The Geography of Phytochemical Races

158 3 After the Ice
as wood permeability (important for production of glued products), pH, bending
strength, and brittleness, etc., are well known in the industry. Such factors, of vital
importance for commercial applications, and likely based upon genetic differences
to a certain extent; however, do not fi gure in taxonomic considerations.
Although the races described above were statistically signifi cantly different,
a degree of intergradation was evident. Thus, the northern inland race and coastal
race intergrade in central British Columbia, northeastern Washington, and northern
Idaho as well as in the mountains of central and east central Oregon. The coastal
race intergrades with the Sierra Nevada race in coastal and northern California.
A subsequent study, involving over 300 trees from 30 localities throughout
California and southern Oregon, confi rmed intergradation of the Sierra Nevada
race with the coastal race north of about 40°N latitude. Pure, unhybridized Sierra
Nevada trees occurred south of 40°N latitude (Zavarin and Snajberk, 1975). The
chemical data suggested a closer alignment of the Sierra Nevada race with the
inland races than with the coastal form. The present-day geographical separation
of the Sierra Nevada and inland races is thought to have occurred as a result of the
development of the Great Basin through increasing aridity that occurred during
the Pliocene-Pleistocene epochs.
The third paper in this set Zavarin and Snajberk (1976) described their efforts to
detect chemical races within big cone Douglas fi r. Analysis of the cortical monoterpenoid
fraction of 33 trees revealed that the major component was α-pinene,
with β-pinene, 3-carene, and limonene present in lesser amounts. The monoterpene
profi les of different populations varied somewhat from each other, but the overall
profi le of big cone Douglas fi r was clearly different from that of Douglas fi r. There
was no evidence for gene fl ow between the southernmost population of Douglas
fi r at Lompoc and the closest population of big cone Douglas fi r at Figueroa, sites
separated by only 34 km.
A recent examination of conifer terpenes and their interaction with bark beetles
involves Pseudotsuga menziesii as one of the subject taxa (Pureswaran et al. 2004).
Quantitative analysis of leaf and bole terpenes was conducted on P. menziesii,
Pinus contorta var. latifolia Engelm. (lodgepole pine), Picea engelmannii × glauca
(interior spruce), and Abies lasiocarpa × bifolia (interior fi r) (nomenclature from
that paper) growing sympatrically at three sites in British Columbia. Collections
were made along a transect running south to north over a distance of about 475 km
[Princeton in the south (49°25′N, 120°35′W), 100 Mile House in the center and
Prince George in the north (53°55′N, 122°49′W)]. A fourth sample of P. menziesii
from Maple Ridge, B.C., represented the coastal form of Douglas fi r.
The four species shared the same array of simple terpenes, but signifi cant differences
in amounts of individual compounds were observed. The differences were
considered large enough to support the idea that species-specifi c bark beetles were
responding to the individual mixtures of compounds produced by the trees. In the
case of Douglas fi r, for example, (+)-α-pinene rose from being a minor component
of bole terpenes in the Maple Ridge (coastal) collection to signifi cant contributor in
trees from the Princeton site, to being the major compound in mixtures at the 100
Mile House and Prince George sites. (−)-β-Pinene followed much the same pattern.