Twenty-two years of vegetation succession on the constructed Danish Island Peberholm.

Peberholm is a constructed Danish island in the Øresund strait. It was primarily constructed by calcareous clay from the sea floor, and is traversed by a highway and a railway. Being constructed from material without a seed bank, Peberholm constituted a good opportunity to study primary succession in an anthropogenic context. In this study, data from a survey of the vascular plant community of Peberholm was studied. The data span over a 22 year-period, between 1999 and 2020. The development of the flora was analysed with regards to indicators for environmental factors and vegetation types, as well as occurrence of alien species or species of conservation concern. Peberholm experienced a rapid succession during its first five years. The effects of the initial ground disturbance quickly wore off, resulting in a relative decline in plant communities associated with ruderal land. These highly anthropogenic habitats were replaced with grasslands. The shrubification also began early on. The rapid initial changes were then replaced with a much slower but also more continuous change, resulting in the development of both more natural grasslands and an increased shrubification. Although several rare or threatened species colonized Peberholm from the beginning, the conservation value of the flora on a whole increased during the succession process of forming more natural vegetation types. The succession process demonstrated at Peberholm has more in common with the succession at urban soils than with naturally occurring primary succession