern Europe. However, previous results on fragments of grassland have been ambiguous. In the present study the species richness of vascular plants was investigated in 63 patches of grassland and heathland scattered in an agricultural and forested landscape using multiple linear regression. The relationship between species richness and patch area, isolation and local habitat conditions including heterogeneity were examined. Area was an important determinant of species richness, both in the full data set and in a subset of small habitat patches. In contrast, spatial isolation and habitat heterogeneity were not important factors determining species richness. Differences in soil acidity were accounting for a large proportion of the variance in species richness. This result is probably due to differences in the size of the regional species pools of grasslands with different levels of soil pH.

Abstract: The richness of vascular plants in all patches of dry semi-natural grassland within a landscape was investigated. The patch level richness was scaled up to the level of parish to match data on land-use intensity from Iron Age through historical time. Three measures of diversity were obtained: the local species pool, an area-independent diversity measure (the slope of the species number vs log area regression line), and the �-diversity. A gradient through the study area in the density of grassland and a corresponding clinal variation in grassland plant species diversity were found. Explanatory models were built by partial least squares regression and conventional stepwise multiple regression. Data on contemporary environmental conditions in the grassland patches and in the parish as a whole were added first, and then data on continuously older times in sequence. In the stepwise regression analyses the variables were also added in the opposite sequence. The results show that contemporary conditions are able to explain the major part of the variation in all diversity measures. Variables concerning former land-use do, however, add significantly to the explanation of variation in local species pool and in the area-independent diversity, but not in _-diversity. It is concluded that patterns of land-use intensity from the Iron Age and onwards have contributed significantly to the shaping of local species pools, and thereby the richness of grassland communities.

Abstract: Eriksson & Jakobsson (1998) developed a heuristic model predicting species' regional abundance from their seed mass. The model took as a starting point the diversity of seed masses found in single communities (Westoby et al. 1996). This phenomenon does not, however, fit the theoretical predictions of a particular seed-mass being most fit in a given environment (Smith & Fretwell 1974). Rees & Westoby (1997) showed that a game theoretic approach would allow for variation in seed mass within communities. The Eriksson-Jakobsson model had two basic assumptions: i) given in a microsite a seedling emerging from a large seed wins over one from a small seed (a game rule supported empirically by Eriksson (1997) and Turnbull et al. (1999)), and ii) a trade-off between seed mass and seed number (Harper (1977), empirically supported by Shipley & Dion (1992), Turnbull et al. (1999) and Jakobsson & Eriksson (2000)). In other words, an inverse relationship between colonisation ability (large, but few seeds) and dispersability (many, but small seeds) was assumed. The model predicts that species with intermediate-sized seeds will gain larger regional abundance than either larger or smaller-seeded species. Eriksson & Jakobsson (1998) identified the species with intermediate-sized seeds by use of the absolute deviance in log seed mass from the community median log seed mass. Data from Danish grasslands were used in an empirical test of the model's validity, both by phylogenetically corrected and traditional cross-species analysis.

Abstract: Two parapatric ecotypes of Silene nutans, exhibiting distinct allozyme patterns, morphology and autecology were investigated for differences in exudation of low-molecular weight organic acids from germinating seeds, and for differences in seed phosphorus content. The calcicolous ecotype is restricted to calcareous soils, and the silicicolous one predominantly occurs on acid soils, and sometimes, although less frequently, on neutral to alkaline soils. No clear difference was found between ecotypes. However, within the silicicolous ecotype seed samples showed marked differences in exudation pattern and seed phosphorus content depending on origin along the soil acidity gradient. Seeds of low-pH origin exuded more dicarboxylic acids (malic+succinic acid, oxalic acid) and had a lower phosphorus content than seeds of high-pH origin. The exudation of dicarboxylic acids from seeds of low-pH origin is probably an adaptation to adverse conditions (aluminium toxicity) on acid soils. The pattern is similar to that found among different cultivars of wheat. It is contrasted to the pattern found on comparison of a suite of calcifugous and calcicolous species, where exudation of di- and tricarboxylic acids is associated with solubilisation of recalcitrantly bound phosphorus and iron in calcareous soils.

Abstract: Eighty-five patches of semi-natural grassland of varying size scattered in a agricultural landscape were investigated for their flora of vascular plants. Relationships between species richness and patch area, spatial isolation and local habitat conditions including heterogeneity were examined. Differences between single species and among groups of species defined by life-history traits were also investigated. Area was shown to be an important determinant of species richness irrespective of habitat heterogeneity. Isolation in space and habitat heterogeneity also play signifi- cant roles. These results are consistent with results from a multitude of studies on fragments of ancient deciduous woodland in northern Europe. They are, however, contradictory to results from previous studies in grasslands within the same region. Seed mass and dispersal syndrome were poor predictors of the degree to which the species were affected by isolation of grassland patches. Seed mass deviation from community median could explain a small percentage of the variation in regional abundance. Logistic regression on species occurrences showed that few species are associated with large patches, and less than half seem to avoid isolated patches.

Abstract: The potential community species richness was predicted for 85 patches of semi-natural grassland in an agricultural landscape in Denmark. The basis of the prediction was a very large data set on the vegetation, soil pH and topography in Danish grasslands and related communities. Species were inserted into potential species pools according to their preferences regarding soil acidity and water availability (expressed as potential solar irradiation), and to the ranges in these two factors observed in each grassland patch. The difference between the predicted and the observed patch-level species richness, community richness deficit, varied considerably among patches. Community richness deficit exhibited a negative relationship with patch area, and for small patches a positive relationship with patch isolation.

Abstract: A hierarchic classification of Danish semi-natural grassland vegetation on well-drained soils is presented. TWINSPAN was used for clustering of 614 samples of grassland vegetation with continuous coenoclines, yet total turnover in species composition in more dimensions. The optimal hierarchic level of clustering was determined by Indicator Species Analysis. The classification was interpreted in terms of variables relating to abiotic environment and vegetation structure and to major ecoclines previously identified by gradient analysis. The twelve final clusters were compared to syntaxa of formal phytosociology and to communities in the British Vegetation Classification. Criteria for achieving floristically homogeneous clusters without sacrificing the ecological interpretability and validity of the clusters in time and along geographical gradients are discussed.

Abstract: We present a gradient analysis of 620 vegetation samples covering most of the floristic and environmental variation in semi-natural grassland vegetation on well-drained soils in Denmark. Vegetation was sampled using frequency in subplots. Explanatory variables were surface inclination, aspect, pH, geographical co-ordinates together with indications of soil type. Detrended Correspondence Analysis revealed four floristic gradients that could be interpreted in ecological terms by measured variables supplemented with site calibrations based on weighted averaging of Ellenberg's indicator values. All four axes were interpreted using rank correlation statistics, and linear and non-linear multiple regression of sample scores on explanatory variables. The first gradient was from dry calcareous to humid acidic grasslands; the second reflected an underlying gradient in fertility; the third reflected regional differentiation and the fourth was associated with variation in intensity of competition as indicated by association with calibrated Grime-CSR values for the plots. We applied subset ordination to the data as a supplement to traditional permutation and correlation statistics to assess the consistency of ordination results. DCA axes 1 and 2 were consistent in space and time. This gradient analysis is discussed in a context of plant strategy theory and species diversity models. Ecocline patterns lend support to the view that grazing not only favours the ruderal strategy but also the stress-tolerant strategy. The low rank of competition as an explanatory variable for the floristical gradients supports the notion that competitive effects play a subordinate role for species composition compared to microclimate and soil conditions in infertile semi-natural grasslands.

Abstract: 50 plots on grassland on well-drained soil were analyzed for the species composition of vascular plants, macrofungi, bryophytes, lichens, hepatics and for 20 environmental variables. A dca-ordination showed an overall influence of land-use history on species composition. dca-axis 1 was strongly correlated with species diversity of vascular plants. High species diversity is found to result from the combined action of high pH, high CaCO3-content, high age of turf, intensive grazing and absence of fertilization. A DCCA-ordination lead to the proposal of 22 species as indicators of old, unameliorated grasslands in Denmark.

Abstract: Biotic communities in Northeast Greenland have an insular character as a consequence of the complex geomorphologic nature of the ice-free land and its interdigitation with glacial ice and the sea. Post Pleistocene movements of most plants and animals into the region have generally followed East and North Greenland coastal routes, and the majority of the plants have North American affinities. Climatic change, bringing about reduction in the extent of sea ice adjacent to the coast and changes in seasonality and associated precipitation and air movements, influences patterns of activity, growth, reproduction and dispersal of all life forms present. Climate associated changes in the biotic communities of the region are altering inter-species interactions, notably pollination, seed dispersal and plant-herbivore relations. Sexual reproduction and dispersal of propagules, primarily seeds, are essential processes underlying maintenance of genetic biodiversity in plant communities in Northeast Greenland. Wind and water transport of seeds are primary methods by which plants disperse and become established in the High Arctic, but birds and mammals are also involved. In Northeast Greenland, dispersal of viable seeds may occur by passage through the guts of geese and muskoxen. Research at Zackenberg on the role of insects in pollination of flowering plants has shown that Diptera species, primarily flies, dominate among the insect species visiting flowers each summer. Diptera, Lepidoptera (butterflies and moths), Hymenoptera (bumble bees and small wasps) and one Hemiptera (true bugs) species have constituted the primary pollinators at Zackenberg. Arctic willow Salix arctica, white arctic bell heather Cassiope tetragona and mountain avens Dryas octopetala, are the primary species represented in the pollen present on pollinating insects at Zackenberg. The effects of climate warming that may enhance environmental conditions for plant growth in Northeast Greenland and accelerate invasion of new species will also be tied to the relationship of specific plant species to their insect pollinators. Those plants that are self pollinated may have an initial advantage in an environment where insects and their plant relationships are being altered by the changing climate. An increase in growth and dispersal of shrubs in the Arctic is occurring as a consequence of climate warming. Increases in shrubs with more upright growth form, especially willows, will generate microhabitats not previously present in the High Arctic. The new habitats will make possible the invasion of new insect, mammal and bird herbivores, as well as their parasites and predators.

Abstract: Northern Europe is in the forest zone, but wild megaherbivores have maintained grass-dominated vegetation here for the last 1.8 million years. Continuity of the grassland biome through glacialinterglacial cycles and connection to steppe vegetation has resulted in the evolution, immigration, and survival of a large number of grassland species. During the last millennia the effect of wild ungulates has been replaced by domestic grazers and hay making, and the persistence of grassland biodiversity depends on livestock farming. Local diversity is the outcome of colonisations and extinctions. Colonisations can be enhanced by maintaining networks of grasslands where species can migrate between sites, and by proper management that promotes establishment of new individuals. Extinction risk may be lowered in large grasslands, which may support large populations, and by proper management that promotes coexistence of species. Extinctions are accelerated by changes in environmental conditions favouring a few competitively superior plant species, especially increase in soil fertility. During the last century, natural grasslands in Europe have faced a dramatic loss of area and increased isolation of the remaining fragments, cessation of proper management, and increased load of nutrients. To achieve successful grassland biodiversity conservation there needs to be close cooperation between conservation managers and livestock farmers. For that, grassland management should take into account evolutionary and ecological rules behind the grassland biodiversity.Northern Europe is in the forest zone, but wild megaherbivores have maintained grass-dominated vegetation here for the last 1.8 million years. Continuity of the grassland biome through glacialinterglacial cycles and connection to steppe vegetation has resulted in the evolution, immigration, and survival of a large number of grassland species. During the last millennia the effect of wild ungulates has been replaced by domestic grazers and hay making, and the persistence of grassland biodiversity depends on livestock farming. Local diversity is the outcome of colonisations and extinctions. Colonisations can be enhanced by maintaining networks of grasslands where species can migrate between sites, and by proper management that promotes establishment of new individuals. Extinction risk may be lowered in large grasslands, which may support large populations, and by proper management that promotes coexistence of species. Extinctions are accelerated by changes in environmental conditions favouring a few competitively superior plant species, especially increase in soil fertility. During the last century, natural grasslands in Europe have faced a dramatic loss of area and increased isolation of the remaining fragments, cessation of proper management, and increased load of nutrients. To achieve successful grassland biodiversity conservation there needs to be close cooperation between conservation managers and livestock farmers. For that, grassland management should take into account evolutionary and ecological rules behind the grassland biodiversity.