FOREST INFLUENCES. 



Professor J. B. Reynolds, Ontario Agricultural College. 



At the present time much is being said and written concern- 

 ing the forest. Forestry problems include a consideration of 

 forest management, of the forest as a resource, and of the forest 

 as a condition. The last question, the forest as a condition, 

 comprises the subject of this paper, and upon this subject I shall 

 try to present the best information available. 



Dr. Fernow states this question topically, as follows: 

 The forest exerts an influence 



I. Upon the climatic condition within its own limits and 

 beyond. 



II. Upon the distribution and character of the waterfiow. 

 III. Upon the mechanical condition and erosion of the soil 

 under its cover. 



I. The climatic influence of the forest is, conjecturally, four- 

 fold" (1) Upon the temperature of the air and of the soil ; (2) upon 

 winds and storms; (3) upon evaporation and the humidity of 

 the air • (4) upon the precipitation — rain and snow. I say con- 

 jecturally, for the influence of the forest upon precipitation is by 

 no means estabHshed, or generally admitted. 



Control of Temperature by the Forest. 



The forest exerts its influence upon temperature by reason, 

 principally of the tree-crowns. These shade the ground and 

 prevent the heat of the mid-day sun from having its full effect; 

 conversely the same crowns check the radiation of heat from the 

 forest soil and air at night and in winter. Thus, the maximum 

 temperatures within the forest are lower than those m the open, 

 while the minimum temperatures are somewhat higher. In sum- 

 mer the lowering of the maximum is much greater than the rais- 

 incT of the minimum. In winter the extremes are about equally 

 reduced Hence, the net effect of the forest in summer is. to 

 lower the mean temperature of the forest air; and m winter, this 

 cooling effect almost or entirely disappears. The net annual re- 

 sult is to cool the air— the mean annual temperature within the 

 forest being lower than that in the open; and to moderate it. the 

 extremes of high and low, both daily and annual, being reduced 

 The moderating effect of the forest is much greater than its cool- 



