36 , PRACTICAL FORESTRY. 



ence in the amount of rain caught than most observers claim for the 

 whole action of the forest. The rainfall of two stations at unequal 

 heights above sea level is sometimes wrongly compared, because the 

 difference in rainfall may be caused by the difference in altitude. 

 Finally, the best observations that have been made point to different 

 conclusions. For example, measurements taken in Prussia go to 

 show that there is an increase of rain over the forest, and that it is 

 greater the higher the station. Thus, near the level of the sea it was 

 only 1.25 per cent greater than over the open country, while at alti- 

 tudes between 2,000 and 3,000 feet it reached 43 per cent. Observa- 

 tions made at Nancy, in France, which lies about 700 feet above the 

 sea,, show an average yearly increase of 16 per cent. The Bavarian 

 observations, on the contrary, do not indicate more rain over the 

 forest. The best evidence at hand fails to show a decrease in rain- 

 fall over the United States in the last hundred years, in spite of the 

 immense areas of forest that have been burned and cut. But it 

 should not be forgotten that most of those areas have grown up 

 again, first with brush, and afterwards with trees, so that the pro- 

 portion of land covered with leaves is still very large in aU that part 

 of the country which was once under forest. In India, again, a large 

 amount of statistics has been collected which leads to the conclu- 

 sion that forests do influence rainfall. The truth probably is that 

 more rain falls over the forest than over open country similarly 

 placed, but how much more it is impossible to say. The excess falls 

 chiefly in the form of summer showers. One of the best authorities 

 has estimated the difference at 10 per cent. 



FALLEN BAIN. 



Whatever doubt there may be about the action of the forest in pro- 

 ducing rain, there is none about its effect on rain water after it has 

 fallen. When rain falls over a dense forest from less than one-tenth 

 to about one-fourth of it is caught by the trees. A small part of 

 this water may reach the ground by running down the trunks, but 

 the greater part of it is evaporated, and so increases the humidity of 

 the air. That which passes through the crowns falls upon the forest 

 floor, which sometimes has an absorbing power so great that it can 

 hold for a while a rainfall of 6 inches. Yet this water does not 

 remain in the porous floor, but in the end runs off into the streams, 

 or is evaporated, or sinks into the ground. That which gets into the 

 ground is either taken up by the roots or goes to feed the springs and 

 water courses. 



Rain which falls over a bare slope acts differently. It is not caught 

 by the crowns nor held by the floor, nor is its flow into the streams 

 hindered by the timber and the faflen waste from the trees. It does 



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