VEGETATION OF THE SANTA CATALINA MOUNTAINS. 25 



relatively little activity is observable in May and June, at least away 

 from arroyos and springs. In the Upper Encinal the early months of 

 spring partake of the rest which is then predominant in the Forest 

 region. The deciduous trees begin foliation in late April or early May 

 and some of the root perennials are not far behind them in their earliest 

 activity. The duration of the arid fore-summer being slightly less in 

 the Upper Encinal than in the Lower Encinal, and its intensity being 

 also less, there is not so decided a break, among the herbaceous peren- 

 nials between the first activity of spring and that of the humid mid- 

 summer, as there is in the Lower Encinal and the Desert. 



THE LOWER ENCINAL. 



The species which chiefly characterize the Lower Encinal at its 

 desert edge have already been mentioned : Quercus oblongifolia, Quer- 

 cus arizonica, Juniperus, Vauquelinia, Dasylirion, Nolina, Yucca macro- 

 carpa, Arctostaphylos pungens, Agave palmeri, and Agave schottii. All 

 of these are much more abundant at 5,000 feet than at 4,500 except 

 Quercus oblongifolia, which is a tree of very narrow vertical range, rarely 

 occurring above 5,200 feet and reaching its limit at 5,600 feet on steep 

 south slopes. At 5,000 feet the Encinal has been augmented by the 

 appearance of the common trees Quercus emoryi and Pinus cembroides 

 (pinon) and by the shrubs Garrya wrightii, Mimosa biuncifera, Rhus 

 trilobata, and Rhamnus crocea var. pilosa (see plates HA, 15, and 16). 



The only characteristic Desert species which persist throughout the 

 Lower Encinal are: Carnegiea gigantea, a single young individual of 

 which has been seen at 5,100 feet; Opuntia versicolor, which reaches 

 5,500 feet; Fouquieria and Echinocactus wislizeni, which reach 5,600 

 to 5,800 feet; and Mamillaria grahami, which ascends to 7,000 feet. 

 So far as known, no other plants occurring on the Bajadas or in any 

 of the other non-palustrine desert habitats range to elevations above 

 6,000 feet.* There are at least a few species found in canons and near 

 constant water which range from the elevation of the Desert to more 

 than 6,000 feet. Several of the typical desert genera are represented 

 at higher elevations by species which seldom range as low as the Upper 

 Desert region. Two species of Opuntia (platopuntias) are found 

 throughout the Encinal, growing in thin soil or on rocks, and reaching 

 their highest occurrence solely on ridges or upper slopes. One of these 

 species has been found on a sharp rocky ridge at 7,200 feet, which is 

 the highest known occurrence of a platopuntia in the Santa Catalinas. 

 Mamillaria arizonica ranges from the Upper Desert to nearly 7,000 

 feet; Echinocereus polyacanthos ranges from about 5,000 feet to 7,800 

 feet, which is the highest elevation at which any cactus has been found 

 in these mountains. Agave palmeri and Yucca schottii are also fre- 



* This statement is made only with respect to the Santa Catalinas. The influence of the 

 character of the underlying rock and of the elevation of the surrounding desert each serves to 

 determine indirectly the vertical limits of desert species. 



