-HELTER-B-ELT DEMONSTRATIONS ON THE GREAT PLAINS. 
Cave Hills and Slim Butte< 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 
River in Xorth 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 semi arid. 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. 
