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Abstract 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.
Löfgren et al. (Fri,) studied this question.