The Geography of Phytochemical Races

3.2 North American Conifers 143
homogeneous profi le with α- and β-pinenes, 3-carene, and β-phellandrene as major
components, with lesser amounts of α-phellandrene, myrcene, limonene, and
terpinolene. Statistical analysis revealed little in the way of geographic patterning,
which is in accord with the view that silver fi r occupied a single refugium south of
the Cordilleran ice in Washington and Oregon during the most recent glacial episode
(Hultén, 1937, as cited by Zavarin et al., 1973). It was noted that A. amabilis is a
slow migrator and that it may still be in the process of northward movement.
Two closely related species of fi rs are Abies grandis, which occurs in northern
California, Oregon, Washington, Idaho, Montana, and southern British Columbia at
mid elevations, and A. concolor, which enjoys a more southerly range at somewhat
higher elevations. Populations from northern and eastern California have been recognized
as A. concolor var. lowiana (Gord.) Lemm., whereas those form Nevada,
Utah, Colorado, New Mexico, and Arizona constitute var. concolor. Populations
along the Pacifi c Coast and in Washington, British Columbia, northern Idaho, and
northern Montana are considered to be typical A. grandis, whereas populations in
northern California, central and eastern Oregon, southern Washington, and eastern
Idaho exhibit features that suggest incursion of genes from A. concolor. Features
by which the two taxa can be distinguished include stomatal placement, needle-tip
shape, needle length, and the color of bark periderm.
Analysis of the cortical turpentine of A. grandis revealed a mixture consisting for
the most part of α- and β-pinenes, camphene, β-phellandrene, and bornyl acetate.
Present in lesser amounts were 3-carene, limonene, myrcene, and tricyclene (Zavarin
et al., 1977). Camphene and 3-carene fi gure signifi cantly in distinguishing between
A. grandis and A. concolor. An earlier study (Zavarin et al., 1975) had revealed that
A. concolor could be resolved into three distinct chemical races on the basis of relative
amounts of two compounds: (1) the Rocky Mountain race with large amounts
of camphene and 3-carene; (2) the Cuyamaca race from southern California and
northern Baja California characterized by large amounts of 3-carene and only trace
amounts of camphene; and (3) the western race with these two compounds present
in only trace amounts. Abies grandis turpentine exhibits large amounts of camphene
and has 3-carene in trace amounts only. Based on the monoterpenes of the intermediate
populations, the workers concluded that introgressive hybridization had
occurred and might still be occurring.
The comparatively low level of interpopulational variation in the monoterpenes
of A. grandis resembles that for A. amabilis commented upon above. As noted by
Zavarin et al. (1977), it is likely that A. grandis occupied much the same areas during
interglacial periods that it occupies now. Advancement of the ice sheet forced its
retreat to refugia in Washington and Oregon. Present-day populations in the northern
parts of its range, therefore, represent a return to the interglacial situation. The general
lack of chemical variation observed suggests a relatively slow northward progress
during which time comparatively little differentiation has occurred. Halliday and
Brown (1943) considered the present-day distribution in British Columbia as having
resulted from postglacial migration of fi r along the coast toward Vancouver Island
and along the Kootenai Valley toward the moist Rocky Mountains. Pollen records in
the Puget Sound area, the Cascade Range of Washington, and northern Washington