The Geography of Phytochemical Races

148 3 After the Ice
Efforts to remedy this situation were made by Forrest (1980a, 1981) who investigated
the cortical oleoresin constituents of trees collected from 150 sites throughout
the range of the species. Three compounds were found to be ubiquitous, α-pinene,
β-pinene, and β-phellandrene; three were seen consistently but in smaller amounts,
camphene, α-terpinene, and terpinolene; and two, limonene and 3-carene, were
highly variable, ranging from absent to moderate concentrations. Fairly clear-cut
chemotype patterns emerged from GC analysis three of which were common: type
A = β-phellandrene >> β-pinene ∼ α-pinene; type B =β-phellandrene > β-pinene >
α-pinene; and type C = β-pinene > β-phellandrene > α-pinene. Three subtypes were
identifi ed based upon presence, absence, or relative concentrations of 3-carene and
limonene: 1 = 3-carene and limonene either absent or present in low concentrations;
2 = 3-carene present in moderate to high concentrations; and 3 = limonene present
in moderate to high concentrations. Several patterns, based on relative amounts of
the pinene isomers, referred to as “rare types”, were identifi ed that tended to be
restricted to small areas. Finally, an “introgression” type, his type E, was identifi
ed that was characterized by relatively high concentrations of camphene along
with high concentrations of α-pinene and/or β-pinene. Type E trees occurred in
southwestern Northwest Territories and west central Alberta and were thought to
have resulted from introgression with Jack pine, Pinus banksiana Lambert. There
was fair agreement between chemotypes and subspecifi c taxonomy, except for
subsp. murrayana, which could not be distinguished from subsp. latifolia on the
basis of the terpene data.
The next step in the analysis was to determine the geographic distribution of the
various types. Type A1 trees (that is, type A-subtype 1), for example, were found to
occur in north coastal British Columbia, the Queen Charlotte Islands, and western
Vancouver Island. Local, or at least comparatively short distance, differences were
common in the database as one sees in the differences between western Vancouver
Island trees and those on the eastern side of the island where high β-pinene and
3-carene concentrations were observed in concert with decreased amounts of
β-phellandrene. Type C1 trees were characteristic of the Puget Sound area, with A1
and B1 types present in populations along the coastal strip of Washington and Oregon.
One feature of the distribution of chemical types in the context of refugia, and subsequent
gene fl ow, is the homogeneous nature of populations at the southern and
western peripheries of the range of lodgepole pine. Uniformity of these populations
might be the result of the founder effect, or, alternatively, peripheral populations
might have resulted from local selection. The most heterogeneous populations were
those in central British Columbia with others extending farther to the north and
northeast. In these areas, population density is high and thus open to greater pollen
exchange. Forrest (1987) discussed this feature of lodgepole pine in terms of possible
glacial refugia at the northern extent of the species. Despite the considerable
amount of information provided by these studies, we are left with questions that
cannot be answered, principally, what has been the direction of movement of genes
in this system? What is needed to answer this—and the same question can be asked
about virtually all studies of this sort—is a phylogenetic hypothesis that provides a
framework of interpopulation relationships. We do not know, for example, whether