EFFECTS OF FORESTS UPON LOCALITY 5 



localities, to agricultural interests. It is most advisable that 

 as much shelter as is possible should be provided for farms 

 in exposed districts. 



As regards the Salubrity of the Atmosphere. The 

 atmosphere in woodlands is always more free from impurities 

 than the atmosphere in more thickly populated districts. It 

 usually shows a remarkable absence of bacteria and of 

 carbonic acid gas ; and on the other hand, it usually 

 contains more oxygen and ozone than the atmosphere near 

 towns. Then again, in the neighbourhood of Pine woods or 

 forests of Silver Fir or Douglas Fir, it is probable that the 

 atmosphere will contain more ozone than is found in other 

 forest areas, and there will usually be found also appreciable 

 quantities of hydrogen peroxide (H 2 O 2 ), owing to the oxida- 

 tion of turpentine. 



Conclusion. Now, with reference to the foregoing, it 

 is evident that afforestation may sometimes be judiciously 

 carried out, even though there be no direct pecuniary returns 

 by the sale of timber. For instance, the planting of -water 

 catchment areas is in practically all cases desirable, not 

 only on account of any probable increase in the rainfall, but 

 chiefly because any sudden floods are largely avoided and 

 the water is more gradually drained from the land, and the 

 supply is thus more constant. And inasmuch as this is so, 

 smaller reservoirs will suffice for any given supply ; and 

 thereby the expenses of the whole undertaking can usually 

 be greatly reduced. 



And then again, the planting of trees will often be advis- 

 able in order to provide shelter for farms or houses in exposed 

 localities. And so, also, afforestation may often advisedly 

 be embarked upon in order to render the adjoining country 

 fit for agricultural purposes. And though such opportunities 

 are not very frequent in this country, partly on account of 

 the moist climate which already naturally prevails, yet they 

 do exist. 



In this connection, it may be well to note that in Belgium, 

 and in other places in Europe, certain tracts of land, formerly 

 useless for agriculture, have been rendered fertile in conse- 



