No. 5.] THOMPSON — FOREST PLANTING. 315 



This result can be accomplished only by means of cultivated forests. 

 The extent of the forests to be effective, must be commensu- 

 rate with the vast area. The forests must be planted in such 

 form as will generally shield the earth's surfcice from the sun's 

 rays, and afford the greatest possible general resistance to surface 

 winds, and harbor insectivorous birds ; provide for the constant 

 and equul distribution of electrical currents ; provide for equal- 

 izing temperature and moisture ; prevent the rapid flow of surface 

 water; make provision for the retention of snow, and the pre- 

 veudoQ of the driftiuii- of the soil of cultivafed areas. 



As yet QO general system of planting has beea put in operation 

 to meet these requirements. In the group form of planting 

 generally in vogue, for the purpose of growing timber for econ- 

 omic use, there may be a manifestation of some beneficial climatic 

 results. It is apprehended, however, that such form of planting- 

 can but otherwise result in sudden changes in temperature, and 

 in such disturbance of electrical and atmospherical currents as 

 tend to increased occurrences of tornadoes and cyclones, as in- 

 stanced in the destructive effects of storms in Kansas, Nebraska 

 and Iowa, where they seem to increase in frequency and in des- 

 structive power in a ratio corresponding with the increase of the 

 erection of habitations and other surface improvements and the 

 increased area and growth of the cultivated forests planted in the 

 group form. 



It must be concluded, therefore, that the shelter-belt system is 

 the best form of forest-planting for extensive plains. This form 

 of planting has been advocated for many years in America. The 

 principal, if not :ill the experiments in this direction, have been 

 made by iudividiial effort in isolated areas, and on a small scale, 

 having usually been made to the extent of a few rows of trees 

 around buildings, stock yards, gardens, and in some instances, 

 around farms of considerable extent. These plantings have gen- 

 erally been made with the object of obtaining shelter only. 



This system of planting on a more extensive scale, hovever, in 

 which the shelter-belts are to be planted with all the trees needed 

 for economic use, as well as for the purpose of shelter is, if we 

 except the Des Coteaux, the Black Hills, and isolated mountains, 

 applicable to the general topographical features and climatic re- 

 quirements of the Great Plains. 



These forest belts may be planted seven to ten rods wide 

 around all sides of each IGd acre tract of land, or the shelter-belts 



