mPERU UBi^^rV 



24 VEGETATION OF A DESERT MOUNTAIN RANGE. 



wrightii, Dalea wislizeni, Calliandra eriophylla, Hymenopappus mexi- 

 canus, Artemisia ludoviciana, Dalea alhiflora, Asclepias linifolia, Fran- 

 seria tenuifolia, Baccharis thesioides, Ayenia microphylla, and Anisolotus 

 argensis. The commonest summer ephemerals are Eriogonum abertia- 

 num and Eriocarpum gracile. 



The flood-plains and the banks and beds of the arroyos in the Upper 

 Desert are, in general, more like the arroyos of the desert in their 

 vegetation than like those of the Encinal region. The largest tribu- 

 taries of Sabino Canon are somewhat less rich in aquatic and palustrine 

 plants than the lower portion of the canon, and merely because of 

 their steeper gradient and less regular flow. The forest which occupies 

 the flood-plains of Sabino Basin is chiefly made up of Quercus emoryi, 

 Quercus arizonica, Platanus wrightii, and Cupressus arizonica. The 

 smaller flood-plains and arroyos of the Upper Desert have few of these 

 trees but occasional individuals of Populus and open thickets of Bac- 

 charis emoryi and Baccharis sarothroides, together with Franseria 

 amhrosioides, Ingenhousia triloba, Erythrina fiabelliformis, Croton texen- 

 sis, Calliandra eriophylla, Brickellia californica, Gymnosperma corym- 

 bosa, Amorpha californica, Bouvardia triphylla, and Stachys coccinea 

 (see plate 10a). 



THE ENCINAL REGION. 



Some of the distinctive species of the Lower Encinal are found at 4,000 

 feet and other forms, characteristic of the Upper Encinal, extend upward 

 into the Forest Region as far as 8,000 to 8,600 feet. The Lower Encinal 

 may be said to have its commencement, however, in the open orchard- 

 like stands of Quercus oblongifolia and Quercus arizonica, which occupy 

 northerly slopes at about 4,300 feet. At an approximate elevation of 

 5,000 feet the open Encinal may be found on all slopes except the steepest 

 southerly ones, while on steep northern slopes it already forms nearly 

 closed stands. The dense stands of the Upper Encinal region begin to 

 appear on southerly slopes at about 5,800 feet, and persist to the eleva- 

 tion of 6,200 to 6,400 feet, where large pines begin to dominate the 

 physiognomy and the true forest may be said to begin. 



The activities of growth and flowering which are so conspicuous on 

 the Desert in the season of winter rains are very much reduced in the 

 Lower Encinal and are practically absent in the Upper Encinal. 

 Leaves are retained by the evergreen oaks and the sclerophyllous shrubs 

 throughout the winter and are shed in April or May, simultaneously 

 with the first growth of shoots and the renewal of foliage. Extremely 

 few of the ephemerals which often carpet the Desert in January are 

 to be found in the Encinal region. There is some activity on the part 

 of root perennials in the Lower Encinal during the months of March 

 and April, and flowers may be found on species of Sphoeralcea, Calo- 

 chortus. Verbena, Pentstemon, Eriogonum, and Lesquerella. Such activ- 

 ity is commonly stopped by the advent of the arid fore-summer, and 



