Maike Isermann

Soil pH and species diversity in coastal dunes

Soil pH was measured at two different spatial scales in coastal dunes on Norderney, North Sea, and in Mecklenburg-Vorpommern, Baltic Sea, Germany. Relationships between the variability in soil pH, species richness and species diversity are presented. Species richness and diversity were highest in grey dunes, where soil pH was at intermediate levels; both variables were lower in yellow and brown dunes. The variability in pH increased with increasing species diversity and also with scale. Overall, soil pH variability decreased with increasing vegetation cover. The lowest pH heterogeneity was found in heath dominated by Empetrum nigrum L. and grey dunes dominated by Campylopus introflexus (Hedw.) Brid. Increasing abundance of dominant species and decreasing species diversity of vegetation apparently reduces soil heterogeneity. Decreasing species diversity of vegetation is likely to explain decreasing variability in soil pH.

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

ABSTRACT 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. Nomenclature: Wisskirchen & Haeupler (1998). Abbreviations: Nor = Norderney; Spi = Spiekeroog

Randomvs non-random sampling: Effects on patterns of species abundance, species richness and vegetation-environment relationships

From a strictly statistical perspective, most of the commonly used statistical tests cannot be performed on vegetation data obtained using a non-random sampling design. Despite this, non-randomly sampled plots such as phytosociological relevés still make sense: because they may focus on objectives not appropriately addressed by random sampling, such as the study of rare plant communities or species; and because random sampling is often more time-demanding and expensive. Considering the huge body of phytosociological data available, an interesting question arises: if we compare randomly and non-randomly sampled data sets, to what extent do the results of our analyses differ with respect to various species and vegetation parameters?We present an attempt to tackle this question by comparing two data sets collected in a 25 km2 area close to the city of Bremen, northwestern Germany: the first data set consisted of 30 subjectively (non-randomly) placed, homogeneous plots across different plant communities, each of which was laid out in a nested design including 9 sizes from 0.5 m2 to 1,000 m2. The second data set consisted of 30 (again nested) plots randomly selected and located with a GPS device; plots were rejected only if they for some reason were inaccessible. The data collection was the same for both data sets: presence-absence of all vascular plants was recorded for the different plot sizes, and soil samples were collected for the determination of the values of some important environmental variables. For the comparison of the two data sets, we used either the complete data sets or sub-sets of those plots located in woodlands.The main results included the following: (1) Species abundance patterns: Random sampling resulted in a larger number of common and a smaller number of rare species than non-random sampling. (2) Species richness at different spatial scales: For the small plot sizes, the number of species in the non-randomly placed plots was higher than in the randomly placed plots, while the differences were less pronounced at larger spatial scales. As a consequence, also the parameters of species-area curves differed between the data sets, especially in the sub-set including woodland plots. (3) Vegetation differentiation: In random sampling, there was considerable redundancy, i.e., there were several plots with high floristic similarity. (4) Vegetation-environment relationships: The ordination scores of the non-randomly placed plots showed a larger number of significant correlations to soil parameters than the scores of randomly placed plots. The results suggest that conclusions drawn from the analysis of non-randomly placed plots such as phytosociological relevés may be biased, especially regarding estimates of species abundance and species richness patterns.

Patterns in Species Diversity during Succession of Coastal Dunes

Abstract The humped-back relationship in species diversity during succession was tested using vegetation in a coastal sand dune system of the German Wadden Sea island of Spiekeroog. Permanent plots were studied over 15 years along a spatial chronosequence from young grey dunes to old brown dunes. Species diversity, succession rate, and environmental indicator value were used to evaluate multitemporal dynamics of the ecosystem. Long-term development of the dune vegetation was reflected along the chronosequence, whereas fluctuations of plant communities were analyzed by short-term changes of each permanent plot. The study confirmed the intermediate stress theory, whereas highest species diversity was reached at the transition zone of the environmental gradients. Total species richness showed humped-back relations along the xerosere. Hotspots in species diversity varied with the life form group. Highest richness of herbaceous plants was reached in semidynamic young grey dunes, whereas highest richness of bryophytes and lichens shifted due to competition effects to the driest parts of the dune gradient in older successional stages. Moreover, the study confirmed the biodiversity-stability theory, with highest ecosystem stability at highest diversity. More stable environments showed lower succession rates than dynamic, disturbed environments. Thus, during secondary succession with probably repeated disturbance, the succession rate was higher and no clear direction of vegetation development was found in comparison to primary succession. The succession rate in a primary series represented a unimodal relation with total species richness. Thus, species-poor vegetation often dominated by one species, such as heathlands, as well as species-rich vegetation, showed lowest succession rates. These communities probably are more stable due to a balanced species combination represented by higher evenness.

Biological Flora of the British Isles: Eryngium maritimum

Summary 1. This account presents information on all aspects of the biology of Eryngium maritimum L. (Sea Holly) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation. 2. Eryngium maritimum is a native perennial hemicryptophyte, with a large taproot, spiny and leathery leaves and a pale bluish inflorescence. It has a more or less continuous distribution in suitable habitats along the coasts of Great Britain and Ireland up to about 55° N, but it is more scattered further north. On the west coast, it is found south of the Hebrides, and on the east coast, with some exceptions, south of Yorkshire. In Europe, it has a wide, but mainly southern temperate, European distribution along the coasts of the Atlantic Ocean, the Baltic, the Mediterranean, and the Black and Azov Seas. Its northern distribution limit is at c. 60° N. 3. Eryngium maritimum grows typically on sand and shingle beaches, foredunes and yellow dunes, as well as in semi-fixed grey dunes. Its habitats have full sunlight and are more or less dry. It occurs in many coastal plant communities from the beach inland, and because of its wide European distribution, it occurs with members of several different biogeographical species groups. 4. Protected from grazing by its spininess and sclerophylly, E. maritimum is nevertheless vulnerable to direct damage by trampling. It supports few insect herbivores, probably because of chemical defences. Historically, it has had a great number of medicinal uses. 5. Eryngium maritimum is unable to withstand competition from faster and more densely growing plant species. In many coastal regions, in both temperate and mediterranean parts of Europe, it is one of the rarest and most threatened plant species, mainly because of habitat loss and land-use changes.

Classification of European and Mediterranean coastal dune vegetation

Aims: Although many phytosociological studies have provided detailed local and regional descriptions of coastal dune vegetation, a unified classification of this vegetation in Europe and the Mediterranean Basin has been missing. Our aim is to produce a formalized classification of this vegetation and to identify the main factors driving its plant species composition at a continental scale. LocationAtlantic and Baltic coasts of Europe, Mediterranean Basin and the Black Sea region. - Methods: We compiled a database of 30,759 plots of coastal vegetation, which were resampled to reduce unbalanced sampling effort, obtaining a data set of 11,769 plots. We classified these plots with TWINSPAN, interpreted the resulting clusters and used them for developing formal definitions of phytosociological alliances of coastal dune vegetation, which were included in an expert system for automatic vegetation classification. We related the alliances to climatic factors and described their biogeographic features and their position in the coastal vegetation zonation. We examined and visualized the floristic relationships among these alliances by means of DCA ordination. - Results: We defined 18 alliances of coastal dune vegetation, including the newly described Centaureo cuneifoliae-Verbascion pinnatifidi from the Aegean region. The main factors underlying the differentiation of these alliances were biogeographic and macroclimatic contrasts between the Atlantic-Baltic, Mediterranean and Black Sea regions, along with ecological differences between shifting and stable dunes. The main difference in species composition was between the Atlantic-Baltic and Mediterranean-Black Sea regions. Within the former region, the main difference was driven by the different ecological conditions between shifting and stable dunes, whereas within the latter, the main difference was biogeographic between the Mediterranean and the Black Sea. - Conclusions: The first formal classification of the European coastal dune vegetation was established, accompanied by an expert system containing the formal definitions of alliances, which can be applied to new data sets. The new classification system critically revised the previous concepts and integrated them into a consistent framework, which reflects the main gradients in species composition driven by biogeographic influences, macroclimate and the position of the sites in the coast-inland zonation of the dune systems. A revision of the class concept used in EuroVegChecklist is also proposed.

Invasive Rosa rugosa populations outperform native populations, but some populations have greater invasive potential than others

Increased performance of invasive plant species in their introduced range vs. their native range has been previously documented. However, performance differences among invasive populations have rarely been explored, despite this information being central to understanding the evolution of invasiveness as well as being a useful basis to inform management of invasive species. To examine variation in performance among populations of Rosa rugosa in its introduced range, and whether introduced populations perform better than native populations, we quantified growth and reproductive traits in five invasive populations in northwest Europe and two native and declining populations in China. Overall, we found that the introduced R. rugosa populations we sampled performed significantly better than the sampled native populations for growth and reproductive traits (2 to 4 fold increase). However, there was significant variation for most traits among the five invasive populations, demonstrating that some introduced populations we sampled were more successful invaders than others. Our findings provide a useful foundation for management of invasive R. rugosa in Europe, and support the recent call for more intra-species research in invasive species biology.