The presence of hybridization among coexisting species of Quercus section Lobatae raises questions regarding the selection of mother trees to control seedling quality. Currently, trees are selected as a seed source on the basis of whole tree silvic characters. There are two sympatric red oak species in northern Wisconsin, Q. rubra L. (northern red oak) and Q. ellipsoidalis E. J. Hill (northern pin oak). We characterized 30 mother trees and their seedlings to assess the potential for selecting red oak seed sources based on silvic characters of the mother tree. Mother trees were selected based on whole tree silvic characters to represent Q. rubra L., Q. ellipsoidalis E. J. Hill and their putative hybrids. Mother trees were then characterized by leaf and acorn morphometric analyses and by isozyme profiles. One-year-old bareroot nursery seedlings raised from seeds collected from these mother trees were characterized by height, diameter and number of lateral roots. Height and diameter growth were also measured the year after planting these nursery seedlings. Multivariate analyses revealed two, rather than three, distinct mother tree groups: Q. ellipsoidalis and Q. rubra plus putative hybrids. Thus, whole tree silvics are not adequate for differentiating northern red oak and hybrids. However, analyses, particularly of leaf morphology, isozymes and seedling performance, provided evidence of a continuum between the two species, consistent with the existence of hybrids among the mother trees. Whereas Q. rubra and putative hybrids could not be distinguished, Q. ellipsoidalis trees were distinguished on the basis of whole-tree silvic characteristics, or by acorn, leaf or seedling morphological characteristics. Thus, Q. ellipsoidalis can be distinguished and removed from the publicly collected seed source to improve seedling quality.
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Vol. 143 • No. 1