Coastal Dune Communities Research Articles

Plant spectral diversity from high‐resolution multispectral imagery detects functional diversity patterns in coastal dune communities

AbstractQuestionRemote sensing is a fundamental tool to monitor biodiversity and spectral diversity may represent a proxy for different biodiversity facets such as taxonomic (TD) and functional diversity (FD). We used fine‐resolution multispectral imagery to explore spectral diversity (SD) patterns across spatial scales (i.e., plot, transect, area), and assess SD relationships with TD and FD along an environmental gradient.LocationCoastal sand dune, Viareggio, Italy (“Migliarino–San Rossore–Massaciuccoli” Regional Park, 43°83′ N, 10°25′ E).MethodsWe measured TD as species richness, while SD and FD were computed using probability density functions based on pixel and species position in multivariate spaces. We compared SD and FD patterns in space occupation, and we tested whether these patterns are coordinated along the sea–inland gradient. We also assessed univariate relationships between SD and biodiversity facets, and we tested how these facets were partitioned across scales.ResultsWe found a strong correspondence between functional and spectral patterns in space occupation and along the environmental gradient, with a lack of significance when considering TD. However, TD and SD showed higher variation at broader scale while most FD variation occurred at plot level.ConclusionBy measuring FD and SD with a common methodological framework, we demonstrate that SD approximates functional patterns in plant communities. Moreover, we show that SD retrieved using high‐resolution images can capture different aspects of FD, and that the occupation of the spectral space is analogous to the occupation of the functional space.

Effects of invasive Rosa rugosa on Baltic coastal dune communities depend on dune age

Rosa rugosa Thunb. (Japanese Rose) is one of the most invasive species in Europe. It spreads spontaneously in coastal areas of western, central and northern Europe, posing a threat to dune habitats, including those indicated in the EU Habitats Directive as particularly valuable. R. rugosa has already been reported to displace native plants and alter soil properties. However, little is known about how these effects are mediated by the habitat context or the invader condition (health, ontogenetic stage). This study addressed that gap by examining vegetation and soil in 22 R. rugosa-invaded sites, half of which were in yellow dunes and the other half in grey dunes, i.e. two habitats representing the earlier and later stages of dune succession. The study was conducted on the Hel Peninsula (Poland’s Baltic coast). R. rugosa had a significant impact on dune vegetation, but the impact was strongly dependent on the habitat type. In the yellow dune sites, R. rugosa outcompeted most resident plant species, which translated into a strong decline in their total cover and richness. The invasion was almost not accompanied by changes in soil properties, suggesting that it affected the resident vegetation directly (through space takeover and shading). In the grey dunes, R. rugosa caused a shift in species composition, from that characteristic of open communities to that typical of forests. In this habitat, a significant increase in the soil organic layer thickness under R. rugosa was also observed, which means that both direct and indirect effects of the invasion on the vegetation should be assumed. Finally, a negative relationship was found between the total chlorophyll content in R. rugosa leaves and the parameters of resident plant communities, showing that the invasion effects can vary not only across habitats, but also with the condition of the invader. The results may have practical implications for managing R. rugosa invasions in coastal sand dune systems. Since R. rugosa accelerates grey dune succession, protecting this habitat may be more urgent and, at the same time, more complicated than protecting dunes at the earlier stages of development.

Alien plant colonisation and community homogenisation: cause or consequence? A test in coastal dunes

Evidence of the effects of alien plant colonisation on plant communities is often hindered by the fact that similar patterns in community composition can arise through a variety of processes. The objective of this study is to determine whether changes in species composition in coastal dune communities depend on the colonisation of a neophyte plant, Oenothera stucchii, or on concurrent processes that favour its colonisation. We hypothesised two scenarios: 1) a direct impact of O. stucchii on colonised communities, leading to displacement of native species; or 2) no direct impact of O. stucchii, i.e. the species colonises plant communities by exploiting disturbances that lead to the rearrangement of plant communities. We used the species-habitat network approach to identify potential drivers of changes in species composition, assuming that changes in the structure of the species-habitat network depend on the nature of the driving process. We demonstrated that changes in species composition in plant communities were due to species rearrangement, with colonised communities characterised by more homogeneous composition of species. We suggest that changes in plant communities may not depend on colonisation by O. stucchii per se, but on concomitant processes that affect coastal dune communities while promoting colonisation by O. stucchii.

Growth-survival trade-offs and the restoration of non-forested open ecosystems

The growth-survival trade-off has been extensively documented for phanerophyte species, whereas there is little evidence for non-phanerophyte species. However, information on the growth-survival trade-offs in non-phanerophyte species could be of great use in non-forested open ecosystem restoration by providing insights for plant production and transplantation, thus impacting the planning of cost-effective restoration actions. In this study, we explored the relationship between growth and survival of individual plants of non-phanerophyte species used in a coastal dune restoration project, and we investigated whether plant functional traits explained patterns of trade-off between growth and survival. We monitored 355 individual plants of 13 perennial non-phanerophyte species belonging to foredune and transition dune communities every 30 days after planting and calculated relative growth and survival rates. In addition, we regressed the relationship between growth and survival on values of leaf and floral traits. We found that, besides being a widely recognised axis of life history variation in phanerophyte species, the growth-survival trade-off can also be observed in perennial non-phanerophyte species. Species of different coastal dune communities (i.e., foredune vs. transition dune communities) differed with respect to the growth-survival trade-off, with plant species of foredune communities exhibiting higher growth but lower survival rates than plant species of transition dune communities. Leaf dry matter content and mean number of floral displays explained species position on the growth-survival trade-off axis; species with relatively high growth and low survival rates exhibited an acquisitive strategy, with low values of leaf dry matter content, but also a low sexual reproductive effort, as revealed by low number of floral displays. In contrast, plant species with relatively low growth and high survival rates exhibited a conservative strategy but also high sexual reproductive effort, suggesting that trade-offs occur in resource allocation among vegetative and reproductive plant structures. The trade-off we found between growth and survival in perennial non-phanerophyte species provides useful insights for planning cost-effective ecosystem restoration actions of non-forested open ecosystems, especially when the actions are nature-based and involve planting individual plants. The results of this study suggest that individual plant production for coastal dune restoration should disproportionately target plant species of foredune communities because they have low survival rates associated with low sexual reproductive effort. Planning plant production based on ecological knowledge of plant species’ growth and survival after planting in the field could help achieve restoration goals while meeting project cost-effectiveness requirements.

Differentiating Footprints of Sympatric Rodents in Coastal Dune Communities: Implications for Imperiled Beach Mice

AbstractIdentifying techniques for conducting frequent, effective, and inexpensive monitoring of small mammals can be challenging. Traditional approaches such as livetrapping can be laborious, expensive, detrimental to animal health, and ineffective. Passive approaches such as tracking (e.g., from tracks on the ground or footprints collected at a tracking station) have been shown to lessen those burdens, but a problem with tracking, particularly for rodents, is the uncertainty in identifying species from footprints. To address the need for a more accurate method of identifying small mammal tracks, we measured footprints from live-captured rodents and developed a classification tree for distinguishing between subspecies and species using footprint widths treated as having known or unknown identification. We captured rodents within or near the coastal dunes of Florida and Alabama with a focus on areas occupied by threatened and endangered beach mice Peromyscus polionotus subspp., whose populations warrant regular monitoring but whose tracks are not easily distinguished from those of some sympatric species. We measured 6,996 front and hind footprints from 540 individuals across eight species. The overall accuracy of our classification tree was 82.6% and we achieved this using only the front footprint width. Footprint width cutoffs for species identification were < 5.5 mm for house mice Mus musculus, 5.5–6.7 mm for beach mice, and 6.7–8.3 mm for cotton mice Peromyscus gossypinus. We were most successful in confirming the identity of beach mice: we correctly classified approximately 94% of beach mice, while we misclassified fewer than 6% as house mice and fewer than 1% as cotton mice. When we input a beach mouse individual into the classification tree as of an unknown species, we correctly identified 78.1% of individuals as beach mice from their tracks, and most incorrect identifications were of house mouse tracks. Our study demonstrates that researchers can identify sympatric rodent species in coastal dune communities from tracks using quantitative classification based on footprint width. Accurate identification of beach mice or other imperiled species from tracks has important management implications. Not only can wildlife managers determine the presence of a species accurately, but they can monitor populations with considerably less effort than livetrapping requires. Although our study was specific to coastal dune communities, our methods could be adapted for the creation of a classification tree for identifying tracks from suites of species in other areas.

Back into the past: Resurveying random plots to track community changes in Italian coastal dunes

Resurveying studies are commonly appreciated as a means to monitoring temporal changes in plant diversity. However, most of them still rely on phytosociological plots, which, although representing an invaluable source of data, can lead to biased estimates of vegetation changes. At the community-level, temporal changes can be quantified by means of beta-diversity measures. However, compositional variation can be the result of two different, often contrasting, processes: turnover and nestedness. In this context we test the effectiveness of resurveying approaches based on quasi-permanent plots in revealing temporal changes in herbaceous communities of Mediterranean coastal dune systems. Indeed, due to their being highly dynamic, coastal dunes can be considered ideal habitats for implementing such tools. In particular, we quantified temporal changes in species composition occurred over 10–15 years by calculating Sørensen index of dissimilarity and, in order to determine whether the change was really driven by species turnover, we partitioned Sørensen index into its two components of turnover and nestedness. At the same time, since diagnostic species are considered to be particularly sensitive to habitat modifications and helpful in assessing changes in the ecological structure of a community, we analyzed temporal changes in the occurrence and cover of diagnostic species of the investigated habitats. Results show that coastal dune communities of our study area underwent consistent changes during the analyzed time-span. Almost 25% of the historical plots disappeared. Major transformations, mainly driven by species turnover, involved upper beach communities, embryonic and mobile dunes, as revealed by the parallel analysis of beta diversity and diagnostic species. This work shows how resurveying approaches can efficiently reveal useful insights on vegetation dynamics, therefore providing a solid basis for the implementation of effective conservation strategies, especially in endangered habitats.

The effects of erosion and accretion on plant communities in coastal dunes in north of Turkey

Coastal erosion resulted in dramatic changes in the structure of coastal dune communities for example many characteristic species may be removed from dune zones. The effects of coastal erosion on coastal dune communities in north of Turkey were investigated along seashore–inland gradient. It has been found that the severity of erosion caused to increase the differences among coastal dune communities. Our results also implied that embryonic shifting dunes represented by Achilleo maritimo–Elymetum farcti (EU Habitat 2110) and shifting dunes along the shoreline with Ammophila arenaria (white dunes) represented by Medicagini marinae–Ammophiletum arundinacea (EU Habitat 2120) were more prone to coastal dynamics. It has been found that the severity of erosion caused to increase the differences among coastal dune communities.

Constraints to native plant species establishment in coastal dune communities invaded by Carpobrotus edulis: Implications for restoration

Carpobrotus edulis, an alien chamaephyte species from South Africa, severely invades and represents one of the greatest threats to coastal plant biodiversity in regions with Mediterranean climate worldwide. Although actions have been promoted to eliminate it, these efforts have failed to restore dunes to the natural, preinvasion stage.We tested, by means of field and laboratory experiments, how C. edulis alters soil chemistry by causing residual effects on soil, and examined whether these effects decrease germination, survival and growth of a common native chamaephyte dune species Malcolmia littorea. We also recorded species diversity to find out which species can establish after the removal of the invasive C. edulis. To link both measures, we monitored changes in soil characteristics over 1year after the removal of the invader, by analyzing both soil chemical properties and extracellular enzymes.C. edulis lowers soil pH, Ca and Na content and increases organic content, salinity and nitrogen and phosphorus concentration. The effects of the invader on the growth of M. littorea during the first growing season were very weak, despite strong negative effects in the early stages of this species’ population development that decreased total germination and survival.Overall, the soil characteristics and activity of the microbial community tend to recover back to pre-invasion conditions in plots from which C. edulis is removed. In contrast, the establishment of native dune vegetation is constrained, as indicated by lower species diversity in restored compared to non-invaded areas. This is because regenerating dunes are occupied by opportunistic ruderal species that compete with native dune plants of conservation value and restrict their establishment.

Arrival order among native plant functional groups does not affect invasibility of constructed dune communities

Different arrival order scenarios of native functional groups to a site may influence both resource use during development and final community structure. Arrival order may then indirectly influence community resistance to invasion. We present a mesocosm experiment of constructed coastal dune communities that monitored biotic and abiotic responses to different arrival orders of native functional groups. Constructed communities were compared with unplanted mesocosms. We then simulated a single invasion event by bitou (Chrysanthemoides monilifera ssp. rotundata), a dominant exotic shrub of coastal communities. We evaluated the hypothesis that plantings with simultaneous representation of grass, herb and shrub functional groups at the beginning of the experiment would more completely sequester resources and limit invasion than staggered plantings. Staggered plantings in turn would offer greater resource use and invasion resistance than unplanted mesocosms. Contrary to our expectations, there were few effects of arrival order on abiotic variables for the duration of the experiment and arrival order was unimportant in final community invasibility. All planted mesocosms supported significantly more invader germinants and significantly less invader abundance than unplanted mesocosms. Native functional group plantings may have a nurse effect during the invader germination and establishment phase and a competitive function during the invader juvenile and adult phase. Arrival order per se did not affect resource use and community invasibility in our mesocosm experiment. While grass, herb and shrub functional group plantings will not prevent invasion success in restored communities, they may limit final invader biomass.

Competition strength of two significant invasive species in coastal dunes

To investigate the effect of increased nutrient availability on competition amongst invasive and native plants, I measured changes in above and below ground biomass of Chrysanthemoides monilifera spp. rotundata (bitou bush) and Asparagus aethiopicus (asparagus fern) competing with two native species, Banksia integrifolia and Ficinia nodosa, under high- and low-nutrient regimes. Bitou bush, as a primary invader, was competitive under all conditions lowering the growth of native species in both high and low nutrients. Asparagus fern as a secondary invader, did not influence growth of native species but responded, like bitou bush, to high nutrients. Native species were generally negatively affected by increases in nutrients. With bitou bush soils often providing higher nutrients, the chance of secondary invasion by asparagus fern is more likely, although asparagus fern is unlikely to invade low nutrient soils quickly. The invasive species, therefore, differed in their competitive ability in these coastal dune communities.

Are competitive effects of native species on an invader mediated by water availability?

AbstractQuestionClimate change processes could influence the dynamics of biotic interactions such as plant competition, especially in response to disturbance phenomena such as invasional processes. Are competitive effects of native species on an invader mediated by water availability?LocationGlasshouse facility, New South Wales, Australia.MethodsWe constructed competitive hierarchies for a representative suite of species from coastal dune communities that have been invaded by the Asteraceae shrub, bitou (Chrysanthemoides monilifera subsp. rotundata). We used a comparative phytometer approach, where the invader species was grown with or without a suite of native species in glasshouse trials. This was used to construct competition hierarchies under two water stress conditions: non‐droughted and droughted. The treatments were designed to simulate current and potential future water availability respectively.ResultsWe found that the invader experienced fewer competitive effects from some native species under water stress, particularly with regard to below‐ground biomass effects. Native species were often poor competitors with the invader, despite their adaptation to periodic water stress in native coastal environments. Of the native species with significant competitive effects on the invader, functionally similar shrub species were the most effective competitors, as expressed in below‐ground biomass. The relative position of species in the hierarchy was consistent across water treatments based on below‐ground bitou biomass, but was contingent on water treatment when based on above‐ground bitou biomass.ConclusionsThe competitive effects of native species on an invader are affected by water stress. While the direction of response to water stress is species‐specific, many species have small competitive effects on the invader under droughted conditions. This could allow an increase in invader dominance with climate change.

Recruitment limitation of native species in invaded coastal dune communities

Recruitment limitation may limit the ability of sites to regenerate after disturbances such as weed invasion and weed management. We investigated seed bank constraints and dispersal limitation in coastal dune communities on the east coast of Australia. The ability of sites to regenerate naturally following weed removal was assessed in coastal dune communities invaded by the invasive alien, bitou bush (Chrysanthemoides monilifera subsp. rotundata). To investigate recruitment limitation, seed banks and vegetation of invaded, native, intensively managed (selective application of herbicide and some re-vegetation) and extensively managed (large-scale, non-selective herbicide application) sites were compared. We investigated the dispersal mechanisms of species in the seed bank and vegetation to determine if communities might be dispersal-limited, i.e. contain significant numbers of species with only short-distance dispersal capabilities. Species richness and composition of soil seed banks differed from the vegetation in foredunes and hinddunes. Invasion depleted seed banks further. About half of the species had short-distance dispersal mechanisms indicating the potential for dispersal limitation. Secondary weed invasion following management was evident although alien species occurred in both seed banks and vegetation. Our results indicated that coastal dune communities suffer recruitment limitation. Native, managed and invaded dune communities appear to be both seed bank and dispersal-limited although management and invasion exacerbates recruitment. Regeneration of coastal dune communities will require active reintroduction of species, particularly those with short-distance dispersal mechanisms.

Impact of microhabitats on the heterogeneity of seedling emergence in a Mediterranean coastal sand dunes community

Seedling emergence and establishment was monitored in 3 microhabitats during growing seasons in a Mediterranean coastal sand dune community in Poleg Stream Nature Reserve, Israel. Seedling emergence varied temporally among the 3 microhabitats, with a delay in the timing of seedling emergence in shrub understoreys due to lower soil average temperatures and lower irradiance. In contrast, seedling emergence on trails was advanced because of more intense irradiance and higher soil temperatures on their more exposed soil surfaces. Microhabitats showed significant differences in individual densities, species diversity, and species richness of total seedlings (P < 0.0001). Open areas generally possessed significantly greater total seedling densities, species diversity, and species richness compared to shrub understoreys and trails. Twelve key species and 5 functional groups showed significant microhabitat preferences. Seedling patterns indicated that emergence responses could account for observed patterns of variation in the 5 functional groups and dominant species populations. In this semi-arid ecosystem, negative interactions between the shrub canopy species (white weeping broom) and its understorey occurred for seedling establishment because of lower seed densities in the seed bank, a larger amount of litter on the soil surface, and the dense woody canopy. On the trails, trampling decreased plant diversity and discouraged the establishment of most functional groups and key species except annual grasses and Polycarpon succulentum and Cutandia philistaea. The variability in seedling response patterns for the different microhabitats will assist in understanding the patchy regeneration strategies of this coastal sand dune community and provide a basis for vegetation management.

Spatial patterns of association at local and regional scales in coastal sand dune communities

AbstractQuestions: Are positive understorey‐dominant associations important in physically severe dune communities and does the strength of positive associations vary with disturbance at the local scale and with stress at the regional scale? Do associational patterns observed at the neighbourhood scale predict diversity at higher scales?Location: Coastal sand dunes, Aquitaine (France).Methods: Associational patterns with five dominant species were recorded along a local gradient of disturbance and a 240‐km long regional gradient. Density, richness, cover and variance ratio of understorey species were recorded in quadrats located in dominant and in open areas. Spatial pattern of dominant plant species was recorded using a distance‐based method.Results: Positive understorey‐dominant associations were most frequent at both regional and local scale, although negative associations with understorey species were observed for one of the five dominants. At the regional scale, there was a shift in the magnitude of spatial associations, with higher positive associations in the most stressful sites, whereas spatial associations where not affected by the local disturbance gradient. Positive associations were not related to the size of the dominants but rather influenced by the identity of the dominant species.Conclusions: Our study highlights the potential crucial role of facilitation together with the importance of turnover of the dominants in explaining large‐scale variation in diversity. However, because positive associations may also be attributed to environmental heterogeneity or co‐occurrence of microhabitat preferences of species, experiments are needed to fully assess the relative importance of facilitation versus other drivers of community diversity.

Ontogenetic shifts in interactions of two dominant shrub species in a semi‐arid coastal sand dune system

AbstractQuestion: How does the interaction between two dominant shrub species in a coastal sand dune community change during their life history? Does this interaction influence their population dynamics?Location: A semiarid coastal sand dune system in southeast Spain.Methods: For 3 years we monitored physiological status, growth and reproductive effort of Juniperus phoenicea and Pistacia lentiscus, the dominant shrub species, growing either alone or in close spatial association. We also recorded adult mortality patterns and characterized seedling survival, soil properties and microclimate conditions beneath canopies and in bare ground.Results and conclusions: There was a strong bi‐directional interaction between the two studied species, with a net balance that changed in sign with increasing plant development. While mature individuals facilitated the establishment of seedlings of both species, adult mortality patterns suggested asymmetric competition at later life stages. The interaction with Pistacia negatively affected growth of juniper and contributed to its high mortality rates, while juniper had almost no effect on mature Pistacia individuals. Physiological data suggested that Pistacia had a competitive advantage over juniper, most likely because of differences in rooting patterns and tolerance to salinity, which may determine the source of water available for each species. Community dynamics are governed by facilitation at the seedling stage and shaped by differences in physiological traits in adult plants. Plant‐plant interactions, which are strongly affected by environmental gradients, are important drivers of community dynamics in this system.

The effect of microhabitats on vegetation and its relationships with seedlings and soil seed bank in a Mediterranean coastal sand dune community

We examined species composition and diversity of vegetation and soil seed bank associated with different microhabitats in Mediterranean semiarid sand dune community, to identify which functional groups or species benefit from trampling, and to provide a basis for management. In this community microhabitats were found to significantly influence species abundance and biomass of dominant functional groups and dominant species. The open patches generally have the greatest species richness, diversity and productivity. The highest value of similarity occurred during June to September and the lowest value occurred in April when seedling emergence stopped but before new seeds dispersed. Shrubs did not benefit their understorey plant functional groups except for perennial forbs and Apiaceae due to their denser canopy and larger litter amount. Trampling decreased the species diversity of vegetation and did not facilitate the establishment of herbaceous plants, but was beneficial for some functional groups such as Apiaceae and Brassicaceae as well as some species such as Polycarpon succulentum. A positive relationship was found between productivity and diversity in this community and on the trail, but the relationship in the open area and shrub understorey was not significant. This work can provide a deeper understanding of small-scale vegetation processes and mosaic patterns of distribution.

NEGATIVE EFFECTS OF VERTEBRATE HERBIVORES ON INVERTEBRATES IN A COASTAL DUNE COMMUNITY

Although competition has been a major focus in ecology for the past century, most empirical and theoretical studies in this area have emphasized interactions between closely related species. However, there is growing evidence that negative interactions among distantly related taxa also occur and may be far more important than previously thought. In this study, we took advantage of an 11-year-old replicated vertebrate-exclosure experiment in a coastal dune community in northern California, USA, to examine the effects of the two most common vertebrate herbivores (jackrabbits and black-tailed deer) on the abundance of the three most visible invertebrate herbivores (two snail, a moth, and a grasshopper species). Our results indicate that four of the six possible pairwise interactions were significantly negative for the invertebrates. Jackrabbits reduced the abundances of snails by 44-75%, tiger moth caterpillars by 36%, and grasshoppers by 62%. Deer reduced the abundances of snails by 32%, increased the abundances of caterpillars by 31%, and had no measurable effect on grasshopper abundance. Our data also revealed that jackrabbits significantly decreased the volume of forbs and common shrubs and the flowering by grasses in our study plots. We were unable to detect an effect of deer on these measures of vegetation. These results suggest that by changing vegetation, jackrabbits may reduce invertebrate populations that are limited by food, protective structures, or microclimate provided by plants. Of these three mechanisms, only shade was strongly supported as limiting snail numbers in smaller-scale manipulations. In most systems, as in this one, the number of pairs of distantly related herbivores far exceeds the number of pairs of congeners. Since interactions among distantly related herbivores may be common in many cases, these interactions are likely to be important and should receive far more attention from ecologists.

The Spatial Patterns of Functional Groups and Successional Direction in a Coastal Dune Community

Various methods have been devised to classify plants into functional groups, yet little work has investigated how these groups differentially impact succession with spatially explicit mechanisms. In a sand dune plant community on Galveston Island, Texas, we categorized plants by their functional traits, mapped the topographical contours of the sand dunes as a first-order effect to describe the spatial distribution of environmental stress, and quantified the second-order within- and between-group associations of the plants within specific bands of these contours using Ripley's K analysis. We then quantified the influence of spatially explicit functional traits on the direction of succession over time. We found evidence that the spatial pattern of the plants at one time exerted an influence on the pattern of the plants at a later time, based on their functional traits, thereby influencing the direction of sand dune succession. This study describes the spatiotemporal mechanics that lie behind sand dune plant succession: a process that has been a classical example of facilitation for ecologists, a plant community that is at risk from global sea-level rise and hurricanes, and an important rangeland resource that is being restored around the world for its ecological, range production, and coastal protection value.

Management regimes for a plant invader differentially impact resident communities

Management of plant invaders causes disturbance and the compounding effects of both invasion and management on biodiversity merit rigorous assessment. We explored the impacts of both plant invasion and management disturbance in coastal dune communities of Australia invaded by the introduced shrub bitou bush ( Chrysanthemoides monilifera ssp. rotundata). We compared the effects of intensive, manually based invader control with those of extensive control (mainly herbicide spraying from aircraft) across fore dune communities. We examined one management regime, which was typically intensive, in hind dune communities. Our main aim was to test the prediction that intensive methods would achieve better biodiversity outcomes than extensive approaches in fore dune communities. We found that extensive management created native species complements that diverged from non-invaded sites while intensive management approached non-invaded site conditions. However, intensively managed sites were also richer in other exotic species than extensively managed sites. Thus, while biodiversity outcomes were better under intensive management, the risk profile of such sites was increased by the greater array of exotics that could potentially replace the original invader. The positive effects of management evident on some fore dunes were not found in hind dunes, where managed sites had the highest exotic species richness and similar bitou bush seedling abundance as both non-invaded and bitou-invaded sites. Hind dune managed sites were also compositionally distinct from non-invaded sites. Thus fore and hind dune communities exhibited different responses to bitou management regimes.

Flowering phenology and pollen-to-ovule ratio in coastal dune communities near Eurosiberian-Mediterranean border in the NW Iberian peninsula

Summary Pollen-to-ovule ratios and flowering phenology were studied in 15 of the most important entomophilous species of the coastal dunes of the northwest Iberian Peninsula, located bioclimatically in the Cantabro-Atlantic territory but with significant Mediterranean influence. Specifically, we aimed to answer the following questions: 1) Does P/O ratio show any consistent pattern in entomophilous dune species ? 2) Does flowering phenology differ in any consistent manner between the outer active-dune habitat and the inner fixed-dune habitat? 3) Do intra- or interspecific flowering overlap differ between active dunes and fixed dunes ? 4) Does flowering phenology accord with that observed in Eurosiberian or Mediterranean territories ? P/O ratios were in all cases within the range reported for xenogamy. In general, active-dune species flowered later than fixed-dune species and showed lower and more variable intraspecific flowering overlaps. The Mediterranean influence is particularly marked in the fixed dune, in which the peak flowering periods mostly occur somewhat earlier than in the active dune.