From the authors
In Poland the role of beavers in the Holocene evolution of valleys was recognised relatively late. In 2016 a book written by M. Rurek, Z. Śnieszko and M. Makohonienko titled Contemporary and fossil beaver ponds in small river valley on the area of Bory (North European Plain) was published by the Publishing House of the Kazimierz Wielki University in Bydgoszcz. It cited a relationship between the course of the Holocene evolution of small river valleys and beaver colonization. After the book was published, the team, composed of M. Rurek, Z. Śnieszko and M. Hojan, continued field work and desk studies. Since the 2016 edition contains only a brief summary and titles of figures in English, it was not suitable for readers who were not speakers of Polish. The present English language version also contains certain results of studies carried out by M. Rurek and Z. Śnieszko published in the above-mentioned Polish book as well as materials obtained as a result of continuing their studies with the participation of M. Hojan. We believe that the data collected so far allows us to present a new model of the evolution of small river valleys that in the Holocene period were inhabited by beavers in the last Pleistocene deglaciation zone in the North European Plain. The evolution of many valleys was determined by the presence of beavers and the effect of Holocene climate changes was relegated to a secondary position. In Poland beavers appeared in the late Pleistocene. In the Middle Ages they were subject to special protection in connection with their valuable fur and meat and the castoreum, that is, exudate from beaver’s castor sacs. In the 11th century, Bolesław Chrobry, king of Poland, imposed a ban on beaver hunts on the territories under his rule. At that time, the office of beaver hunt master (so-called castorarius), who supervised the territories inhabited by these animals, was established. In Poland the population of beavers has survived to these days in spite of the fact that in the 1950s there were only 130 of them. Now, their number is estimated at more than 130 thousand. Due to the relatively early decrease in the population of Castor fiber in many regions in Europe it was forgotten that in the past the European beaver was an inseparable element of the Holocene biome of the European forests and had a significant impact on the water regime in the catchments of this zone. In Poland, despite the recent publication of works on the effects of the present-day expansion of these rodents, there is still no interest in how they shaped the historical image of the valleys in the Holocene. To fill this gap, it is necessary to provoke discussion about effective methods of recognising the signs of beaver activity in Holocene sediments accumulated on the flood plain. We started our studies in small valleys (order 1 and 2 according to Strahler’s system) in the area where beavers appeared immediately after the last deglaciation and where they were significant landscape forming agents until the 19th century. We identified numerous circumstances pointing to a large share of beaver pond sediments in the structure of the studied sections of valleys. But we are not pioneers in this respect. American researchers formulated such findings as early as the first half of the 20th century. However, they were not supported by extensive studies of flood plain sediments in many catchment areas of the temperate forest zone. This was due to serious difficulties recognising sediments that without any doubt could be associated with the activity of beavers. The established criteria for recognising beaver pond sediments within our study area most likely do not exhaust all the possible methods of diagnosis. By publishing the results of our studies, we wish to take a position on research postulates about collecting comparative data from various areas that have already been formulated in reference literature. Works describing relict beaver ponds are still rare. Publishing the results of our modest studies, at the same time, we wish to suggest that, given the present state of knowledge, the old model explaining the evolution of valley bottoms in the zone of evergreen forests without taking the results of the activity of Castor fiber into account cannot be maintained any longer.