Flora and habitat of potato pits on kame hills in north-eastern Poland

The research was carried out in north-eastern Poland in the vicinity of the village of Hacki (52 degrees 50 ' 00 '' N; 23 degrees 11 ' 20 '' E). This area is distinguished by an exceptionally numerous agglomeration of kames (10). Previous archaeological and soil research showed that kames have been inhabited by man from the iron age, and that the following stages of colonization are reflected in three levels of fossil soils. In modern times local people use the base of kames for the storage of potatoes over the winter. The potato pits are a cultural curiosity found only in this area. They are dug out in the cohesive, fine-grained substratum, which is the building material of kames, down to 1.5-2 m deep. Research plots (16) with a surface area of about 2-5 m(2) were established in the potato pits in 1990. In the summer of the same year 16 phytosociological surveys were performed and soil samples taken. The investigated habitats are characterized by very low humidity. The concentration of carbon in the samples from potato pits dug out at the foot of a kame hill (the site of a settlement in the past) results probably from the occurrence of soil from the Roman period. At the present time the pits are covered by poor ruderal flora (approx. 10 species in one phytosociological survey). It is distinguished from other communities of such type by a low participation of species occurring in the xerothermic grasslands.