760 FOREST-LITTER. 



leaves and moss, of absorbing and retaining water, and the 

 consequent reduced evaporation of water from the soil. 



The more sloping the ground, the greater is the value of the 

 litter in preventing torrents and floods; on slopes in the shallow 

 soil, over rock, sand or gravel, it is absolutely necessary to 

 maintain the litter, in order to protect the fertile soil below it 

 from erosion. 



The amount of water which is retained by the absorptive 

 action of the soil-covering is considerable ; dry coniferous 

 needles can absorb 4 to 5 times their weight in water, 

 dry beech leaves 7 times, and mosses 6 to 10 times this 

 amount, without allowing it to dribble away. This absorptive 

 power of the soil-covering is increased further by that of 

 humus for water- vapour, which, becoming condensed in the 

 cool soil, increases the supply of moisture. 



Once the soil-covering is saturated thoroughly with water 

 from atmospheric precipitation, it passes on the superfluous 

 water to the subjacent soil, in the numerous interstices 

 of which it is distributed, and thus reaches the roots of the 

 trees. Slight showers, which are so necessary for natural 

 regeneration under a shelter-wood, and during the dry 

 season are fully absorbed by the litter, do not reach the 

 plants' roots. In this respect, the litter is the more hurtful, 

 the thicker it is. But if the rain is sufficiently heavy, the 

 litter prevents too rapid evaporation of the water in the soil. 



E. Eamann (1895) found, that the soil in dense crops of 

 trees, with plenty of litter, is less moist than the soil of 

 agricultural land ; when the leaves come out in spring, their 

 transformation causes a considerable loss of water from the 

 deeper layers of the soil ; shaded glades in a wood are much 

 moister than the soil of an old crop of trees. Hoppe (1900) 

 also showed that the soil in dense crops of trees with litter 

 was less moist than in clearings. Ebermayer* has proved 

 experimentally that the soil-covering of leaves and needles 

 evaporates water 2J times less than does a forest soil without 

 litter. There is a difference in this respect between leaf- 

 litter and moss-litter. Wollny showed that the soil-covering 



* " Die Physikalischep Kimvcrkun^en dcs \V;i.l<lrs :iut' Lut'l u. 



