THREA TENED ARIDITY ON THE PACIFIC SLOPE 167 



but on examination one finds that most of them contain only- 

 aborted seeds. Round about the trees the ground is thickly 

 strewn with berries, but the lack of seedlings proves how few of 

 the seeds possess germinating power and indicates that the gen- 

 eral climatic conditions are not favorable to seed germination. 

 In many localities extensive burns are found. They have rav- 

 aged the edges of the forests or plowed wide swaths through what 

 once were very dense and uniform stands. Some of these burns 

 are very old, the stumps indicating that perhaps a century or 

 more has passed since the fires. Others are comparatively re- 

 cent. Reforestation does not take place on the burned-over areas. 

 Tbey become a part of the adjacent, arid, treeless tracts. Places 

 occur in the midst of heavy stands entirely devoid of trees and 

 stumps. It is probable that they represent extremely ancient 

 burns, showing that reforestation in the juniper growth has prac- 

 tically ceased on areas contiguous to the main body of aridity. 

 It is not alone when fire has swept the juniper forest out of ex- 

 istence that one notices a lack of reforestation. It is also to be 

 seen adjacent to settlements where the growth has been cut clean 

 for domestic uses, and the great number of detached groves and 

 scattered individuals dispersed over the plains are arguments in 

 the same general line. It is, of course, impossible to say with 

 absolute certainty that all these outlying groups are parts of a 

 uniform juniper forest, which once extended over the entire 

 plains regions of eastern Oregon, yet from analogy we are justi- 

 fied in concluding that such is the fact. The fires and direct 

 human agencies which are cutting into the larger bodies of for- 

 est at the present time produce just such detached groves and 

 scattered individuals, and the gaps give every promise of remain- 

 ing permanently deforested. 



The forest of western juniper extends up to the subhumid 

 areas, where it meets the western yellow pine. It even goes be- 

 yond a strict line of demarcation and penetrates several miles 

 into, the yellow-pine areas. It has been noticed that in many 

 places the juniper produces an abundance of full}'' developed 

 seeds and a plentiful supply of seedlings where it comes in con- 

 tact with the subhumid regions. Such would be a natural result 

 of the more favorable moisture conditions prevalent there. 



Accompanying the front of the semi-arid wave, comes a tree 

 which, in these regions, can endure neither the same high degree 

 of aridity as the juniper nor so great a humidity as the yellow 

 pine. This is the mountain mahogany, Cercocarpus ledifolius, 



