Contents - Previous - Next

This is the old United Nations University website. Visit the new site at http://unu.edu

2. Land classification and mapping in China

Zhao Songqiao
Institute of Geography, Chinese Academy of Sciences, Beijing

Abstract

A national classification and mapping programme has been under way in China since 1978. The programme is designed to evaluate the nation's land resources. A scheme for land type classification and mapping is proposed on the basis of the physical attributes of the land. Seven naturel regions are recognized in China, below which a number of first- and second-order land types are identified mainly on the basis of macro- and microlandforms and other surface features.

Land classification in China has a history of 2,500 years. In the ancient classic, Zhouli (The Rites of the Zhou Dynasty), five major land types were identified: forested mountains, hilly land, level plains, riverine lowland, and swampy depressions. A more sophisticated classification scheme was recorded in the Guanzi. a classic written during the Warring States Period (475-221 B.C.), in which China was divided into three first-order land-use types plains, hills, and mountains - and 25 second-order categories. These schemes are among the earliest land classification systems in the world. Land classification and evaluation continued to be of major interest to Chinese scientists in the ensuing dynasties. such research being closely related to agricultural production and land taxation.

Since the foundation of the People's Republic of China in 1949, scientific research on land classification and agricultural production has made rapid progress, and many studies on land classification and evaluation have been completed in different parts of the country. Since 1978, a serious and comprehensive land-classification and mapping programme has been in progress. The programme has the two basic purposes of providing reliable and detailed data on China's geographical environments and an evaluation of the nation's land resources and their agricultural capabilities. The programme will result in the production of a series of maps on land classification. The entire country will be mapped at a scale of 1 :1,000,000, the major provinces and regions at 1 :200,000, and sample study areas at 1 50,000. The programme is scheduled to be completed by 1985.

A Scheme for Land Classification and Mapping

Any land area can be classified into a number of types on the basis of physical attributes. The exact number of types to be determined depends on several factors, including the purpose of classification, and the financial and manpower resources and time available for the task. Since the ultimate purpose of our classification of land types is to use China's land resources more efficiently for national and regional economic development, and since we are still at an early stage of the national land-type study, we have tentatively divided China into the major natural regions. Within each major natural region a two level scheme of land-type classification has been adopted.

The natural regions are the foundation of land-type classification and mapping. A natural region is characterized by a relative homogeneity of temperature and moisture conditions and of soil and vegetation types. The first-order land types within a natural region of China are identified mainly on the basis of macrolandforms and are listed according to the elevation of each type, from lowlands to high mountains. They thus approximate the "land systems" of the Australian CSIRO. The first-order land types are the major mapping units for the nation as a whole, at a scale of 1:1,000,000.

The second-order land types are generally identified and delimited by relatively homogeneous meso- or microlandforms and surface materials in the hilly regions, and by similar soil and vegetation subtypes in the plains. Such units also have similar suitability and capability of land use. These second-order land types approximate the "land units" of the CSIRO. They are the major mapping units for China's provinces and large regions. Several adjacent and genetically similar second-order land types may be grouped into a first-order land type.

In the development of this land-classification system, some small areas located in different natural zones and in areas with firstorder land types have been carefully selected for detailed sample studies. Such small areas have been mapped at scales larger than 1 :25,000. They have been studied mainly on the basis of micro-landforms or detailed soil type and vegetation formation, which may be used for the identification of third-order land types should the need arise.

This approach to land classification is based on geomorphological and biological processes and their mutual relationships. All physical and biological factors must be viewed collectively in the determination of land types at all levels, since it is their interplay which gives rise to landforms and landscapes.

The Natural Regions of China

The starting point of this land-classification system is the delimitation of natural regions (see the Introduction to this volume). Three large physical realms can be recognized in China, the humid east, the arid northwest, and the Tibetan Alpine realm (table 2.1). 1 Based on the areal differences of temperature conditions, the humid eastern realm can be further divided into four natural regions. The arid northwest is divisible into two natural regions, demarcated mainly on the basis of moisture conditions. The Tibetan Alpine realm forms a single natural region because of its broad horizontal homogeneity of natural conditions. Most of these seven natural regions can be subdivided into natural subregions.

Each natural region and subregion can be further divided into natural zones on the basis of either vertical zonation or horizontal variation of surface features. A natural zone has fairly uniform temperature and moisture conditions as well as similar zonal soils and vegetation, and, consequently, similar suitability and capability of land use.

TABLE 2.1. Principal Climatic Indices of Natural Regions of China

a. The accumulated temperature of each region is the sum total of temperature in the period when the temperature is >=10°C The term is also known as "active temperature" because most plants begin to grow only when the temperature is above 1 0°C It may be pointed out that the accumulated temperature for spring wheat to mature is more than 1,400°C whereas that for corn is more than 2,000°C. The term is widely used in China in both climatological studies and for biophysical regionalization,
b. Computed according to the following empirical formula:

where St>=10°C denotes accumulated temperature during >=10°C period, Sr>=10°C is the total precipitation in mm during the same period, while 0.16 is a constant.

When:
1<1.0, the region is humid, with forests as the dominant natural vegetation;
I = 1.0 1.5, it is subhumid, with forest-steppe dominating;
I = 1.5 2.0, it is semi-arid, with steppe dominating;
I = 2.0 4.0, it is arid, mainly desert-steppe;
1>4.0, it is extremely arid, predominantly desert

TABLE 2.2. The Natural Zones of China

a " Drab" or " cinnamon " soils, a sub-class of "cambisols " (FAO-UNESCO, Soil Map of the World) denotes soils characterized by such a colour.

Twenty-two natural zones have been identified in China (table 2.2).

To demonstrate first- and second-order land-type classification in China's varied natural environment, a number of areas with diverse natural features are presented below as examples.

Land Types in the Tropical Humid Region

China has only a small humid tropical area, occupying 1.6 per cent of the total area of the country. Two natural zones can be recognized in this region, the equatorial rainforest, a laterite zone restricted to the southernmost islands in the South China Sea, and the tropical monsoon forest, a coastal and hilly laterite zone. The major land types on Hainan Island are listed in table 2.3. and the south-western part of the island is mapped in figure 2.1.

Land Types in the Subtropical Humid Region

The subtropical humid region is extensive in Central and South China, where it occupies 26.1 per cent of the country's land area. This region can be divided into four subregions. The southern and central subtropical subregions are characterized by evergreen broad-leaved forests and yellow earths, whereas the northern subtropical subregion has decidous broad-leaved forests and yellow-brown earths. Deep longitudinal valleys abound in the South-west China subregion. As a whole, the entire region is either mountainous or hilly, a characteristic basic to the classification of land in this region. Table 2.4 provides a land-classification system in the zone of southern sub-tropical evergreen broad-leaved forests with lateritic red and yellow earths. Table 2.5 gives a system for the South-west China subregion based on Tenchuan, Yunnan Province.

Fig. 2.1. First- and Second-level Land Types in South-western Hainan Island

TABLE 2 .3 Land Classification System, Hainan Island

TABLE 2.4. Land Classification System in the Zone of Southern Subtropical Evergreen Broad-leaved Forests on Lateritic Red and Yellow Soils

TABLE 2.5. Land Classification System in the Tengchong Area, Yunnan

TABLE 2.6. Land Classification System in the Zone of Semi-xerophilous Deciduous Broad-leaved Forests on Leached Grey Soils

Land Types in the Warm-Temperate Humid and Subhumid Region

This region includes a large part of North China and the southern portion of Liaoning Province, and occupies 10.2 per cent of the total land area of the country. It is essentially a transitional belt between the subtropical south and the temperate north and between the humid east and the subhumid or semi-arid western regions. This region can be divided into two distinct subregions. The first is the humid and subhumid North China and southern Liaoning plains, which contain two natural zones, the deciduous broad-leaved forests on brown forest soils zone, and the semixerophilous deciduous broad-leaved forests on leached drab soils zone. The second is the

Loess Plateau, which has three natural zones, the zone of semixerophilous deciduous broad-leaved forests on leached drab soils, that of the semi-xerophilous broadleaved forests and foreststeppes on drab soils, and the steppes on black loessic soils zone. The major diversifying factors in land classification for the former subregion are the horizontal zonation in the plains and vertical zonation in the bordering mountainous areas, whereas for the latter they are mainly landform features. Two tentative landclassification systems for the region are proposed in tables 2.6 and 2.7. Figure 2.2 shows the patterns of land types in the sample area of Xifeng, Gansu Province, in the Loess Plateau subregion.

Land Types in the Temperate Humid and Subhumid Region

This region includes the entire north-east of China except southern Liaoning, and occupies 8.1 per cent of the country's total land area. The region has flat, fertile plains with extensive virgin land awaiting reclamation, and rugged, forested mountains, which contain important reserves of timber. Three natural zones can be identified, the zone of needle- and broad-leaved mixed forests on dark brown forest soils, the Taiga zone, and the zone of the forest-steppe on black earths and chernozems. The landform features stand out again as the major factors in land classification, although both latitudinal and longitudinal zonation are also important. From the Niu Jiang Plain north-westward to the northern Greater Khingan Range, a series of land types appear in succession (table 2.8). The land types of the Sanjiang Plain are shown in figure 2.3.

Fig. 2.2. Land Types on the Loess Plateau near Xifeng, Gansu Province

Fig. 2.3. First- and Second-level Land Types in the Sanjiang Plain, Heilongjiang Province

TABLE 2.7. Land Classification System in the Zone of the Steppes on Black Loessic Soils, Loess Plateau Subregion

TABLE 2.8. Series of Land Types from the River Niu Plain, North-westward to the Greater Khingan Range

TABLE 2.9. Land Classification System in the Steppes-Chestnut Soils Zone of the Temperate, Semi-arid Region

Land Types in the Temperate Semi-arid Region

This region, occupying 5.9 per cent of China's total land area, coincides roughly with the so-called Inner Mongolian Steppe, and contains the best grassland in China. The region has only one natural zone, that of steppe on chestnut soils. The major factors in land classification are landform features and their spatial variations (table 2.9).

Land Types in the Temperate and Warm-Temperate Arid Region

Besides the north-western Tibetan Plateau, the arid region is widespread in North-west China, occupying 21.4 per cent of the total land area of the country (30.8 per cent, if the north-western Tibetan Plateau is included). It can be divided into two subregions, temperate and warm temperate. The former includes three natural zones, the zone of desert-steppe on brown desertsteppe soils, that of piedmont desert-steppe on sierozems, and the zone of desert on grayish-brown desert soils. The latter subregion has only one natural zone, that of desert on brown desert soils. The region is composed mainly of extensive plateaux and basins, and hence the major factors of land classification are surface materials, though in the surrounding high mountains vertical zonation is also conspicuous. Using the central Hexi Corridor as an example, the region's land classification system is shown in table 2.10 and figure 2.4.

Fig. 2.4. Land Types in the Hexi Corridor, Gansu Province

TABLE 2.10. Land Classification System in the Zone of the Desert on Greyish-Brown Desert Soils in the Hexi Corridor

a. Takyr refers to particular clayey soils that exhibit polyhedral surface cracks when dry (cf. "Takyric Yerrnosois", FAD-UNESCO, Soil Map of the World,

TABLE 2.11. Land Classification System in the Vertical Zone of the Meadow-Steppe and Meadow in the Mid-western Tibetan Plateau Region

Land Types in the Tibetan Plateau Region

The Tibetan Plateau, with an area of more than 2.5 million km² and an average elevation of more than 4,000 m above sea-level, is the largest and loftiest plateau in the world. It occupies 26.7 per cent of the total land area of China. Except for the southern Himalayan slopes, which belong to the northern margin of the tropical humid region, the plateau proper can be divided into three subregions. The first is subhumid Tibetan Plateau, which occupies about 4 per cent of China's total land area and has only one natural zone, the vertical zone of meadows and needleleaved forests. Second is the widespread semi-arid Tibetan Plateau, which occupies about 13.3 per cent of China's total land area and has two natural zones, the vertical zone of forests, meadows and meadow steppes and which lies chiefly around the Koko Nor (Qinghai Hu), and the vertical zone of meadow-steppes and meadows which is widespread in the west-central Tibetan Plateau. The third natural zone is the arid Tibetan Plateau, which occupies about 9.4 per cent of the total land area of China, and where two natural subzones are present, the zone of plateau arid deserts, and that of plateau frigid deserts. In each of the natural zones, the major factors of land classification are invariably the landform features and their impact on the other physical factors. Taking the most widespread vertical zone of meadowsteppes and meadows as an example, a tentative landclassification system of the region is presented in table 2.1 1.

Conclusion

Only a few of China's many natural zones and only the first- and second-order land types have been presented tentatively in this chapter. Fieldwork has so far been limited and sample studies are few, and much more painstaking scientific work on the Chinese system of land classification remains to be undertaken. Also more sophisticated principles and methodologies of land classification and mapping need to be applied to the work. In short, we have only just begun to understand China's land resources. For the next three to five years, but particularly in the next two, further large-scale sample studies and more mediumscale field mapping of large areas as well as aerial mapping in different natural zones will be undertaken to facilitate the early completion of a better and more sophisticated land-classification system for the whole country.

continue

Contents - Previous - Next