Tracing changes in the extent of urban grasslands through space and time

Urban grassland restoration has the potential to mitigate biodiversity loss in cities, but effective restoration planning calls for an accurate understanding on how and why the extent of grasslands in cities changes through time and ongoing urbanization. This can help assess regional baselines for grassland restoration and identify urban grasslands of high biodiversity value, but also more broadly to reflect on the aims and outcomes of restoration in different parts of the city. In this paper, we use historical and contemporary spatial data to quantify the extent of different types of grasslands across the late 19th-century and present-day Helsinki capital region, Finland. We assess the overall and spatially explicit changes in grassland extent between these periods and link these changes to patterns of land cover change, with spatial overlap analyses. Our results suggest that urban green infrastructure supports many types of contemporary grasslands, but to a smaller extent and primarily in different places compared to the historical semi-natural grasslands in the 19th-century landscape preceding urban development. Changes in grassland extent in the study region comprise local increases and decreases between the two time periods examined, with land cover changes related to urbanization underlying both of these changes. Grasslands that remain in the study region are dispersed across a diverse set of land cover types, with urban land cover such as parks, sports fields, and road verges hosting the majority of contemporary grasslands. Our results help identify diverse pathways for fostering biodiversity typical to grasslands in cities.