CHAPTER V. 



Local Effects of Forests on the Rainfall. 



In preceding chapters the principal subject has been the effect of 

 forests on humidity, and any mention made of rain has been only in- 

 cidental. In tiiis chapter that prominence is given to this ; and it is 

 the local effects in contradistinction to the effects of forests, or of the 

 destruction of these over a wide expanse of country, which is brought 

 under consideration. 



In these preceding chaptei's oftener than once mention has been 

 made of the rainfall as supplying indications of humidity, or of com- 

 parative aridity ; and looking at these we have found that though the 

 desiccation of some countries has followed the destruction of forests, 

 in others no appreciable effect has been produced on the quantity of 

 rainfall over a wide expanse of country. But we have found marked 

 effects on the humidity of both soil and climate pi-oduced over a more 

 limited range, both by the destruction of forests and by the planting 

 of trees where they were not before, or where they had been destroyed. 

 And by further limiting and localising our observations we may be 

 able, with advantage, to follow up the observations which have been 

 made, and ascertain more satisfactorily the meteorological effects of 

 forests in relation to moisture. As a preliminary to the consideration 

 of the effect of forests on the rainfall, it may be well to consider how 

 rain and rivers are produced. 



It may be hundreds are prepared, if asked, Whence comes the rain 1 

 and, Whence come the rivers 1 to tell that the rain comes from the 

 clouds, and the rivers, from springs among the hills. But we require 

 to go a little further in our consideration of the matter before we can 

 determine the effects of forests and of the destruction of forests on 

 the rainfall and on rivers. Whence come the clouds 1 Oh, from the sea. 

 And how do they spring from the sea 1 — And how are they formed 1 — 

 And how can the formation of them be affected by forests, or by land 

 denuded of forests, as in some cases both the rainfall and the rivers 

 appear to be 1 — And wliy is it so in these cases and not in others ? 



These and a hundred other questions suggest themselves on our 



