FIFTH NATIONAL CONSERVATION CONGRESS 197 



enrich with moisture the passing air currents, and in this way help to carry it in 

 larger quantities into the interior of continents. The destruction of such forests, 

 especially if it leaves the ground bare or partly covered with only weak vegetation 

 which does not transpire large quantities of water, must inevitably affect the cli- 

 mate, not so much the climate of the region in which the destruction took place 

 but the drier regions into which the prevailing air currents flow. 



FORESTS AND STREAMFLOW 



THE effect of forests upon streamflow in level countries differs from that of 

 forests in hilly or mountainous regions. In a level country where there is 

 no surface run-off, forests in common with other vegetation act as drainers 

 of the soil. Hence the importance in draining the marshy lands and improving 

 hygienic conditions. In such countries their effect upon streams is unimportant. 



In a level country any vegetable cover tends to reduce the amount of water 

 available for streamflow. This has been clearly shown by numerous experiments 

 in many countries. In a level country a soil cover with vegetation of some kind 

 surrenders to the ground water a much smaller amount of water than bare soil 

 with no vegetation at all and a forest, at least a spruce forest, less than field 

 crops. The only vegetative cover which uses up more water than a spruce forest 

 is an overflow meadow which can draw upon a supply of water in addition to 

 the precipitation. In bare soil in a level country the only loss is from evaporation 

 from the soil. This amount has been found to be on an average in temperate 

 climates of about 50 per cent of the precipitation. In this country experiments 

 with corn have demonstrated the lowering effect of plant growth upon the avail- 

 able ground water. Thus, during the growing season of 1899-1900, the mean 

 height of ground water under corn was lower than that of fallow land and this 

 lowering effect has been felt to a depth of over 7 feet below the surface. Accord- 

 ing to some European investigators, the desiccating influence of a spruce forest 

 extends to 31.5 inches, and according to Russian investigators, even from 10 to 

 15 feet. 



The forest, like any other vegetable cover, desiccates the layer of soil within 

 which its roots are active, and since the roots of forest trees go to a much greater 

 depth than the roots of cultivated crops, this has led to the conclusion that forest 

 cover absorbs more moisture, and therefore desiccates the soil to a greater depth 

 than any other vegetable cover. 



The lowering effect on ground waters of the forest is well known from 

 practical experience. The afforestation of the swamp lands of southern France, 

 called the Landes, with maritime pine, brought about a lowering of the water 

 table. In Italy the water table in swamps has been lowered by planting eucalypts, 

 and in many swampy regions in Europe the drainage ditches, which before af- 

 forestation were always full of water, after planting became entirely dry. 



As a net result of all these experiments in different parts of the world, the 

 effect of forests in a level country because of its desiccating effect upon the soil, is 

 different from that in mountainous country. In the plains and in level country 

 the forest: 



