半干旱丘陵区,一般年降水量在300～400毫米,地面高低起伏不平,地貌景观以低山丘陵为主。在这类地区,由于雨量较少,气候寒冷,林业生产一直是个薄弱环节。解放后,这些地区虽然栽过不少树,但多成为“小老树”,甚至根本不能成活。例如商都县八股地林场栽植 Semi-arid hilly areas, the general annual rainfall of 300 to 400 mm, the ups and downs of the ground level, the landscape mainly hilly. In these areas, forestry has been a weak link because of less rainfall and cold weather. After the liberation, although many trees were planted in these areas, they often became “little old trees” and could not even survive at all. For example, Shangdu County, eight farm planting