cause. In the drier west, human wood harvesting and overgrazing by livestock are probably more important. The grazinglands of northern China, although vast, are a threatened resource. More detailed descriptions of the topography and vegetation of each region of the northern grasslands appear below.
The three provinces of the Northeast (previously known as Manchuria)—Heilongjiang, Jilin, and Liaoning—account for about 5% of the northern grasslands (Map 1-3). The relatively high rainfall, dense human population, and intensive development of this region have converted most grasslands to farmlands, leaving only the northern and western borders as grazinglands. In these provinces, elevations are higher in the north than in the south and fall sharply from the Daxinganling [Great Hinggan] Mountains in the west, onto the Manchurian plain in the east. In the northernmost province of Heilongjiang, the Xiaoxinganling [Lesser Hinggan] and Yilehuli mountains exceed 1000 m, creating a topography of rolling hills, pock-marked by alkali basalts of recent volcanic origin. Three major east-flowing rivers empty onto the Sanjiang Plain at the northeastern tip of the province, forming a low-lying swampy delta. The Songnen Plain, a faultbound depression in central Heilongjiang, is the northern extension of the huge North China Plain. The southeast mountainous area is defined by the active Tan Lu. fault, whose uplift produced the Changbai Mountain range that ends as a peninsula into the Bohai Sea. The Songnen and Sanjiang Plains have been formed by subsidence, whereas recent uplifting along active faults has produced the mountain ranges bordering these depressions. During the Pleistocene, alluvial deposits developed along the flanks of the depressions and lacustrine deposits formed in the central areas of the plains. The geology of Jilin Province is closely related to that of Heilongjiang. Central Jilin contains the southern extension of the Songnen Plain, bounded on the west by the Daxinganling and the east by the Changbai Mountains. Liaoning, the southernmost of the three provinces, faces southward to the Bohai Sea. Eastern Liaoning is dominated by the Changbai Mountains, whose western boundary is marked by the active, strike-slip, Tan Lu fault. The Songliao Plain stretches into the center of the province and steps up gradually westward to the Mongolian Plateau.
The "forest steppe" of western Manchuria is distinguished from the "typical steppe" in neighboring Inner Mongolia by its higher rainfall (350–600 mm), dark chernozem soils, and higher productivity. The dominant grasses of the Northeast are Stipa grandis and Aneurolepidium chinense, commonly called ''sheepgrass" [yangcao]. Even as late as the Qing Dynasty (1644–1911), this area was heavily forested, although recent immigration and development have greatly reduced natural vegetation of all types and caused serious soil erosion.