IMPORTANT WINDS. 11 



comparable to that of field crops. For special purposes, however, 

 such as the protection of valuable orchards and the shelter of homes, 

 the utility of the windbreak may be so great that its timber value 

 need not be considered. In most of the eastern half of the United 

 States the farmer's woodlot will generally take tm^lace of rows or 

 narrow belts. Perhaps occupying a site not suited to cultivation, 

 it will yield a good revenue from its crop of valuable hardwoods. 



(2) In regions with less than 30 inches of annual precipitation the 

 conservation of moisture becomes so important that in open level 

 country windbreaks are extremely valuable for the protection of 

 fields, pastures, and meadows. This is also true in the more rolling 

 lands of the South, where, even with greater precipitation, the con- 

 stantly high temperature during the growing season accelerates 

 evaporation. From Texas and Oklahoma to Kansas, Nebraska, and 

 South Dakota, hot southerly winds, with a remarkable capacity for 

 moisture, prevail throughout the growing season, and in years with 

 less than the normal rainfall they have done immense damage. The 

 past few years, however, have witnessed very little damage, and there 

 has grown up the feeling that the climate of the region has perma- 

 nently changed both by a decrease in winds and an increase in the 

 rainfall. Records of the Weather Bureau for several of the stations 

 west of the Missouri River, however, show that the recent group of 

 wet years corresponds to a similar group about 1 880, with dry years 

 in the early nineties. There has been no permanent change in the 

 climate, and there is good reason to believe that a series of dry years 

 will follow the present period of abundant moisture. The records 

 of wind movement at several stations, for the same period, show a 

 slight decrease in the last 15 years as compared with the preceding 15, 

 and it seems likely that if the observations of the Weather Bureau 

 had been made near the ground rather than at the tops of buildings 

 an even greater difference would have been noted. It would be 

 strange, indeed, if the thousands of barriers which have grown up 

 where formerly no trees existed had had no general effect in reducing 

 the velocity of surface air currents. However, there has been no 

 change in the universal conditions which cause general winds, and 

 the removal of the objects which have locally broken them will 

 quickly and certainly bring about a return to original conditions. 



In the northern part of the Mississippi Valley, from the prairies of 

 Montana to the Dakotas and Minnesota, and even in northern Indiana 

 and Michigan, the anticyclonic winds of summer may blow very per- 

 sistently, and while frequently injurious to grain, hay, and other 

 crops, the cooler and moister quality of the air reduces their dam- 

 aging capacity, and little provision has been made to check them. 

 In this northern region, from eastern Washington to the Lakes, the 

 northerly blasts of winter and the spasmodic Chinook wind of spring 



