The impact of Wallachian settlement on relief and alluvia composition in small valleys of the Carpathian Mts. (Czech Republic)

•Impact of Wallachians on relief and deposits of mountain catchments was studied.•Relief and alluvia of mountain streams provide a good record for human impact.•Deforestation and grazing caused alluvia aggradation at river mouths.•Decline of human impact caused channel incision and sediment erosion.•Human impact and LIA impact amplified each other affecting relief development.

The impact of the Wallachian settlement on small mountain catchments has been studied at the example of Å korňanský and Hartisov Streams (Moravskoslezské Beskydy Mts, Western Outer Carpathians). Between the 16th and the 19th centuries the Wallachian people introduced pastoral management originating from the woodless Balkans to the forested mid-altitude mountain area under study. This area was subjected to rapid settlement, intense grazing in forests and slash-and-burn deforestation. To assess the geomorphic effects of Wallachian activity in the catchments studied, grain size, structure, organic matter content, and the plant macrofossil composition of the alluvia forming terrace levels in the mouths of the Å korňanský and Hartisov Streams were analysed. Radiocarbon dating, 137Cs and 210Pb analyses and dendrochronological dating were also applied to determine the age of the alluvia studied. The results were compared with land-use and land-cover changes recorded on archival maps and pictures, and with population changes in the study area. It was found that the two successive trends of catchment settlement and later depopulation have led to the development of inset terraces on the outlet fans of the Å korňanský and Hartisov Streams. In the study catchments both settlement/deforestation and depopulation/land abandonment occurred very rapidly which also caused abrupt geomorphic changes. Before human disturbance, fluvial erosion and the redeposition of older Pleistocene deposits predominated. As a result coarse, gravel alluvia were deposited within stream channels. The stage of massive overbank accumulation of fine-grained alluvia was a reflection of intensified delivery of slope material into valley floors from catchments deforested by the Wallachians. The later stage of vertical incision of channels resulted from the decrease of sediment supply from hillslopes to river channels during catchment depopulation and afforestation.