Journal of Heredity Advance Access originally published online on October 26, 2005
Journal of Heredity 2005 96(6):627-634; doi:10.1093/jhered/esi115
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Genetic Structure Inside a Declining Red Oak Community in Old-Growth Forest
From the United States Department of Agriculture, Forest Service, North Central Research Station, Hardwood Tree Improvement and Regeneration Center, Purdue University Department of Forestry and Natural Resources, West Lafayette, IN 47907–2033 (Aldrich and Michler); Purdue University Department of Forestry and Natural Resources, West Lafayette, IN 47907–2033 (Parker and Rhodes); and Hardwood Tree Improvement and Regeneration Center, Purdue University Department of Forestry and Natural Resources, West Lafayette, IN 47907–2033 (Glaubitz)
Address correspondence to Preston R. Aldrich, Department of Biological Sciences, Birck Hall 341, 5700 College Road, Benedictine University, Lisle, IL 60532–0900, or e-mail: paldrich{at}ben.edu.
Problems with oak regeneration have been documented in the last 50 years at numerous sites in the Midwestern United States. We applied nuclear microsatellites to examine the demographic and fine-scale spatial genetic structure of red oaks in two old-growth stands in Indiana. Oaks in one stand have declined in numbers over the past several decades whereas oaks in the other, smaller stand have increased. Large amounts of genetic variation were maintained within stands, and there was slight but significant differentiation among stands. There was significant but weak isolation by distance genetic structure within the large stand, likely reflecting family structure. No significant differences exist in allele frequencies or in levels of genetic diversity between cohorts that remain well represented within each stand, even between medium-sized adults and those antedating European settlement of the area. However, a virtual absence of smaller size classes in the forest interior of the large stand represents the early stages of a genetic bottleneck in what had been the core habitat of this stand. Whether future generations of this old-growth stand will retain the present genetic character depends on the oaks regenerating at the forest margins, absent any major changes in disturbance regimes. Similar demographic and genetic dynamics are likely occurring in a large number of remnant oak forests across the Midwest.