The genetic structure and the conservation of the five natural populations of Pinusradiata

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Abstract
Pinusradiata is restricted to three mainland coastal populations in California and two island populations off Baja California, Mexico. In this study each population was divided into two geographic stands based on natural disjunctions within populations. In addition to the division mentioned above, each mainland population was also divided into a number of ecological stands based on ecological and environmental criteria. Genetic variation was measured by analysing 31 allozyme loci electrophoretically using germinated seed from 272 families across all stands and populations. Moderate levels of allozyme variation were found as shown by population averages for mean number of alleles per locus (1.79), percent polymorphic loci (46.4%, 0.99 criterion), and expected heterozygosity (0.098). In fact, the overall genetic diversity in P. radiata (HT = 0.117) is low compared with that of other conifers. In comparison with populations, the levels of allozyme variation in both ecological and geographic stands were slightly lower (means across ecological stands: A = 1.56, P = 39.3%, and He = 0.095). Of the total genetic diversity in P. radiata, 16.2% could be apportioned between populations, a high proportion for a conifer. In contrast, only 2.0 and 1.3% of the genetic diversity on average within mainland populations was between ecological and geographic stands, respectively. These results indicate a low level of genetic differentiation within populations, at least based on the ecological or geographic criteria used in this study. The implications and usefulness of these findings for the development of insitu conservation strategies are discussed.