Danish Grasslands Research Articles

Decline in large-seeded species in Danish grasslands over an eight-year period

To demonstrate possible community selection on seed size, a time-series analysis of cover data from 236 Danish grassland sites was performed in a linear model. Across four grassland habitat types and during an eight-year period, there was a significant decline in large-seeded species. Therefore, it was not possible to corroborate the initial hypothesis that a historical increase in nitrogen deposition and the observed vegetation changes towards taller and more competitive plant species favored plant species with large seeds. In the analysis, the continuous seed size variable was used to group plant species into functional types. This method was chosen in order to account for the sampling process of the cover data and is in contrast to most other analyses of trait selection, where the community weighted mean of the traits is used as the dependent variable.

Selection against ruderals in Danish grasslands over an eight-year period

In order to investigate what community selection forces are operating on Grime's CSR strategies in different semi-natural grassland habitats that were not subjected to successional processes, a time-series analysis of 2946 Danish grassland plots from an eight-year period with pin-point plant cover data was conducted. Grime's CSR strategies were used for grouping plant species into functional types, which were then treated as dependent variables in a time-series analysis. Across four grassland habitat types, there was significant selection against ruderal plant species during the eight-year period. Furthermore, the monitoring data indicated that the decreasing cover of ruderals may, in part be, due to reduced grazing pressure of large herbivores. As a consequence of the findings in this study and others, it may be suggested that increased disturbance, e.g. by large herbivores, is a suitable management strategies for grassland habitats.

Ongoing decline in insect-pollinated plants across Danish grasslands.

Loss of habitat, eutrophication and reduced grazing intensity are known drivers of landscape-level changes in plant species composition; however, consequences of the massive decline in insect abundance are still to be understood. Pollinator decline can reduce seed set in plants relying on insects for successful reproduction. This may result in a reduced recruitment of insect-pollinated plant species with associated changes in species composition. So far, large-scale studies addressing this issue have relied on few data points-typically consisting of 'historic' records of numbers of insect-pollinated plants compared to present-day records. Such comparisons can provide information as to whether the diversity of insect-pollinated plants has changed, but not whether the process is still ongoing. Here, we use nationwide monitoring data of plant species richness in Danish grasslands from the period 2004-2014, covering 244 grassland sites and encompassing more than 790 flowering plant species. We show an ongoing decrease in insect-pollinated, but not wind-pollinated, plant species across different habitat types. In both dry calcareous and Nardus grasslands, loss of insect-pollinated plants was greatest at sites with low grazing intensity. However, insect-pollinated plants also declined from sites with higher grazing intensity, and plants requiring more specialized insect pollination tended to decline most. In addition to changes in plant diversity driven by land-use intensification, loss of pollinators may also play a role in reducing the richness of insect-pollinated plants. Ongoing reduction in floral richness could further increase the threat to insects relying on these plants as a food source.

Indication of a reduction in the cover of thin‐leaved plants in Danish grasslands over an eight‐year period

AbstractQuestionAccording to leaf economics spectrum theory, the historic changes in several environmental factors, e.g. land use and nitrogen deposition, are expected to lead to selection of a change in the relative proportion of thin‐leaved and thick‐leaved plant species. However, it is generally unknown how fast plant communities respond to environmental changes.LocationDenmark.MethodsTime‐series analysis of Danish grassland pin‐point plant cover data from an eight‐year period.ResultsAcross four grassland habitat types, the cover of thin‐leaved plants was found to decrease significantly, but generally only limited trait selection was observed on leaf traits (specific leaf area [SLA] and leaf dry matter content [LDMC]). The mostly negative result may partly be due to the relatively conservative analysis, where the continuous plant trait variables are used for grouping plant species into functional types, which are then treated as dependent variables. This method was chosen in order to account for the sampling process of the vegetation data and is in contrast to most other analyses of trait selection, where it is the community‐weighted mean of the traits that is used as the dependent variable.ConclusionsOnly limited leaf trait selection was observed in semi‐natural grasslands that was not subjected to successional processes.

Survival and flowering of hybrids between cultivated and wild carrots (Daucus carota) in Danish grasslands

Many crop species are able to hybridize with related weedy or wild relatives, which could lead to transfer of cultivar genes, and among them transgenes, into wild populations. It is not clear, however, whether the hybrids and their descendants are able to survive and reproduce in natural habitats, as inherited cultivar traits may be maladaptive under such conditions. To test this, we produced hybrid (F(1)) seeds by controlled crosses between wild [see text for formula] and cultivated carrots (Daucus carota ssp. carota and ssp. sativa, respectively) and sowed them into three Danish grasslands of different age, in parallel with seeds of wild carrots. Replicate plots were sown in fall and spring. Survival and flowering of the emerging plants were monitored for the following three years. Both hybrid and wild carrots survived and flowered in highest frequency at a recently disturbed site, and much less at two older sites. Hybrids emerged in higher proportions than wild carrots in the first year and survived to similar or slightly lower frequencies at the end of the experiment. Hybrids flowered as frequently or slightly less frequently than wild plants, and developed fewer and smaller umbels. Despite a somewhat lower reproductive potential compared to wild carrots, first generation hybrids between cultivated and wild carrots are likely to survive and produce offspring in natural grasslands in Denmark. This, together with other studies, suggests that cultivar genes may transfer relatively easily into wild carrot populations.

Plant and arbuscular mycorrhizal fungal diversity – are we looking at the relevant levels of diversity and are we using the right techniques?

Plant and arbuscular mycorrhizal fungal diversity – are we looking at the relevant levels of diversity and are we using the right techniques?

Developing a classifier for the Habitats Directive grassland types in Denmark using species lists for prediction

Abstract. This paper describes the use of supervised methods for the classification of vegetation. The difference between supervised classification and clustering is outlined, with reference to their current use in vegetation science. In the paper we describe the classification of Danish grasslands according to the Habitats Directive of the European Union, and demonstrate how a supervised classification can be used to achieve a standardized and statistical interpretation within a local flora. We thereby offer a statistical solution to the legal problem of protection of certain selected habitat types. The Habitats Directive protects three types of Danish grassland habitats, whereas two remaining types fall outside protection. A classification model is developed, using available Danish grassland data, for the discrimination of these five types based on their species composition. This new Habitats Directive classification is compared to a previously published unsupervised classification of Danish grassland vegetation. An indicator species analysis is used to find significant indicator species for the three protected habitat types in Denmark, and these are compared to the characteristic species mentioned in the interpretation manual of the Habitats Directive. Eventually, we discuss the pros and cons of supervised and unsupervised classification and conclude that supervised methods deserve more attention in vegetation science.

Developing a classifier for the Habitats Directive grassland types in Denmark using species lists for prediction

This paper describes the use of supervised methods for the classification of vegetation. The difference between supervised classification and clustering is outlined, with reference to their current use in vegetation science. In the paper we describe the classification of Danish grasslands according to the Habitats Directive of the European Union, and demonstrate how a supervised classification can be used to achieve a standardized and statistical interpretation within a local flora. We thereby offer a statistical solution to the legal problem of protection of certain selected habitat types. The Habitats Directive protects three types of Danish grass- land habitats, whereas two remaining types fall outside pro- tection. A classification model is developed, using available Danish grassland data, for the discrimination of these five types based on their species composition. This new Habitats Directive classification is compared to a previously published unsupervised classification of Danish grassland vegetation. An indicator species analysis is used to find significant indicator species for the three protected habitat types in Denmark, and these are compared to the characteristic species mentioned in the interpretation manual of the Habitats Direc- tive. Eventually, we discuss the pros and cons of supervised and unsupervised classification and conclude that supervised methods deserve more attention in vegetation science.

On the seed mass–regional abundance relationship: the Eriksson & Jakobsson (1998) model does not apply to Danish grasslands

Eriksson & Jakobsson (1998) developed a heuristic model predicting species regional abundance from their seed mass. The model took as a starting point the diversity of seed masses found in single communities (Westoby etal. 1996). This phenomenon does not, however, fit the theoretical predictions that seeds of a given mass will be fittest in a given environment (Smith & Fretwell 1974). Rees & Westoby (1996) showed that a game-theory approach would allow for variation in seed mass within communities. The ErikssonJakobsson model had two basic assumptions: (i) in a given microsite, a seedling emerging from a large seed will out-compete one from a small seed (a game rule supported empirically by Eriksson (1997) and Turnbull et al. (1999)), and (ii) that there is a trade-off between seed mass and seed number (Harper 1977) (empirically supported by Shipley & Dion (1992), Turbull et al. (1999) and Jakobsson & Eriksson (2000)). In other words, it assumes there to be an inverse relationship between colonization ability (large, but few seeds) and dispersability (many, but small seeds). The model predicts that species with intermediate-sized seeds will gain larger regional abundance than either largeror smaller-seeded species. Eriksson & Jakobsson (1998) identified the species with intermediate-sized seeds by use of the absolute deviance in log seed mass from the community median log seed mass. Data from Danish grasslands were used in an empirical test of the model's validity, both by phylogenetically corrected and traditional cross-species analysis.

Deficit in community species richness as explained by area and isolation of sites

Abstract . The potential community species richness was predicted for 85 patches of seminatural grassland in an agricultural landscape in Denmark. The basis of the prediction was a very large dataset on the vegetation, soil pH and topography in Danish grasslands and related communities. Species were inserted into potential species pools according to their preferences regarding soil acidity and water availability (expressed as potential solar irradiation), and to the ranges in these two factors observed in each grassland patch. The difference between the predicted and the observed patch‐level species richness, community richness deficit, varied considerably among patches. Community richness deficit exhibited a negative relationship with patch area, and for small patches a positive relationship with patch isolation.

Distribution of VA mycorrhizal endophytes amongst plants from a Danish grassland community

Roots from four co-occurring plant species were examined for the infection anatomy of their VA mycorrhizal (VAM) endophytes at three harvests. From the same location, roots from seven plant species were used to inoculate cucumber plants ( Cucumis sativus L.). The endophytes recovered on these bait plants were characterized on the basis of their isozyme pattern after polyacrylamide gelelectrophoresis (PAGE). The presence of particular groups of endophytes was dependent on the host plant and the harvest time. Difference in isozyme pattern from the bait plants indicates that different plant species, although growing together, may not share VAM endophytes.