hide
Free keywords:
Eastern Poland
IndVal
Kohonen’s artificial neural network
Macrofossil
Oribatid mite
Palaeoecology indicator
Pollen
Self-organising map
Abstract:
Late glacial and Holocene environmental history of Lake Łukie and its catchment is reconstructed from the lake sediments. This shallow lake is situated in the marshy Polesie region in eastern Poland. Sediments began to accumulate in the lake in the Older Dryas. On the basis of macrofossils, pollen, and Oribatida remains, and with the use of Kohonen's artificial neural network (self-organising map, SOM), six stages (corresponding to subclusters X1, X2, X3 in cluster X, and Y1, Y2, Y3 in cluster Y) of the lake history were distinguished, and indicator taxa of each stage were identified from the indicator value (IndVal) index. During the transition period corresponding to the border between X and Y, the ecosystem transformed in the broad sense from the protocratic to mesocratic phase in a 5-point scale transformation of the landscape in the glacial–interglacial cycle. All the steps involved in post-glacial history succession during interglacial cycles include changes in climate, soil, and biotic interactions. Indicator taxa for the subsequent SOM subclusters X1, X2, and X3 are associated with the first phase of the protocratic glacial–interglacial cycle. The transformation that occurs on the level of cluster Y (subcluster Y1) is the mesocratic phase (ca. 9000–5000 14C age BP), which is characterised by high temperatures and development of closed forest (climax forest). Subcluster Y2 corresponds to the transformation of forest cover during the oligocratic phase (ca. 5000–3000 14C age BP), which is associated with decreasing forest share and deteriorating soils. Finally, subcluster Y3 can be associated with the telocratic phase, characterised by the influence of a more oceanic climate (from ca. 2500 14C age BP) with declining temperatures, higher humidity, and milder seasonal contrasts, which contributed to the development of more open vegetation and infertile soils. This stage also corresponds to an increased human activity and landscape transformation, such as from forests to cornfields and from wetlands to meadows. Interestingly, the currently strictly protected brittle naiad (Najas minor) was present in the lake during the Atlantic, Subboreal, and Subatlantic periods; however, this species is not listed as being part of the present vegetation and may have become extinct relatively recently.
