Jürgen Dengler

SPECIES RICHNESS OF VASCULAR PLANTS, BRYOPHYTES AND LICHENS IN DRY GRASSLANDS: THE EFFECTS OF ENVIRONMENT, LANDSCAPE STRUCTURE AND COMPETITION

We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m2 plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric.

European grassland ecosystems: threatened hotspots of biodiversity

Biodiversity is not homogenously distributed over the globe, and ecosystems differ strongly in the number of species they provide. With this special issue we highlight the ecology and endangerment of one of the most diverse ecosystem of Europe: the European grassland ecosystems. The selected 16 contributions describe interactions from below-ground to the atmosphere and focus on (1) effects of abiotic and biotic on species diversity, (2) the impact of various factors along spatial and temporal gradients, (3) the relevance of falling abandoned and eutrophication—including countervailing management strategies like encroachment; and (4) intraspecific effects based on physiology, genetics and intraspecific plasticity. The contributions cover fungi, plants, and invertebrates and highlight effects taking place at the level of ecosystem, species community, species, populations, and also within individuals (physiology and genetics).

Effect of land abandonment on the vegetation of upland semi-natural grasslands in the Western Balkan Mts., Bulgaria

Abstract The area of semi-natural grasslands in Bulgaria has decreased tremendously in the past century due to agricultural intensification or abandonment. As these grasslands host valuable biodiversity, conservation measures are needed for their sustainable maintenance. We studied the effect of pastureland abandonment on plant communities at the Ponor Mt., a part of the Balkan Mts., Bulgaria. Data on floristic composition, vegetation structure and several abiotic parameters were collected in 137 randomly located 16-m2 plots in 2008. Canonical correspondence analysis (CCA) was used to analyse how species composition is related to abiotic and land use factors. Analyses of covariance (ANCOVAs) were used to test for the effects of sheep grazing vs. abandonment on vegetation structure and composition. The main environmental factors explaining the compositional variation were related to the altitude, sheep grazing and soil depth. Pastureland abandonment led to an increase in vegetation height and of the richness of mesophytes and leafy plants, and red-list species. Grazed plots had higher total species richness, more xerophytes, rosette forming and spring-flowering species. To ensure the persistence of the species of both the open grasslands and mid-successional grassland communities, the management should be carried out in an extensive way and with a zonation regime.

Advances in the conservation of dry grasslands: Introduction to contributions from the seventh European Dry Grassland Meeting

Abstract Dry grasslands in Europe are mostly of zoo-anthropogenic origin, but nevertheless they are among the most diverse plant communities of the world at small spatial scales, and they support a significant proportion of the biodiversity of the continent. Both agricultural intensification and abandonment of former dry grasslands caused dramatic losses in area and quality of this habitat type during recent decades. Here we report from the 7th European Dry Grassland Meeting, organised by the European Dry Grassland Group (EDGG) in Smolenice, Slovakia, in 2010. Under the motto “Succession, restoration and management of dry grasslands” one hundred researchers from throughout Europe discussed conservation issues of this threatened habitat type. We give a brief introduction to those nine articles that are included in this Special Feature. With contributions from many different countries and various dry grassland types, they address issues of conservation value, succession, management as well as regeneration and restoration. We conclude that the diversity of dry grasslands and their conservation problems require further research to develop adequate management techniques under changing frame conditions. However, also the frame conditions, such as the incentives for certain land use practices provided by the Common Agricultural Policy of the European Union need to be addressed if long-term success in conservation of dry grasslands is intended.

Pitfalls in Small-Scale Species-Area Sampling and Analysis

Analyses of the dependency of species richness (S) on area (A), the so-called species-area relationships (SARs), are widespread approaches to characterize and compare biodiversity patterns. This article highlights – with a focus on small-scale SARs of plants in continuous ecosystems – how inappropriate sampling methods or theoretical misconceptions can create artifacts and thus may lead to wrong conclusions. Most of these problems have been recognized before but continue to appear regularly in the scientific literature. The following main points are reviewed and discussed: i) Species richness values and SARs depend on the measurement method (any-part vs. grid-point system); ii) Species-richness values depend on the shape of the analyzed plots; iii) Many published SARs are not true SARs but instead represent species sampling curves or their data points consist of richness totals for incontiguous subplots; iv) Nested-plot design is the preferred sampling method for SARs (the claim that this approach would cause pseudoreplication is erroneous); v) SARs should be constructed using mean values of several counts for the smaller areas; vi) SAR functions can be fitted and selected both in the S- and the log S-space but this must be done consistently for all compared function types. It turns out that the finding of non-power function SARs in many studies is due to a lack of awareness of one or several of the named points. Thus, power-function SARs are even more widespread than a recent review would suggest. I therefore propose to use the power law as a universal model for all types of SARs but to test whether the slope z varies with spatial scale. Finally, I urge readers to be aware of the many pitfalls in SAR studies, to fully disclose methodology, and to apply a meaningful and consistent terminology, especially by restricting the terms “species-area relationship” and “species density” to situations in which each data point represents a contiguous area.

The impact of livestock grazing on plant diversity: an analysis across dryland ecosystems and scales in southern Africa

A general understanding of grazing effects on plant diversity in drylands is still missing, despite an extensive theoretical background. Cross-biome syntheses are hindered by the fact that the outcomes of disturbance studies are strongly affected by the choice of diversity measures, and the spatial and temporal scales of measurements. The aim of this study is to overcome these weaknesses by applying a wide range of diversity measures to a data set derived from identical sampling in three distinct ecosystems. We analyzed three fence-line contrasts (heavier vs. lighter grazing intensity), representing different degrees of aridity (from arid to semiarid) and precipitation regimes (summer rain vs. winter rain) in southern Africa. We tested the impact of grazing intensity on multiple aspects of plant diversity (species and functional group level, richness and evenness components, alpha and beta diversity, and composition) at two spatial scales, and for both 5-yr means and interannual variability. Heavier grazing reduced total plant cover and substantially altered the species and functional composition at all sites. However, a significant decrease in species alpha diversity was detected at only one of the three sites. By contrast, alpha diversity of plant functional groups responded consistently across ecosystems and scales, with a significant decrease at heavier grazing intensity. The cover-based measures of functional group diversity responded more sensitively and more consistently than functional group richness. Beta diversity of species and functional types increased under heavier grazing, showing that at larger scales, the heterogeneity of the community composition and the functional structure were increased. Heavier grazing mostly increased interannual variability of alpha diversity, while effects on beta diversity and cover were inconsistent. Our results suggest that species diversity alone may not adequately reflect the shifts in vegetation structure that occur in response to increased grazing intensity in the dryland biomes of southern Africa. Compositional and structural changes of the vegetation are better reflected by trait-based diversity measures. In particular, measures of plant functional diversity that include evenness represent a promising tool to detect and quantify disturbance effects on ecosystems.

Mind the gaps when using science to address conservation concerns

AbstractConservation science and conservation action are assumed to have identical goals. However, in reality, there is a strong divide between research and practical conservation that has been mostly discussed with respect to the ‘knowing-doing gap’, i.e. the results from science are not being translated into practical management. In this commentary, we argue that there is not one but there are at least three different types of gaps impeding a positive impact of science on conservation: (1) the knowing-doing gap; (2) the thematic gap that exists between the topics addressed by conservation science and the problems faced in conservation; and (3) the disciplinary gap, i.e. the lack of communication and cooperation between different fields of science, e.g. between fundamental biodiversity research and conservation research. These different gaps have different origins and require different means to be overcome. In a survey, scientists from the field of conservation research (all contributing to this special issue on European grasslands) assessed the importance of these three gaps. They highlight that the disciplinary gap is just as relevant as the knowing-doing gap, while the importance of the thematic gap between practical conservation needs and theoretical conservation science is, in the view of the authors, of less importance. Also, the respondents identified the complexity of academic content in scientific publications as an additional cause for knowing-doing gaps. Based on our survey and various other studies analysing these gaps, we suggest two ways to overcome the gaps: if you consider yourself to be a conservation scientist make sure to address questions of relevance for conservation issues, if you are a scientist interested in fundamental issues, be open to mutual interaction and translation of scientific results with conservation scientists. The knowing-doing gap could be addressed by more readily translating the theoretical findings into practical advice. “Conservation Journals” could, for instance, require a second “Conservation Management Abstract”, which has to be published open-access, and back-to-back with the conventional abstract.

Montane-subalpine tall-herb vegetation (Mulgedio-Aconitetea) in central Europe: large-scale synthesis and comparison with northern Europe.

Many incompatible classifi cations have in the past been applied to the class of European montane-subalpine tall-herb communities (Mulgedio-Aconitetea). The aim of our paper is to develop a consistent classifi cation of all vegetation types of this class from temperate and boreal Europe, derived from a database of individual relevés. We compiled available relevés from central, western and northern Europe. After excluding plots dominated by woody species, those outside the range of 9 – 50 m2 size, and stands with prevailing diagnostic species of other classes, 993 relevés remained for the classifi cation, mainly from central Europe. We used cluster analysis (group linkage with fl exible beta and Sørensen index) to analyse the structure of the dataset, and translated the results into a syntaxonomic system. The major division is between the temperate order Calamagrostietal ia vi l losae and the newly described northern European order Epilobio lact i f lori-Geranietal ia sylvat ic i. The temperate order can be subdivided into fi ve alliances: (i) subalpine tall-forb communities (Adenostyl ion al l iar iae), (ii) tall-forb communities of montane-subalpine eutrophic pastures (Rumicion alpini), (iii) subalpine tall-forb and tall-grass communities that are closely related to alpine meadows (Calamagrostion vi l losae), (iv) mainly montane tallgrass and fern communities of acidic soils (Calamagrostion arundinaceae), and (v) montane tall-forb communities (Arunco dioici-Petasit ion albi). The northern European order was not divided further at present because too few data were available. We characterise all syntaxa from the alliances upwards ecologically and fl oristically, provide a revision of their nomenclature, and list the included associations. We also discuss the methodological problems any supra-national classifi cation has to face due to the high heterogeneity of such data and the lack of a continent-wide relevé database of all vegetation types. The use of a priori lists of diagnostic species for the delimitation of the focal syntaxon and the restriction of the analysis to relevés with similar plot sizes turned out to be crucial to derive consistent results. This study demonstrates that the analysis of a comprehensive supra-national database of individual relevés can provide insights that go beyond what is achievable at a regional scale or by comparison of synoptic tables.

The basiphilous dry grasslands of shallow, skeletal soils (Alysso-Sedetalia) on the island of Öland (Sweden), in the context of North and Central Europe

The basiphilous dry grasslands of shallow, skeletal soils (Alysso-Sedetalia) on the island of Oland (Sweden), in the context of North and Central Europe

The Palaearctic steppe biome: a new synthesis

The Palaearctic steppes range from the Mediterranean basin towards China, forming one of the largest continuous terrestrial biomes. The literature on steppe ecology and conservation is vast but scattered and often not available in English. We provide a review of some key topics based on a new definition of steppes, which includes also Mediterranean steppes and alpine rangelands of the Asian Highlands. Revisiting the terrestrial ecoregions of the world, we estimate that the Palaearctic steppe biome extends over ca. 10.5 million km2. Major chorological regions differ in their macroclimatic niche with a clear distinction between Middle Asia with its winter precipitation and the Central Asian summer-rain regions of the Mongolian plateau and of Tibet. Steppe soils store large amounts of carbon, yet the sequestration potential is debated and depends on land use. Major physiognomic-ecological steppe types include forest-, typical-, desert-, and alpine-steppe, which vary in the importance of grasses, mainly C3 species. The steppes host a specialised fauna, and Middle Asia, Tibet, and especially Mongolia, have large herds of migrating ungulates. The share of pristine and protected sites is low in the steppe regions, with conversion into croplands being the most important land use impact in Europe, Middle Asia, and the Mediterranean, while grazing has a severe impact in some parts of Mongolia and Tibet. There are major gaps in our knowledge on: (1) the effects of climate change on the crucial seasonal patterns; (2) the role of steppe soils in the global carbon budget; and (3) the ecology and distribution of most animal groups except vertebrates.