246 RESULTS OF COMPARATIVE OBSERVATIONS : BAVARIA. 



est, 03, and in the same period in 1870 Gl per cent, less tban in the open 

 air, a result in perfect harmony with the influence of the forest on the 

 evaporation of a free water surface. In some months the evaporation 

 of moisture in the soil in forests is one-third, and sometimes even only 

 a fourth, of that in the fields. The influence of forests is especially 

 shown alter a long-continued rain, as in August and September, 1870. 



Influence of the litter of forests iipon the evaporation fro7n the soil. 



This is doubtless one of the most important questions in forestry. 

 For the purpose of determining it numerically two atmometers were put 

 up in dense woods, each filled with half a foot of earth, capillarily satu- 

 rated, one being covered with litter in normal condition of leaves or 

 moss, and the other not covered. The mean of all observations is shown 

 in a subsequent table. 



Evaporation from soil in the open fields, compared with that from litter- 

 covered wood-soil. 



In a forestal and economical point of view, it is of great interest to 

 know the influence which forests strewn with litter have upon the re- 

 tention of moisture in the earth. The observations in this respect show 

 the following conclusions. 



In other words, the evaporation is from three to eleven times greater 

 in the fields than in litter-covered woods, the general average being 7.2 

 times as great in 18G9, and 7 times in 1870. From these direct obser- 

 vations we are enabled to express the following general conclusions so 

 far as relates to the mouths from April to October : 



1. The forests alone, without litter, diminish the evaporation of water 

 in the soil, as compared with the open fields (in the mean of the two 

 years observed), 62 per cent. 



2. The litter covering in the forest diminishes the evaporation still 

 further 22 per cent. 



3. Forests and litter together reduce evaporation 84 per cent. 



4. In litter-covered forests the evaporation is GO per cent, less tban in 

 uncovered forest soil. 



While in the open fields 100 parts of water evaporate from satu- 

 rated naked earth, the uncovered soil of woods yield but 38 per cent, and 

 the litter-covered soil but 15 per cent. Or, calling the loss from uncov- 

 ered wood soil 100, the amount from the same covered with litter is 40 

 per cent.^ 



' The relatively large amount in May, as compared with other mouths, is explained 

 by the fact that, at the beginning of observations iu each year, the soil at some sta- 

 tions was uot thoroughly saturated with water. 



* Observations made near the Forest School at Nancy led to results corresponding 

 in the main with those above given, the amount iu the fields being about five times 

 greater than in the litter-covered woods. 



