Distribution of Vegetation on a Simplified Globe.—The distribu tion of trees, bushes, and grasses over the earth's surface seems at first sight to be most complicated. It follows definite laws, however, as may be seen from a comparison of the accompanying table with Fig. 89. The table shows how vegetation would be distributed on a simplified globe, such as we have used in discussing climate. The map shows, in a general way, the actual distribution. By comparing the map with the table we can see how the distribution of plants is affected not only by the zonal arrangement of temperature and moisture on the earth's surface, but by the relief of the lands, and especially by the presence of moisture. Far larger areas bear sparse vegetation because of aridity than because of low temperature.
(1) Equatorial Rain Forest.—Close to the equator a: simplified globe would be surrounded by a zone of the densest kind of equatorial rain forest. It is called the rain forest because the dry seasons are here so short that the ground never becomes parched, and most of the year there is a superabundance of moisture. As the temperature is always high, vegetation can grow rapidly at all times. The trees rise to great heights and form a somber canopy which shuts out the sunlight. The forest is mostly uninhabited, and the few people who dwell in it are uncivilized savages like those of the Amazon Basin. On the map this kind of forest does not form a continuous equatorial belt, because it is interrupted not only by the oceans but by moun tains and plateaus. Nevertheless it covers vast areas in the Amazon and Congo basins and in the East Indies and the Malay Peninsula. Smaller outlying areas of similar forest are found on the rainy east coasts of Central America and Brazil, on the west coast of India and the Malay Peninsula, and at the base of the eastern Himalayas.
(2) Tropical Jungle.—Poleward of the tropical regions, approxi mately in latitudes to 15°, the rainfall on a simplified globe though still abundant, would diminish and the dry season become longer than at the equator. Hence the equatorial rain forest would give place to the kind of forest called tropical jungle. Many of the trees in such a forest are of large size. More, however, are moderate in height and in some of the drier parts bushes become abundant. The chief characteristic of the typical jungle is the *way in which vegetation runs"riot. The plants crowd upon one another so closely that a person unskilled in the lore of the forest may lose himself in five minutes. This is the part of the world where it is easiest for
man to get a living. Hence in the cleared portions, the population is often dense, but the people do not stand high in civilization. In America the jungle regions comprise large areas in Central America and the northern part of South America, together with southeastern Brazil. In Africa there is a good deal of jungle on the borders of the equatorial forest and also in Abyssinia, Madagascar, and along the eastern coast, but owing to the high altitude the proportion of jungle is less than in other tropical regions. In Asia, the best examples of jungle are in southern India, Indo-China, and the drier parts of the East Indies, while northern Australia also has a considerable area.
(3) Tropical Scrub.—Although equatorial rain forests'and tropical jungle are the two most typical kinds of vegetation in the warmest parts of the earth, there are also vast areas of scrub and grassland Both of these are more or less mixed with the jungle and with each other by reason of variations in soil, altitude, and relief. On a sim plified globe the scrub would form a band on each side of the equator where the jungle diminishes in height and vigor because of the increase in the length of the dry season as one gets farther from the equator. In the scrub regions the bushes are green fully half the year, but lose their leaves during the dry season and look like a second growth in an American woodlot late in the autumn. Occasionally, however, a bare bush covered with great red, white, yellow, or purple flowers makes one realize that he is within the tropics and only 10° to from the equator. In Fig. 89 it is not easy to show the location of areas of tropical scrub with any accuracy because they are apt to be small and scattered. They occur, however, in many parts of southern Mexico and Central America, central and southern Africa, the drier parts of the plateau of India, and the northern portion of Australia. Although civilization is low in such regions, it is often higher than in the jungle regions, as appears in Yucatan and the northern part of the Deccan Plateau in India. This is because disease is less rife than in the insect-infested jungle regions, more work is needed to get a living, and more care must be taken to provide food for the long dry season.