Changes in the Soil and Vegetation Cover on Small Islands of the Empress Eugénie Archipelago (Peter the Great Gulf, Sea of Japan) in the Holocene

Abstract

Geobotanical, soil, and biostratigraphic studies have been conducted on small islands of the Eugénie Archipelago to assess the current state of their ecosystems. The main factors determining the soil and vegetation cover composition, structure, diversity, and dynamics in the Holocene were multidirectional climatic fluctuations caused by variations in insolation. These variations resulted in a restructuring of the atmospheric and seawater circulation and in sea level fluctuations. It is established that, in warm epochs, the area covered by forests was increasing, and broad-leaved forests with high species richness predominated; during cold phases, the tree vegetation was sparser, birch and alder predominated in its composition, and the share of broad-leaved species was significantly lower. Anthropogenic impacts included the introduction of weeds, fires, the development of erosion processes, and soil turbation. The modern vegetation cover on the studied small islands of the Eugénie Archipelago consists of anthropogenically altered low-growing broad-leaved shrub–forb forests with lianas, shrub–semishrub phytocoenoses, halophytic vegetation of beaches, and the petrophytous vegetation of coastal rocks. The soil cover is represented by zonal soils: brown forest soils with mostly thin and strongly skeletal profiles. The following main differences between vegetation covers on small and large islands of the archipelago are identified: the predominance of grass–shrub vegetation, including Artemisia gmelinii thickets, and low-growing forests whose formation is determined by continuous wind impacts. Local conditions are favorable for the active development of humification and humic–illuvial processes resulting in the formation of deeply humus soil profiles. Small areas of the studied islands and their flattened relief determine more seaward conditions manifested in the composition of plant communities and the predominance of halophytic groups in the overwash zone and shrub–semishrub communities with dwarf linden in windward areas. The protected Japanese yew species occurs singly on the less accessible island of the Pakhtusov Islands. The significant share of forest vegetation determines the predominance of epiphytic lichens in the lichen cover, epilithic species typical for open ecotopes occur on rocky outcrops, and halophytic species occur in the overwash zone.