West Siberian Broadleaf and Mixed Forests

Category: Forest Biomes.

Geographic Location: Europe.

Summary: The western Siberian broadleaf and mixed forests lie at the juncture of the tundra and mixed forest regions north of Kazakhstan. Also known as hemiboreal forest, the biome is rich in animal and plant diversity.

The Siberian broadleaf and mixed forests define a slender ecoregion that lies at the southern edge of the broad Siberian taiga biome, just north of Kazakhstan. The Russian taiga is the largest forest in the world; forests cover 48 percent of the Siberian landscape and represent 20 percent of all of Earth’s forested lands. The Siberian Broadleaf and Mixed Forests biome is also known as the western Siberian hemiboreal forest, because the area is located halfway between the temperate and boreal zones. This area encompasses the western edge of the North Asian hemiboreal region.

Hemiboreal forests are a relatively new ecological designation, as they refer to specific conditions and habitats common to boundary communities, and forests located at the juncture of boreal tundras and temperate-zone forests.

The Siberian hemiboreal forests lie at the southern edge of the Euro-Siberian biogeographic region that falls inside the Palearctic ecozone, a vast belt that runs across North America and Eurasia, including lands in Canada and Scandinavia. This expansive ecozone is characterized by temperate broadleaf and mixed forests, and by conifer forests. Because North America was once connected to Eurasia via the Bering Strait land bridge, these areas have similar plant and wildlife habitats. Hemiboreal forests are the remnants of broad tracts of forests that flourished long ago; many did not survive the last periods of ice-age glaciation. The current climate supports a rich and diverse ecology here, despite clear-cutting, frequent fires, and poaching.

Vegetation

The western Siberian landscape is varied, with broad overlaps of particular types of vegetation. From north to south, the landscape transitions through five bioclimatic zones: tundra, forest-tundra, taiga, forest-steppe, and steppe. The complexity of this distribution creates integrated biophysical relationships that are difficult to describe even with the use of sophisticated, high-resolution radiometric technologies.

Biophysical relationships are further complicated during wide-scale events such as fires. The quantification of the processes of secondary succession stages, and the levels of carbon dioxide and water vapor available for heterotrophic respiration, are vital indicators of net biome productivity. The structure, age, and composition of regenerating areas are important to identify during recovering succession periods.

Fragmentation of Siberian hemiboreal landscapes due to fire and other causes, with subsequent plant dispersal and the disconnection of native ecosystem habitats, has accelerated the decline of biodiversity across the ecozone. Native forests were originally abundant. Birches dominated northern reaches. In more temperate southern areas, Siberian firs and Siberian spruces shared the biome as dominant tree species, along with tilias—a genus with 30 different trees known by various names including lime, linden, and basswood. Frequent fires have altered this distribution of species, often replacing native canopies with secondary successions of birches and aspens.

The hemiboreal forests provide habitats for more than 400 other plant species, including shrubs and nemoral (wood or grove) grasses. Taiga and steppe species are commonly found along the western Siberia forest corridor.

Fauna

Bird types in these Siberian forests include white partridge, snowy owl, gulls, and loons. Geese, swans, and ducks migrate into the region—accompanied by mosquitoes, gnats, and other insects. Indigenous birds include the demoiselle crane, steppe eagle, great and little bustard, finches, kestrels, and other falcons.

The taiga forest zone is home to such large mammals as European elk, brown bear, reindeer, lynx, and sable. Forest birds here include owls and the nightingale. The broadleaf forests also contain wild boars, deer, wolves, foxes, minks, snakes, lizards, and tortoises. The forests of southeastern Far Eastern Russia are home to Siberian tigers (Panthera tigris altaica), also known as the Amur tiger—among the world’s largest cats—as well as the Amur leopard, bears, musk, and various deer species. Rodents such as marmots; hamsters; and five species of suslik, a type of ground squirrel, inhabit the steppes.

Endangered animals include Coregonus tugun, a ray-finned fish of the Lena River basin; Siberian crane or Siberian white crane (Grus leucogeranus); tawny owl or brown owl (Strix aluco); and a subspecies of the European beaver, Castor fiber pohlei. The Siberian tiger is a critically endangered species impacted by habitat encroachment from logging and poaching.

Environmental Threats

Accurate topographical surveys of western Siberia land cover are essential to climate studies and efforts to simulate potential feedback relative to global warming. Land-atmosphere exchanges of energy, water, carbon dioxide, and other greenhouse gases are relative to the composition and structure of a given ecoregion. Current scenarios suggest that boreal species will migrate to the north as temperatures rise. Some data suggests that woody vascular species already are found in taiga areas.

Some scientists believe that if this expansion continues, the atmosphere will react with corresponding declines in albedo (visual surface brightness when viewed with reflected light) and increased absorption of solar energy, leading to additional heating of the atmosphere. These transitions are expected to have a profound affect on the Siberian landscape. It is predicted that by 2080, more than half of Siberia will be covered with forest-steppe and steppe ecosystems. New temperate broadleaf forests will contribute to fuel loads and add to subsequent fire hazards.

Wetlands are notoriously difficult to represent in geographic data profiles, particularly data sets derived from satellite imagery. It is estimated, however, that roughly 20 percent of the western Siberian forest lands are swamplands, including riparian stretches of the Irtysh River basin. Extensive lakes and wetlands in western Siberia contribute to the accumulation of organic peat carbon.

Ice-core records of atmospheric methane in the western Siberian lowlands suggest that accumulations have accelerated dramatically during the Holocene period, creating a vast, long-term carbon dioxide sink and global methane source. These reserves represent roughly 26 percent of all terrestrial carbon accumulated since the last glacial maximum. During periods of global warming, peats will decompose, releasing carbon dioxide into the atmosphere. However, these processes are difficult to assess quantitatively, given the paucity of information about the depth, age, and content of Siberian peat accumulations.

Conservation Efforts

Regrettably, the lands of the western Siberian hemiboreal forest are not included in the Russian system of protected lands known as zapovedniks. Closely related areas include the Orenburgsky Zapovednik at the far western Kazakh border, and the Olekminsky Zapovednik of central Siberia. The Pleistocene Park project, the brainchild of researcher Sergey A. Zimov, is of interest to climatologists worldwide. This project is the result of intensive research on a vast ecosystem that stretched across the northern latitudes of Canada, Europe, and China at the end of the Pleistocene era. One grassy corner of eastern Siberia survived the onslaughts of glacier advances and was the center of a highly diverse community of coexisting mammals, including mammoths, bison, horses, reindeer, musk oxen, elk, moose, saiga antelope, and yaks.

In 1980, Zimov founded the Northeast Science Station in Cherskii in the Republic of Sakha (Yakutia), and in 1989, he initiated the Pleistocene Park Project. On a 62-square-mile (160-square-kilometer) plot of grassland, project partners have reintroduced some Pleistocene mammals, including yak, steppe bison, musk ox, Kalmykian cow, Yakutian horse, and reindeer, to the Siberian plains. Genetic cloning techniques could even make it possible to reintroduce the great woolly mammoths native to Eurasia 10,000 years ago.

Zimov and his scientists hope to re-create the ecological conditions that existed just before the Holocene era. It is the assumption of the project directors that restoring that ecology could effectively cool the atmosphere, mitigating the escalating feedbacks of global warming, including the migration of species northward. Project plans include a fivefold expansion of this grassland habitat.

Bibliography

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