Alexander M. Omelko

Phytogeography of higher units of forests and krummholz in North Asia and formation of vegetation complex in the Holocene.

The modern vegetation pattern of Northern Asia has an uninterrupted history of development from Tertiary boreo-nemoral vegetation complex. The most dramatic transformation of this complex took place in the Pleistocene Maximum, when the low temperatures along with severe climatic aridisation caused a qualitative change of the vegetation in the broad areas of mainland Asia and provided an opportunity for migrations of drought- and cold-tolerant species. This paper focuses on the problem of the contributions of major Asian fl oristic centres to the formation of major vegetation types of Northeast Asia in the changing climatic conditions of the Pleistocene and Holocene. The increasing temperature and humidity in the beginning of Holocene caused the formation and expansion of nemoral forests belonging to the order Tilio-Pinetalia koraiensis composed mainly of humidity-dependent Sino-Japanese species, and nemoral Quercus mongolica forests that included drought-tolerant species of Central Asian origin. In the boreal zone, the larch forests reached the coast of the Arctic Ocean in a relatively short period between 10000 and 6000 years BP. Perhaps this period is the time of formation of the order Ledo-Laricetalia cajanderi composed of species adapted to extremely cold winters, hot summers and cold soils lying on top of the layer of permafrost. The ultra-continental climate in conditions of relatively high temperatures caused deepening of the active soil horizons and differentiation of the order Lathyro-Laricetalia, characterised by the presence of drought-tolerant species of Central Asian and Sino-Japanese origin. These climatic and edaphic conditions appeared to be unfavorable for mesic species. Therefore, the areas with an ultra-continental climate represent an important biogeographical limit for mesic Beringian and Sino-Japanese species. Increasing oceanicity in the period of 5000 - 3500 years BP caused forest retreat that led to the formation of the youngest zonal order of Northern Asia, the Larici-Betuletalia divaricatae characterised by domination by cold tolerant shrubs from the genera Betula, Alnus and Salix.

FORMATION OF AMUR LINDEN (TILIA AMURENSIS RUPR.) POPULATION MOSAIC IN THE STAND OF KOREAN PINE-BROADLEAVED FOREST IN THE SOUTH OF THE RUSSIAN FAR EAST

The study of Amur linden (Tilia amurensis Rupr.) mosaics structure, which is one of significant edificators of low-disturbed Korean pine-broadleaved forests, is nowadays a very important task for understanding the functioning and maintaining the equilibrium state of ecosystems relatively untouched by human activity. In this connection, this paper is aimed at describing the structure and the process of mosaics formation of Amur linden (T. amurensis), one of the dominant stand species of Korean pine-broadleaved forests. Our study is based on the data collected during the field seasons of 2012–2016 in the two permanent plots (1.5 hectares and 10.5 hectares in size) located at the Verkhneussuriysky Research Station of the Federal Scientific Center for Biodiversity, Far East Branch of the Russian Academy of Sciences. As a result we analyzed the structure and described the process of population mosaics formation of Tilia amurensis in Korean pine-broadleaved forests in the south of the Russian Far East. We demonstrated that the transformation of mosaics structure, formed by the plants of different generative state, passes from group allocation (immature plants) to almost random (generative plants). The separated pregenerative plants are situated too far from each other to interact in the revealed groups. Therefore the group allocation at different stages of development is connected with inhomogeneous environmental conditions and determined by local history of disturbances in the stabd.

Poleward migration of the destructive effects of tropical cyclones during the 20th century

Significance Long-term variability in tropical cyclone (TC) activity is of high relevance for the development of adaptation and mitigation strategies; however, our current knowledge is based mostly on short-term records, with strong discrepancies among various datasets. We used tree-ring records of past forest disturbances to show rapid increases in the destructive effects of TCs during the 20th century. Long-term changes in TC activity imply that the recent poleward migration of TCs is not within the range of long-term natural variability and may be associated with climate change. Our findings are important, as affected regions were formerly situated at the edge of areas affected by TCs, and these areas are more sensitive to TC hazards because of a lack of experience-based adaptation strategies. Determination of long-term tropical cyclone (TC) variability is of enormous importance to society; however, changes in TC activity are poorly understood owing to discrepancies among various datasets and limited span of instrumental records. While the increasing intensity and frequency of TCs have been previously documented on a long-term scale using various proxy records, determination of their poleward migration has been based mostly on short-term instrumental data. Here we present a unique tree-ring–based approach for determination of long-term variability in TC activity via forest disturbance rates in northeast Asia (33–45°N). Our results indicate significant long-term changes in TC activity, with increased rates of disturbances in the northern latitudes over the past century. The disturbance frequency was stable over time in the southern latitudes, however. Our findings of increasing disturbance frequency in the areas formerly situated at the edge of TC activity provide evidence supporting the broad relevance of poleward migration of TCs. Our results significantly enhance our understanding of the effects of climate change on TCs and emphasize the need for determination of long-term variation of past TC activity to improve future TC projections.