关键词: 北京山区, 土地类型图, 地形面, 地貌形态, 垂直带, 制图, 地带, 土地分级, 自然地理, 土地分异

Abstract: The mountain regions north of Beijing occupies the western part of Yen Shan which, runs eastward to Shanhaiguan and forms the northern border of the North China Plain. The climate belongs to the semi-humid warm temperate type, with a cold winter and a hot summer. Average annual precipitation is about 800 mm in the front ranges and decreases to abont 500 mm in the sheltered valleys. Deciduous forest of a semi-xerophytic type is the common vegetation. Drap soil is developed under this climatic and botanical environment.Field investigations revealed that a great variety of landscape exists in this mountain region. A system of classification of land types has been attempted. This classification is based on the knowledge of physical geography and especially on the ana-lysis of the physical factors controlling the differentiation of the landscape.Firstly, altitudinal zonation has to be considered. Although the altitude is not very high, from about 50 m in the foothills to over 2,000 m at the summit, vertical zona-tion of natural landscape is clearly manifested. Three vegetation-soil zones may be distinguished:1. The lower part of the mountain below 1200 m is covered by shrubs and grasses of semi-xerophytic and meso-xerophytic types. Small patches of Pinus tabulaeformis and Quercus dentala, Fraxinus bungeana may be found here and there in sheltered and protected areas. This is a secondary growth, the result of interference of human activities since historic times. Deprived of the protection of forest cover, erosion is very intensive in this part of the mountain. Mass wasting, such as mudflows, are com-mon features which cause great damage to property and loss of life.2. Above 1200 m and up to 1850 m is the second zone. It is rather well covered by a deciduous forest, dominated by various species of oak (Quercus aliena, Q. varia-bilis, Q. accussima), birch (Betula platyphylla, B. duhurica) and poplar (Popular davidiana). Shrubs and grasses form the undergrowth of the deciduous forest, but they are different in species from those in the lower mountain. Brown forest soil is the typical soil. Due to the protection of the forest cover, mudflowa seldom occur in this zone.3. Above 1850 m to the top of the mountain the deciduous forest is superseded by mountain meadow which is underlaid by a layer of black meadow soil. It constitutes a distinctive zone by itself. The meadow is used for pasture during the summer.Next to altitudinal zonation, lithology deserves special attention. Lithological character is an important factor in the formation of landforms, soils and vegetation. For example, we found granite and limestone form very different landscape in this part of Yen Shan. Granite usually forms rounded or undulating landforms, covering with a thick layer of regolith and a mixed forest of pines and oak. Brown forest soil is developed whereever granite occurs. In limestone area karstic landforms are found, with only a thin veneer of weather materials. Cypress (Biota orientalis) usually takes the place of pines. Drap soil is usually developed wherever limestone occurs. Loess which appears in different altitudes forms a typical landscape by itself, characterized by flat or undulating top and vertical slope under water erosion. The typical soil is drap soil, most of the loess covered land is cleared for cultivation. Alluvial deposits along the valley constitute another type of landscape. The new deposits beside the river channel forms flood plains, while the older deposits further away from the river forms terraces. The flood plains and the terraces are the most fertile land in the mountain region and become the centre for agriculture and settlement. However, the occurrence of summer flood may be a hazard to the crops and inhabitants in the valley.Mountain landscape is further diversified by the erosion of miming water. Moun-tain slopes are intensively dissected and form mesorelief and microrelief. Slopes may be gentle or steep, convex or concave. The effect of aspects of slope is also quite evident. In the upper par