FOREST INFLUENCES 23 



doubt, of great importance, and for fixing the light, easily 

 blown sand of the plains the binding action of the forest is 

 no less useful. The water from heavy rains, checked in its 

 descent by meeting first with the foliage of the trees, is better 

 retained in forest soil than on bare land. Under a close 

 cover of trees there collects a humus soil formed from the 

 decay of fallen leaves. Through this sponge-like soil-cover- 

 ing the rainwater slowly filters, and its passage is further 

 retarded by the stems and roots of the trees. In this way 

 the erosive effect of violent rains upon bare hillsides is 

 obviated. This is often a very serious danger, not only 

 because the good soil is washed away, but also on account 

 of lower lying fertile lands being covered by boulders, 

 gravel, and sand brought down in the flooded waters. An 

 importance must be attached to forests in such localities 

 quite apart from the timber they produce. The Alps 

 afford, perhaps, the best examples of this class of forest, 

 but the unchecked, wasting action of violent rains can be 

 clearly seen in Britain upon many hills reduced to a state of 

 barrenness. 



In the case of shifting sands, the roots of trees, shrubs, 

 and wild plants, and the covering of vegetable humus formed 

 from dead leaves serve to bind the soil. What forest growth 

 has done in this matter may be clearly seen in the " Landes " 

 of Gascony, or along the southern shores of the Baltic. 

 On the other hand, and in striking contrast to these districts, 

 are the great arid wastes of Central Russia, which bear 

 such melancholy evidence to the improper handling of the 

 natural forest over this precarious class of land. When level 

 tracts of loose soil, without forest or other cover, are exposed 

 to the wind, sand-dunes are apt to be formed. These advance 

 in the direction of the prevailing wind, often invading valuable 

 agricultural land. 



Woods, which, from their position or the nature of the 

 ground, exist not merely for the sake of what they produce, 

 but also for the physical benefit of the area or of neighbour- 

 ing districts, are called Protection Forests. 



