Long-term vegetation changes in Nardus grasslands indicate eutrophication, recovery from acidification, and management change as the main drivers

By Cord Peppler-Lisbach, Nils Stanik, Natali Könitz & Gert Rosenthal

Flowering aspect in spring of species-rich Nardus grasslands in one of the re-survey plots that maintained its high biodiversity level (Rhön Mountains, Central Germany). Photo credit: Nils Stanik.

The environment around us changes continuously and almost everywhere. Vegetation changes over the years often happen very gradual and require a detailed and extended view to be unveiled. For example, the gain or loss of single species may happen slowly, when growing conditions become more and more (un)favourable. In order to uncover these changes, we need long-term studies, in which the previously documented vegetation and environmental conditions are compared with the current situation.

Species-rich grasslands are an important part of our biotic environment and are already in the focus of biodiversity protection around the world. They not only harbour a high number of threatened species but also provide essential ecosystem services to the wider community. One typical type of these grasslands on acid, nutrient-poor soils are Nardus grasslands that are characterised by matgrass (Nardus stricta) and other low-productive plant species. Despite their formal protection under European laws, their geographical distribution declined considerably over the last decades. Whereas vegetation changes in these grasslands and their reasons are well documented in the Atlantic climate region of Western Europe, we have only a little knowledge about recent vegetation changes in this grassland type in the Continental climate region of Europe.

In our study, we re-surveyed vegetation plots in two mountain regions in Central Germany, which had been initially surveyed in 1971 and 1986/1987. Our aim was to detect long-term vegetation changes and to investigate whether the underlying drivers of potential vegetation changes correspond to those identified in Western Europe. To associate changes to potential drivers, we compared the past and current soil conditions and management of the plots. Moreover, we analysed data on atmospheric deposition of Nitrogen and Sulphur, which are important drivers for the biodiversity of grasslands.

The comparison of both photographs shows an increase in nutrient-demanding species (e.g. Trifolium pratense) and a decrease in dwarf-shrubs (i.e. Calluna vulgaris). The picture on the left documents the status of the plot at its initial survey in 1986 and the one on the right documents the status at its re-survey in 2012. Photo credit: Cord Peppler-Lisbach (left) and Natali Könitz (right).

Consistently across our study regions, we found considerable changes in the vegetation of Nardus grasslands, which could be linked to different environmental drivers. For instance, increased nutrient-demanding species from agricultural grasslands and a decrease of low-nutrient indicator species indicated rather clear signs of nutrient enrichment by Nitrogen (Figure 2). The vegetation response to less acidic conditions, after a drastic decline of atmospheric Sulphur deposition, was the increase in soil pH and the decline of acid-tolerant species. Insufficient management contributed additionally to the vegetation changes because fallow indicator species were favoured and small-growing herbaceous species declined accordingly. In both regions, changes in soil pH and management had the most significant influence on changes in total species richness and species composition.

Overall, the findings of our study regions indicate significant signs of nutrient enrichment by atmospheric Nitrogen pollution, a trend towards less acidic conditions of the soil and insufficient management to be responsible of the detected changes. Those correspond to reports of vegetation changes in the Atlantic region of Europe and highlight the large-scale validity of processes that influence vegetation changes in Nardus grasslands of Europe.

The study was supported by financial resources of the University of Kassel and the University of Oldenburg, Germany.

This is a plain language summary for the paper of Peppler-Lisbach et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12513).  Nils Stanik and Cord Peppler-Lisbach prepared the post.