INFLUENCE OF EDWARDS PLATEAU T1MBEK. 25 



is known to everyone. It is ;ilso a mutter of common observation 

 that forest denudation is followed by marked changes in the character 

 of -iream Mow and in the permanency of springs. Forests also pro- 

 teet from drying winds and sunshine, and tend to maintain a higher 

 water-level in the soil. A natural but mistaken inference from these 

 facts is that an absence of forests makes a dry climate. It may be that 

 forest removal over large areas does appreciably lessen precipitation, 

 though conclusive evidence of this has never been secured, but a suf- 

 ficient explanation of all that has just been said is found in the 

 undoubted truths that a moist climate favors forest growth, and that 

 forests economize the rainfall by retarding evaporation and equalizing 

 distribution. 



Bearing these facts in mind as a preliminary caution against drawing 

 too wide conclusions from what may be said, it is possible to set forth 

 certain ways in which the forests of this region may exercise more or 

 le>^ influence on the climate. How important this influence may be is 

 another matter. The climatic features likely to be chiefly affected are 

 temperature and humidity. To discover by observation within the 

 region itself to what degree forest growth does actually influence these 

 would be exceedingly difficult, if not impossible; especially in view of 

 the marked instability of weather conditions as well as wide variations 

 within short distances which, as alread}^ remarked, characterize this 

 transitional zone. Such facts can be established anywhere only after 

 the most careful and long-continued meteorological observations and 

 measurements. Some general principles, however, are now commonly 

 accepted by students of forest problems, and by fitting these to the 

 conditions which we know to exist in the Edwards Plateau region cer- 

 tain deductions may fairly be made. But the method thus employed 

 is. so far as the particular locality is concerned, theoretical, not experi- 

 mental, and at best can lead only to very indefinite conclusions as to 

 the actual extent of the influence on climate which it is possible to 

 ascribe to the forests of the plateau. 



INFLUENCE UPON TEMPERATURE. 



In the first place, the forest cover furnishes a canopy against the 

 sun's rays, which, with the accumulated soil and debris incident to for- 

 est growth, prevents intense heating of the rocks. The burning sen- 

 sation of the reflected midday heat is vividly present to those who 

 have toiled on horseback or in a stage over the stony wastes of the 

 Devils River and Pecos countries during midsummer. Here an endless 

 stretch of bare limestone is exposed to the most intense sunlight, until 

 the air feels like the blast from a furnace. The transpiration of water 

 vapor which is constantly going on from the leaf surface of a forest 

 also operates to reduce the temperature to some degree, just as drink- 

 ing water is commonly cooled in this dry air by suspending it in the 



