The palaeoecology of Alnus (alder) and the Postglacial history of floodplain vegetation. Pollen percentage and influx data from the West Midlands, United Kingdom

Abstract

SUMMARY: The Postglacial history of Alnus is of particular relevance to the palaeoecology of wetlands and floodplains. The ecological histories of floodplain sites differ from those on dry‐land or from hydroseres. This paper uses pollen percentage and influx data to investigate floodplain succession and woodland development on floodplains in the West Midlands, the primary site being Wilden Marsh near Stourport, Worcestershire. The floodplain at Wilden probably underwent a three‐phase succession during the early Postglacial; Betula was replaced by Salix spp. which were out‐competed by Alnus. Alnus was present prior to its expansion, which is seen as the result of increasing soil stability, pedogenesis and decreased free drainage related to floodplain development and not necessarily to climatic change or anthropogenic disturbance. During the late Postglacial Alnus declines and Salix frequently increases again due to floodplain deforestation and utilisation, which was partly facilitated by altered soil conditions caused by hydrological change. The advantages of small floodplain sites for the differentiation of vegetation pattern is illustrated by the identification of a non‐floodplain pollen component dominated by Tilia.