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I. Land-use evaluation and classification

1. Major land-type categories of China
2. Land classification and mapping in China
3. Classification scheme for the 1:1,000,000 map of China's land resources
4. Supplement to the preliminary standard classification system for land evaluation in China
5. Land use on the Lake Taihu Plain
6. Salt-marsh resources of China

1. Major land-type categories of China

Xi Chengfan
Institute of Pedology, Chinese Academy of Sciences. Nanjing, Jiangsu Province

Abstract

Because of its large size, China's natural environment and natural resources are extremely diverse and complex. The following major land use categories can be distinguished: eastern lowlands (further divided into four sub-regions). the arid north-west, and high mountain ranges and the Oinghai-Xizang (Tibet) Plateau.

One of the first requisites for understanding China's land resources is to classify the nation into major land-type categories, since a classification will contribute to planning for the better use of resources. This chapter presents a general overview of the major land types of China. Detailed, comprehensive systematic studies of each land-use type are urgently needed.

With an area of 9,600,000 km², China is a huge and physically diverse country. Hydrothermal conditions are varied, ranging from humid conditions in the south-east to the arid north-west (table 1.1). Thermal conditions change latitudinally (table 1.2), south-eastern China being either humid tropical or subtropical, whereas the north-west, in central Eurasia, is extremely arid with a mean annual precipitation of only some 50 mm, under warm continental thermal conditions.

TABLE 1.1. Regional Differences in Humidity

TABLE 1.2. Temperature Regimes

China is predominantly mountainous, approximately 66 per cent of the total land area being mountains and hills. which attain their highest elevation in south-western China, where ranges culminating in Mt. Qomolangma 18,848 m) overlook the Qinghai-Xizang (Tibet) Plateau, which averages 4,000-5,000 m above sea-level. Adjacent to the Qinghai-Xiang Plateau is a series of ranges with elevations of 1,000-4,000 m. The chief intermontane basins are the Sichuan Basin, in the humid subtropical region, and the Tarim Basin, in the extremely arid, warm continental inland region. Among the major plateaux are the Yunnan and Guizhou Plateaux, in the south, and the Loessal and Mongolian Plateaux, in the north.

Eastern China is a lowland region with great plains and river valleys dividing low mountains. The vast Songliao Plain and the North China Plain both lie north of the River Yangzi. In the Yangzi and Zhu valleys are several large alluvial and lacustrine plains.

Such a diverse physical environment has given rise to various types of soils and vegetation. Consequently, the land-use types are varied, and eight major types are distinguished and described in the remainder of this chapter.

The Eastern Lowlands

Eastern China, including the islands in the South China Sea, occupies a vast territory extending from approximately 4°N to 53°30'N. It is mainly a lowland region with lakes, plains, hills, and scattered low mountain ranges that rarely exceed 1,000 m in elevation. In the eastern lowlands four sub-types of land use may be distinguished, as described below.

1. Tropical Rainforest and Subtropical Evergreen Area with Ferro-Allitic Soils (Oxisols and Ultisols)

This sub-type is characterized by rainforest and monsoon forest in the tropics and by evergreen broadleaf forest in the remainder of the region. Most of the soils are in different stages of allitic weathering (i.e. silica has been largely removed and the clay fraction is dominated by Al and Fe components). Latosols (Oxisols) with comparatively strong allitic weathering are found on Hainan Island and the Leizhou peninsula, where the mean annual temperature (>23°C) and the accumulated temperature (> 10°C) approximates 8,000°C (up to 9,000°C in some years). The mean annual precipitation is >1,500 mm. Topographically, the lowland's coastline has rolling hills and terraces. The tropical islands in the South China Sea are geologically young, most being formed by coral reefs where phospho-calcic soils developed from guano are abundant.

Under hot and humid conditions, rice can be triple cropped, sweet potatoes grown all year round, cassava planted in most places, and rubber cultivated in the south. Tropical crops such as coffee, cacao and coconuts are produced.

The area from the Zhu Delta to the Yangzi Valley, between approximately 18°N and 30°N, is characterized by rolling hills and low mountains with ferro-allitic red and yellow soils (ultisols). It is an area of evergreen broadleaf forests, the major species of which are Castanopsis spp., Schima spp. Cinnamomum spp., and Lithocarpus, all mixed with Calamus spp. The main species of the mixed forests is Quercus spp., with ferns and rhododendron constituting the principal understorey plants. After deforestation, the trees Pinus massoniana, Acacia. and Cyclobalanopsis, and Cunninghamia lanceolata. mixed with the grasses Miscanthus and Themeda spp., grow as the major secondary plants. Various species of bamboo are also abundant in this area.

The middle Yangzi valley has a subtropical climate with a mean annual temperature of 16°C to 20°C, the accumulated temperature > 10°C is between 5,000 and 7,000°C, the annual frost-free period is 220 to 300 days, and the average annual precipitation is 1,000 to 2,200 mm. The natural vegetation is dominated by evergreen broadleaf trees. Two crops of rice or a ricewheat rotation characterize the region's intensive agriculture. Tea, tung oil (Aleurites fordii), and citrus are widely planted in this region, and longan (Nephelium longana) and lichee (N. Iitchi) are concentrated in its southern part.

The Sichuan Basin, situated in the middle course of the River Yangzi and surrounded by high mountains and plateaux, has climatic conditions and fertile soils that support a high agricultural productivity, especially in the Chengdu Plain, which has been irrigated for more than two millennia. Maize, millet, citrus and vegetables are grown on the hill slopes of the basin and rice is cultivated in the gullies.

In the Yangzi valley and its tributaries most plains and gully areas are in rice cultivation. As a result of the flooded-field rice agriculture that has been practiced here for centuries, both the chemical properties of the soil and its morphological features have been greatly changed. Such changes are also found on the terraces where irrigation water is available and where the soil solum is thick. Terracing is one rational way to use slopeland in this humid subtropical region. In certain parts of this region the land is less productive, as in the many deeply dissected gullies where paddy fields suffer from waterlogging by underground cold springs, which reduces soil temperatures for rice plants and inhibits the aeration needed for their root development.

In Yunnan and Guizhou Provinces and the Guangxi Zhuang Autonomous Region, limestone areas totalling about 400,000 km² have been highly weathered and leached under the prevailing humid tropical conditions. Three types of karst landform are recognized in those regions. First are ridges and depressions characterized by round depressions distributed among high ridges and bare limestone outcrops. Surface water is scarce and the watertable deep. Rendzina and terra rossa, in the depressions, are the main soil types. They are characterized by a relatively thin solum and are used mainly to raise dry farming crops such as maize and beans. The problem of drought is quite severe and this type of land generally has a low productivity. Second are pillars (erosional remnants) and valleys where eroded depressions have coalesced to form narrow valleys with pillars along their sides. Maize, beans and sorghum are raised in the valleys, and the steeply sloping pillars are either forested, or planted with tung oil trees or bamboo. Sheep and goats are grazed on the shallower slopes. Third are flat, open plains with depressions, lakes, and rivers formed after further dissection and leaching. Those between the hills and lakes are used as rice paddies and the foothills are dry farmed for corn, beans and fruits.

2. Plains and Hilly Areas in North China with Semi Humid and Warm Temperate Climate, Deciduous Forests, and Loessal Soils

North of the River Huai and the Qinling Mountains, the climate becomes semi-humid and warm temperate, with a mean annual precipitation of 500 to 700 mm, and a mean annual temperature of 9-13°C. The natural vegetation in the eastern part of North China is dominated by broadleaf deciduous trees, especially Quercus spp. and Tilia spp. The soils are luvic (i.e., leached and acidic) brown earths. The western part is drier with a mean annual precipitation of 500 mm or less. The natural vegetation contains mixed broadleaf forests, shrubs, and grasses. The soils are calcareous with a heavy surface accumulation of pseudomycelium, a threadlike deposit of CaCo₃, that looks like mycelium.

In much of North China, annual double cropping or biannual triple cropping is common. Wheat is the winter crop, and maize, sweet potatoes, and peanuts are the major summer crops. Apples, pears, peaches, chestnuts, walnuts, and jujubes (Ziziphus spp.) are widely produced.

The Shandong and Liaodong peninsulas are rolling and hilly with elevations from 200 to 400 m above sea-level. There the luvic brown earths are formed by the weathering of granitic masses. After denudation, the soils become sandy and skeletal, yet still suitable for applegrowing.

The immense, flat North China Plain was formed by the deposition of alluvia by the laterally shifting channels of the Yellow River. It consists of interbedded clay and silty materials. On the natural levees and alluvial fans are large areas where peanuts or pears are cultivated. Clay soils are common in lowland areas or depressions, and are normally used for planting wheat and sorghum. Between the natural levees and the clay depressions, the interbedding of clay and sand results in a complex solum, and the high water-table has led to salinization and alkalinization. Solonchaks occur along the coast.

The Loessal Plateau, in the middle course of the Yellow River, and exceeding 500,000 km² in area, may be subdivided into dissected loessal plateaux, dissected loessal ridges, and eroded loessal hills. On the dissected loessal plateaux the darker loessal soils form a solum 1.5 to 2 m thick, but which is low in organic matter (1-2 per cent). The dissected gullies may reach a depth of 100 m and on their steep slopes loessal soils have an even lower organic matter content (0.5 per cent). Over large parts of the Loessal Plateau the surface soil has been completely eroded, leaving only skeletal and immature soils. Owing to drought and the low organic content of the soil, the region's agricultural production is low and uncertain.

3. North-eastern Plains and Mountains with a Continental Humid and Semi-Humid Climate

The climate is continental and humid in North-east China. In the eastern section the average annual precipitation is 500-700 mm, with a frost-free period of about 120 days. The accumulated temperature > 10°C is only 2,200°C. The two major plains in North-east China are the Songliao Plain and the Sanjiang Plain. In the former, the average annual rainfall is 450-600 mm, the frostfree period is about 110-150 days, and the accumulated temperature is 2,000-2,500°C. Although the growing season in the Songliao Plain is relatively short, rice, sugar-beet, soybean and sorghum can be cultivated, since rainfall and temperature maxima coincide in summer.

In the gently sloping Sanjiang and Songliao Plains, Baijiang soils with associated black soils are common. The black soils are limefree and have a thick, mollic solum (30-60 cm) and high humus content (3 10 per cent). Meadow and swamp soils are common in low-lying areas. In the western portion of the Songliao Plain, the climate becomes semi-arid and chernozems occur. In low-lying areas soda-solonchaks are common.

Bordering these two plains in the North-west are the Greater Khingan Mountains (Xiao Xingan Ling), a major timber-producing area. The Changbai Mountains run north-south between the Sanjiang and the Songliao Plains. In these highland regions coniferous and broadleaf mixed forests are widespread, the soils humusrich dark-brown earths. Some Taiga forests occur in the north.

4. Mongolian Steppe

South-west of the Greater Khingan Mountains lies the gently rolling Mongolian Plateau, where the climate is dry and the vegetation is dominated by short grasses. In this region the humus content of the soils decreases with the increase of calcium carbonate and salt content, and wind erosion in the Tarim Basin has resulted in many unique landforms.

With an average annual precipitation range of 100-150 mm and occasional winter snow, the Junggar Basin is cooler and slightly more moist than the Tarim Basin. Most sand dunes are stable or semi-stable in the Junggar Basin.

In neither basin is agriculture possible without irrigation, but since both are surrounded by high mountains of 3,000 7,000 m, the Qilian and Altun Mountains to the south and the Tian Shan and Altay Shan in the north, meltwater from snowfields and glaciers is enough to support farming. Near the edges of allovial fans, large oases with silty desert soils have been centres of irrigated agriculture for millenia. The principal crops are cotton, wheat, maize, grapes, pears, and melons.

Fig. 1.1. Vertical Zonation of Vegetation and Soils on the South Slope of the Tibetan Plateau

Fig. 1 2. Variations in Vegetation and Soils to the North and South of the Qinling Mountains

High Mountain Ranges and Qinghai-Xizang (Tibet) Plateau

There are high moutains in various parts of China. In addition to the Tian Shan and the Qilian Shan in the arid north-west, the Himalayas lie to the south-west and the north-south trending Hengduan Mountains are in the south. In most of these highlands the vegetation and soils exhibit distinct vertical zonality, and some special soil types occur, such as a particular type of cold "desert" soil in periglacial regions. The so-called "desert" soil is in a physiologically dry state. Above the tree-line, soils under grasses and shrubs are dark and contain high levels of humus.

On the Qinghai-Xizang (Tibet) Plateau, with elevations of 3,7005,200 m, agriculture is possible only in the river valleys. Most vegetation is either Alpine meadow or Alpine steppe, and Alpine steppe soils are common. Black soils and mixed tall grasses in the east give way to chernozems and steppe in the west. Grasses of the species Grammisia decrease and Artemisia increase westward, until in the western part of the plateau dry steppe and semi-desert vegetation occur. The soil types change westward from chestnut to brown-pedocal, and in the steppe region scattered soda-saline soils and patches of saline and alkaline soils associated with chestnut soils occur. Large areas of active, semi-stable and stable sand dunes occur in the steppe.

Arid Land in North-west China

The vast territory of the continental zone can be divided into two regions by the 250 mm annual isohyet. East of the line dry farming is possible without irrigation or with only supplementary, seasonal irrigation. To the west lies arid North-west China. Geographically, the arid areas are situated in central Eurasia where climatic conditions are extreme and where extensive, gobi(gravel) deserts and sandy deserts occur. Most of the sandy deserts contain mobile dunes, which may reach a height of 200-300 m.

The Tian Shan Range, 4,000-6,000 m above sea-level, divides the vast Xinjiang Region into two parts, the Tarim Basin in the south and the Junggar Basin in the north. With a mean annual precipitation of only about 30 mm, the former is among the driest warm continental deserts on earth. Its accumulated temperature > 10°C is only 2,500-3,000°C, and the Tarim Basin contains extensive tracts of gobi desert. Where soils occur they are brown desert soils, which, in appearance, resemble salt- or gypsumcrust. The total soluble salt content in the soils may be between 50-60 per cent. Vegetation cover in the gobi areas is sparse, at less than 5 per cent coverage, and as a consequence, severe wind erosion has occurred.

The soils of the plateau are characterized by a low rate of decomposition. Thus plant roots form a closely interwoven, feltlike layer in the surface soils. These black, felty soils are fairly humid. By contrast, some soils formed under comparatively arid steppe conditions may contain very little organic matter.

The vertical zonation of vegetation and soils is wellexemplified on the south slope of the Tibetan Plateau (fig.1.1), where the mountains rise to more than 8,000 m within a distance of some 10 km. Soils and vegetation may exhibit considerable differences on different sides of a high mountain range, in which case, the range may serve to delimit cartographically two distinct land types. The Qinling Mountains is a good example of this (fig.1.2). North of the range is the Loessal Plateau with a warm climate, calcareous loessal soils, and deciduous forests. Wheat and cotton are widespread. South of the range is the subtropical region with luvic and slightly allitic soils under broadleaf evergreen forests, and an agricultural system based on a rice and winter wheat rotation.

In this brief chapter, the major land-use categories of China have been presented in a generalized manner. For a more detailed division, the reader should consult chapter 2.

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