2 On the Relation between Forest Lands 



average annual rainfall over equatorial regions is about 

 104 inches, this amount is decreased to 



85 inches in latitude 10° 



70 „ 



j) 



20° 



40 „ 



a 



30° 



30 „ 



J5 



40° 



25 „ 



J5 



50° 



20 „ 



JJ 



60° 



Our rainfall is approximately in accordance with this 

 law, and although local causes may determine a greater or 

 less amount, the coast-line yearly average may be taken 

 as 33 inches. It would appear, therefore, that our annual 

 average of about 30 inches is what we might naturally 

 expect. Locality, however, has such an important influence 

 in the distribution that in some places not widely separated 

 the annual amount of rainfall will vary as much as 9 

 inches. The question, therefore, presented to us is this : — 

 Does the presence or absence of forest land govern this 

 unequal distribution ? Will clearing away timber affect the 

 rainfall by diminishing or increasing it in any particular 

 locality, or in any other way ? and (what is also of the 

 greatest importance) do forest lands aid or prevent the 

 natural conservation of the rain which falls to our share ? 

 On these points climatic statistics are meagre, and from only 

 a few countries can we derive any definite experience. 

 This colony has not been settled for a sufficiently long 

 period to afford unmistakable evidence ; and in discussing 

 the question, we must in a large measure necessarily fall 

 back upon the principles and canons of physical science. 



Experience, however, supplies us with one or two 

 important facts, first amongst which is that no marked 

 diminution of average annual rainfall over any exten- 

 sive region can be traced solely to denuding the earth's 

 surface of forests, although the local effects of such a pro- 

 ceeding are usually well marked. 



If we take countries in temperate latitudes where absence 

 of forest is the normal condition of the surface, we find, with 

 some exceptions, the average annual rainfall agrees fairly 

 with the distribution according to latitude, as given above ; 

 but this average is made up by excessive falls at one portion 

 of the year, or at isolated times, with excessive dryness and 

 scarcity of water as the usual state of things. In some of the 

 timberless districts at the Cape of Good Hope, the beds of 

 the streams, which are dry or nearly so three-fourths of the 



