Introduction

Grasslands on ocean islands are characteristically azonal landscape elements. Grassland communities are broadly distributed on islands located both in the boreal zone [6, 50] and on tropical islands in the Pacific Ocean [28]. Grasslands in a forest zone, at least dry land grasslands, are typically a result of anthropogenic activity and their origins are associated with the degradation and destruction of forest vegetation during human settlement and local economic development. The interest in the origin of grasslands communities on islands is in may ways connected with the stability of island landscapes. An additional question is what density of human population is necessary for island grassland communities to shift irreversibly and to set off catastrophic changes in vegetation cover. Paleogeographic study of Holocene deposits on Polynesian and Micronesian islands, where grasslands have developed on windy, dry coastlines show that grassland communities are natural, climate influenced formations that have existed for several thousand years and that these grasslands arose long before human settlement of the islands [27, 28].

Without addressing the difficult issue of the structural and functional organization of grassland ecosystems or their floristic composition, questions which have already been studied in detail [6, 7 and others], we want to discuss in this article the question of the age of grassland communities and to analyze the paleogeographic conditions during which they developed on temperate zone ocean islands. The Southern Kuril Islands (Kunashir, Iturup, Shikotan Islands, other islands of the Lesser Kuril Ridge) were selected as the research region. The availability of a large volume of paleogeographic information provides an opportunity to reliably reconstruct paleogeographic conditions in the late Pleistocene and Holocene [19].

Soil profiles (Figure 1) were selected as the key feature for a reconstruction of grassland communities because data on pollen spectra in soils are the most instructive for reconstructing local vegetation groups and they reflect the habitat conditions for individual species [9]. Although grass pollen does not move great distances, aerial pollen transfer is very important in the formation of the pollen spectra. L. M. Mokhova confirmed this when studying the structure of pollen rain and subfossil spectra for different layers of sediment on Kunashir Island [23]. A soil's pollen spectra should demonstrate the individual stages in the development of grassland communities. At the same time, the interpretation of the pollen spectra in soils present certain challenges since, as a rule, changes in fossil soils in the initial spectrum occur in response to aeration and moisture regime, to specificity of physical and chemical of soil processes and micro biotic factors [9]. Significantly less pollen is preserved in soils than is preserved in marshlands, alluvial and lake facie [47]. Interpretation of radiocarbon data obtained for humic acid soils reveals no single pattern. The renewal of humus occurs in paleosols close to the surface. Thus, the most reliable dating is obtained from buried soils that are shielded from the carbonic exchange zone [1].

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