Heritability of first-order lateral root number in Quercus: implication for artificial regeneration of stands
Natural regeneration of oak (Quercus) species in the USA has been easy to obtain on the lower quality xeric sites (site index less than or equal to 20 m at age 50) by developing advanced oak reproduction before stands are harvested. This approach has not been successful with Q. rubra, Q. pagoda, or Q. alba growing on highly productive river bottom, cove or other mesic sites (site index greater than or equal to 23 m at age 50) because developing seeedlings are overtopped by initially faster-growing and more shade-tolerant competitor species common on these sites. Artificial regeneration to increase percentages of these three valuable multiple-use species in specific stands has not been satisfactory because of limitations imposed by planting stock quality and by the traditional technology used to manage newly established stands. After the number of first-order lateral roots (FOLR) produced by an individual seedling was shown to be a highly heritable trait, artificial regeneration trials were started by the USDA Forest Service's Institute of Tree/Root Biology. A nursery fertility protocol was developed that could reliably and consistently produce seedlings of specific sizes. Thereafter, a seedling evaluation system was developed utilizing the parameters of FOLR, root collar diameter (RCD), and height (HT) for selecting seedlings for outplanting. On mesic sites, survival and early growth for Q. rubra has been very good, with height growth of 4-5 m in 3-8 years. Trials are now being conducted with Q. pagoda and Q. alba. Methods for devoping evaluation systems for oak sepcies grown in nurseries under conditions different than the ones used in this study are discussed.