Aspects of epicormic development in Quercus alba (L.) and other eastern North American oak species in relation to genetics, tree vigor and silvicultural treatments

Andrew Meier, Purdue University

Abstract

Epicormic buds and branches are a common occurrence on trees and are an integral part of woody plant development. They allow trees to respond quickly to changing environmental conditions by providing secondary meristems capable of capturing newly available light or refoliating a tree following damage. However, epicormic branches also produce knots in lumber and have the potential to cause losses in economic value when they form on tree boles. As a result, epicormics can be a major silvicultural and tree improvement problem for high value tree species. Since epicormic development has generally been thought of a function of tree vigor and genetics, the main objective of this project was to assess the relative influence of these two components on epicormic development in white oak (Quercus alba L.) and other common eastern North American oak species. Because epicormic branching has not been a widely studied topic, no published review of the literature is available. Chapter 1 encapsulates descriptions of epicormics in tree species from around the world and identifies common trends among them. Research has demonstrated that the number of epicormic branches on a tree at any point in time is influenced by epicormic bud dynamics. Further, epicormic development within a given species is likely a predictable trait. By understanding epicormics in the terms of the epicormic strategy, the relative influences of environment and genetics on different stages of epicormic ontogeny can be determined. The remaining chapters focused on understanding epicormic development in eastern North American oak species. For Chapters 2 and 3, a crop tree release (CTR) treatment was implemented in a 25 year old white oak progeny test with trees of known families. Chapter 2 describes the development of epicormic branches on the released study trees over a period of three years in relation to tree vigor and genetics. Overall, there was no significant increase in the mean number of epicormics per study tree (p = 0.940), but a significant (p < 0.001) increase in the size of those branches. Genetics and tree vigor appeared to influence epicormic development differently, with individual families having a stronger influence on the size of branches (dˆ = 0.228) than on the number ( dˆ < 0.001). Relative to genetics, vigor components were more important predictors of epicormic branch characteristics. However, pre-treatment epicormic characteristics had a stronger influence than either genetics or vigor on the overall epicormic response. In Chapter 3, trees that were removed in the course of the CTR treatment in Chapter 2 were used to analyze the development of epicormics prior to silvicultural intervention. The internal structure of these logs was recreated using computed tomography (CT) scanning. The development of epicormics over time was assessed by counting structures and classifying them in terms of different stages of epicormic development. This portion of the study showed that variables related to ontogeny and tree vigor had strong influences on epicormics dynamics, but that the genetic component was minor. The number of sequential branch knots was the most significant predictor (p < 0.001) of numbers of epicormics, while diameter growth was strongly related with epicormic control (p < 0.001). The final component of this project was an assessment of the importance of 23 vigor, site and exposure related variables on epicormic development in merchantable oak stands across the state of Indiana. For this study, 21 clearcuts from 8 sites with an average time since harvest of 3.5 years were selected. Site related variables were generally less important than tree vigor related variables. Overall, tree diameter was the most important variable; large trees (> 38.9 cm dbh) and stands with larger average tree diameters were less prone to epicormic branching. There was a significant difference in average branch numbers between white oak, which had the lowest number of branches (x¯ = 4.41) and black oak ( Q. velutina Lam.), which had the most (x¯ = 9.1, p = 0.042).

Degree

M.S.

Advisors

Saunders, Purdue University.

Subject Area

Forestry

COinS