Forest Influences. 19 



soil from the beating of heavy rains; and thus keeping it in a 

 more loose and receptive condition. 



(5) By the shade and by its control of the winds it holds the 

 snow cover until late in the spring, thus giving opportunity for 

 the water to penetrate the ground slowly instead of running off 

 in floods. 



Of these factors 1 , 3 and 4 (a) tend to diminish the amount 

 of water in the soil, and thus to lower the water-table. The other 

 factors tend to increase the water supply relatively, and to raise 

 the water-table. 



(1) The amount of rainfall intercepted has been variously 

 stated by different experimenters. Of course, a light shower is 

 almost entirely intercepted by the tree-crowns of a dense forest, 

 and given back to the air immediately as vapor ; while the greater 

 part of a heavy or long continued rain must reach the ground. 

 On the average from 10 to 20 per cent, of the total rainfall is 

 intercepted. This amount is, of course, a direct loss to the forest 

 soil. 



(2) As has been already stated, the wind-breaking power of 

 the forest is one of its most important influences The cold, dry 

 winds of winter, sweeping unchecked over the vast treeless plains 

 of the North- West make it exceedingly difhcult to rear fruit trees. 

 Still more destructive to tree life is the warm, dry wind known 

 as the Chinook. The Chinook, in Northern America, has been 

 known to consume entirely in twelve hours a snow cover of 2 \ feet 

 deep, and to raise the temperature 57 degrees in 24 hours, while 

 the humidity fell in the same time from 100 to 2 1 per cent. It is 

 probable that the treeless state of the North- West is the result 

 of these sudden and extreme changes of temperature and humi- 

 dity. If a forest could be interposed in the path of the Chinook, 

 its \vell-known action in checking the velocity of the wind, and 

 in preventing extremes of temperature and humidity, would re- 

 sult in self-preservation. At any rate, the beneficial effects of 

 shelter belts, clumps of trees, or wooded areas, upon orchards and 

 crops that lie to the leeward is unquestioned. The high winds 

 are checked, and the fruit trees are not subjected to winter 

 drought. The snow is allowed to lie evenly, and to remain longer. 

 The general effect, summer and winter, of the forest in reducing 

 evaporation is most beneficial. An Illinois farmer sums up his 

 observation u])on this matter thus: "My experience is that now, 

 in cold and stormy winters, wheat protected by timber belts 

 vields full crops, while fields not protected yield only one-third 

 of a crop. Twenty-five or thirty years ago we never had any 

 wheat killed by winter frosts, and every year a full crop of peaches, 

 which is now rare. At that time we had plenty of timber around 

 our fields and orchards, now cleared away." 



