166 THREATENED ARIDITY ON THE PACIFIC SLOPE 



600 feet to 3,000 feet on the eastern Washington plains and from 

 4,000 feet to 5,000 feet in the regions between the Bitter Roots 

 and the main crest of the Rocky mountains. 



THE REGIONS OF SEMI-ARIDITY 



From the arid regions we enter those termed semi-arid. We 

 meet here a forest growth. It is one which throughout these 

 regions is strictly typical of semi-arid environments. As it comes 

 most closely in contact with the highest degree of aridity and 

 has to bear the full force of the ultimate and permanent defor- 

 esting processes, its condition and aspect become doubly inter- 

 esting. This forest growth is wholly composed of junipers 

 belonging to the following species : 



Juniperus monosperma, One-seeded juniper. 

 Juniperus occidentalis, Western juniper. 

 Juniperus scopulorum, Mountain juniper. 



They occur in the various semi-arid districts as follows : West- 

 ern juniper, in eastern Oregon and probably on the Snake River 

 plains; mountain juniper, on the areas between the Rocky and 

 Bitter Root mountains, thence extending into the eastern Wash- 

 ington plains; one-seeded juniper, on the Snake River plains 

 and along the hills bordering this river valley nearly to its con- 

 fluence with the Clearwater. 



The western juniper is the most abundant of these species and 

 forms true forests. It occurs as close and absolutely pure stands 

 in many localities. The most extensive are found in Crook and 

 Wasco counties, in Oregon, where it covers areas of over 100 

 square miles, with a stand twice as heavy as the ordinary stand of 

 yellow pine in Oregon and Washington. Outside of these large 

 tracts the species occurs in small groves or aggregates, or as scat- 

 tered individuals, throughout most of the plains region of east- 

 ern Oregon. These juniper forests exhibit clearly the second 

 period of the general phase of progressive extinction, that of 

 deficient reproductive capacity. 



The western juniper reaches large dimensions on the eastern 

 Oregon plains. Individuals occur with basal diameters up to six 

 feet. It is a species of slow growth, centuries being required to 

 produce such large trees as just noted. In examining the stand, 

 one is struck by the great preponderance of old trees, the com- 

 paratively small percentage of young, and the marked deficiency 

 of seedling or sapling growth. It is noticeable that the older 

 trees produce enormous quantities of galbuls — juniper berries — 



