A graphic technique for identifying superior seed sources for central hardwoods

To maximize forest production, foresters need to plant the best genotypes provided by forest geneticists. Where should the forest geneticist search for the best seed sources? How far can one go south, or north to find them? The answer may rely on the species and the location of the test plantation. For example, when black walnut trees were tested in Illinois, Indiana, Missouri, and southern Michigan, trees from southern seed sources grew faster than those of local and northern seed sources. However, in Iowa and Minnesota, trees from northern sources were generally larger than trees from southern sources, and in Kansas and Ohio, tree size was not associated with latitude of seed source (Bey 1973, 1979). As the number of plantation Increases, we may find that the most southern plantation will have only northern seed sources and the most northern plantation will have only southern seed sources, we may not be able to make a simple statement as to the best seed zone for each plantation location. Since a picture is better than a thousand words, we suggest a simple graphic solution useful to answer these questions.