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

Abstract

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 presentday 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).

The comparison of archaeobotanical data and the oldest documentary records (14th–15th century) of useful plants in medieval Gdańsk, northern Poland

“…The study covered the areas of Główne Miasto (the Main Town), Stare Miasto (the Old Town) as well as Wyspa Spichrzów (Granary Island). Research problems deal with the reconstruction of the local environment and its transformation in the course of city development (Latałowa et al 2009;Ś więta-Musznicka et al 2011Ś więta-Musznicka et al , 2013 and the history of exploitation of useful plants from the early Middle Ages until well into the modern period. Within the latter, issues such as the plant foods in the diets of different social classes in different historical periods and in different parts of the town, or the trade in plants, including the import of luxury goods, were thoroughly examined (Badura 2003(Badura , 2011Latałowa et al 2007).…”

Survival and reproduction of the aquatic fernSalvinia natans(L.) All. during expansion in the Vistula Delta, south Baltic Sea coast

“…In the Gdan´sk area, close to the western edge of the delta, the plant was sparse in the 5th and 6th centuries and massively abundant in the 7th and 8th centuries. These data come from palaeoecological studies carried out on archaeological sites distributed within the historical area of the city of Gdan´sk (S´wie ta- Musznicka et al 2011). Temperatures along the southern coast of the Baltic Sea were higher in the latter than in the former period (Seppa¨and Poska 2004;Sillasoo et al 2009).…”

New palaeoclimate reconstructions based on multidisciplinary investigation in the Ferdynandów 2011 stratotype site (eastern Poland)

“…The spe cies in hab its mainly eutrophic wa ters of large or shal low and slow-flow ing rivers, oxbow lakes, ditches and chan nels (Cas per and Krausch, 1980). For the de vel op ment of its megaspores, it re quires tem per atures of win ter months not fall ing be low 0°C (OEwiêta-Musznicka et al, 2011).…”