Questions:To what extent does the long-term process of grassland succession reflect changes in nutrient availability or other effects of grassland history? Plant communities in ancient, semi-natural pastures include many species associated with nutrient-poor soils. However, semi-natural pasture communities can also develop on previously arable sites -as nutrient levels decline over time. In Europe, Ellenberg N-values represent species' overall nutrient preferences and are often used as a proxy for soil nutrient availability. But how well do N-values actually reflect species' relationships with measured nutrient concentrations during grassland succession?Location: A successional series of grazed, previously arable to ancient, grasslands on the Baltic island of Öland, Sweden. Methods:We collected data on community composition and soil nutrient (phosphorus, ammonium, nitrate) concentrations. We used Bayesian joint-community modelling to parameterize species' relationships with nutrients and grassland age, and quantified the relative contributions of the variables. Species responses were then compared with Ellenberg N-values. Results:Phosphorus was the best explanatory variable for most species. However, species occurrences were not simply explained by gradients in particular nutrients, but by combinations of different nutrients and grassland age. There was overall agreement between N-values and species' nutrient responses -although the occurrences of species with identical N-values may be explained by different nutrients.Species with high and low N-values represent more reliable nutrient indicators than intermediate-N species, but their occurrences also reflect other factors that, as with nutrients, depend on the grassland age. Conclusions:Our results confirm that Ellenberg N provides a robust indication of the overall nutrient preferences of individual grassland species. However, in grassland sites developing on previously arable land -where nutrient availability is strongly associated with habitat age -N-values may represent an integrated response not only to nutrients but also to other historical processes that drive grassland community assembly. |

No abstract

The NDVI is a remotely sensed vegetation index that is frequently used in ecological studies. There is, however, a lack of studies that evaluate the ability of the NDVI to detect fine‐scale variation in grassland plant community composition and species richness. Ellenberg indicators characterize the environmental preferences of plant species—and community‐mean Ellenberg values have been used to explore the environmental drivers of community assembly. We used variation partitioning to test the ability of satellite‐based NDVI to explain community‐mean Ellenberg nutrient (mN) and moisture (mF) indices, and the richness of habitat‐specialist species in dry grasslands of different ages. The grasslands represent a gradient of decreasing soil nutrient status. If community composition is determined by the responses of individual species to the underlying environmental conditions and if, at the same time, community composition determines the optical characteristics of the vegetation canopy, then positive relationships between the NDVI and mN and mF are expected. Many grassland specialists are intolerant of nutrient‐rich soils. If specialist richness is negatively related to soil‐nutrient levels, then a negative association between the NDVI and specialist richness is expected. However, because grassland community composition is not only influenced by abiotic variables but also by other spatial and temporal drivers, we included spatial variables and grassland age in the statistical analyses. The NDVI explained the majority of the variation in mF, and also contributed to a substantial proportion of the variation in mN. However, variation in specialist richness and the lowest values of mN were explained by grassland age and spatial variables—but were poorly explained by the NDVI. Synthesis and applications. The NDVI showed a good ability to detect variation in plant community composition, and should provide a valuable tool for assessing fine‐scale environmental variation in grasslands or for monitoring changes in grassland habitat properties. However, because the concentration of grassland specialists not only depends on environmental variables but also on the age and spatial context of the grasslands, the NDVI is unlikely to allow the identification of grasslands with high numbers of specialist species.

We use Helianthemum oelandicum subsp. oelandicum as a model for studies of mechanisms shaping the diversity in a rapidly radiating lineage of the H. oelandicum aggregate. Locally, correlations between drainage conditions (using GIS to measure variation in the micro-topography on the more or less horizontal bedrock) and frequency of alleles of Mendelian genes for pubescence indicated that hairs are markers of adaptation to the unique environmental conditions (drought and periodic flooding) on the alvar habitats of Öland. An allozyme study showed that 1 and 4% of the genetic diversity is partitioned among two varieties and natural populations, respectively. FST for hair alleles was up to ten time greater than FST for allozymes. Öland rose above sea level after the LGM, which makes it possible to date the onset of the post-glacial diversification on the island. Only two, mainly allopatric, plastid DNA haplotypes were detected, H1 and H2. The southern Helianthemum oelandicum subsp. oelandicum var. canescens has only H1, whereas the more widespread var. oelandicum possesses both haplotypes. A restricted occurrence of haplotype H1 in the core area of var. oelandicum in the central Öland, coincided with the highest elevation on the island, probably representing the post-glacial arrival of the species on the island.