6 TROPICAL AGRICULTURE 



With the extension of stock grazing, the forest trees were 

 destroyed, especially on the upper elevations, and the forest 

 destruction was soon followed by the loss of moisture from 

 the soil due to the increased evaporation under the exposure 

 to the constant trade winds. The soils of these islands are 

 fine clay in mechanical texture and are readily carried away 

 as dust in the wind. During a period of moderately strong 

 trade winds a continuous dust cloud from the Island of Kahoo- 

 lawe is visible for 50 to 75 miles. Parts of the island have 

 been eroded by the wind to a depth of over 200 feet since the 

 destruction of the forest growth on the higher elevations. 

 Similar results from wind erosion are to be seen on Lanai, 

 but the damage has not progressed so far as on Kahoolawe. 

 On Lanai there are regions where the soil has been carried 

 away to a depth of 50 feet, in some cases leaving columns with 

 a small shrub or a bit of grass or native plants which escaped 

 destruction and have remained in their original position, thus 

 holding the soil in place and checking the action of the wind 

 while all of the adjacent soil is blown away. A few of these 

 isolated columns of soil standing at a height of 30 to 50 feet 

 give an extremely bizarre aspect to the landscape. 



While the old contention as to the effect of forests upon the 

 rainfall of a given locality has been unfortunately obscured 

 and unnecessarily complicated by exaggerations on both sides 

 of the argument, it is-cettain that the presence of a forest 

 covering on the tops of the mountains of islands lying within 

 the trade-wind belt actually increases the rainfall and is of 

 great benefit in regulating the distribution and conservation of 

 the water of these islands.^ It should be remembered that rain 

 storms on islands in the trade-wind belt are of a decidedly 

 different nature from those which occur on continental areas, 

 particularly in northern cUmates. As a rule, precipitation dur- 

 ing the prevalence of the trade wind occurs not as a result of 

 the formation of a definite storm area, but as a result of a cool- 

 ing and compression of air due to its impinging upon the 



