Krestov. Distribution of vascular plants in Northeast Asia: climatic controls and historical background

Distribution of vascular plants in Northeast Asia: climatic controls and historical background

Pavel V. KRESTOV ^{1, 2}
¹ Botanical Garden-Institute FEB RAS, Vladivostok, Russia
² Institute of Biology and Soil Science, Vladivostok, Russia

The development of vegetation on the east of Asia is controlled by polar, boreal and temperate macrobioclimates. Basic variations of vegetation along the gradient of continentality within a zone depend on the combination of the yearly heat and precipitation distribution and can be classified into 7 climatic types: hyperoceanic, oceanic, suboceanic, maritime, continental, subcontinental and ultracontinental. In the boreal zone, the areas with the highest continentality values are occupied by the deciduous coniferous forests, and the areas with lowest continentality values – by broadleaved deciduous forests dominated by Ermann’s birch. The ombroevapotranspirational index calculated for vegetation orders shows that continental boreal forests of Asia occur in critical conditions of significant moisture deficit, which normally do not support forest vegetation. The most important source of water in dry areas of the boreal zone is melting permafrost. Climatic oceanicity results in formation of a specific vegetation complex composed of humidity-dependent and frost-intolerant species adapted to the short growing seasons. The strong accumulation of snow causes a 2-3 week delay of its melting and a considerable shortening of the growing season. Increasing longevity of deep snow cover leads to vegetation transformation from forests to tall herb meadows through the stage of alder krummholz. Fluctuating humidity and balancing of continentality–oceanicity were the major factors affecting the vegetation changes in the Holocene. At time of late Pleistocene aridification the climate favoured intensive migration of Central Asian steppic floristic elements which make up a significant component of the modern flora of south-western and eastern Siberia. Xeric and mesoxeric floral elements with a great number of neoendemics from the mountains of southern Siberia characterize the Rhytidio-Laricetea. Aridification in the temperate zone led to distinctive separation of insular and mainland vegetation complexes in Northern Asia with a retreat of thermophilous species especially on the mainland. The increase in temperatures and humidity caused a rapid expansion of larch forests over great areas up to the Arctic coast in the period 10000–5000 yrs BP and the formation of the Ledo-Laricetalia characterized by wetland vascular species and bryophytes with circumboreal distribution. Forest retreat at about 3500 yrs BP led to the formation of extensive thickets dominated by shrubby birches, willows and larch woodlands. One of the most important refugia for the humidity-dependent vegetation in the Pleistocene was the north-western coast of Pacific Ocean, which still supports many Tertiary relics. All zonal vegetation types of Northern Asia show strong floristic relationships to Beringia and northern Pacific Islands. The present study was undertaken with the support of the Russian Foundation for Basic Research (grants no. 10-04-00985 and 11-04-92112).