SHELTEE-BELT DEMONSTEATIONS ON THE GREAT PLAINS. Q 



Cave Hills and Slim Biittes in South Dakota, and the Pine Hills in 

 southeastern Montana. 



SOILS. 



There is great diversity in the types of soil that characterize the 

 northern Great Plains region. These soils range from sand and 

 sandy loam through silt and clay loam to heavy clay and shale. In 

 general there is a large proportion of clay in the subsoil, giving it a 

 high water-holding capacity. In certain sections small areas of hard- 

 pan are found which the roots of the trees seem unable to penetrate. 

 Cultivation of this type of clay soil is ineffective in making these 

 areas suitable for tree growth. Another small proportion presents a 

 deep gravel subsoil on which trees do not thrive. There are also 

 occasional spots where the percentage of alkaline salts is high enough 

 to stunt or kill out a planting of trees. 



A fairly extensive sand-dune area is found in the northeastern 

 corner of the region, in and southeast of the valley of the Mouse 

 Eiver in North Dakota. Here the water table is quite near the sur- 

 face, and such trees as willow and aspen are found growing natu- 

 rally in slight depressions that occur in the prairie. Groves of trees 

 planted on timber claims in this area have maintained themselves 

 and made excellent growth. 



CLIMATE. 



The northern Great Plains are in what is known as the dry-land 

 farming area of the United States. The climate has been classified 

 as semiarid. It may be more accurately described as variable, chang- 

 ing from season to season from almost humid conditions to almost 

 arid, but with a relatively low average annual precipitation ranging 

 from 10 to 20 inches. Another uncertain factor is the seasonal dis- 

 tribution of the rainfall. It is possible for a comparatively low rain- 

 fall favorably distributed to produce normal plant growth, while a 

 much higher rainfall unfavorably distributed may result in damage 

 to a plantation through lack of moisture at some critical period of 

 the growing season. Very high summer temperature and very low 

 winter temperature, coupled with frequent strong winds throughout 

 the entire year, combine to make this one of the most severe regions 

 for tree growth in the United States. 



Table 1 gives the highest, lowest, and average seasonal and annual 

 precipitation at 10 field stations of the Bureau of Plant Industry in 

 the area for the 5-year period from 1916 to 1920, inclusive. It also 

 gives the average seasonal evaporation for the same years. Most of 

 these stations have United States Weather Bureau records of precipi- 

 tation covering a period of 15 to 45 years. The average precipita- 

 tion for the entire period of the record is given in the table. 



