FOREST COMMUNITIES 429 



the subdued light of the forest interior. A recent classification gives 

 the following: 2 



8. The air above the forest (not permanently occupied by any 



species). 

 7. Trees extending here and there above the main forest roof, 



125 ft. or more high. 

 6. The upper forest canopy, 75-80 ft. high. 

 5. Lower tree tops, 40-60 ft. high. 

 4. Small trees, 20-30 ft. high. 

 3. Higher shrubs, 10 ft. high. 

 2. Forest floor and low herbs. 

 1. Subterranean stratum. 



The animal life in tropical rain-forests is much affected by the fact 

 that, unlike forests in the temperate zones, there is an astonishing 

 number of different species of trees within a small area. Even in tem- 

 perate mixed forests barely 10-15 species of trees are present, while uni- 

 form stands of oak or beech and maple or pine may stretch for miles. 

 On the other hand, 400-500 species of trees and some 800 species of 

 woody plants have been described from the Cameroon forest; seldom 

 do two specimens of the same tree stand side by side, and fruit-bearing 

 trees are usually widely separated. More rarely the stands are uniform, 

 as when palms dominate a low-lying region to the exclusion of other 

 types. In the usual mixed forest of the tropics some trees may be los- 

 ing their leaves while others have a fresh foliage; still others may be 

 in blossom while fruit hangs ripe on the neighboring tree. Only in such 

 a forest can stenophagous, nectar-feeding or fruit-eating forms exist 

 the year round. 



The leafy canopy casts a heavy shade which prohibits grass from 

 growing within the denser types of forests and limits grass-eating 

 animals to non-forested regions or to the forest margin. Brilliantly 

 colored animals, birds in particular, disappear in the leaf and branch 

 tangle of the tree tops and appear gaudy only when one has the ani- 

 mal in hand. The dense vegetation retains the internal forest moisture 

 and makes for such constancy of temperature that it rarely falls 

 below 21-22° or rises above 28-29°. 27 Such hothouse air is in marked 

 contrast with that of the open tropical grasslands and, together with 

 other factors in the forest environment, makes forest-dwelling mam- 

 mals tend to be smaller than neighboring varieties from the open 

 country. Thus the tapir of the Guiana forests is smaller than that from 

 the savanna; 28 and the forest buffalo and the leopard of Africa are 

 relatively dwarfed forms. 29 The same tendency is seen among the 

 human inhabitants. 30 



