The Geography of Phytochemical Races

152 3 After the Ice
components (up to 1.5% of total monoterpene fraction) included camphene, sabinene,
myrcene, β-phellandrene, γ-terpinene, terpinolene, and p-cymene. In general,
levels of variation within and among populations were high with very little difference
between the profi les of trees from coastal British Columbia and Washington
and those from the Rocky Mountains, all of which suggested that these populations
have occupied their current range for a comparatively short time. Critchfi eld (1984)
suggested, on the basis of glacial history, fossil evidence, and dispersibility factors,
that P. monticola reoccupied this region some 5800–7000 years ago, having survived
in a refugium in southwestern Oregon.
From central Oregon south, however, the situation appears to have been quite
different. Again we rely on the occurrence of 3-carene to provide insights into the
events of the past. With few exceptions, most populations with the C allele were
observed in the southeastern Sierra Nevada Mountains in California with frequencies
of the allele often approaching 100%. Moreover, Zavarin et al. (1990) suggested
that these populations, including some that are quite isolated, originated from
a second refugium that lay east of the area glaciated during the Wisconsin period.
Following retreat of the ice, P. monticola expanded from its southern refugium both
toward the west and north. At some point, the northward expansion would have
brought trees with the southern genotype into contact with trees from the northern
refugium that was, in their turn, moving northward into Washington and British
Columbia and southward into the northern Sierra Nevada.
A discussion of the bristlecone pines requires comment on all three members
of Pinus sect. Parrya Mayr subsect. Balfourianae Engelm.: P. aristata Engelm.,
the Rocky Mountain bristlecone pine; P. longaeva D. K. Bailey, the Great Basin
bristlecone pine; and P. balfouriana Grev. & Balf., the foxtail pine. Until 1970, the
term bristlecone pine referred only to P. aristata, but the situation changed with the
recognition of P. longaeva by D. K. Bailey (1970). More specifi cally, P. aristata
occurs in the Rocky Mountains of Colorado south into New Mexico and in a disjunct
population in the San Francisco Mountains in north central Arizona (map
reference Flagstaff). Pinus longaeva occurs in Utah, extensively in the mountains
of east central Nevada, and disjunctly in the Spring Mountains of southern Nevada,
and in the White Mountains of east central California (Fig. 3.9). (The proximity of
P. longaeva and P. balfouriana will be commented on below.)
Until the work of Zavarin and Snajberk (1973a), the only chemical information
available on the bristlecone pines was the report by Haagen-Smit et al. (1950) that
the major component of P. longaeva (at that time referred to as P. aristata) turpentine
was α-pinene and, interestingly, that the optical rotation of α-pinene from
P. longaeva and southern specimens of P. balfouriana was dextro rotatory (+26.12°
and +23.72°, respectively), whereas that of northern specimens of P. balfouriana
was levo rotatory (−10.23°).
The fi rst comparative study of monoterpenes in these taxa was that of Zavarin
and Snajberk (1973a) who examined wood monoterpenes from 67 trees at three
sites representing P. aristata, and four sites representing P. longaeva and reported
very signifi cant differences. The major component of P. longaeva turpentine was,
as originally reported by Haagen-Smit et al. (1950), α-pinene, which constituted