measuring the amount of genetic variation in species populations has been a concern of evolutionary biologists since the time of Darwin. A variety of techniques have been used, ranging from the common garden approach of Turresson (1922, 1925) and others (e.g., Clausen, Keck, and Hiesey, 1940, 1948) to the DNA sequencing studies of modern workers. These studies, whether morphometric, physiological, developmental, or biochemical, have demonstrated that most species populations contain relatively large amounts of genetic variation. Good examples of these kinds of studies can be found in the forest genetics literature. Because of the commercial importance of forest trees, genetic variation within and between tree populations has been unusually well documented. The majority of forest tree species have considerable amounts of genetic variation within, as well as between, populations (Libby et al., 1969; Stern and Roche, 1974; J. W. Wright, 1976). A notable exception is red pine (Pinus resinosa), in which little genetic variation has been demonstrated (Fowler, 1964, 1965; Fowler and Lester, 1970; Fowler and Morris, 1977). This is remarkable, since red pine ranges from Wisconsin to Nova Scotia and from northern Pennsylvania to central Ontario. Other forest tree species occurring in essentially the same environments as those inhabited by red pine have been shown to have considerable genetic variation.
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