Vegetation changes in urban grasslands over 25 years in the city of Zurich, Switzerland

Abstract

Many studies have demonstrated significant alterations in the species composition of grasslands in Central Europe over the past decades due to multiple drivers of anthropogenic environmental change. Most such studies deal with dry, acidic, wet or alpine grassland types, while little is known about changes in mesic grasslands, particularly in urban areas. To investigate the effects of anthropogenic environmental change on such grasslands, we resurveyed a selection of plots in the city of Zurich (Switzerland) approximately 25 years after their original recording. First, we checked whether 241 extensively used mesic grasslands (belonging to the Arrhenatheretalia elatioris) in the city were still grasslands, and whether their management had changed. Then we resurveyed a representative subset of 30 quasi-permanent plots of 50 m2. We tested whether biodiversity metrics, mean ecological indicator values, community weighted means (CWMs) of functional traits or the presence of individual vascular plant species had changed. We found that 15% of the original grasslands had been lost due to changes in land use during this period. Of the remaining grasslands, most of the former meadows were still mown, while many of the former pastures had been transformed into meadows. Measures of alpha diversity had not changed significantly for the 30 plots. However, species composition now indicated nutrient poorer, less base-rich and less ruderal site conditions, while CWMs of specific leaf area (SLA) had decreased and that of seed mass increased. In stands that were managed by mowing in both periods there was practically no change, while there was a pronounced change in those that had been transformed from grazing to mowing. In general, five species showed a significant increase and 16 species a significant decrease in frequency, with no obvious ecological difference between winners and losers. Alien species were rare in both periods and showed hardly any trend, except Veronica persica, which became rarer. In conclusion, more extensively used grasslands have survived to date than would be anticipated in such a rapidly growing city as Zurich. Their quality has hardly changed during the past Manuscript received 09 May 2021, accepted 07 August 2021 Published online 31 October 2021 Co-ordinating Editor: Valentin Klaus 424 quarter century, and if changes occurred, they are rather attributable to the intentional change of management from grazing to mowing. The relatively good ecological state of these urban grasslands might be due to a lower agricultural land use pressure than outside urban areas, as well as a constant management of many of these grasslands with a conservation focus. By maintaining these grasslands in their current state, they may have the potential to contribute to the conservation of biodiversity in urban areas.