14] VEGETATIONAL TYPES OF TROPICAL LANDS 439 



vegetation, there often occur, along rivers, ' fringing forests ' which 

 are evergreen and otherwise reminiscent of the rain forest (although 

 usually less luxuriant). 



In spite of the widespread destruction wrought by Man particularly 

 during the past century, it has been computed that one or other 

 form of tropical rain forest or ' seasonal ' forest {see below) still 

 occupies about half of the total forested area of the world. 



Tropical Forests with a Seasonal Rhythm 



Where marked dry seasons occur in the otherwise humid tropics 

 and the dominants are dependent upon seasonal rainfall, the vegeta- 

 tion presents a much more varied appearance. Here conditions 

 tend to be so ' critical ' that slight differences in the climate or soil 

 may introduce marked changes in the plant formations. Actually, 

 regions with one or sometimes two pronounced dry seasons of several 

 months' duration occupy a much greater area in the tropics than 

 those with a constantly humid climate and luxuriant evergreen 

 vegetation. Such ' seasonal ' climates of marked extremes are par- 

 ticularly characteristic of the interiors of continents. When their 

 areas are timbered and tropical or subtropical, they may be classified 

 in the following three main groups of descending water-availability : 



I. Widespread though variable are the monsoon forests or similar 

 ' seasonal ' forests, developed in regions enjoying abundant rainfall 

 during the wet season, but having this alternating with a pronounced 

 drought lasting from four to six months or sometimes longer. The 

 total amount of rainfall is usually less than in tropical rain forests, 

 being commonly between loo and 200 cm. per annum if we include 

 in this category areas dominated by a rather wide range of deciduous 

 types ; and there are marked daily and seasonal changes in tempera- 

 ture as well as, commonly, strong winds. Often the character of the 

 forest has been changed by human interference, to which its main- 

 tenance may even be due, for the dominants are apt to be fire- 

 resistant. 



Monsoon or allied forests are found in the areas of the true 

 monsoons in India, Burma, Indo-China, and southwards to northern 

 Australia, as well as on the margins of the tropical rain forest in 

 Africa, Madagascar, Indonesia, and Central and South x\merica. 

 Their vegetation is not as luxuriant as that of the tropical rain forest, 



