from: Encyclopedia of Earth:
<<An ecoregion is a contiguous area characterized by well-defined similarity in flora and fauna as well as geomorphology, climate and soils; ecoregions are generally relatively large geographic units on the order of 50,000 square kilometers or more. Ecoregions may be terrestrial or marine, and do not recognize any political boundaries or landscape alterations by humans. Generally an ecoregion is depicted by a geographic descriptor coupled with a biome identity, further articulating one or more specific climatic or dominant plant community appellations: for example, Chilean Mattoral or Madagascar Dry Deciduous Forests.
There are several alternative formal naming schemes for the Earth's ecoregions; one of the most widely used, developed by the World Wildlife Foundation, recognizes 867 separate ecoregions. Because of the very large scale of an ecoregion, the landscape is not monolithic, but may have pockets of ecological diversity; however, the ecoregion is defined by its preponderant vegetative, geological and meteorological composition. Correspondingly boundaries between regions are sometimes diffuse, resulting in a broad ecotone.>>
Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth February 21, 2010; Last revised Date July 4, 2012; Retrieved January 12, 2013 http://www.eoearth.org/article/Ecoregion?topic=49597
example: Alashan Plateau semi-desert.
Here is a list of most ecoregions which cover parts of Mongolia. The list is also linked in the sidebar, so that it is easily accessible later, too.
TEMPERATE BROADLEAF & MIXED FORESTS
ecoregion: Manchurian mixed forests
This ecoregion lies almost completely outside Mongolia, and touches it border in the easternmost part of the country only (in Nömrög).
TEMPERATE CONIFEROUS FORESTS
ecoregion: Altai montane forest and forest steppe
ecoregion: Khangai Mountains conifer forests
ecoregion: Sayan montane conifer forests
ecoregion East Siberian taiga
This ecoregion lies immediately to the north of Mongolia, but shows several features which are typical for the northernmost forests of the country.
TEMPERATE GRASSLANDS & SHRUBLANDS
ecoregion Daurian forest steppe
ecoregion Mongolian-Manchurian grassland
ecoregion Selenge-Orkhon forest steppe
MONTANE GRASSLANDS & SHRUBLANDS
ecoregion Altai alpine meadow and tundra
ecoregion Khangai Mountains alpine meadow
DESERTS & XERIC SHRUBLANDS
ecoregion Alashan Plateau semi-desert
ecoregion Eastern Gobi desert steppe
ecoregion Gobi Lakes Valley desert steppe
ecoregion Great Lakes Basin desert steppe
Encyclopedia of the Earth: Ecoregion