The flooded grasslands, or meadows, of Eurasia extend along the Amur River, Nenjiang River and Ussuri River Basins located in northeastern China and southeastern Russia. The areas provide important migrating sites for bird species, including six of the world's fifteen cranes. The majority of plant roots in these meadow systems are concentrated in the top 50 cm (19.7 in) of the soil profile with few roots penetrating deeper than 50 cm (19.7 in). Key threats to the flooded grassland regions include mining for oil and natural gases and encroachment of agricultural systems. Mean annual precipitation is between 400 mm (16 in) and 450 mm (18 in), with rains following continental monsoon patterns. The grasslands are interspersed with boreal forests composed of birch and coniferous species, and approximately 20% of the land is unmanaged.