Steps Toward Butternut (Juglans cinerea L.) Restoration

Butternut (Juglans cinerea L.), a lesser-known relative of black walnut (Juglans nigra L.), is a native tree species beneficial for wildlife, valuable for timber, and part of the great diversity of species in the eastern forests of North America. Populations of butternut are being devastated by butternut canker disease, caused by the fungus Sirococcus clavigignenti-juglandacearum (V.M.G. Nair, Kostichka, & Kuntz), which is thought to be introduced to North America. The disease causes multiple branch and stem cankers that eventually girdle trees. Small population sizes, lack of sprouting, and shade intolerance exacerbates the disease and results in permanent losses of butternut across the native range. Fortunately, healthy, canker-free butternut trees have been found proximal to diseased trees, indicating that a breeding approach could be a feasible strategy for producing and reintroducing resistant butternuts. A successful restoration program will require an understanding of genetic variation in open-pollinated seedlings, genetic basis of disease resistance, seedling establishment procedures, site requirements, and a greater understanding of disease development over time.

This dissertation is divided into six parts, with the overall goal of insight into butternut ecology and management techniques which could be used to guide restoration decisions for this important species. The first two parts are an introduction and a literature review. In the third section, butternut seedlings were propagated in nursery progeny plantings to determine the genetic and phenotypic variability among one-year-old seedlings in a controlled environment. Part four outlines the disease development of butternut seedlings across progeny in resistance screening plantings at various locations. Part five aims at aiding restoration techniques by determining the impact of phenotypic and genetic variables on establishment success across various planting sites with different silvicultural treatments. Part six describes the dynamics of a large population of healthy and diseased butternut trees including disease development across temporal scales. The information gained from this research will be directly used in gene conservation strategies, the construction of disease resistant breeding orchards, and in determining appropriate restoration techniques.