IOWA ACADEMY OF SCIENCES. 57 



diate vicinities are uniformly cooler in summer and warmer 

 in winter.* 



They conserve the moisture of the soil. The fine leaf- 

 mould which naturally accumulates in groves forms a 

 sponge which greedily takes up the water which falls as 

 rain or snow, and this is later given off by springs. Rapid 

 evaporation is prevented, but instead the trees pump up 

 water from the more thoroughly saturated soil and throw 

 it off gradually into the air through the leaves, thus sup- 

 plying moisture for the local summer showers which are 

 the salvation of our crops. Forests cannot be classed 

 with the general causes which determine the precipitation 

 of abundant rains in the spring and fall, but their effect 

 upon local showers is consistent with scientific observa- 

 tions upon the physiological activity of trees and green 

 plants in general, and cannot be successfully questioned. 

 It is absurd to state that growing crops replace groves 

 in all the good work accomplished in the direction 

 of conserving moisture. Crops are left upon the ground 

 during only a portion of the season. Moreover, they appear 

 so late in the season that they cannot aid in the retention 

 of that moisture which results from melting snow, or 

 which is precipitated in the early rains. Crops canoot 

 therefore, conserve moisture to the same extent, though in 

 kind their work is like that of aW green plants. 



Forests prevent erosion. In the roughest timbered 

 country even the lightest leaf-mould on the steepest 

 slopes is practically undisturbed by torrents of rain, and 

 the waters which are drained from such surfaces are clear, 

 since they carry but little eroded material. As quickly as 

 the forest is cleared the spongy surface soil is washed away, 

 and even the harder sub-soils are washed out. The result 

 is noticeable along all of our larger streams which have 

 been deprived in large part of- their bordering native 

 groves. The material which is being washed from the 

 exposed slopes is choking up our streams, and sandbars 

 and mudbars are rapidly increasing. 



•For results and data of observations on effect of forests on temperature and moisture, 

 see Forest Influences, Bulletin No. 7, Forestry Div. , U S. Dept. of Agr. , 1893; and 11th 

 Ann. Rep. Agr. Ex. Sta., Univ. of Wis. , pp. 292-326, 1895. 

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