10 



Thus it will be seen that the great wheat-growing district of the 

 valley of the Red River of the North has a precipitation practically 

 identical with that of western Kansas, and slightly less than the 

 Staked Plains of Texas. The southern region, however, has more 

 wind, higher temperature, greatly increased evaporation, and a more 

 uneven distribution of rainfall. These are adverse conditions for 

 planting and growing trees, and to overcome them requires an intel- 

 ligent selection of species and a system of cultivation which reduces 

 the evaporation of soil moisture to a minimum. 



EFFECT OF FORESTS ON CLIMATE. 



Many of the residents of the Plains region believe that increased 

 cultivation of the soil, forest planting, and the building of reservoirs 

 to catch storm waters will cause a permanent increase in the precipi- 

 tation. But this theory is unsupported by proof. The records that 

 have been kept long enough to warrant any general conclusions indi- 

 cate simply wet and dry periods of variable length, which result in a 

 fixed average precipitation. Much has been said concerning the 

 effect of forests on climate, but little is known exactly, and most of 

 what is known contradicts the popular beliefs. The most that can 

 be said from the facts at hand is that an increase of precipitation by 

 forests is not demonstrated. Even were it otherwise, planting suf- 

 ficient to affect general climatic conditions would need to be on so 

 large a scale as to be wholly impracticable. 



On the other hand, observations show that within the forest ex- 

 tremes of both heat and cold are modified and that the evaporation 

 from a water surface is less than one-half that in the open, while 

 the evaporation from soil covered with forest litter is about one- 

 eighth that from bare fields. Forests check the run-off to a great 

 extent. The amount of water transpired by a forest is considerably 

 less than that given off by a similar area of ordinary agricultural 

 crops. 



These facts point to conclusions about which there is no doubt. 

 Forests are conservers of moisture. They are the best natural means 

 of saving the water that falls, and are of great utility for this rea- 

 son, regardless of their problematical effect upon the amount of 

 precipitation. 



The principal effect of tree planting on the climate of western 

 Kansas will be to check the winds and lessen evaporation in the im- 

 mediate vicinity of the plantation. 



a For a detailed discussion of the climate and geology, the reader is referred 

 to publications of the U. S. Weather Bureau, and the paper, " The High Plains 

 and Their Utilization," in Vol. IV of the Twenty-first Annual Report of the 

 U. S. Geological Survey. 

 [Cir. 101.] 



