144 A MANUAL OF FARM GRASSES 



lap and there may be rains in 'both summer and winter, 

 followed by two grazing seasons. 



The northern portion of the Great Basin is a vast 

 plateau, the dominant plant of which is the sage brush 

 (Artemisia tridentata). This region is often referred to 

 as sage brush plains. It is scarcely a desert but is so 

 classified here because it is arid or semiarid. It affords 

 many species of grasses that furnish forage during the 

 spring and early summer. Chief among these are certain 

 native species of bluegrass {Poa Sandbergii Vasey, and 

 several other species of Poa). 



The foothills of the Pacific Coast region furnish excel- 

 lent forage after the winter rains but become brown and 

 sere during the summer. One of the most important 

 native species is California bluegrass (Poa scahrella 

 Benth.). This region has been invaded by a host of 

 introduced annuals which are driving out the native 

 grasses and themselves furnish an inferior forage. These 

 annuals are grazed during the early growth before the 

 seeds are produced. The most conspicuous of these 

 intruders are several kinds of brome grass (species of 

 Bromus) and wild barley (species of Hordeum). 



HUMID FORESTS 



In general the forests occupy the mountain ranges, 

 except the upper part of the higher peaks. The timber 

 line is approximately 1 1 ,000 feet altitude in the southern 

 mountains and about 6,000 feet at the north. The lower 

 limit of the forest depends upon the rainfall. In the 

 eastern Rocky Mountains the forest meets the plains, in 

 the Great Basin it meets the desert and sage brush plains. 



