THE FORESTER AND HIS WORK 225 



regulate the water supply of large areas and act 

 as irrigation reservoirs, thus preventing floods 

 and excessive erosion. This sort of forestry is 

 adapted to steep and broken mountain regions, 

 and is the kind most practised in the Eocky 

 Mountain districts, where protective forestry 

 and irrigation problems are matters of great 

 importance. 



The third type is the commercial or supply 

 forest, whose object is primarily the raising and 

 harvesting of wood for profit. This type of 

 forestry is self-supporting and requires skilful 

 management in every particular. It rests upon 

 a purely commercial basis, just as farming does, 

 and is really a department of agriculture. It 

 is carried on upon a scale large enough to war- 

 rant the employment of a large force of men 

 and the building of a railroad. The employees 

 in this type of forest plant for the future and 

 reap the harvests of by-gone ages. 



Forestry is made up of three great branches : 

 Silviculture, which is the growing of forest 

 trees; Lumbering, which is the harvesting and 

 marketing of the crop; and Dendrology, which 

 includes the sciences upon which the art of for- 

 estry is based. The latter branch is really tree 

 Jbotany, and is made up of no end of interesting 

 details concerning the life processes of the trees 



