Original paper

Journal of Paleolimnology

, Volume 45, Issue 3, pp 369-383

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Salvinia natans in medieval wetland deposits in Gdańsk, northern Poland: evidence for the early medieval climate warming

  • Joanna Święta-MusznickaAffiliated withDepartment of Plant Ecology, University of Gdańsk
  • , Małgorzata LatałowaAffiliated withDepartment of Plant Ecology, University of Gdańsk Email author 
  • , Józef SzmejaAffiliated withDepartment of Plant Ecology, University of Gdańsk
  • , Monika BaduraAffiliated withDepartment of Plant Ecology, University of Gdańsk


Large numbers of sub-fossil remains of the aquatic fern Salvinia natans (L.) All. have been found in several early medieval sites in Gdańsk, N. Poland. This record indicates a population expansion of this species around 7th–8th century A.D., similar to the recently observed rapid spread and high population dynamics of S. natans in northern Poland, which recent studies have attributed to climate warming. Our results suggest that in the Vistula deltaic area the S. natans expansion in the Early Middle Ages (7th–8th century A.D.) was similarly stimulated by climate warming, while its subsequent decline was mainly due to climate cooling, especially during the Little Ice Age. Warmer winters and springs and a longer growing season seem to be the most important factors forcing the expansion of S. natans in medieval times. According to our data, the co-occurrence of S. natans with other aquatic plant species was similar in both the medieval and present-day vegetation. Also, the high density of S. natans in the medieval population caused impoverishment of the local ecosystems in a way that has been observed in recent water bodies affected by invasive pleustophytes (free-floating plants).


Early medieval climate warming Palaeolimnology Palaeoecology Invasive plants Aquatic ecosystems Salvinia natans Vistula deltaic area