4 AN INTRODUCTION 



open ground, since the temperature by night in woodlands 

 is higher. 



As regards Soil Moisture. Woodlands exert a consider- 

 able influence upon soil moisture. For the canopy of the 

 trees and the layer of humus prevent rapid evaporation of soil 

 moisture; and the layer of humus, which is hygroscopic, 

 also absorbs moisture, as it were, like a sponge. On 

 account of this latter property, the layer of humus, assisted 

 also by the obstruction afforded by the roots and crowns of 

 the trees, prevents the rapid disappearance of any rainfall ; 

 and it prevents the consequent flooding of streams and 

 rivers ; and it prevents also the washing away and denuda- 

 tion of the soil. Consequently, the duration of the beneficial 

 effects of rainfall is prolonged ; especially is this the case in 

 the early spring, before active transpiration has begun. 



It should be noted that in the summer months, an area 

 covered by trees will utilise a far greater quantity of water 

 than is lost by evaporation from the surface of bare land. 

 For although soil evaporation is less in woodlands than on 

 bare, open land, an enormous quantity of water is transpired 

 by the trees. Another effect produced by trees is that the 

 water table is lowered ; and, for this reason alone, the liability 

 to floods is lessened ; for a greater quantity of water must be 

 absorbed before flooding can take place. 



As regards Protection against Erosion and Denudation. 

 The beneficial effect which trees exert with respect to any 

 direct erosion by rainfall has just been noticed. But losses 

 sustained by erosion and denudation from other causes, such 

 as that characterised by landslips and caused by the action 

 of underground water or other agencies, can often be avoided, 

 or at any rate lessened, by the judicious planting of trees and 

 shrubs ; for their roots will help to bind the soil together. 

 In this connection, the planting of stoloniferous shrubs, or 

 trees which shall afterwards be kept coppiced, will generally 

 be more advantageous than if an attempt be made to grow 

 mature timber. 



As regards Shelter and Protection from Storms. The 

 presence of woodland is often of the greatest value, in exposed 



