Prior to the formation of the North Sea during the mid-Holocene, North-Western Europe was connected through the Doggerland landmass. Whilst it has been known for the past century that forests grew in Doggerland, it has not been clear how this environment compares to the surrounding European areas. Here, we reconstruct the palaeoecology of a river system from the Late Pleistocene to the late Holocene using sedimentary ancient DNA (sedaDNA) from 252 sediment samples from 36 cores spanning the length of the river system and headwater area. We determined that in low kinetic energy environments 95-98% of sedaDNA originates from local deposition and 2-5% is associated with influxed sediments, enabling the identification of secure deposits. High energy environments are insecure with 15-70% of sedaDNA associated with reworked and influxed sediment. Secure sediments reveal the presence of several tree species such as Alnus, Quercus, Ulmus and Corylus over 16000 years ago, and thermal indicator tree species like Tilia several thousand years earlier than has been recorded for surrounding European areas. In this area we also detect the presence of Pterocarya, previously unobserved since the Hoxnian. These observations are consistent with colonization from glacial refugia closer than the classic southern Europe refugia.
