Martin Diekmann, Christian Andres, Thomas Becker, Jonathan Bennie, Volker Blüml, James M. Bullock, Heike Culmsee, Miriam Fanigliulo, Annett Hahn, Thilo Heinken, Christoph Leuschner, Stefanie Luka, Justus Meißner, Josef Müller, Adrian Newton, Cord Peppler-Lisbach, Gert Rosenthal, Leon J.L. van den Berg, Philippine Vergeer & Karsten Wesche
Semi-natural grasslands are among the most diverse vegetation types in Western and Central Europe, holding the world records in local plant species richness. They are characterized by a combination of low or moderate fertilization and extensive, continuous management. Owing to the introduction of agro-industrial farming, many semi-natural grasslands were either transformed into cropland or forest, or subjected to more intense land use practices, associated with increased addition of nutrients, the use of pesticides and sowing mixtures and, in wet areas, also drainage. In our study, we wanted to know in how far grasslands have changed over time, and whether their species richness has decreased due to changes in environmental conditions.
For this, we used studies of so-called permanent plots in which sites with old inventories of the plant species composition were re-surveyed to examine the changes in species composition and richness. By means of a literature search and by obtaining data through our scientific networks we were able to retrieve 23 data sets, most of which are from wet grasslands in Germany and from dry grasslands in the United Kingdom and Germany. All data sets were analyzed by the same type of statistical analysis.
In nine of the studies from wet grasslands, total species richness had declined, only in three studies there had been an increase (see the figure below). The species loss was even more pronounced for the wet grassland specialists. In both cases we found that, the longer the time between surveys was, the more species got lost.
With the exception of sites located in nature reserves, many wet grassland specialists had almost or completely disappeared, such as Senecio aquaticus (see photograph above). Many former wet grasslands were over the past decades transformed into species-poor sow meadows dominated by grasses (see photograph below). The main reason for the pronounced changes in the vegetation were drainage, fertilization and more intensive management.
In dry grasslands and other grassland types, total species richness did not consistently change, but also here the number of habitat specialists declined. Dry grasslands are most resistant to temporal changes, as they are water- and nutrient-limited and cannot be improved by fertilization (or can be, but to only a small extent).
The results of our study document the widespread deterioration of semi-natural grasslands, especially of those types that can easily be transformed into high production grasslands.
This is a plain language summary for the paper of Diekmann et al. published in the Journal of Vegetation Science.