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 whichis 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 
