Short Grass is only a few inches high, occurring in a temperate region with rainfall of 15 to 3o in., with a long drought and a cold rest period. The grama, buffalo-grass, spear-grass and needle-grass are valuable for grazing. The better portion of this land is used for dry farming. The soil is dark brown with an accumulation of carbonate at a depth of 8 in. to 3 ft. below the surface. The world area of this grassland is about 1,200,000 sq.m., chiefly in North America, South America, Africa and Russia.
Desert Grass Savanna, sometimes called Orchard or Thornbush Steppe, consists of a carpet of short or low bushy grasses, includ ing grama-grass, buffalo-grass, wire-grasses, and scattered small trees, with leguminous and other shrubs. Rainfall is from io to 20 in., and there is a long, hot drought period. About 2,300,000 sq.m. are occupied by this type of grassland; it is valuable as grazing land of low-carrying capacity. About 140,000 sq.m. are valuable agriculturally, producing cotton, sorghums and peanuts.
Mountain Grassland occurs on the high mountains in the tropics. The climate is temperate with 4o to 6o in. of rain. The grasses are chiefly species of blue-stem (Andropogon) (Eragros tis) and dropseed-grass (Sporobolus). It is generally valuable grazing land, and under cultivation produces temperate crops as well as bananas and coffee and is similar to the Temperate Rain Forest. The world area is about 790,000 square miles.
Marsh Grass occurs in the great swamp areas and consists of coarse grasses. It supports a fauna valuable for meat, furs and ivory, but without drainage is of no agricultural value. The world area is about ioo,000 square miles.
Salt Desert Shrub occupies the low, undrained saline basins in all desert regions. It is valuable for grazing land, but for agricul ture it must be leached of salt. The world area is about 30,000 square miles.
Desert in the true sense is seldom found, but at least during much of the year many areas seem lifeless. The flora is abundant in species if not in individuals, and the plants are adapted to the extremes of drought and uncertain moisture supply. The world area in Africa, Asia, South America and Australia is about 2,400,00o sq.m. and is of little value.
Tundra (including Alpine Meadow) shows mixed botanical composition. The growth period is short with a long, cold rest period. In summer the temperature rises gradually to 6o° or 6° F, and during the continuously dark winters the temperature falls to 40° F below zero. This area is valuable for grazing land, though not especially productive. The circumpolar world area is about 4,400,000 square miles. (H. L. Sic) In an inventory of the world's resources it is as important to consider the soil in its crop-producing capacity as it is to estimate the reserves of coal, copper and oil, substances more commonly thought of in this connection. All of our food, our clothing and many of our utensils, implements and ornaments come either directly or indirectly from the land. (See FOOD SUPPLY OF THE WORLD.) The crop producing capacity of the soil is, however, a natural resource in a somewhat different way from that represented by coal or oil. These substances have a definite entity and can be estimated in tons and gallons. Once depleted they are manifestly gone. The soil, on the other hand, is a resource because of its ability to produce crop-plants. This capacity varies, it may be much reduced and then be definitely rebuilt.
While an accurate and complete tabulation of the soil resources of the world is impossible, the table in the next column gives some idea of the situation. (See SOIL; AGRICULTURE.) Besides indicating the magnitude of the soil resources in acres, the table shows the proportion of the landed area available for crop-plants. This in connection with the population has an im portant bearing on the possible agricultural and silvicultural independence of each country. Such countries as Argentina, Can ada, Australia and Russia can support much larger populations. Their forest resources in terms of population are also great.