INDIRECT UTILITY. » 



SECTION II.— THE INDIRECT UTILITY OF FORESTS. 



A piece of land bare of vegetation throughout the year is 

 exposed to the full effects of the sun and air currents and the 

 climatic conditions which are produced by these agencies. If, on 

 the other hand, a piece of land is covered by a growth of plants, 

 and especially by a full crop of trees, it enjoys the benefit of certain 

 agencies which modify the effect of sun and wind on the soil and 

 the adjoining layer of air. These agencies are the following : — 



(1) The crowns of a full crop of trees provide a dense roof at a 

 certain distance from the ground which intercepts the rays of the 

 sun and the falling rain, obstructs the movement of air currents 

 and reduces radiation of heat during the night. 



(2) The leaves, flowers and fruits, augmented by certain plants 

 which grow in the shade of trees, form a layer of organic matter 

 or humus, which protects the soil against changes of temperature 

 and greatly influences the movement of water and air in it. 



(3) The roots of the trees penetrate into the soil in all directions 

 and bind together a loose soil or loosen a too firm soil. 



The effects of these agencies have been observed and recorded 

 from time immemorial. In all such cases, however, other agencies 

 were also at work at the same time, and the observations were not 

 always sufficiently accurate and direct to decide in how far the 

 produced effect was due to those other causes. The effect of 

 forests is modified by many matters, such as geographical position, 

 elevation, aspect, gradient, general configuration of the locality, 

 the nature of soil and subsoil, the extent of the wooded area and, 

 last but not least, the composition and density of the forest. 

 Hence, it is difficult to apportion correctly the effect of the 

 different agencies. The consequence was exaggerated confidence 

 and belief on the part of some observers and doubt and unbelief 

 on the part of others. This led in modern times to the commence- 

 ment of accurate observations, first by Becquerel in France, and 

 Noerdlinger and Krutzch in Germany. A thoroughly practical 

 and conclusive method was, however, not introduced until the 

 year 1867, when Mathieu in France and Ebermayer in Germany 

 started so-called parallel or double stations, one being situated 

 inside a fully stocked forest and the other at some distance from 

 its boundary in the adjoining open country, all other conditions, 

 such as soil, elevation, etc., being as near as possible the same in 



