98 SYLVICULTURE IN THE TROPICS 





rt. i 



importance to have some definite information for the 

 areas covered with forests which are leafless part of 

 the year, and still more for the more open formations, 

 such as savannah-forests and thorn -forests. In the 

 last-named class the forest is not only more open, but 

 the organs of transpiration are formed so as to reduce 

 evaporation to a minimum. 



But if proofs are not sufficiently abundant as regards 

 the influence of different classes of forests on rainfall, 

 they are abundant as regards their influence in storing 

 up rain-water and in preventing sudden floods. This is 

 especially the case in hilly countries. On level land 

 it is possible that, as the Chief of the Washington 

 Weather Bureau asserts, ploughed land takes up and 

 retains as much water as soil under forest does ; this 

 would, no doubt, depend greatly on the amount of 

 humus and fallen leaves lying on the ground in the 

 forest. But this is not the only consideration. Once 

 the surface soil is filled to saturation the remainder flows 

 off, and, under tropical rains especially, the rush of water 

 within the forest is checked to a much greater degree 

 than in open land; and not only is the danger of erosion 

 greater in the latter, but there is also a greater danger 

 of sudden floods due to the watercourses being filled 

 more rapidly. Unfortunately, also, within the Tropics 

 all cleared land is not under plough or under grass, but 

 large areas are bare and barren, the result of a thriftless 

 system of shifting cultivation ; the surface is hard and 

 not easily accessible to water, and the major portion of 

 the water runs off and is lost. 



The effects of denudation caused bv rain-water on hill 

 slopes have been studied and verified for many years. 

 In Europe the damage caused in the Alps and in the 

 Pyrenees has resulted in special legislation, and in the 

 starting of extensive re -afforestation schemes. In 

 America the Forestry Bureau has published much 

 literature, accompanied by numerous excellent illustra- 

 tions, in order to educate the people of the United States, 

 and to make them realise the necessity of taking pre- 



