Geographical variation in the monoterpenes of Pinus contorta oleoresin

The monoterpene composition of the shoot cortical oleoresin allowed the natural range of Lodgepole pine (Pinus contorta) to be divided into chemically distinct regions. The trees examined were all grown in Britain from seed originally collected from 150 localities in north-west America. Those from the central area of the natural range contained a wide variety of monoterpene pattern-types, while those from more peripheral areas tended to be more exclusively characterized by their own specific pattern-types. Chemical evidence for introgression with Jack pine (P. banksiana) was detected in trees originating from central British Columbia, and there was also a highly localized and pronounced region of introgression chemotypes in coastal populations near the border of Oregon and California. Variations between trees grown in replicate plots and at different sites in Britain were small, and the results indicated that resin analysis of a sample of 25 trees was usually sufficient to determine the region of origin of an unknown population.