Long-term effects of environmental alterations in protected grasslands – Land-use history determines changes in plant species composition

Abstract

Nutrient-poor, semi-natural grasslands are among the most species-rich ecosystems across Europe. However, due to the transition from pre-industrial farming to modern agriculture, the extent of such grasslands has greatly decreased and the remaining patches have often suffered from habitat deterioration. Here, we analysed the effects of land-use and climate change as well as of nitrogen deposition on plant communities of dry (sand) (n = 118) and wet grasslands (n = 30) in a protected area, representative for the NE German young moraine landscape. Our study revealed that over a time period of 25 years, plant species composition in protected grasslands has changed considerably. Overall, plant species richness increased in both dry and wet grasslands from 1994 to 2019. The number of threatened species, however, decreased in dry but increased in wet grasslands. Land-use history was identified as the major driver of changes in species composition within the studied semi-natural grasslands. In wet grasslands, after >30 years of abandonment prior to the first survey, species-rich communities such as the Molinietalia have successfully been restored through the re-introduction of continuous, low-intensity management (mostly mowing once in late summer) shortly before the first survey. This has led to an increase of often threatened, light-demanding species of nutrient-poor wet grasslands. In dry grasslands, however, changes in vegetation were often contrary to those in wet grasslands; for example dry grasslands exhibited an increase in the nitrogen indicator value while it decreased in wet grasslands. Overall, open, nutrient-poor dry grasslands rich in stress-tolerant and often threatened species have been replaced by dense, more mesophytic grasslands with competitive generalists and some ruderal annuals. These successional changes were caused in particular by (i) an increase in abandonment on the least productive soils, (ii) undergrazing in permanent pastures and (iii) an insufficient time period since the re-introduction of grazing combined with a too low grazing pressure in new pastures on more productive soils. Nitrogen deposition was a further driver, especially on more acidic, dry soils. Additionally, grassland ruderalization was favoured by cropping of some plots and climate change since warm winters and severe summer droughts have led to an increase of annual ruderal species.