In equatorial regions, which have an abundant rainfall throughout the year, agriculture is directed toward fruits and roots; only in certain districts can it include cereals, and then only rice and maize. The temperate grains demand some dry summer weeks for their maturity. Excessive moisture in Ireland has practically excluded wheat-growing, which in England and Scotland also is restricted chiefly to the drier eastern counties.[1421] It thrives, on the other hand, in Manitoba and the Red River region even with a short season of scant rainfall, because this comes in the spring when moisture is most needed.[1422] Most important to man, therefore, is the question how and when the rainfall is distributed, and with what regularity it comes. Monsoon and trade-wind districts labor under the disadvantage of a wet and dry season, and a variability which brings tragic results, since it easily reduces a barely adequate rainfall to disastrous drought. These are the lands where wind and weather lord it over man. If the rains hold off too long, or stop too soon, or withhold even a small portion of their accustomed gift, famine stalks abroad.
Temperature and zonal location.
Temperature, the other important element of climate, depends primarily upon zonal location, which has far different historical results from central and peripheral location, continental and insular. It determines the amount of heat received from the sun, though air and ocean currents may redistribute that heat within certain limits, and humidity or aridity modify its effects. Still zonal distinctions remain. The great climatic regions of the earth, like the hot, wet equatorial belt or the warm, dry trade-wind belts or the cool, well-watered temperate zones, constitute, through the medium of their economic products and their climatically imposed methods of production, so many socio-political areas, regardless of ethnic and political boundaries. The Berber nomads of the northern Sahara live much as the Semitic Bedouins of the Syrian desert or the Turkoman stock of arid Turkestan. They have the same tribal government, the same scattered distribution in small groups, the same economic basis of subsistence, though of different races and dominated respectively by France, Turkey and Russia. The history of the tropical Antilles has in both its economic and political features paralleled that of the East Indies since the early 16th century. Temperate South America promises to follow in the historical footsteps of temperate North America, South Africa in those of Europe and temperate Australia.
Reactions of contrasted zones.
While people of the same latitude live approximately under the same temperature conditions, those of contrasted zones are subjected to markedly different influences. They develop different degrees of civilization, wealth, economic efficiency, and density of population; hence they give rise to great historical movements in the form of migration, conquest, colonization, and commerce, which, like convection currents, seek to equalize the differences and reach an equilibrium. Nature has fixed the mutual destiny of tropical and temperate zones, for instance, as complementary trade regions. The hot belt produces numerous things that can never grow in colder countries, while a much shorter list of products, coupled, however, with greater industrial efficiency, is restricted to the Temperate Zone. This explains the enormous importance of the East Indian trade for Europe in ancient and medieval times, the value of tropical possessions for commercial countries like England and Holland. It throws light upon the persistence of the tropical plantation system in the Dutch East Indies and republican Mexico, as formerly in the sugar and cotton fields of the Southern States, with its relentless grip upon the throat of national life in hot lands.
Temperate products from tropical highlands.
Tropical regions, however, may profit by the fact that their mountains and plateaus permit the cultivation of temperate crops. India during the last century has introduced tea culture extensively on the Assam and Nilgiri Hills, and in the Himalayan valleys up to an altitude of 7000 feet.[1423] Besides this temperate product, it has put large areas into cotton, chiefly in the peninsular plateau of the Deccan, and by means of these two crops has caused a considerable readjustment in world commerce.[1424] Nevertheless, here the infringement of the principle of tropical production in the torrid zone is after all slight. In tropical America, on the other hand, the case is quite different; this region presents an interesting paradox in relation to its foreign commerce. Here the highlands are the chief seats of population. They contain, moreover, the most industrious and intelligent native stock, due to geographical and historical causes running back into the ancient civilizations, as well as the largest proportions of immigrant Europeans. This is true not only of the Cordilleran states from northern Mexico to the borders of Chile, but also of Brazil, whose center of population falls on the plateau behind Rio de Janeiro and Santos. The isolation of these high plateaus excludes them to a serious extent from foreign trade, while their great altitude permits only temperate products, with the exception of sub-tropical coffee, which is their only crop meeting a great demand. The world wants, on the other hand, the long list of lowland tropical exports which torrid America furnishes as yet in inadequate amounts, owing to the lack of an industrious and abundant lowland population. Commerce will eventually experience a readjustment in these localities to the natural basis of tropical production; but how soon or how effectively this change will take place depends upon the question of immigration of foreign tropical peoples, or the more difficult problem of white acclimatization.[1425]