600 PROTECTION AGAINST SWAMPS. 



surface of the crowns of the trees standing on the area. The 

 greater the amount of leaf-canopy, the more atmospheric pre- 

 cipitation falling on it is evaporated, and so much the less 

 reaches the ground. Broadleaved trees act in this manner 

 during the season of growth, but evergreen conifers throughout 

 the year. In addition to this, the absorptive action of the 

 roots, and the power of transpiration possessed by the foliage 

 of trees must be reckoned, as well as the suppression of swamp 

 moss by the cover of the trees. 



Observations made between 1868 and 1871 at the double 

 Bavarian meteorological stations, which are in pairs in the 

 forest and in the open show that according to the season from 

 25 per cent, to 32 per cent, of atmospheric precipitation (rain, 

 snow, &c.), and averaging 26 per cent, for the whole year, did 

 not reach the ground directly, but remained on the crowns of 

 the trees. In 1882, Fautrat found that 20 to 27 per cent, of 

 rainwater remained on the trees in Alsace-Lothringen. Much 

 of this water, however, drops from the foliage or trickles down 

 the stems of the trees to the ground. 



There are certain localities for instance, level land with an 

 impermeable substratum and high atmospheric temperature 

 where swampiness of the soil is, on the contrary, increased by 

 forests. In such cases, the rapidity of evaporation depends on 

 the unimpeded action of the sun's rays and of dry winds', and 

 clearing the ground of forests will increase the effects of these 

 forces. 



The action of forests, where the soil-covering of dead leaves, 

 moss, and humus is carefully preserved, in maintaining moisture 

 near the surface of the ground and protecting the soil from the 

 effects of insolation and drying wind, is very valuable on hot 

 aspects and steep slopes, especially in hot countries, where 

 water may be thus stored in the spongy soil-covering. A 

 steady supply of water is thus maintained in springs on the 

 hillside, while the absence of tree growth, on the other hand, 

 allows rainwater to drain rapidly down and causes floods 

 after heavy rainfall, and the watercourses may run nearly 

 dry during the hotter months of the year. 



Ebermeyer has proved by numerous observations that on a 

 heavy clay soil, the root-zone of a spruce forest, from 16 to 32 



