Factors affecting Self-Pruning in Northern Red Oak (Quercus rubra L.)

Northern red oak (Quercus rubra L) is an important timber species in \nthe United States, and especially in Wisconsin, where the 1996 growing stock \nwas over 2.7 billion cubic feet. Northern red oak is the highest valued timber \nin Wisconsin. Defects in stem quality lower timber value, but thinning and \npruning regimes can be used to reduce these defects, at a cost. Northern red \noak is a self-pruning species, and this characteristic may be used to reduce the \ncost of producing high-quality wood. The objectives of the study were to 1) \ndetermine how forest stand density affects tree characteristics and self-pruning \nin northern red oak, and 2) to recommend practices, which incorporate the \nregulation of stand density, to encourage self-pruning in northern red oak. \nFifty trees were sampled from ten stands in northern and central Wisconsin. \nData collected included stand density and density around the sample trees, \ndbh, total height, height, length, and diameter of the lowest living and dead \nbranches, and crown area. Predictive models were developed to describe the \ntree characteristics. BA/acre was found to be a significant variable in the \nmodels for percent clear bole and rate of crown recession (two descriptors of \nself-pruning), but the models themselves were not good predictors. \nA secondary study included in this research sought to determine the \ngenetic make-up of the sample trees. Northern red oak and northern pin oak \n(Quercus ellipsoidalis) hybridize in the wild and both are located in \nWisconsin. Northern pin oak is not a self-pruning species. Past studies have \nbeen unable to find a strong method for determining if a tree is a northern red \noak, a northern pin oak, or a hybrid of the two. For the purposes of the study, \ntrue northern red oak were required. The secondary study used RAPDs \n(Random Amplified Polymorphic DNA) in an attempt to first find a genetic \nmarker to distinguish between the two species and then to determine if the \nsample trees were true northern red oak. Several primers were tested. The \ngenetic study was inconclusive and more research is needed to find a distinct \nnorthern red oak genetic marker.