8] MODIFICATION AND DISTRIBUTIONS OF CROPS 247 



countries south of the Himalayas comprise nearly lOO per cent, of 

 the trees. The species of tropical hardwoods in an area are often 

 very numerous, India, for example, being estimated to have fully 

 2,000. The dominance tends to be intricately mixed, although Teak 

 {Tectona grandis) and various members of the Dipterocarp and Pea 

 families are often prominent. Important commercially, if not 

 always ecologically, are Ebony (various plants including Diospyros 

 ebenum), Satinwood {Chloroxylon swietenia), and Burmese Rosewood 

 {Pterocarpus indicus). 



South America, as we have seen, bears a greater proportion of 

 forested area than remains on any other continent. Nearly 90 per 

 cent, of its forest is tropical hardwood — mainly dense rain forest 

 which characterizes the great river basins and tends to be very 

 luxuriant and intricately mixed (there are said to be over 2,500 

 different tree species in the Amazonian forests alone). In some 

 drier areas an open deciduous type of tropical forest occurs, and on 

 the high mountains are mixed forests of Conifers and temperate 

 hardwoods. Important woods of tropical America include Balsa 

 {Ochroma lagopiis s.l., the lightest of commercial timbers), Spanish- 

 cedar [Cedrela odorata s.l., forms of which are native in some areas 

 but introduced in others), Greenheart [Ocotea rodioei), Lignum- 

 vitae (species of Gtiaiaciim), Locust {Hymenaea coiirharil), and 

 Mahoganv (chieflv Swietenia macrophylla and S. tnahagoni, of which 

 the latter has been widely introduced). 



In Africa, contrary to popular conception, forests cover only about 

 II per cent, of the land area. Tropical hardwoods predominate, 

 comprising some 97 per cent, of the forests. Here again there are 

 two main types, of which the dense and much-mixed rain forest is 

 the more extensive but is replaced by an open, park-like type where 

 the rainfall amounts to only 30-40 inches per annum. Of the woods 

 that have so far been exploited, an outstanding example is the 

 African Mahogany {Khaya senegalensis), which is widely exported. 



Although in Australia forests cover only a very small proportion 

 of the land area, in New Zealand the percentage is about 26 and in 

 Oceania 71. In Australia tropical hardwoods predominate — par- 

 ticularly species of Eucalyptus and Acacia — and in Oceania they make 

 up the entire forest. On the other hand in New Zealand 68 per 

 cent, of the forests are coniferous and the remainder temperate 

 hardwoods, though the genera tend to be different from those pre- 

 dominating on other continents. 



