REFORESTATION IN NORTHERN IDAHO 



45 



sides and their ravines and canons will in the course of time 

 be reclaimed by a new growth of yellow pine and Douglas fir 

 can not be prevented so long as ground fires do not occur and 

 natural growth conditions are not obliterated. 



An example of the yellow pine, our hardiest tree pioneer, tak- 

 ing possession of an extremely xerophytic situation was care- 

 fully observed on Kamiak Mountain during the summer of 

 1913. Near the top of the mountain where the soil is rocky, 



Fig. 8. A prairie on the exposed south slope of a quartzite butte near Viola, 

 Idaho. It is being invaded by yellow pines which occupy the crest and the north- 

 west side of the butte and the ravine in the foreground. 



Pinus ponderosa has succeeded in establishing itself on the ex- 

 posed south slope. A weekly record was kept of the evaporating 

 power of the air and of the moisture content of the soil near the 

 edge of a group of pine trees under cover of which a few three- 

 and four-year-old seedlings were growing. On May 10 a 25 cm. 

 core of this quartzitic soil contained 21% of its dry weight (at 

 105°C.) of water. The soil moisture gradually decreased until 

 on July 24 only 7.4% remained, and this was reduced to 4% 



