VEGETATION.—The forest vegetation of a great part of South America is extremely rich and varied, and this is accounted for by the high temperature of the intertropical region, the abundance of moisture resulting from large areas having either no dry season or but a short one, and the fact that many of the rivers overflow their banks during a considerable part of the year.
The most luxuriant tropical rain and monsoon forest covers a great part of the Andes in Colombia and Venezuela, and stretches along the north-east coast of the continent to beyond the mouth of the Amazon ; it extends up that river and its tributaries, and southward along the eastern slope of the Cordillera for a considerable distance. Throughout the whole of this region the general characteristics of the forest are the same. There is a great variety and constant intermixture of species, and among the more important products are rubber, dyewoods, cabinet woods, medicinal plants, and fruit trees, which are bound together by lianes and covered with epiphytes. Hence the forest is gloomy, and in the continual struggle for light the trees grow to a great height. This type of vegetation reappears along the south-east coast of Brazil between the fifteenth and thirtieth parallels, where, as already mentioned, there is considerable rainfall.
The greater part of the Guiana Highland, and of the llanos which lie to the west and north of the Orinoco, is typical savanna—grass land scantily dotted with trees. The Brazilian upland also, with the exception of the valleys of the larger rivers and the coast regions, is to a large extent covered with savanna. The dry season lasts for over three months, and it is only in districts where a supply:of water can be obtained during that period that trees are found. Elsewhere grass, shrubs, and arboreal cacti cover the ground, and this inter mixture of woodland and grassland is characteristic of the Matto Grosso. In the north of eastern Brazil, where the rainfall is low,
occur the caatingas, which are light forests consisting of thorny shrubs, while in the south the campos are covered with long grass intermingled with araucaria thickets. The Gran Chaco, a region of summer rainfall, is characterised by thorny scrub, palm groves, and in places even by dense arboreal vegetation.
Further south, in the Argentine, especially around La Plata estuary, come the great undulating grassy plains called the pampas. Here the rainfall is well distributed throughout the year, the vege tative season warm, and the desiccating winds unfavourable to tree growth. In the slight depressions or cafiados, where water tends to collect, the grass grows in close formation, but on the intervening ridges an open formation prevails. West of the pampas there stretches towards the Andes a woodland region, the trees of which are very varied, but, with few exceptions, are char acterised by " stunted growth, scraggy ramification, light crowns, and rich formation of thorns." In the west and in the south, this thorn forest passes into poor steppe.
Along the west coast of the continent from about the thirtieth parallel southward, the lower slopes of the mountains are covered in the north, where Mediterranean conditions prevail, with sclero phyllous woodland, in the centre with temperate rain forest, of which laurels and beeches and a very dense undergrowth are the characteristic features, and in the south with summer forest consisting largely of beech.
The desert regions of South America extend along the western coast from the Gulf of Guayaquil to Northern Chile, the vegetation everywhere being exceedingly poor. On the Cordilleran Plateau, within the tropics, is the Puna, covered with a stiff xerophilous grass, while further south Alpine plants and shrubs prevail.