Characterization of stem volume and form tradeoffs in a northern red oak (Quercus rubra) breeding population in early stages of selection

Abstract

Quercus rubra half sib progenies (N = 93) expressed high levels of variance for both growth and stem form traits in three locations in Indiana, USA at age 11 or 12. Height, diameter, and volume were measured and sweep, branch angle, forking, and branch retention were rated using a (+ / −) system. Families selected for volume showed no unfavorable increases in sweep or branch angle and only a slight increase in branch retention. Northern red oak (Quercus rubra L.) is the most planted hardwood in the central USA. Red oak seeds from sources with improved growth and form are unavailable in the Central Hardwood Region, in part because the absence of agreed methods for stem form evaluation diminishes the effectiveness of selection. To identify red oak families improved for growth and to determine if a simple + / − rating system could identify red oak families with improved form. We evaluated 93 open-pollinated families of 11 or 12-year-old red oak growing in three sites in central Indiana (USA) for height, diameter, volume, and four traits rated as + / − : sweep, branch angle, forking, and branch retention. Family × location effects were significant for all quantitative traits but not for any binary traits; differences among families were significant for all traits at all sites. Heritabilities for most traits were high. Selection of the top 20 families for volume at each site resulted in no change in population means for sweep or branch angle and only a small increase in the retention of large limbs. A + / − rating system to evaluate hardwood form can help breeders deliver improved red oak to landowners when more complex systems are impractical.