Minimizing epicormic branch formation on Louisiana leading commercial bottomland red oaks

Abstract

The goal of this study was to isolate biological, natural, and silvicultural factors that encourage the production of epicormic branches on bottomland red oak saw-timber trees and to use this information to help landowners and forest managers reduce epicormic branches in stands dominated by bottomland red oaks. Quercus nigra, Q. pagoda, Q. phellos, and Q. texana, the most common commercial bottomland red oaks in Louisiana, were evaluated in this study. Both qualitative and quantitative variables were assessed in this study. The following attributes were collected from each sample tree and primary competitor: site class, basal area, crown class DBH, presence or absence of epicormic branches, soil series, flooding regime, total tree height, height to base of live crown, live crown ratio, localized disturbance, and distance to nearest competitor. A total of 768 trees were evaluated, of which 384 trees displayed epicormic branching and 384 were without epicormic branches. Sample trees of all four species were equally distributed across four crown classes (dominant, co-dominant, intermediate, and suppressed). Equal numbers of all four oak species were collected to maintain homogeneity within the dataset. Logistic and Poisson regressions were used to analyze the data. An á level of 0.1 was considered effective for significance in this exploratory research. Logistic regression analysis yielded three variables significant in relation to the probability of epicormic branch occurrence. Variables significantly affecting the probability of epicormic branch production were total height of the sample tree, distance from the sample tree to the primary competitor, and crown class of the nearest primary competitor. The Poisson regression analysis was used to evaluate the number of epicormic branches a tree might produce. In this analysis dbh of the sample tree, crown class of the primary competitor, disturbance, flooding regime, and live crown ratio of sample trees were significant in relation to the number of epicormic branches produced. Tree, site, and environmental characteristics isolated as being important to epicormic branch production produced a means for evaluating the potential development of epicormic branches. These factors in concert provide the forester or land manager with a simple means of enhancing bottomland red oak value. The driving mechanism for sudden appearance of epicormic branches seems to be related to reduced tree vigor as affected by competition (or relative vigor based on relative height to competitors) and site stress factors. Taller trees with less competition from similar sized trees have a reduced probability of epicormic branches.