_Pinus ponderosa_
_P. lambertiana_
_Libocedrus decurrens_
_Abies concolor_
_Quercus Kelloggii_
_Ribes nevadense_
_Ribes Roezlii_
_Arctostaphylos sp._
_Ceanothus cordulatus_
The crest of the range, from the upper limit of the chaparral
association at roughly 6000 feet to the limited areas of boreal flora
above 8500 feet elevation, is covered by yellow pine forests. On the
desert slope of the range the coniferous forests which extend down to
about 6000 feet represent the best development of this association,
while the coniferous forests on the coastal side of the drainage divide
are often more or less diluted by chaparral elements. For example,
yellow pines on the Pacific face of Blue Ridge at 7000 feet elevation
often grow in association with scrub oak and mountain-mahogany.
Few mammals are resident in the typical yellow pine forest as
characterized by dense coniferous timber and little herbaceous or brushy
growth. Here most of the species recorded actually find optimal
conditions in an adjacent habitat. The forest probably harbors surplus
individuals from adjacent preferred habitats, or, as in the case of
chipmunks and ground squirrels, the forest often serves as forage ground
while nearby brushy areas are utilized for breeding and shelter. The
abundance of birds in the timber contrasts strikingly with the paucity
of mammals there. The lack of a seed-producing understory, and the open
duff-covered stretches of ground on which rodents would be extremely
vulnerable to predation, probably in part account for the scarcity of
rodents.
Within the general area encompassed by the yellow pine forest there are
two major habitats, namely coniferous forest and chaparral. The
species of plants comprising the chaparral of the Transition Life-zone
are different from those comprising the chaparral of the Upper Sonoran
Life-zone on the Pacific slope. In the chaparral of the Transition
Life-zone, basin sagebrush and snowbrush grow in extensive patches in
clearings in the timber. Dense thickets of choke cherry cover many damp
hollows, and these thickets harbor the houses of _Neotoma fuscipes_. The
food and shelter afforded by these chaparral areas importantly influence
the local distribution of rodents: for example, _Dipodomys agilis_ and
_Perognathus californicus_ in the yellow pine area are found only in
association with chaparral, being completely absent from wooded areas.
The severe winter weather in this association must force many of the
mammals into periods of inactivity. Probably during the long periods in
the winter when snow covers the ground the heteromyids and sciurids
remain below ground.