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The evolution of the late Holocene environments has been reconstructed on the basis of multiproxy studies of peat sequences. The vegetation response to short-period climate fluctuations has been traced. Early in the late Holocene there were birch forests with oak and other broadleaf trees; vast areas were occupied by forb meadows. Under cooling (3250 yr BP) the shrub pine (Pinus pumila) became the landscape-forming species, and since 2490 yr BP Selaginella selaginoides appeared in abundance. The Little Ice Age was marked by the disappearance of broadleaf trees and widely spread heath land communities. The higher stands of the lake level were related to warmings (3660-3590; 3450-3180; 2960-2840; 2410-2260 cal yr BP). Shallowing coincided with short-term coolings (3590-3450; 3180-2960; 2840-2410; 2260-2150 cal yr BP) marked by reduced precipitations. The dune ridge formation began during the longest cooling accompanied by a minor regression. The dunes were stabilized and a paleosol developed similar to 2340-2260 yr BP. A younger generation of eolian sands developed during the Little Ice Age. An ecological effect of volcanic ashfalls has been estimated. The local biotic components seem to have been most afflicted by the eruption in the north of Iturup in similar to 2100-2300 cal yr BP, when CKr tephra up to 30 cm thick was deposited. The ages of 4 strongest tsunamis that occurred over the last 3660 years were determined. They appeared to be related to the earthquakes with focuses close to Urup Island or south of it. The lake microflora shows ecological effect of the marine water invasions.