Climate.—Bolivia lies wholly within the torrid zone, and
variations in temperature are therefore due to elevation, mountain
barriers and prevailing winds. The country possesses
every gradation of temperature, from that of the tropical lowlands
to the Arctic cold of the snow-capped peaks directly above.
This vertical arrangement of climatic zones is modified to some
extent (less than in Argentina) by varying rainfall conditions,
which are governed by the high mountain ranges crossing one
corner of the republic, and also by the prevailing winds. The
trade winds give to S. Bolivia a wet and dry season similar to
that of N. Argentina. Farther north, and east of the Cordillera
Oriental, rains fall throughout the year, though the summer
months (November–March) are usually described as the rainy
season. On the west side of the Cordillera, which extracts the
moisture from the prevailing easterly winds, the elevated plateaus
have a limited rainfall in the north, which diminishes toward the
south until the surface becomes absolutely barren. Brief and
furious rain-storms sometimes sweep the northern plateau, but
these are not frequent and occur during a short season only.
Electrical wind storms are frequent in these high altitudes.
Bolivia has a wide range of temperature between places of the same latitude. The natives designate the Bolivian climatic zones as yungas, valle or medio yungas, cabezera de valle, puna and puna brava. The yungas comprises all the lowlands and the mountain valleys up to an elevation of 5000 ft. The temperature is tropical, winter is unknown and the atmosphere is exceedingly humid. The mean temperature, according to official estimates, is 70° F., but this probably represents the average between the higher elevations and the low country. The valle zone includes the deep valleys from 5000 to 9500 ft., has a warm climate with moderate variations in temperature and no cold weather, is sub-tropical in character and productions, and is sometimes described as a region of perpetual summer. The cabezera de valle, as the name indicates, includes the heads of the deep valleys above the valle zone, with elevations ranging from 9500 to 11,000 ft.; its climate is temperate, is divided into regular seasons, and is favourable to the production of cereals and vegetables. The puna, which lies between 11,000 and 12,500 ft., includes the great central plateau of Bolivia. It has but two seasons, a cold summer or autumn and winter. The air is cold and dry, and the warmer season is too short for the production of anything but potatoes and barley. The mean temperature is officially estimated as 54° F. The puna brava extends from 12,500 ft. up to the snow limit (about 17,500 ft.), and covers a bleak, inhospitable territory, inhabited only by shepherds and miners. Above this is the region of eternal snow, an Arctic zone within the tropics. In general, the sub-tropical (valle) and temperate (cabezera de valle) regions of Bolivia are healthy and agreeable, have a plentiful rainfall, moderate temperature in the shade, and varied and abundant products. There is a high rate of mortality among the natives, due to unsanitary habits and diet, and not to the climate. In the tropical yungas the ground is covered with decaying vegetation, and malaria and fevers are common. There are localities in the open country and on exposed elevations where healthy conditions prevail, but the greater part of this region is considered unhealthy. The prevailing winds are easterly, bringing moisture across Brazil from the Atlantic, but eastern Bolivia is also exposed to hot, oppressive winds from the north, and to violent cold winds (surazos) from the Argentine plains, which have been known to cause a fall of temperature of 36° within a few hours. According to the Sinópsis Estadistica y Geográfica de la República de Bolivia (La Paz, 1903), the average mean temperature and the annual rainfall in eastern Bolivia are as follows: 10° S. lat., 90.8° F. and 31.5 in. rainfall; 15° S. lat., 86° F. and 30.7 in. rainfall; 20° S. lat., 81° F. and 30 in. rainfall; and 25° S. lat., 76.8° F. and 29.3 in. rainfall.
Fauna.—The indigenous fauna of Bolivia corresponds closely to that of the neighbouring districts of Argentina, Brazil and Peru. Numerous species of monkeys inhabit the forests of the tropical region, together with the puma, jaguar, wildcat, coati, tapir or anta, sloth, ant-bear, paca (Coelogenys paca) and capybara. A rare species of bear, the Ursus ornatus (spectacled bear) is found among the wooded Andean foothills. The chinchilla (C. laniger), also found in northern Argentina and Chile, inhabits the colder plateau regions and is prized for its fur. The plateau species of the viscacha (Lagidium cuvieri) and the widely distributed South American otter (Lutra paranensis) are also hunted for their skins. The peccary, which prefers a partially open country, ranges from the Chaco to the densely wooded districts of the north. There are two or three species of deer, the most common being the large marsh deer of the Chaco; but the deer are not numerous. The armadillo, opossum, ferret and skunk are widely distributed. The amphibia are well represented throughout the lower tropical districts. Alligators are found in the tributaries of the Paraguay and their lagoons, lizards and turtles are numerous, and the batrachians are represented by several species. Snakes are also numerous, including rattlesnakes and the great boa-constrictors of the Amazon region.
The most interesting of all the Bolivian animals, however, are the guanaco (Auchenia huanaco) and its congeners, the llama (A. llama), alpaca (A. pacos) and vicuña (A. vicugna), belonging to the Camelidae, with the structure and habits of the African camel, but smaller, having no hump, and inhabiting a mountainous and not a level sandy region. They are able to go without food and drink for long periods, and inhabit the arid and semi-arid plateaus of the Andes and the steppes of Patagonia. The guanaco is supposed to be the original type, is the largest of the four, and has the greatest range from Peru to Tierra del Fuego. The llama and alpaca were domesticated long before the discovery of America, but the guanaco and vicuña are found in a wild state only. The llama is used as a pack animal in Bolivia and Peru, and its coarse wool is used in the making of garments for the natives. The alpaca is highly prized for its fine wool, which is a staple export from Bolivia, but the animal is reared with difficulty and the product cannot be largely increased. The vicuña also is celebrated for its wool, which the natives weave into beautiful and costly ponchos (blanket cloaks) and other wearing apparel. The guanaco is hunted for its skin, which, when dressed, makes an attractive rug or robe. The slaughter of the guanaco and vicuña is rapidly diminishing their number. The rearing of llamas and alpacas is a recognized industry in the Bolivian highlands and is wholly in the hands of the Indians, who alone seem to understand the habits and peculiarities of these interesting animals.
Of birds and insects the genera and species are very numerous and interesting. The high sierras are frequented by condors and eagles of the largest size, and the whole country by the common vulture, while the American ostrich (Rhea americanus) and a species of large stork (the bata or jaburú, Mycteria americana; maximum height, 8 ft.; spread of wings, 8 ft. 6 in.) inhabit the tropical plains and valleys. Waterfowl are numerous and the forests of the warm valleys are filled with song-birds and birds of beautiful plumage. Many species of humming-birds are found even far up in the mountains, and great numbers of parrots, araras and toucans, beautiful of feather but harsh of voice, enliven the forests of the lowlands.
Like other South American states, Bolivia benefited greatly from the introduction of European animals. Horses, cattle, sheep, goats, swine and poultry were introduced, and are now sources of food and wealth to a large part of the population. Mules are used to a large extent as pack animals, but they are imported from Argentina. Silkworms have been bred with success in some departments, and the cochineal insect is found wherever the conditions are favourable for the cactus.
Flora.—Owing to the diversities in altitude the flora of Bolivia represents every climatic zone, from the scanty Arctic vegetation of the lofty Cordilleras to the luxuriant tropical forests of the Amazon basin. Between these extremes the diversity in vegetable life is as great as that of climate and soil. The flora of Bolivia has been studied less than the flora of the neighbouring republics, however, because of the inaccessibility of these inland regions. Among the more important productions, the potato, oca (Oxalis tuberosa), quinoa (Chenopodium quinoa) and some coarse grasses characterize the puna region, while barley, an exotic, is widely grown for fodder. Indian corn was cultivated in the temperate and warm regions long before the advent of Europeans, who introduced wheat, rye, oats, beans, pease and the fruits and vegetables of the Old World, for each of which a favourable soil and climate was easily found. In the sub-tropical and tropical zones the indigenous plants are the sweet potato, cassava (Manihot utilissima and M. aipi), peanuts, pineapple, guava, chirimoya (Anona cherimolia), pawpaw (Carica papaya), ipecacuanha (Cephaelis), sarsaparilla, vanilla, false jalap (Mirabilis jalapa), copaiba, tolu (Myroxylon toluiferum),
