Jörg Ewald

The calcareous riddle: Why are there so many calciphilous species in the Central European flora?

The pool of the Central European flora consists of a majority of vascular plant taxa that are restricted to very base rich and calcareous soils. Ellenberg indicator values for Germany indicate that this floristic pattern is one of the potentially most powerful determinants of the richness of modern temperate plant communities. Considering the example of the forest flora, which, as the putative natural core of the species pool, exhibits the same skew, it is shown that neither the frequency of suitable soil types nor other correlated ecological factors can explain this striking pattern. Also, the ramification of higher taxa offers no indication of higher evolution speeds in calciphilous plants. As an alternative, it is hypothesized that Pleistocene range contractions have caused the extinction of more acidophilous than calciphilous species, because acid soils were much rarer when refugial areas were at their minimum. If this is correct, one of the most significant ecological patterns in the contemporary distribution of plant diversity must be regarded as a result of ecological drift imposed by a historical bottleneck.

A critique for phytosociology

Abstract Phytosociology is a subdiscipline of plant ecology that describes the co-occurrence of plant species in communities. Gradient analysis and classification are its complementary tools. Various peculiarities and anachronisms of Central European phytosociology conceal its similarity with Anglo-American approaches. Phytosociology deserves to be updated as a part of modern vegetation science that can build on a vast heritage of high-quality data and the tools to store and analyse them in ways that go beyond syntaxonomy. By providing a context to more specialized pure and applied research, it has a crucial role to play in understanding community structure, ecosystem functioning and biological evolution. Abbreviations: AAPE = Anglo-American plant ecology; CEPS = Central European phytosociology; PS = Phytosociology.

A probabilistic approach to estimating species pools from large compositional matrices

Abstract Species pools are increasingly recognized as important controls of local plant community structure and diversity. While existing approaches to estimate their content and size either rely on phytosociological expert knowledge or on simple response models across environmental gradients, the proposed application of phytosociological smoothing according to Beals exploits the full information of plant co-occurrence patterns statistically. Where numerous representative compositional data are available, the new method yields robust estimates of the potential of sites to harbour plant species. To test the new method, a large phytosociological databank covering the forested regions of Oregon (US) was subsampled randomly and evenly across strata defined by geographic regions and elevation belts. The resulting matrix of species presence/absence in 874 plots was smoothed by calculating Beals’ index of sociological favourability, which estimates the probability of encountering each species at each site from the actual plot composition and the pattern of species co-occurrence in the matrix. In a second step, the resulting lists of sociologically probable species were intersected with complete species lists for each of 14 geographical subregions. Species pools were compared to observed species composition and richness. Species pool size exhibited much clearer spatial trends than plot richness and could be modelled much better as a function of climatic factors. In this framework the goal of modelling species pools is not to test a hypothesis, but to bridge the gap between manageable scales of empirical observation and the spatio-temporal hierarchy of diversity patterns.

Ecological preferences of alien plant species in North-Eastern Germany

The large, comprehensive vegetation database of Mecklenburg-Vorpommern/NE Germany with 51,328 relevés allowed us to study an entire regional flora of 133 non-native plants (NNP, immigration after 1492 AD) with regard to their preferences to all kinds of habitats and along different ecological gradients. For each relevé, we computed average Ellenberg indicator values (EIV) for temperature, light, moisture, reaction, nutrients and salt as well as plant strategy type weights. We partitioned the dataset into relevés with and without occurrences of NNP and compared them with respect to the relative frequencies of EIVs and strategy type weights. We identified deviations from random differences by testing against permuted indicator values. To account for bias in EIV between community types, NNP preferences were differentiated for 34 phytosociological classes. We tested significance of preferences for the group of NNP as a whole, as well as for single NNP species within the entire dataset, as well as differentiated by phytosociological classes and formations. NNP as a group prefer communities with high EIVs for temperature and nutrients and low EIVs for moisture. They avoid communities with low EIV for reaction and high EIV for salt. NNP prefer communities with high proportions of ruderal and low proportion of stress strategists. The differentiation by phytosociological classes reinforces the general trends for temperature, nutrients, moisture, R and S strategy types. Nevertheless, preferences of single species reveal that NNP are not a congruent group but show individualistic ecological preferences.

The Partial Influence of Norway Spruce Stands on Understorey Vegetation in Montane Forests of the Bavarian Alps

Abstract Natural mixed forests of European beech (Fagus sylvatica), Norway spruce (Picea abies), and silver fir (Abies alba) were widely replaced by spruce-dominated stands in the montane belt of the northern Calcareous Alps in historical times. This accounts for changing forest structure, diversity, and hemeroby. Observations in other parts of Europe suggest that this development should have led to a replacement of the native understorey vegetation by species typical of coniferous forests and to an increase in plants that are indicators for acidity and nitrogen. The statistical relationships between understorey vegetation structure and species richness, Ellenberg indicator values, and the proportion of Norway spruce in the tree layer were studied in 84 stands selected in a stratified random design in the Bavarian Alps, while controlling for the influence of the natural environment. The results show that the richness of coniferous forest species and the occurrence of acid indicators have been significantly favored by Norway spruce canopies, while understorey species characteristic of deciduous forests and nitrogen indicators have not been affected. While bryophytes and some shallow-rooted vascular plants respond positively to a coniferous canopy, most vascular plants are resilient to changes in the canopy. This can be attributed to the high buffering capacity of the soils under the mountain forests studied.

Formalized classification of European fen vegetation at the alliance level

Phytosociological classification of fen vegetation (Scheuchzerio palustris-Caricetea fuscae class) differs among European countries. Here we propose a unified vegetation classification of European fens at the alliance level, provide unequivocal assignment rules for individual vegetation plots, identify diagnostic species of fen alliances, and map their distribution. 29 049 vegetation-plot records of fenswere selected fromdatabases using a list of specialist fen species. Formal definitions of alliances were created using the presence, absence and abundance of Cocktail-based species groups and indicator species. DCA visualized the similarities among the alliances in an ordination space. The ISOPAM classification algorithm was applied to regional subsets with homogeneous plot size to check whether the classification based on formal definitions matches the results of unsupervised classifications. The following alliances were defined: Caricion viridulo-trinervis (sub-halophytic Atlantic dune-slack fens), Caricion davallianae (temperate calcareous fens), Caricion atrofusco-saxatilis (arcto-alpine calcareous fens), Stygio-Caricion limosae (boreal topogenic brown-moss fens), Sphagno warnstorfii-Tomentypnion nitentis (Sphagnumbrown-moss rich fens), Saxifrago-Tomentypnion (continental to boreo-continental nitrogen-limited brown-moss rich fens), Narthecion scardici (alpine fens with Balkan endemics), Caricion stantis (arctic brown-moss rich fens), Anagallido tenellae-Juncion bulbosi (Ibero-Atlantic moderately rich fens), Drepanocladion exannulati (arcto-borealalpine non-calcareous fens), Caricion fuscae (temperate moderately rich fens), Sphagno-Caricion canescentis (poor fens) and Scheuchzerion palustris (dystrophic hollows). The main variation in the species composition of European fens reflected site chemistry (pH, mineral richness) and sorted the plots from calcareous and extremely rich fens, through rich andmoderately rich fens, to poor fens and dystrophic hollows.

Species-specific and generic biomass equations for seedlings and saplings of European tree species

AbstractBiomass equations are a helpful tool to estimate the tree and stand biomass production and standing stock. Such estimations are of great interest for science but also of great importance for global reports on the carbon cycle and the global climate system. Even though there are various collections and generic meta-analyses available with biomass equations for mature trees, reports on biomass equations for juvenile trees (seedlings and saplings) are mainly missing. Against the background of an increasing amount of reforestation and afforestation projects and forests in young successional stages, such equations are required. In this study we have collected data from various studies on the aboveground woody biomass of 19 common tree species growing in Europe. The aim of this paper was to calculate species-specific biomass equations for the aboveground woody biomass of single trees in dependence of root-collar-diameter (RCD), height (H) and the combination of the two (RCD2 H). Next to calculating species-specific biomass equations for the species available in the dataset, we also calculated generic biomass equations for all broadleaved species and all conifer species. The biomass equations should be a contribution to the pool of published biomass equations, whereas the novelty is here that the equations were exclusively derived for young trees.

Regionalizing Indicator Values for Soil Reaction in the Bavarian Alps – from Averages to Multivariate Spectra

We present an approach to produce maps of Ellenberg values for soil reaction (R-value) in the Bavarian Alps. Eleven meaningful environmental predictors covering GIS-derived information on climatic, topographic and soil conditions were used to predict R-values. As dependent variables, Ellenberg indicator values for soil reaction were queried from plot records in the vegetation database WINALPecobase. We used an additive georegression model, which combines complex prediction models and the increased prediction accuracy of a boosting algorithm. In addition to environmental predictors we included spatial effects into the model to account for spatial autocorrelation. As we were particularly interested in the usefulness of averaged R-values for spatial prediction, we applied two different models: (1) a geo-additive regression model that estimates mean R-values and (2) a proportional odds model predicting the probability distribution over R-values 1 to 9. We found meaningful dependencies between the R-value and our predictors. Both models produced the same spatial pattern of predictions. Spatial effects had an impact only in the first model. The main drawback of mean R-values is the oversimplification of complex conditions of soil reaction, which is entailed by averaging and regression to mean values. Therefore, regionalized average indicator values provide only limited information on site-ecological characteristics. Model 1 failed to predict the range and shapes of original indicator spectra precisely. In contrast, the second model provided a more sophisticated picture of soil reaction. To make the multivariate output of model 2 comparable to that of model 1, we propose to plot the distribution in a three-dimensional color-space. In addition, comparison of both models based on a multiple linear regression model resulted in a R2 of 0.93. The proportional odds model is a promising approach also for other indicator values and different regions as well as for other ordinal-scaled ecological parameters.

The TRM Model of Potential Natural Vegetation in Mountain Forests

Due to advances in spatial modeling and improved availability of digital geodata, traditional mapping of potential natural vegetation (PNV) can be replaced by ecological modeling approaches. We developed a new model to map forest types representing the potential natural forest vegetation in the Bavarian Alps. The TRM model is founded on a three-dimensional system of the ecological gradients temperature (T), soil reaction (R), and soil moisture (M). Within such a “site cube” forest types are defined as homogenous site units that give rise to forest communities with comparable species composition, structure, production and protective functions. The three gradients were modeled using regression algorithms with area-wide, high resolution geodata on climate, relief and soil as predictors and average Ellenberg indicator values for temperature, acidity and moisture of vegetation plots as dependent variables summarizing plant responses to ecological gradients. The resulting predictor-response relationships allowed us to predict gradient positions of each raster cell in the region from geodata layers. The three-dimensional system of gradients was partitioned into 26 forest types, which can be mapped for the whole region. TRM-based units are supplemented by 22 forest types of special sites defined by other ecological factors such as geomorphology, for which individual GIS rules were developed. The application of our model results in an intermediate-scale map of potential natural forest vegetation, which is based on an explicit function of temperature, reaction and moisture and is therefore consistent and repeatable in contrast to traditional PNV maps.

Environmental, Spatial and Structural Components in the Composition of Mountain Forest in the Bavarian Alps

A combined systematic and stratified sampling design was conducted in mountain forests of the Bavarian Alps to find the principal dimensions of compositional variation of vegetation and their environmental drivers. In 1,505 plots species composition, forest types and soil profiles were recorded. Data from 14 climate stations were included. As we hypothesized that the tree layer is more influenced by management than the understorey and that the former modifies the habitat of the latter, the two matrices were analysed separately and the species composition of the tree layer was used as a structural predictor variable for the understorey. We applied constrained ordination to reveal the main gradients in floristic composition and variance partitioning to examine the portions of climatic, edaphic, spatial and structural components. Ellenberg indicator values and a generalized linear model were used to test whether a significant spatial gradient exists from east to west, the main spatial extent of the investigation area. Forest types were used as an overlay to assess the underlying environmental factors. It turned out that explained variance of the tree layer was considerably lower than in the understorey. Tree layer composition was more influenced by climatic variables than by soil. In the understorey, edaphic and climatic variables contributed almost equally to explained variance, but the tree layer had an additional explanatory power. No continentality gradient could be detected within the investigation area. Plant communities were well separated along gradients of acidity, moisture, nutrients and climate, which broadly confirms the known gradients for montane and subalpine zonal forests in the region. The study provides a quantitative synthesis of the knowledge on a diverse set of community types, which has so far been subject to disparate and sectorial treatment in the Bavarian Alps.