§ 8. #Sources of food supply#. The land area of the country in 1910 was about 1,900,000,000 acres, of which 879,000,000 acres were in farms, this being 46 per cent of the total area. A very small part of the remainder is used for residential and commercial purposes, the rest being barren mountains, deserts, swamps, and forests. Of the total in farms a little more than one-half was improved, 478,000,000 acres altogether, a per capita average of 5.2 acres; and a little less than one-half was unimproved, 400,000,000 acres altogether, a per capita average of 4.3 acres. The improved land produced not merely food but many kinds of materials, such as cotton, wool, hides, and lumber, while much of the unimproved land was either in farm wood-lots, or in rough range pasture. Of course the kinds and amounts of produce per acre vary with the climate, particularly with sunshine and rainfall; possibly the proportion of the area of the United States that is true desert and infertile mountain land is greater than that of any other equal area in the temperate zones. The actual productive capacity per acre of the lands of America cannot be expressed in a very helpful way as a general average per acre, but each area must be carefully studied in respect to its climate, rainfall, and possibility of irrigation and drainage. It is evident that a very large number of economic problems must arise in connection with the land supply for food: such as problems of land-ownership, taxation, irrigation, drainage, forestry, and encouragement or limitation of population. We are just beginning to awaken to the needs in this direction. The rivers, lakes, and ocean waters near our coasts are other great sources of food, but no statistics are available to show adequately their yield. Few of them are in private possession and they do not appear at all in a total of "capitals," yet they are more important to the nation than a large part of the land area. They are only beginning to be developed artificially by the propagation of oysters, clams, and fish. The development of a proper policy in this matter is one of our economic problems. There were in 1910 (mostly on farms) about 64,000,000 beef and dairy cattle, 60,000,000 swine, 56,000,000 sheep and goats, and there were raised in the one year nearly 500,000,000 fowls of all kinds.