The natural vegetation is perhaps the best summary of the physical environment, for it reflects the temperature, rainfall, drainage, elevation and soil conditions. In nature, all physical phenomena are interrelated; together, these provide us with an understanding of the physical environment.
The patterns of their distribution and interactions are of crucial importance to us, as we have to depend on these for our sustenance. However, we have substantially modified the natural vegetation and the soils that were present before human intervention and that have been replaced by other forms.
It is important to note that over one- third of the continent’s surface has been cleared for human settlement or given to permanent agriculture. Vegetation in such areas no longer remains “natural”. In most areas of dense settlement the original vegetation has been entirely removed and no trace of undisturbed forest remains.
Thus, the Indus-Ganga plains in India, lower Chao plains in Thailand, the lower basin of Huanghe, Chang Jiang, and Xi Jiang rivers in China are almost covered with cropland. Throughout these and other intensely settled areas in Java (Indonesia) and Japan, imported plants have replaced the indigenous vegetation.
Original cover can only be found in the remote and inhospitable areas, such as northern and northeastern Siberia, and parts of Southeast Asia. Reflecting the growing awareness of the consequences of deforestation and loss of natural vegetation, reforestation is becoming increasingly popular, and preservation and recovery of forest areas has become a national priority for several Asian nations, although this practice is not as widespread as in the U.S.A. or in the European nations.
The nations in the Indian subcontinent, because of their enormous populations and deficiency in timber resources, are sensitive to the issue and have launched several reforestation programmes. China, Malaysia, and Turkey have also included in their national plans aimed at increasing forest lands and in the case of Turkey to reduce timber imports.
Asia’s enormous territory, immense variety of relief and a wide range of climates combine to produce most types of vegetation forms. A dominant feature of the continent’s vegetation is that a larger territory on the western side has no oceanic border, and receives scanty rainfall in relation to summer temperatures that can allow appreciable forest growth. The broad pattern of natural vegetation generally follows the climatic types; it is thus convenient and useful to describe it in association with the climatic patterns of Asia.
The Tundra climatic type correlates with its namesake vegetation, Tundra vegetation that borders the Arctic Ocean. It is a region of cold, treeless plains with permanently frozen subsoil. Lichens, mosses, sedges and some grasses may occupy more favored locations. The Tundra belt extends to 70°N and with further south extensions on high altitudes (Chersk, Verkhoyansk and Kamachatka mountains).
South of the Tundra region is the Taiga, a belt of coniferous forests, or the needle-leaf evergreen forest, with a small, transitional zone of “wooden tundra”. It covers most of Siberia from the Urals to the Pacific and northern part of Japan. The trees have small leaves, deep roots, and thick bark, and thus most species (pine, spruce, fir, etc.) are successful in cold and dry environment. Further east and southwest of Siberia is a transitional zone of coniferous forest mixed with hardy, deciduous trees such as aspen and birch, with sections of grass and shrubs in the drier areas.
Temperate Grasslands, the Steppes:
To the south of Taiga is elongated, unbroken stretch of the Steppes from Ukraine to Manchuria—a broad belt of several thousand miles of temperate grasslands in southern Siberia— a parkland country of open grasses. There is some precipitation although the winters are still very cold, but the extreme temperature ranges of the Taiga are softened by the warm summers. However, the higher elevations in the mountains are covered with forests, and the dry valleys are bare except for the occasional cultivated oases.
Mediterranean Scrubland and Forest:
A belt of scrub forest that is particularly attuned to the Mediterranean climatic regime rims the eastern shore of the Mediterranean that includes the countries of Israel, Lebanon, Syria, Iraq, and the plateaus of Turkey and Iran. The summers are hot and dry; the winters mild and moist. Thus, the circumstances for the plant community are unusual; winters become the growing period.
Plants must adapt to conditions of drought and higher temperatures in summers. They share the adaptive characteristics of small plant size, short leaves, deep roots, and thick barks to retain moisture. The most distinctive vegetation community of this region consists of a scrubland and short trees.
The desert climatic and associated vegetation types are found in the trade wind deserts of the Arabian Peninsula, the deserts of Tibet, Mongolia, and the desert-like steppe-lands bordering the Caspian Sea. The mid-latitude deserts of Tibet and Mongolia in the interior resemble the Arabian Desert only in aridity, but contain a clear altitudinal zonation of vegetation.
Plant cover in the deserts is sparse, with a considerable bare ground dotted by a scattering of individual plants. Typically, the plants are moisture-combating, waxy, deep-rooted or thorny shrubs and sporadic stunted trees. The upper reaches of the highlands in Tibet or Mongolia may be bare, or contain Taiga- and Tundra-like vegetation depending on the amount of available moisture.
This region is associated with monsoon climates. The natural vegetation varies with the amount of annual rainfall. Areas receiving between 40 and 80 inches of rainfall annually contain tropical deciduous (shedding leaves seasonally) forests, and those which receive less than 40 inches have savanna (tall grasses) and steppe-like (of short grasses) vegetation, below which semi-desert and desert vegetation prevails. The monsoon lands have been extensively modified by human settlement and put to cultivation, and little trace of the original vegetation survives.
Tropical rain-forests are typical to the equatorial regions. In Malaysia and Indonesia rainforests cover large section of the countries, whereas in southern Sri Lanka and Java they have almost entirely replaced by agricultural landscapes where plantations of tea, coconut palms, and rubber trees cover the Mountain slopes and hills.
The vegetation consists of evergreen, broad-leafed tall, 2ense, high-crowned trees of several species having a dense canopy above the floor because the region gets a high amount of precipitation throughout the year, and is constantly warm. The savannas and deciduous trees cover the ground, the subequatorial and the areas that lie in the rain shadow on the leeward slopes.
Vegetation in the Mountains:
The mountains of southern and eastern Asia show a remarkable altitudinal zonation in natural vegetation. A zone of forest followed higher up by meadows, and snow cover at the highest elevations is characteristic. On the lower slopes are the broad-leafed deciduous forests, and on higher ground the coniferous trees occur.
Still higher up stunted trees, subalpine meadows and near the highest ridges perennial snow, and glaciers are found in a vertical zonation pattern. Elsewhere in the equatorial region in Malaysia and Greater Sunda Islands, (Indonesia) where the snow line is very high and moist-hot conditions predominate, the vegetation zonation is practically absent.
Along with the climate the distribution of soils is critically important to agricultural productivity, and thus has a special significance for nations of Asia, as most Asians depend on agriculture for their livelihood. In the preceding paragraphs, wide range of interacting natural phenomena: climate, natural vegetation, parent rock material and relief features that determine the development and nature of soils have been discussed for the Asian continent.
Soil classification is both complicated and subject to constant revision. In the case of Asia, the difficulty is compounded by the fact that a large part of it is physically remote, or climatically inhospitable for field surveys. Most of Asia has been surveyed unequally based on different systems with the result that comparable knowledge of soil types and their characteristics is difficult to obtain.
Some part of the continent still remains un-surveyed. In addition, the most commonly used current classification at the present time—that of the U.S. Department of Agriculture known as the Seventh Approximation— has not gained much acceptance in most Asian nations.
It may be interesting and sobering to realize that a small fraction of Asia’s land surface is blessed with really rich soils that have given sustenance to a large mass of humanity.
At the broad scale of our study, it may be convenient to generalize the distribution patterns of soils by recognizing that there are basically three complex processes by which soils are formed; those of the humid latitudes, of the tropical regions and of the deserts. Each of these processes are responsible for the formation of specific types of soils which can be defined in broad terms.
The processes produce either the pedocals or calcium-bearing soils, or the pedalfers, the aluminum-bearing or nitro- gen-bearing soils. The letters “cal”, “al”, “fe” representing three distinctive elements in soils. In simple terms, this division separates the basic soils from the acidic soils. Soil patterns based on such classification point to some general tropical regions.
Two fundamental soil-forming processes operate in the humid regions; podzolization in the cool, wet regions, and Laterization in the hot, wet regions. Podzolization is thought to remove the soluble salts, iron and aluminum compounds from the surface horizons, leaving a gray silica residue; and laterization begins by removing the salts, and transferring the iron and aluminum compounds near the surface with clays accumulating just underneath them.
Soils in the tropical areas are generally lateritic, having varying degrees of red or black color. The soils are rich in aluminum and iron oxides, low in silica; are nearly structureless and generally of low fertility. Most soils of South and Southeast Asia belong to this category. In the Arabian Desert and deserts in Central Asia the soils are usually high in their content of unleached minerals, but may be deficient in their content of nitrogen and humus (decomposed vegetative materials of the wet tropics).
Where the water-table is high, evaporation salts have accumulated in excess near the surface, the soils are alkaline. Such red desert soils cover much of the Arabian Peninsula and northwest India, while higher desert soils cover the rest of southwest Asian countries.
Large parts of northern Asia are covered by podzolic soils of varying, but generally low fertility. These soils cover the mid-to high-latitude locations in the region of well-distributed rainfall (in coniferous forest of a taiga forest zone) from the Urals to Kamchatka. In much of northern China and Manchuria soils belong to the gray-brown podzolic category.
In the Mediterranean lands the pattern of soils is complicated. While cool temperatures and some rainfall produce podzolic conditions during winter, hot summers complicate the conditions when surface evaporation exceeds rainfall and moisture moves upward through capillary action and the podzolization process no longer operates. The grasslands of western Siberia, Manchuria, and most of Anatolia plateau of Turkey are underlain by black prairie and chernozem soils which have good texture and are of generally high fertility.
From the standpoint of agricultural productivity, the most important soils in Asia are the relatively immature soils of alluvial origin that are found in the river valleys. These soils are among the richest in plant nutrients which can maintain their fertility through periodic inundatation by silt-bearing waters from the rivers in flood.
Alluvial soils cover the river valleys of the Tigris-Euphrates, the plains of Indus-Ganga Rivers, the lower Irrawaddy basin, the deltas of the Mekong and the lower basins of Chang Jiang, Huanghe Rivers, as well as the river plains of smaller rivers in India, Malaysia, the Philippines, Taiwan, Korea, and Japan. These, in a very large measure, provide substance to the growing population of Asia.
Several islands of Indonesia and southern Philippines contain active volcanoes that periodically provide a new layer of rich basic soils of recently deposited volcanic materials (not all volcanic soil consists of basic material; some retain their fertility for long periods as these are renewed occasionally by new deposits, and account for enormous densities of rural population in Java and some areas of the Philippines).
Soils in the hilly and mountainous regions are produced by geologic structure, altitude, and temperature conditions to a greater degree than elsewhere. These may be lumped together as montane soils. A good part of the Asian surface of the uplands is too steep for the formation of deep soils. Skeletal soils are found in such areas, much of which are cropped by shifting cultivation, in which the cyclical use of land provides periodic regeneration of plant nutrients.
In northwest China some areas are covered by a thin layer of wind-blown material dating from the retreat of the ice sheet during the most recent Ice Age. This material is known by the term loess, and adds considerably to the natural fertility of the soil and thus to the agricultural productivity of the area.
Surveying the overall picture of soil distribution in Asia, it can be concluded that for its size, much of the continent offers limited opportunities for productive agricultural land. No more than 20 percent of the land surface is estimated to contain soils suitable for agriculture and a good quarter of this percentage contains soils of marginal value.
Tropical and subtropical soils are generally immature and unproductive. The soils of the middle latitudes are themselves suitable, but lack of water is often a key factor. Only the alluvial soils of the river plains and the basic soils produced by the volcanic ejecta are productive soils.
Several of the river basins, where the soils are rich, have been settled for hundreds of centuries and the soil cropped by hundreds of generations of farmers, and where enormous population densities are straining agricultural productivity. In such lands good soil management is an important factor as an agricultural resource.
Most Asian farmers have not taken to farming practices restoring plant nutrients to the soils they farm. The diffusion of the Green Revolution is still limited to a few, selected areas in India, Pakistan, Sri Lanka, the Philippines, and Taiwan where farmers have been making use of superior seeds of hybrid plant varieties, chemical fertilizers, and mechanized farming.