Responses of Dune Plant Communities to Continental Uplift from a Major Earthquake: Sudden Releases from Coastal Squeeze

Vegetated dunes are recognized as important natural barriers that shelter inland ecosystems and coastlines suffering daily erosive impacts of the sea and extreme events, such as tsunamis. However, societal responses to erosion and shoreline retreat often result in man-made coastal defence structures that cover part of the intertidal and upper shore zones causing coastal squeeze and habitat loss, especially for upper shore biota, such as dune plants. Coseismic uplift of up to 2.0 m on the Peninsula de Arauco (South central Chile, ca. 37.5º S) caused by the 2010 Maule earthquake drastically modified the coastal landscape, including major increases in the width of uplifted beaches and the immediate conversion of mid to low sandy intertidal habitat to supralittoral sandy habitat above the reach of average tides and waves. To investigate the early stage responses in species richness, cover and across-shore distribution of the hitherto absent dune plants, we surveyed two formerly intertidal armoured sites and a nearby intertidal unarmoured site on a sandy beach located on the uplifted coast of Llico (Peninsula de Arauco) over two years. Almost 2 years after the 2010 earthquake, dune plants began to recruit, then rapidly grew and produced dune hummocks in the new upper beach habitats created by uplift at the three sites. Initial vegetation responses were very similar among sites. However, over the course of the study, the emerging vegetated dunes of the armoured sites suffered a slowdown in the development of the spatial distribution process, and remained impoverished in species richness and cover compared to the unarmoured site. Our results suggest that when released from the effects of coastal squeeze, vegetated dunes can recover without restoration actions. However, subsequent human activities and management of newly created beach and dune habitats can significantly alter the trajectory of vegetated dune development. Management that integrates the effects of natural and human induced disturbances, and promotes the development of dune vegetation as natural barriers can provide societal and conservation benefits in coastal ecosystems.     

The importance of habitat productivity, stability and heterogeneity for spider species richness in coastal grey dunes along the North Sea and its implications for conservation

In this contribution, we report on patterns of spider species richness in large complexes of coastal grey dunes of northern France, Belgium and the Netherlands. Since grey dunes are considered a priority in Annex I of the EU Habitat Directive, conservation needs attention. Spider diversity is determined by the amount of nutrients available in grey dune patches. The richness of specific xerotherm species, however, is dependent only on the distance of the patches to the sea. Earlier investigation revealed that the richness of these species depends on the patch size. Since coastal dune management aims to focus on the conservation of dune-specific and xerotherm species, patch enlargement and grey dune restoration should receive priority attention and not internal grey dune management. Total spider richness and diversity is hence related to the functioning of the grey dune ecosystem. Eolic dynamics act as typical disturbance factors and are negatively related to species richness, as a result of the low but significant covariation with nutrient availability. The intermediate disturbance hypothesis is not applicable for spider diversity in grey dunes, possibly due to the narrow range of investigated environmental variation.     

Are some communities of the coastal dune zonation more susceptible to alien plant invasion?

Aims Coastal areas, and in particular coastal dunes, are ecosystems strongly affected by the invasion of alien plants. However, few attempts have ever been made to quantify alien species incidence in different communities along the coastal zonation. This work aims to analyze the distribution of alien plants along the coastal zonation of sandy shores on the Tyrrhenian coast, addressing specifically differences among plant communities in abundance of alien plants.Methods The study was performed on recent dunes (Holocene) of the central western coast of Italy. We selected dune landscapes where invasion processes were particularly evident. Vegetation plots were randomly sampled and through cluster analysis, we identified six plant communities corresponding to the typical zonation described for the Tyrrhenian sandy coast of Central Italy. We evaluated and compared frequency and abundance of invasion in these different communities. Further, we investigated how propagule pressure (measured using as proxy human structures) contributed to the observed invasion patterns.Important findings We found a relatively low total number of aliens but also a differential distribution pattern and strong abundance of some of the aliens in specific sectors of the vegetation zonation. The perennial community of transition dunes appears most affected by invasion processes, related almost exclusively to the frequent and widespread Carpobrotus aff. acinaciformis. This alien species reaches high cover values, apparently lowering cover of native species of transition dune plant communities. Higher levels of invasion in the transition dune can be partially explained because of greater propagule pressure in this section of the dune profile. Our findings thus have important conservation and management implications since transition dune communities with Crucianella maritima are rare and protected (sensu Habitat 92/43/EEC Directive) along the entire Italian coast.     

Richness, diversity, and rate of primary succession over 20?year in tropical coastal dunes

The tropical coastal dunes in central Gulf of Mexico have been stabilizing over the last decades resulting in reduced substrate mobility, and promoting primary succession. We describe changes in species richness and diversity in dune vegetation during 20?years. Our questions: (a) Do species richness and diversity increase over time as predicted by models of ecological succession or do they show a hump-backed manner similar to the observations in temperate coastal dunes?, (b) What is the interaction between vegetation cover and diversity and species richness?, (c) Is there a relationship between species diversity and succession rate and does succession rate change over time?, and (d) How do plant functional types change during succession? In order to answer these questions, we set 140 4?×?4?m permanent plots in a mobile dune area and monitored vegetation cover and species richness from 1991 to 2011. In time, diversity increased in a logistic manner toward an asymptotic value once vegetation cover surpassed 60?%. Species richness increased in a humped-back shape, also reaching a maximum peak at 60?% vegetation cover. The succession rate of diversity was measured by the Euclidean distance, and showed a significant humped-back relation, meaning that it was slower in early and late successional stages. The study supports the intermediate disturbance theory. The conservation of coastal dunes vegetation should focus on all, species-poor and species-rich habitats that help to maintain the ecological integrity of these ecosystems. The understanding of community dynamics and diversity patterns becomes an essential component of coastal dune management and conservation.     

Multifaceted Analysis of Patch-Level Plant Diversity in Response to Landscape Spatial Pattern and History on Mediterranean Dunes

Landscape structure is known to critically affect biodiversity. However, although the multi-facetted character of biodiversity is widely recognized, few studies have linked landscape spatial pattern and history simultaneously to multiple facets (taxonomic, functional, and phylogenetic) and spatial components (α, β, and γ) of plant diversity. We set out to reveal whether landscape parameters have specific effects on the separate diversity facets and components of plant diversity at a patch scale on coastal dune landscapes of Central Italy. For each landscape patch, we computed a set of patch-based metrics relying on multi-temporal land-cover maps. Based on a database of plant community plots, on functional traits from field measurements and on a dated phylogenetic tree, we calculated taxonomic (TD), functional (FD), and phylogenetic diversity (PD) within each patch at α, β, and γ level. Diversity measures were then related to the landscape metrics via linear mixed-effect models. Landscape pattern and transformations affected TD only moderately in coastal dune ecosystems. We found much stronger and contrasted effects on FD and PD. FD increased in patches surrounded by human-dominated habitats; PD was higher in fragmented patches, particularly in the Mediterranean macchia. Moreover, landscape pattern affected differently the single communities, the turnover among communities and the pool of species within the patch (α, β, and γ components). Our results call for the combined inclusion of FD and PD and their partitions into ecological analyses, being TD too crude to capture the comprehensive and contrasted response of plant diversity to landscape spatial pattern.     

Effects of the expansion by Hippophaë rhamnoides on plant species richness in coastal dunes

Question: Is the expansion of Hippophaë rhamnoides in coastal dunes associated with a decline in plant species richness, and is this decline best described by a hump‐backed relationship between species number and shrub cover? Location: Grey and yellow dunes on the East Frisian islands Spiekeroog and Norderney. Methods: Total plant species richness as well as the number of herbaceous and cryptogam species were determined in 2001 using plots of 16 m² size. We compared shrubland plots with varying cover of Hippophaë with neighbouring dune grassland plots without shrubs as reference sites. Soil samples were collected to determine the values of some important edaphic variables (pH, organic matter, nitrogen). Results: The shrubland plots with Hippophaë had or tended to have lower soil pH and C/N ratios and higher contents of organic matter and nitrogen than the grassland plots. Total species richness was marginally significantly related to the cover of Hippophaë in a hump‐backed manner on both islands. The pattern was more pronounced for mosses and lichens than for herbaceous species. For all species groups on Spiekeroog and for the herbaceous species on Norderney, the hump‐backed relationship was much improved when using the difference in species number between shrubland and grassland plot as a dependent variable. Relationships could be improved by including the soil parameters as co‐variables. Species richness was highest at moderate levels of shrub expansion, while it was much reduced in very dense shrubland. The decrease in species number is caused by the decline in grassland species typical of the open dunes, including some rare taxa. Conclusions: The expansion of Hippophaë rhamnoides is a serious threat to the plant species richness of open coastal dunes, and needs to be counteracted by management measures.     

Green beach vegetation dynamics explained by embryo dune development

Sandy coastlines are dynamic environments with potential for biodiverse habitats, such as green beaches. Green beach vegetation can develop on nutrient-poor beaches landward from embryo dunes. It is characterised by low-dynamic coastal wetland habitat such as salt marshes and dune slacks. It has been hypothesised that the establishment of green beach vegetation is facilitated by the shelter provided by embryo dunes, however evidence is lacking.We explored the importance of geomorphology and soil conditions on the species richness and turnover of green beach vegetation over a time period of 10 years. We recorded 107 plots along 11 transects over a gradient from beach to dune on the island of Schiermonnikoog, the Netherlands. We characterised transect geomorphology at transect level and soil conditions and vegetation at plot level in 2006 and 2016.We found that the green beach vegetation was highly dynamic, total plant cover increased by 62% within 10 years. In 2006 beach width was an important factor in explaining species richness, with the highest number of species occurring on narrow beaches with a large volume of embryo dunes. In 2016, species richness was positively associated with the build-up of organic matter. Overall species richness declined relative to 2006 and was accompanied by an increase in elevation due to sand burial and the expansion of embryo dune volume.Our data suggests that geomorphology influenced the vegetation indirectly by affecting sand burial rate. Plant species richness declined less at sheltered conditions where sand burial was limited, allowing the build-up of organic matter. This indicates a time-dependent relationship between the development of embryo dunes and plant species richness: embryo dunes can be a source of shelter, thus increasing species richness, but can compete for space over time, lowering species richness again. Our results are relevant for engineering and management of biodiverse sandy shores.     

Plant community response following the removal of the invasive Lupinus arboreus in a coastal dune system

The removal of invasive species is common in restoration projects, yet the long‐term effects of pest management programs are seldom assessed. We present results of a long‐term program to remove the invasive species Lupinus arboreus (lupin) from sand dunes in New Zealand. We evaluate the response of plant communities to lupin removal, by comparing total plant cover, the cover of non‐native and native plant species, and species richness between sand dune sites where lupin removal has occurred, not occurred, and where lupin has never been present. Neither lupin presence nor removal had a significant impact on the foredune environment. Following removal, total and other non‐native plant cover remained higher, and the cover of several native sand dune species remained lower compared with uninvaded sites in the deflation and backdune environments. These changes can be attributed to persistent effects associated with the invasion of lupin, but have also developed in response to lupin removal. The results of this study have implications for restoration projects in sand dunes. Pest management alone is unlikely to be sufficient to restore plant communities. Given the difficulties in restoring plant communities once an invasive species has established, managers should prioritize actions to prevent the spread of invasive species into uninvaded areas of sand dunes. Finally, the response to lupin invasion and removal differed between dune habitats. This highlights the importance of tailoring a pest management program to restoration goals by, for example, prioritizing areas in which the impacts of the invading species are greatest.     

Hard times for Italian coastal dunes: insights from a diachronic analysis based on random plots

Multi-year temporal studies are invaluable tools for monitoring changes in biodiversity through time. However, their applications in coastal ecosystems are still scarce. We investigated temporal trends in coastal dunes analyzing a set of 858 randomly-sampled georeferenced relevés performed between 2002 and 2015 along Central Italy’s sandy coastlines. Specifically, we explored changes in species richness and cover of targeted sandy habitats, we investigated trends in the cover of selected psammophilous native species and we assessed patterns of invasion by means of regression techniques. We observed a significant decrease in species richness and cover of the dune grasslands habitat. The species-level analysis confirmed a negative trend for two characteristic species of dune grasslands, Cutandia maritima and Medicago littoralis, while revealing a similar decline for Crucianella maritima and for Ammophila arenaria subsp. australis, key species of mobile dunes. The most striking trends emerged analyzing patterns in the cover of an invasive alien species, Carpobrotus sp., which showed a concerning increase in shifting dunes. In conclusion, our analyses reveal concerning changes involving dune grasslands, and at the same time hint at “early warnings” of degradation processes traceable in shifting dunes.     

Impacts of a woody invader vary in different vegetation communities

The impact of an exotic species in natural systems may be dependent not only on invader attributes but also on characteristics of the invaded community. We examined impacts of the invader bitou bush, Chrysanthemoides monilifera ssp. rotundata , in fore and hind dune communities of coastal New South Wales, Australia. We compared invader impacts on vegetation structure, richness of both native and exotic growth forms and community variability in fore and hind dunes. We found that impacts of bitou invasion were context specific: in fore dune shrublands, functionally distinct graminoid, herb and climber rather than shrub growth forms had significantly reduced species richness following bitou invasion. However, in forested hind dunes, the functionally similar native shrub growth form had significantly reduced species richness following bitou invasion. Density of vegetation structure increased at the shrub level in both fore and hind dune invaded communities compared with non-invaded communities. Fore dune ground-level vegetation density declined at invaded sites compared with non-invaded sites, reflecting significant reductions in herb and graminoid species richness. Hind dune canopy-level vegetation density was reduced at invaded compared with non-invaded sites. Bitou bush invasion also affected fore dune community variability with significant increases in variability of species abundances observed in invaded compared with non-invaded sites. In contrast, variability among all hind dune sites was similar. The results suggest that effects of bitou bush invasion are mediated by the vegetation community. When bitou bush becomes abundant, community structure and functioning may be compromised.     

Native forest metacommunity structures in Uruguay shaped by novel land‐use types in their surroundings

We explore the effect of land‐use change from extensively used grasslands to intensified silvi‐ and agricultural monocultures on metacommunity structure of native forests in Uruguay. We integrated methods from metacommunity studies, remote sensing, and landscape ecology to explore how woody species distribution was influenced by land‐use change from local to regional scale. We recorded richness and composition of adult and juvenile woody species from 32 native forests, created land‐use maps from satellite image to calculate spatial metrics at landscape, class, and patch levels. We also analyzed the influence of land use pattern, climate, topography, and geographic distance between sites (d) on metacommunity, and created maps to visualize species richness and (dis)similarity between communities across the country. Woody species communities were distributed in a discrete pattern across Uruguay. Precipitation and temperature seasonality shaped species distribution pattern. Species richness and community dissimilarity increased from West to East. Latitude did not influence these patterns. Number of patches, landscape complexity, and interspersion and juxtaposition indexes determine woody species distribution at landscape level. Increasing areas covered by crops and timber plantation reduced species richness and increased community dissimilarity. The spatial metrics of native forest fragments at patch level did not influence metacommunity structure, species richness, and community dissimilarity. In conclusion, Uruguayan native forests display a high range of dissimilarity. Pressure of neighborhood land uses was the predominant factor for species assemblages. Conserving landscape structures that assure connectivity within and among native forest patches is crucial. On sites with rare target species, the creation of alliances between governmental institution and landowner complemented by incentives for biodiversity conservation provides opportunities to advance in species protection focused on those less tolerant to land‐use change.     

Human trampling effects on Mediterranean coastal dune plants

Coastal habitats are particularly vulnerable to recreational impacts because these environments are highly dynamic and continually change in response to biotic and abiotic factors. Sand dune communities are worldwide characterized by high levels of biodiversity, but are often affected by human-induced impacts as those caused by tourist trampling. To understand the effects of human frequentation, trampling, and other human-induced impacts, fencing experiments have been traditionally carried out on coastal dunes. Since in touristic areas dune systems are subjected to different intensities of human frequentations rather than to opening or fencing, in this study we explore the effects of accessibility on vascular plants cover. This study tests the hypothesis that human frequentation on beaches affects spatio-temporal variability of vascular plant abundance on dunes by comparing the plant assemblages of high and low accessible sites in North-East Sardinia (Italy). Our results show that accessibility plays a crucial role in conditioning the percentage of vegetation cover in Mediterranean dunes. In fact, not only we found a perennial vegetation cover that was significantly higher in the sites with low accessibility (and consequently low frequentation), but we also showed that at the sites with high accessibility there were significant differences in vegetation cover between times of sampling (cover was higher before than after summer): on the contrary, differences in perennial vegetation cover among times were not significant at the low frequentation sites. After summer, the difference among low and high frequentation sites in species composition and cover was >90%. Multivariate analysis identified those species that play a pivotal role in differentiating the low and the high frequentation sites. Among them, Crucianella maritima and Sporobolus virginicus can be considered as differential species. Overall, our data show vegetation and plant species responses to human-induced impacts, and are therefore important to support conservation actions in Mediterranean coastal areas interested by mass tourism.     

Understanding the influence of urbanization on invasibility: <Emphasis Type="Italic">Carpobrotus edulis</Emphasis> as an exemplar

Coastal dune areas are valuable ecosystems, generally impacted by habitat destruction and invasive alien species. In this study, we assessed how human disturbance and invasion by Carpobrotus edulis impact the soils and the establishment of native flora in the north-western coastal regions of Spain. We compared soil characteristics (pH, conductivity, water content, nutrients and enzymatic activities) and native plant as well as C. edulis fitness correlates (germination and early growth) between uninvaded and invaded soils from urban and natural coastal dune areas. We found that human disturbance impacts coastal soils by increasing organic matter and water content, modifying soil nutrients and cycles, and reducing the pH in urban soils. The presence of invasive C. edulis further increases these impacts. These changes in soil characteristics allow for the establishment of the native, but ruderal, Scolymus hispanicus and non-native C. edulis, both of which are not adapted to the typically limiting conditions of coastal dunes. In some instances, the coastal dune endemic, Malcolmia littorea, showed no fitness effects in response to urbanization or the presence of C. edulis. These results suggest that human disturbed coastal areas might be more easily invaded than natural areas. More broadly, our findings of differential responses of different native species to disturbance and invasion, illustrate the need for multi-taxon approaches when assessing the impacts of invasive species.     

Fire may mediate effects of landscape connectivity on plant community richness in prairie remnants

Following the predictions of island biogeography and metapopulation theory, efforts to understand and maintain plant communities have focused on spatial attributes such as patch size and connectivity. However, despite a large body of literature, the effects of these spatial attributes remain uncertain, and accumulating evidence suggests that they may interact with local patch characteristics. Here, we assess the role of spatial attributes (patch size and connectivity at two time periods) and of patch quality (indicated by number of years since last fire, as this is a fire‐dependent system) in determining plant species richness at 63 remnant prairie sites in Wisconsin, USA. Our results demonstrate significant main effects of patch size, with larger patches being richer than small patches, and of fire, with recent‐fire sites being richer than fire‐excluded sites. We also report a novel interaction between number of years since fire and patch connectivity. Historical (1950) connectivity was negatively related to species richness at recent‐fire sites, but positively related to species richness at fire‐excluded sites, while current (2000) connectivity and species richness were positively correlated at recent‐fire sites, but unrelated at fire‐excluded sites. Our findings indicate that measures of patch quality such as time since last fire can alter the association between spatial attributes such as patch size or connectivity and species richness.     

Regional and local variation of spider assemblages (Araneae) from coastal grey dunes along the North Sea

Aim This study aims to determine the underlying causes of local and regional patterns of variation in community structure of spiders in coastal grey dunes, and especially whether ecological time constrains the species composition in young and isolated grey dune habitats. Location The study was conducted in coastal dunes from northern France (Boulonnais, Nord‐Pas‐de‐Calais), Belgium (Flemish coastal dunes) and the Netherlands [Amsterdam Water Supply (AWD) dunes and Dunes from the Provincial Water Company North‐Holland]. Methods Spiders were collected with pitfall traps in twenty‐eight grey dune patches in the four areas under investigation. Species composition and environmental parameters (vegetation structure, distance to the sea and the patch‐edge, eolic dynamics and lime richness) were determined. Assemblage composition was related to the regional and local environmental factors with the Primer software package to determine the assemblage‐determining parameters. Differences in species presence were analysed as a function of their habitat preference and distribution range. Results Differences in grey dune spider assemblage structure can mainly be attributed to differences in local sand dynamics and the region. Species from dynamic dunes are mainly present in grey dunes from Belgium and France, while species from non‐dunal xerothermic habitats (chalk grasslands and heathland) occur in both the Boulonnais and the north Holland dune region. These species are absent from geologically young or other xerotherm habitat isolated Flemish coastal dunes. Main conclusion The data show that regional variation in spider assemblage composition results from local landscape characteristics (dynamics in the dune area), the latitude and the connectivity to non‐dunal xerothermic habitats. The strong and moderate geological isolation of dune areas from the Flemish coast and the AWD dunes, respectively, results in the absence of (at least some) species that are primarily bound to heathland and/or chalk grassland. This indicates the importance of ecological time for the assemblage structure. The limited dispersal capacity of the heathland and/or chalk grassland species is probably the main reason for their absence.     

Relationships between Spatial Metrics and Plant Diversity in Constructed Freshwater Wetlands

The diversity of plant species and their distribution in space are both thought to have important effects on the function of wetland ecosystems. However, knowledge of the relationships between plant species and spatial diversity remains incomplete. In this study, we investigated relationships between spatial pattern and plant species diversity over a five year period following the initial restoration of experimental wetland ecosystems. In 2003, six identical and hydrologically-isolated 0.18 ha wetland “cells” were constructed in former farmland in northeast Ohio. The systems were subjected to planting treatments that resulted in different levels of vascular plant species diversity among cells. Plant species diversity was assessed through annual inventories. Plant spatial pattern was assessed by digitizing low-altitude aerial photographs taken at the same time as the inventories. Diversity metrics derived from the inventories were significantly related to certain spatial metrics derived from the photographs, including cover type diversity and contagion. We found that wetlands with high cover type diversity harbor higher plant species diversity than wetlands with fewer types of patches. We also found significant relationships between plant species diversity and spatial patterning of patch types, but the direction of the effect differed depending on the diversity metric used. Links between diversity and spatial pattern observed in this study suggest that high-resolution aerial imagery may provide wetland scientists with a useful tool for assessing plant diversity.     

Mesophilic Actinomycetes in the Natural and Reconstructed Sand Dune Vegetation Zones of Fraser Island, Australia

The natural coastal habitat of Fraser Island located in the State of Queensland, Australia, has been disturbed in the past for mining of the mineral sand ilmenite. Currently, there is no information available on whether these past mining disturbances have affected the distribution, diversity, and survival of beneficial soil microorganisms in the sand dunes of the island. This in turn could deleteriously affect the success of the natural regeneration, plant growth, and establishment on the sand dunes. To support ongoing restoration efforts at sites like these mesophilic actinomycetes were isolated using conventional techniques, with particular emphasis on the taxa previously reported to produce plant-growth-promoting substances and providing support to mycorrhizal fungi, were studied at disturbed sites and compared with natural sites. In the natural sites, foredunes contained higher densities of micromonosporae replaced by increasing numbers of streptomycete species in the successional dune and finally leading to complex actinomycete communities in the mature hind dunes. Whereas in the disturbed zones affected by previous mining activities, which are currently being rehabilitated, no culturable actinomycete communities were detected. These findings suggest that the paucity of beneficial microflora in the rehabilitated sand dunes may be limiting the successful colonization by pioneer plant species. Failure to establish a cover of plant species would result in the mature hind dune plants being exposed to harsh salt and climatic conditions. This could exacerbate the incidence of wind erosion, resulting in the destabilization of well-defined and vegetated successional dunal zones.     

Invasion of coastal dunes by the alien shrub Rosa rugosa is associated with roads,tracks and houses

Mapping the distribution of invasive alien plant species is significant for testing ecological hypotheses and for guiding effective management. Little is known about the distribution of invasive plants at landscape scale, and the factors controlling their dispersal and establishment are still poorly understood. This is the case for Rosa rugosa, an invasive shrub with negative effects on biodiversity in dune ecosystems of NW Europe. The aim of the study was to identify the factors which determine the distribution of R. rugosa in coastal dunes. In a large semi-natural dune area of NW Denmark (2364 ha) all patches of the species (1321, 1.3–59.1 m²) were GPS mapped. Patch distribution was GIS analysed, based on aerial photographs and vegetation maps. The distance of R. rugosa from the most conspicuous landscape elements was compared with randomly placed reference points. The species had invaded 0.35% of the dune landscape, and it was present in all vegetation types and all parts of the study area. Rosa rugosa patches were slightly smaller in grey dunes than in white dunes and brown dunes, and some of the largest patches were found close to villages. The occurrence of the shrub was positively correlated with distance to the coastline, to roads, tracks and houses. We conclude that the distribution of R. rugosa is determined by both natural and anthropogenic factors. It is further discussed how these factors may control dispersal and establishment of the species, and how the results can be used for improved management of coastal dunes.     

Spatial heterogeneity and plant species richness at different spatial scales under rabbit grazing

Herbivores influence spatial heterogeneity in soil resources and vegetation in ecosystems. Despite increasing recognition that spatial heterogeneity can drive species richness at different spatial scales, few studies have quantified the effect of grazing on spatial heterogeneity and species richness simultaneously. Here we document both these variables in a rabbit-grazed grassland. We measured mean values and spatial patterns of grazing intensity, rabbit droppings, plant height, plant biomass, soil water content, ammonia and nitrate in sites grazed by rabbits and in matched, ungrazed exclosures in a grassland in southern England. Plant species richness was recorded at spatial scales ranging between 0.0001 and 150 m(2). Grazing reduced plant height and plant biomass but increased levels of ammonia and nitrate in the soil. Spatial statistics revealed that rabbit-grazed sites consisted of a mixture of heavily grazed patches with low vegetation and nutrient-rich soils (lawns) surrounded by patches of high vegetation with nutrient-poor soils (tussocks). The mean patch size (range) in the grazed controls was 2.1 +/- 0.3 m for vegetation height, 3.8 +/- 1.8 m for soil water content and 2.8 +/- 0.9 m for ammonia. This is in line with the patch sizes of grazing (2.4 +/- 0.5 m) and dropping deposition (3.7 +/- 0.6 m) by rabbits. In contrast, patchiness in the ungrazed exclosures had a larger patch size and was not present for all variables. Rabbit grazing increased plant species richness at all spatial scales. Species richness was negatively correlated with plant height, but positively correlated to the coefficient of variation of plant height at all plot sizes. Species richness in large plots (<25 m(2)) was also correlated to patch size. This study indicates that the abundance of strong competitors and the nutrient availability in the soil, as well as the heterogeneity and spatial pattern of these factors may influence species richness, but the importance of these factors can differ across spatial scales.