Versuche zur Beweidung von Bergwiesen im Harz

Scheidel, U.; Bruelheide, H.: Experimental studies on the effect of cattle grazing of montane meadows in the Harz Mountains.- Hercynia N.F. 37 (2004): 87–101.Montane meadows in the Harz Mountains have traditionally been mown for hay making. In the last decades, this type of landuse has been steadily declining which led the nature conservation authorities to search for alternative types of management, such as cattle grazing. As the effects of cattle grazing on montane meadows were largely unknown, an experiment was carried out in a meadow near Bad Lauterberg in the southern Harz Mountains. This meadow has been grazed by cattle since 1999 following some decades of irregular use of low intensity. In the same year, three plots in each of four different vegetation types were established to compare the vegetation of grazed plots to manually mown and abandoned areas for five subsequent years. In general, changes in the vegetation during the course of the experiment were relatively small and to a large extent weather-dependent. The most important management effects were the reduction of the litter layer and the reduced dominance of species which profit from abandonment such as Rubus idaeus, Thelypteris limbosperma and Galeopsis tetrahit. In this respect, mowing was more effective than grazing. At wet sites and in remote areas that were only grazed with low intensity grazing effects did not differ from abandoned use. However, clearly negative effects of grazing could also not be detected. The conclusion of our study is that grazing as a management practice in montane hay meadows involves the risk of being not effective. Larger time spans than five years are needed to detect significant grazing effects compared to abandoned use. Activities to improve the effectiveness of grazing are discussed.Die Hercynia publiziert Originalbeiträge mit dem Schwerpunkt Ökologie (mit ihren vielseitigen Aspekten der Biodiversität), Botanik, Zoologie, Geologie und Geografie, den anwendungsorientierten Bereichen des Natur- und Umweltschutzes, sowie der Land- und Forstwirtschaft

Positive feedbacks and alternative stable states in forest leaf types

The emergence of alternative stable states in forest systems has significant implications for the functioning and structure of the terrestrial biosphere, yet empirical evidence remains scarce. Here, we combine global forest biodiversity observations and simulations to test for alternative stable states in the presence of evergreen and deciduous forest types. We reveal a bimodal distribution of forest leaf types across temperate regions of the Northern Hemisphere that cannot be explained by the environment alone, suggesting signatures of alternative forest states. Moreover, we empirically demonstrate the existence of positive feedbacks in tree growth, recruitment and mortality, with trees having 4–43% higher growth rates, 14–17% higher survival rates and 4–7 times higher recruitment rates when they are surrounded by trees of their own leaf type. Simulations show that the observed positive feedbacks are necessary and sufficient to generate alternative forest states, which also lead to dependency on history (hysteresis) during ecosystem transition from evergreen to deciduous forests and vice versa. We identify hotspots of bistable forest types in evergreen-deciduous ecotones, which are likely driven by soil-related positive feedbacks. These findings are integral to predicting the distribution of forest biomes, and aid to our understanding of biodiversity, carbon turnover, and terrestrial climate feedbacks

Predator diversity and abundance provide little support for the enemies hypothesis in forests of high tree diversity

Peer reviewedPublisher PD

Diversity and distribution of Raunkiær's life forms in European vegetation

Aims: The Raunkiær's system classifies vascular plants into life forms based on the position of renewal buds during periods unfavourable for plant growth. Despite the importance of Raunkiær's system for ecological research, a study exploring the diversity and distribution of life forms on a continental scale is missing. We aim to (i) map the diversity and distribution of life forms in European vegetation and (ii) test for effects of bioclimatic variables while controlling for habitat-specific responses. Location: Europe. Methods: We used data on life forms of 8883 species recorded in 546,501 vegetation plots of different habitats (forest, grassland, scrub and wetland). For each plot, we calculated: (i) the proportion of species of each life form and (ii) the richness and evenness of life forms. We mapped these plot-level metrics averaged across 50 km × 50 km grid cells and modelled their response to bioclimatic variables. Results: Hemicryptophytes were the most widespread life form, especially in the temperate zone of Central Europe. Conversely, therophyte and chamaephyte species were more common in the Mediterranean as well as in the dry temperate regions. Moreover, chamaephytes were also more common in the boreal and arctic zones. Higher proportions of phanerophytes were found in the Mediterranean. Overall, a higher richness of life forms was found at lower latitudes while evenness showed more spatially heterogeneous patterns. Habitat type was the main discriminator for most of the responses analysed, but several moisture-related predictors still showed a marked effect on the diversity of therophytes and chamaephytes. Conclusions: Our maps can be used as a tool for future biogeographic and macro-ecological research at a continental scale. Habitat type and bioclimatic conditions are key for regulating the diversity and distribution of plant life forms, with concomitant consequences for the response of functional diversity in European vegetation to global environmental changes

Mycorrhizal associations modify tree diversity-productivity relationships across experimental tree plantations

Decades of studies have demonstrated links between biodiversity and ecosystem functioning, yet the generality of the relationships and the underlying mechanisms remain unclear, especially for forest ecosystems. Using 11 tree-diversity experiments, we tested tree species richness–community productivity relationships and the role of arbuscular (AM) or ectomycorrhizal (ECM) fungal-associated tree species in these relationships. Tree species richness had a positive effect on community productivity across experiments, modified by the diversity of tree mycorrhizal associations. In communities with both AM and ECM trees, species richness showed positive effects on community productivity, which could have resulted from complementarity between AM and ECM trees. Moreover, both AM and ECM trees were more productive in mixed communities with both AM and ECM trees than in communities assembled by their own mycorrhizal type of trees. In communities containing only ECM trees, species richness had a significant positive effect on productivity, whereas species richness did not show any significant effects on productivity in communities containing only AM trees. Our study provides novel explanations for variations in diversity–productivity relationships by suggesting that tree–mycorrhiza interactions can shape productivity in mixed-species forest ecosystems

Evenness mediates the global relationship between forest productivity and richness

1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions

Forest age and plant species composition determine the soil fungal community composition in a Chinese subtropical forest

Non peer reviewedPublisher PD

Ellenberg-type indicator values for European vascular plant species

Aims: Ellenberg-type indicator values are expert-based rankings of plant species according to their ecological optima on main environmental gradients. Here we extend the indicator-value system proposed by Heinz Ellenberg and co-authors for Central Europe by incorporating other systems of Ellenberg-type indicator values (i.e., those using scales compatible with Ellenberg values) developed for other European regions. Our aim is to create a harmonized data set of Ellenberg-type indicator values applicable at the European scale. Methods: We collected European data sets of indicator values for vascular plants and selected 13 data sets that used the nine-, ten- or twelve-degree scales defined by Ellenberg for light, temperature, moisture, reaction, nutrients and salinity. We compared these values with the original Ellenberg values and used those that showed consistent trends in regression slope and coefficient of determination. We calculated the average value for each combination of species and indicator values from these data sets. Based on species’ co-occurrences in European vegetation plots, we also calculated new values for species that were not assigned an indicator value. Results: We provide a new data set of Ellenberg-type indicator values for 8908 European vascular plant species (8168 for light, 7400 for temperature, 8030 for moisture, 7282 for reaction, 7193 for nutrients, and 7507 for salinity), of which 398 species have been newly assigned to at least one indicator value. Conclusions: The newly introduced indicator values are compatible with the original Ellenberg values. They can be used for large-scale studies of the European flora and vegetation or for gap-filling in regional data sets. The European indicator values and the original and taxonomically harmonized regional data sets of Ellenberg-type indicator values are available in the Supporting Information and the Zenodo repository

Implementing the formal language of the vegetation classification expert systems (ESy) in the statistical computing environment R

Aims: The machine-readable formal language of classification expert systems has become a standard for applying plot assignment rules in vegetation classification. Here we present an efficient algorithm implementing the vegetation classification expert system in the statistical programming language R. Methods: The principal idea of the R implementation is to solve the assignments to vegetation types not sequentially plot by plot but to parse the assignment rules into (nested) components that each can be evaluated by simultaneous vector-based processing of all plots in a database. Results and conclusions: We demonstrate the algorithm taking the EUNIS classification expert system of European habitat types (EUNIS-ESy) as an example. The R code version of the vegetation classification expert system is particularly useful in large vegetation-plot databases because it solves all logical operations vector-wise across all plots, allowing for efficient evaluation of membership expressions and formulas. Another advantage of the R implementation is that membership formulas are not only readable but can also be produced as a machine-written result, for example as the output of classification algorithms run in R.Publikationsfonds ML

Nitrogen content of herbarium specimens from arable fields and mesic meadows reflect the intensifying agricultural management during the 20th century

Arable fields and mesic meadows have been affected by intensifying agricultural management and nutrient input during the 20th century, but direct evidence for the long-term impact of intensification on plant nutrient contents remains scarce. Non-destructive novel spectroscopic methods can produce such data from herbarium specimens, making it possible to investigate how contents of leaf nutrient traits, especially nitrogen and phosphorus, changed over the last century, and what role habitat type and management practices play. We carried out a resurvey study of functional traits in arable field and mesic meadow communities. We used specimens from two German herbaria with a high coverage of their local floras: the herbaria Senckenberg Görlitz and Senckenberg Haussknecht in Jena. Following specimen information, the same plant species were resampled in the field in 2022 at the same locations. We employed near-infrared spectroscopy to predict leaf nitrogen, phosphorus and carbon content of herbarium and field specimens. Nutrient content changes over time were compared with public records of regional P and N fertilization. Overall, 1270 specimens of 76 species from both herbarium and field were studied, the oldest from the 19th century. Leaf nitrogen and the leaf nitrogen:phosphorus ratio increased significantly through time, while leaf phosphorus and carbon content decreased significantly over time. Arable field species showed a stronger response in leaf phosphorus content and leaf nitrogen:phosphorus ratio than mesic meadow species. The total amount of nitrogen or phosphorus fertilizer applied per year on a regional scale was found to be significantly correlated with the respective leaf nutrient content levels. Synthesis: Our study shows a long-term increase of leaf nitrogen in the studied habitats, paralleling increased chemical fertilizer applications in Germany. Our data indicate a shift from predominantly N-limited towards more P-limited growth conditions. The stronger response of species from arable fields compared to species from mesic meadows could indicate a faster adjustment to environmental pressures. This study thus also serves to showcase the potential of the combination of herbarium collections and NIR spectroscopy