Conservation of genetic diversity in old-growth forest communities of the southeastern United States

Question: How do studies of the distribution of genetic diversity of species with different life forms contribute to the development of conservation strategies? Location: Old-growth forests of the southeastern United States. Methods: Reviews of the plant allozyme literature are used to identify differences in genetic diversity and structure among species with different life forms, distributions and breeding systems. The general results are illustrated by case studies of four plant species characteristic of two widespread old-growth forest communities of the southeastern United States: the Pinus palustris - Aristida stricta (Longleaf pine - wiregrass) savanna of the Coastal Plain and the Quercus - Carya - Pinus (Oak-hickory-pine) forest of the Piedmont. Genetic variation patterns of single-gene and quantitative traits are also reviewed. Results: Dominant forest trees, represented by Pinus palustris (longleaf pine) and Quercus rubra (Northern red oak), maintain most of their genetic diversity within their populations whereas a higher proportion of the genetic diversity of herbaceous understorey species such as Sarracenia leucophylla and Trillium reliquum is distributed among their populations. The herbaceous species also tend to have more population-to-population variation in genetic diversity. Higher genetic differentiation among populations is seen for quantitative traits than for allozyme traits, indicating that interpopulation variation in quantitative traits is influenced by natural selection. Conclusion: Developing effective conservation strategies for one or a few species may not prove adequate for species with other combinations of traits. Given suitable empirical studies, it should be possible to design efficient conservation programs that maintain natural levels of genetic diversity within species of conservation interest.