THE VEGETATION OF THE FOREST-STEPPE REGION OF HUSTAIN-NURUU, MONGOLIA

The vegetation of a forest-steppe region in Hustain Nuruu, Mongolia, w as studied by a phytocoenological approach. Eleven plant communities w ere recognized, comprising four steppe communities, two meadow communi ties, a tussock grassland, two shrub communities, a scrub community an d a woodland community. The botanical and ecological characteristics o f the different communities are discussed, with reference to the exist ing classification of Mongolian plant communities. Analysis of the pre sent data indicates that a refinement or extension of the classificati on system is desirable, especially concerning the steppe(-related) com munities. Discussion of the relative distribution of steppe and forest reveals that in the relatively dry location of Hustain Nuruu grasslan d and shrubland dominate the natural vegetation (88% of the area). For est covers ca. 5% of the area, it is limited to sites where ground wat er is within rooting depth: north slopes above 1400 m (Betula platyphy lla woodland) and along erosion gullies (fragmentary Ulmus pumila gall ery woodland). Under natural conditions forest cover might reach 12%, but it is speculated that wild ungulates could maintain its extension at a lower level. The importance of forest is greater in forest-steppe regions with higher rainfall, but the factors determining the distrib ution of grassland and forest are expected to be similar.