NOTES ON THE DISTRIBUTION OF TREES AND SHRUBS IN THE DES- 

 ERTS AND DESERT RANGES OF SOUTHERN CALIFORNIA, SOUTHERN 

 NEVADA, NORTHWESTERN ARIZONA, AND SOUTHWESTERN UTAH. 



By C. Hart Merriam, M. D. 



The present chapter is made up of a multitude of disconnected notes, 

 jotted down on horseback while traversing the deserts and desert 

 ranges of the southern part of the Great Basin. These notes relate to 

 the vertical and geographical distribution of the trees and shrubs ob- 

 served by me in April, May, and June, 1891, along the route traveled 

 from the north end of Cajon Pass, in the San Bernardino Mountains, 

 California, to the St. George Valley, at the foot of the Hurricane Cliffs, 

 in southwestern Utah, and thence westerly across Nevada to Owens 

 Valley, California, and southward and south westward to the extreme 

 end of the western tongue of the Mohave Desert (Antelope Valley), 

 including the several passes (Walker, Tehachapi, and the Canada de 

 las TTvas) by means of which communication is established between the 

 Mohave Desert on the southeast, and the Bakersfield Plain, or upper 

 San Joaquin Valley, on the northwest. A detailed itinerary of this 

 trip may be found in Part I of the report. In a few instances, notes 

 made by other members of the expedition are added and duly accred- 

 ited; a small number of non-woody plants are admitted to render the 

 list more useful, and in addition to the desert species a few from the 

 Sierra Nevada, mainly conifers, are included. 



Most of the desert shrubs are social plants and are distributed in 

 Avell-marked belts or zones, the vertical limits of which are fixed by 

 the temperature during the period of growth and reproduction. Since 

 the temperature at this season in places of the same latitude depends 

 mainly on altitude, base level, and slope exposure, it follows that the 

 boundaries of the several belts conform largely to the contours of alti- 

 tude, with such flexures as variations in base level and slope exposure 

 impose. 



The principal plant zones conform also to the animal zones, as defined 

 by the limits of distribution of terrestrial mammals, birds, and reptiles. 

 But since these Life Zones are discussed in the first part of the report 



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