FOUEST INFLUENCES. 37 



latter is generally beneficial to vegetation in the formation 

 o^springs and in raising the water level in the.spil. It is evi- 

 dent that the less surface drainage and the more under- 

 ground drainage there is, the greater the spring-water sup- 

 ply, and vice versa. We are, therefore, interested in deter- 

 mining the factors that increase underground drainage and 

 reduce the surface flow. 



It is plain that whatever retards the flow of water over 

 the land, aids itjn sinking into the soil. We find this exem- 

 plified in swamps, where the soft, rough ground retards the 

 surface flow, and in forests, where the foliage checks the 

 water in its descent to the ground and the forest floor 

 retards the surface run-off. Theoretically, such a cover 

 should promote the flow of springs and maintain the height 

 of water in wells, and in practice we find that this is often 

 the case. In some cases, springs had entirely disappeared 

 after the clearing of near-by forests, but have commenced 

 their regular flow since the trees have been allowed to grow 

 again. Springs in turn influence the flow of water in 

 rivers, so that forests about the headwaters of streams often 

 have a most potent effect in maintaining their flow. There 

 is in fact no influence of the forest that is of greater, inipor- 

 tance in the distribution of water supplies than its effect in 

 retarding the run-off, even though its effect in preventing 

 evaporation is very important. 



FOREST INFLUENCES ON AVIND- AND HAIL-STORKS. 



We have seen that the wind-breaking power of the forest 

 is a very important factor in retarding evaporation, and in 

 preventing the drifting of sandy soil and snow. In the 

 forest the air may be rather still, while in the open a pierc- 

 ing gale may be blowing; in consequence there are no bliz- 

 zards in a wooded country. Tornadoes of great force 

 have occasionally broken down wide areas of timber, but 



