president's address. 
627 
arises can we alter the conditions on a larger scale by alternating 
forest and field, or by preserving intact large areas of forest 1 
In reply to this query, it seems to have been shown by the 
forest planting at Lintzel that a considerable change in the 
meteorological conditions resulted. 
Forest cover causes obstruction to the winds and hinders the 
action of the sun's rays upon the soil. A difference in temperature 
and evaporation outside and inside the forest area then arises. 
When the areas of the different kinds are large enough, local 
currents of air will be set up, which will cause the interchange 
of conditions between the two areas. The size and character of 
the forest growth, density, height, situation and composition are 
the factors which determine its influence. It is not trees but 
masses of foliage that do the work. 
On water supply the effect of forest is undoubted. The soil 
acts as a sponge from which the water runs off gradually; remove 
the forest wholesale, and the water rushes along, tearing away soil 
and flooding and injuring growing crops. 
Irrigation is generally advocated for arid regions alone, but it 
is also particularly serviceable in well watered regions, and here, 
as above shown, forest cover materially assists. 
The following observations are of interest : — 
First, as to the difference of conditions within and without the 
forest. On the average the forest is cooler than the open country 
in summer, but about the same in winter, with a warming effect 
in spring, and the evaporation is only one-half that in the open. 
The percentage of rainfall evaporated is about 40% in the open 
and about 12% in the forest, taking the whole year. 
The total quantity of moisture returned into the atmosphere 
from a forest by transpiration and evaporation from the trees and 
the soil is about 75% of the precipitation; other forms of vegeta- 
tion give from 70 to 90% ; bare soil gives only 30%. Gauges in 
European forests catch 75 to 85% of the rainfall, the rest runs 
down the trees, is intercepted or evaporated. 
