Deciphering Sudetic landscape history by using alluvial geoarchives: Holocene environmental changes at Hala Izerska, SW Poland

• First high-lying multiproxy alluvial record for the western Sudetes. • Extensive findings of subfossil tree remains in a stream valley. • Evidence on Holocene sedimentation, forest structure and human impact. • Long-term persistence of a local spruce-forest belt is reconstructed. The potential of alluvial geoarchives for revealing the Holocene landscape history of a Central European low mountain range was systematically evaluated. Sedimentary stream sections and their surroundings in the headwaters of the Izera river at an altitude of approx. 830 m a.s.l. were analysed. An interdisciplinary approach was applied, using data from sedimentology, geochemistry, applied geophysics, palaeobotany, dendrochronology, and historical sciences. Two 250 cm-thick profiles show a variety of alluvial sediment types, including fluvial gravel, sand and silt, lacustrine silt, and peat. Subfossil wood, i.e. coarse woody debris consisting of spruce, was found in certain layers in the profiles as well as in the surrounding stream sections. It dates from the mid- to the late Holocene. Palynological and radiometric data show that the alluvial fillings were formed since the turn of the early to the mid-Holocene. Forest phases were synthesised from the locally available pollen data, which prove a local dominance of spruce forests since the Atlantic biozone. First anthropogenic impulses became evident in the Subboreal in the form of grazing indicators. Human-induced changes in the tree species composition did not take place before the late Subatlantic, i.e. in the 13th century. Historical documents point to the very late clearing of the local mountain forest in the 17th century and the establishment of a scattered settlement. The obtained chronologically long alluvial record since the mid-Holocene represents a new feature compared to the stream fillings previously investigated in the adjacent low mountain ranges. The studied alluvial geoarchive complements well the long-term environmental record derived from peat-bogs in the region.