Towards the reconstruction of subfossil vegetation: an unexpected plant record in Early Holocene sediments of a mire in NE Poland

We reconstructed a subfossil plant community, Sphagnum sect. Acutifolia-Carex, in the development of Borki mire located in NE Poland. The plant community existed in the Early Holocene, from the Preboreal until the middle of the Boreal periods. We found a co-occurrence of both ombrotrophy/oligotrophy and minerotrophy plant taxa indicators, as well as an intriguing concomitance of them with different preferences for acidity and moisture of the substratum. Statistically significant, non-random, positive associations were determined for several pairs of species where such dyads were formed by taxa typical of different habitats. Such a combination of taxa has not been reported, and hence this community does not have many equivalents in subfossil or modern phytocoenosis. Its occurrence at the studied mire supposedly resulted from specific local hydrological conditions during the Early Holocene.