Because of the elevational extremes and attendant climatic contrasts in
the San Gabriel Mountains, there is a rather wide range of environmental
conditions. Four life-zones are represented: Lower Sonoran, Upper
Sonoran, Transition, and Canadian. Within these zones certain ecologic
communities can be recognized; these represent several biotic
provinces. Table 1 shows the relationships between the environmental
categories recognized by the writer in the San Gabriel Mountains. The
biotic province and ecologic community system is that developed by Munz
and Keck (1949), and the life-zone system is that of Merriam (1898).
TABLE 1.--RELATIONS OF THE MAJOR ENVIRONMENTAL CATEGORIES OF THE SAN
GABRIEL MOUNTAINS.
=======================================================================
Biotic province | Plant community | Life-zone | Slope
----------------+--------------------------+-----------------+---------
|1. Coastal sage scrub | Lower Sonoran | Pacific
Californian |2. Southern oak woodland | Upper Sonoran | Pacific
|3. Chaparral | Upper Sonoran | Pacific
----------------+--------------------------+-----------------+---------
Sierran |4. Yellow pine forest and | Transition | Pacific
| limited areas of | Canadian | and
| boreal flora | | Desert
----------------+--------------------------+-----------------+---------
Nevadan |5. Sagebrush scrub | Transition | Desert
| | Upper Sonoran |
----------------+--------------------------+-----------------+---------
Southern Desert |6. Pinyon-juniper woodland| Upper Sonoran | Desert
|7. Joshua tree woodland | Lower Sonoran | Desert
----------------+--------------------------+-----------------+---------
The Californian Biotic Province dominates the biotic aspect of the
coastal slope of the range. Thirty-nine out of the seventy-two mammals
recorded from the San Gabriels are typical of this Province. The coastal
sage-flats at the Pacific base of the mountains and the vast tracts of
chaparral of the coastal slope are included in this Province.
Forming a hiatus between the Pacific and the desert slope is the Sierran
Biotic Province consisting of coniferous forests on the crest of the
range. The chipmunk (_Eutamias speciosus speciosus_) and the introduced
black bear (_Ursus americanus californiensis_) are the only two mammals
which can be considered typical of this area. On the higher peaks of the
range, such as Mount San Antonio and Mount Baden Powell, the Canadian
Life-zone is represented by certain boreal plants.
At scattered points along the crest of the range and on the desert
slope, the Nevadan Biotic Province is represented by the sagebrush scrub
association. No mammals can be considered typical of this region.
The Southern Desert Biotic Province occurs below 6000 feet elevation on
the interior slope of the range, and markedly influences the mammal
fauna of this slope. Twenty-one species of mammals are typical of this
Province.