Canadian Forestry Journal, January, 1920 



21 



THE POLICY OF IRRICATIONISTS. 

 By Col. J. S. Dennis. 



It has always been the pohcy and endeavor 

 of irrigationists who thoroughly understand the 

 basic conditions governing an adequate and re- 

 gular water supply ,to protect our forest areas, 

 and by every means of co-operation with the 

 Department of Forestry, keep wooded areas on 

 water-sheds in a thriving state of growth by 

 fire precautions and reforestation. Every im- 

 portant convention of those mterested m ir- 

 rigation in Canada has drawn up resolutions 

 to protect existmg forests on the water sheds of 

 all streams available, or likely to become avail- 

 able, not only for agricultural purposes, but for 

 domestic and industrial use; and to replant de- 

 nuded areas at the heads of streams so that the 

 sources of the supply of water for all purposes 

 may be maintained for ever. Conventions have 

 urged the establishment of greater fire precau- 

 tions against devastation by fires, and the in- 

 crease of fines in the cases of convictions against 

 travellers, campers and settlers who have occas- 

 ioned the conflagrations. A few years ago the 

 efforts of irrigationists were largely instrumental 

 in securing the reservation of the Rocky Moun- 

 tains Reserve area, comprising more than 13,- 

 000,000 acres on the east slope of the Rockies, 

 and of enormous value to the watershed supply- 

 ing the rivers and creeks of Alberta and the ad- 

 joining prairie province. The association also 

 succeeded in having the reserve of the Cypress 

 Hills enlarged. 



WATER-SHEDS MUST BE PROTECTED. 



Forestation and irrigation are allied and in- 

 terdependant, and for this reason water-sheds 

 must be protected. It has been established be- 

 yond all doubt that forestation has a consider- 

 able effect upon precipitation, and moderates 

 and regulates the flow of moisture in the spring, 

 minimizing the danger of floods, and storing up 

 the melting snow in its springs and vegetable 

 mould. Precipitation is induced in air which 

 has almost reached the point of saturation by 

 contact with some obstruction or the lowering 

 of the temperature. The forests exert a great 

 influence in both ways. On mountain heights 

 their effect may not be very apparent, as the 

 mountains themselves from the necessary ob- 

 struction, but their cooling influence is greater 

 than that of the sun-baked mountain sides, and 

 this is found to increase with the elevation. In 

 level country the influence of a large area of 

 forest is more marked and its cooling and ob- 

 structive effects come into play without the aid 



COL. J. S. DENNIS 



Chief Commissioner of Colonization and Develop- 

 ment, Canadian Pacific Railwav. 



of any other agency. Extensive observations 

 in Europe have been made on the influence of 

 forests on rainfall most of wliich have been 

 quite conclusive in their affirmative results. 



CONSERVATION OF MOISTURE. 



Forest areas have a greater influence upon 

 the run-off by preventing the rapid melting of 

 snow in spring. In the cooler areas of the 

 woods the snow remains upon the ground for a 

 much longer period and gives off its moisture 

 more gradually. The retarding of the spring 

 floods in this manner not only materially de- 

 creases their powers of destruction, but con- 

 serves the moisture which appears later as 

 springs. Again, tlie water flowing from the 

 melted snow, or from showers, is not rapidly 

 seeped in by the rich humus of the forest floor, 

 but is held by the covering of twigs and other 

 vegetable matter which has an absorptive capac- 

 ity of fifty per cent of its own weight. From 

 this the welter is given up slowly or percolates 

 through the earth to springs and streams. It 

 should be taken into account here that a foot 

 of this vegetable covering takes centuries to 

 produce though a single day of forest fire or 

 rush of water by forest clearing will effectively 



