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SIGNIFICANCE OF RELIEF-FORMING ACTIVITIES BY CASTOR FIBER L. FOR THE EVOLUTION OF HOLOCENE FLOODPLAINS OF SMALL RIVER VALLEYS (RESULTS OF STUDIES CONDUCTED IN POLAND)

Snieszko Zbigniew, Miroslaw Rurek, Mariusz Rzetala

Abstract

In Poland, beavers have colonised all types of valley landscapes пїЅ from late glacial coastal lowlands and lake districts in the north of the country to upland and mountainous ones in the south. Studies of geomorphological effects of their presence in valleys of small rivers in the Oder and Vistula River basins have confirmed the results of earlier observations conducted in forest zones of North America and Europe. In Polish territory, effects of the changes related to the beaversпїЅ activities have been studied for at most a few decades. American researchers were the first to suggest the significant contribution of sediments from beaver ponds to the development of Holocene floodplains in small valleys. At the same time, they drew attention to the need to collect materials that would corroborate this thesis in different regions of the world. In recent years, more publications appeared on fossil traces of the beaversпїЅ activity during the Holocene. Still, there is a glaring disparity between the estimated size of the beaver population in the evergreen forest zone in the Holocene and the evidence of their effectiveness in transforming landscapes on the one hand, and geological records in Holocene alluvia on the other hand. Study results indicate that part of Holocene sediments in flood basins and part of the peats covering valley floors, which used to be interpreted as the effect of climate change (flooding associated with climate becoming wetter) or human-induced change, may in fact be related to beaver colonies that were common in the Holocene. During their studies of Holocene alluvia and peat bogs, and also as a result of their queries of archived excavation data, the authors gathered data that point to the prevalence of beavers in Poland since the beginning of the Holocene, and in some cases as early as the late Pleistocene. The authors focused on establishing the criteria that allowed them to distinguish filled-in beaver ponds among the alluvia of which the Holocene floodplain is built. The documentation includes excavated ponds and fossil dams, alluvia containing wood with beaver tooth marks and peat cores containing wood detritus. Methodical experiments were also conducted to test the suitability of the Detektor Duo ground penetrating radar for searching for fossil wood detritus clusters in peat bogs. The authors suggest that conclusions from previous studies of fossil beaver ponds be used to reinterpret the origins of some Holocene alluvial deposits, especially in valleys up to the fourth order in HortonпїЅs system.

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DOI resolver: doi.org/10.5593/sgem2017/11/s01.066

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