VEGETATION OF THE SANTA CATALINA MOUNTAINS. 13 



Encinal belt is essentially a region dominated by sclerophyllous trees 

 and shrubs and by semi-succulent perennials, with an open stand of 

 perennial grasses. It is what is designated by the Forest Service as 

 the " woodland type" of forest. The pine and fir forests are very 

 dissimilar in their floristic composition, but they are much more closely 

 alike vegetistically than are any two of the three major divisions which 

 have been made. A further and more careful examination of the stages 

 which connect the Desert with the Forest will discover not only the 

 inevitable gradations between the three major regions, but also 

 several minor features which cause constantly recurring departures 

 from the typical or ideal vertical distribution of the vegetation. The 

 influence of slope exposure on the vertical ranges of both the individual 

 species and the vegetation itself is a feature which these mountains 

 share with almost all extra-tropical mountains; the distinctive vegeta- 

 tion of flood-plains and streamways is also as clearly noticeable here 

 as in all arid and semi-arid regions; the occurrence of the lowland 

 species at higher altitudes on ridges than in the valleys is also a strong 

 differentiating feature. 



In describing the salient physiognomic and floristic features of the 

 vegetation, and its distributional behavior, it is expedient to recognize 

 primarily the three major divisions of Desert, Encinal, and Forest, 

 and then to take into account secondarily the degree to which the 

 components of these regions intermingle and the extent to which the 

 topographic irregularities of the mountain cause an alternation and 

 interdigitation of the three regions. 



The basal slopes of the mountain between 3,000 and 4,000 feet (915 

 and 1,220 m.) present few vegetational distinctions from the upper 

 bajadas, and almost no distinctions of flora. Between 4,000 and 5,000 

 feet (1,220 and 1,525 m.) there is a rapid elimination of all but a very 

 few of the characteristic desert species, and on north slopes at the 

 latter elevation nearly all of the dominant Encinal forms have made 

 their entry. The upper limit of the Desert may be placed at 4,000 feet 

 for north slopes and 4,500 feet (1,472 m.) for south slopes. The upper 

 edge of the Desert exhibits an attenuated occurrence of all of the larger 

 desert plants and the presence of many perennial grasses and semi- 

 woody plants which occur both in the Encinal Region and on the bajadas 

 of equal or slightly greater elevation in the neighboring portions of 

 Arizona. The extreme upper limit of desert forms is 7,000 feet (2,133 

 m.), an elevation which is reached by a single succulent species. Follow- 

 ing the dissimilarity of the lower and upper portions of the Desert Region 

 they have been described separately. 



The Encinal Region extends from the occurrence of the first ex- 

 tremely open groves of evergreen oaks on north slopes at 4,000 feet up 

 to the first elevation at which the larger pines begin to dominate the 

 physiognomy of the vegetation, at about 6,300 feet (1,920 m.) on south 



