Butternut Restoration Project
An Intraspecific Tree Breeding Program
By Kyle Lombard
New Hampshire Division of Forests and Lands
Forest Health Section
During the mid 1960's, over 500 square miles of butternut veneer, and millions of board feet of butternut lumber were cut annually. Today, over 90% of the remaining butternut is infected with a non-native disease called 'butternut canker', and virtually all cutting of butternut has stopped. Butternut canker disease was most likely introduced from Asia, through the St. Lawrence Seaway, into the ports around the Great Lakes and first noticed in the late 1960's. The disease has now spread east and south to the farthest extent of the butternut's native range. Like Chestnut Blight and Dutch Elm Disease, Butternut Canker has effectively eliminated butternut as a thriving tree species within the northeast forest ecosystem. Most butternut dies within 15 years of infection and virtually all known populations of butternut are now infected.
Symptoms of the butternut canker on the tree include many dead branches, discoloration of leaves in early to mid summer, and the creation of many cankers or dead lesions all over the tree. Signs of the disease include oozing black liquid from wounds, black powdery material surrounding dead spots on the bark, and the formation of target like cankers around the base of the tree.
The New Hampshire Division of Forests and Lands has created a project to harvest shoots and buds, called 'scion wood', from the few apparently disease resistant trees still alive in New Hampshire. By collecting scions from the few resistant trees, we can graft them to black walnut root stock to create a seed orchard of resistant butternut trees. When we cross pollinate between different resistant trees, within the orchard, it's hoped we will produce resistant seed which can then be out-planted in the native forest environment that butternut once dominated. The process is called 'intraspecific tree breeding'.
The project was started in 1996. Since then, we have surveyed more than 3000 possibly resistant trees at over 300 different sites statewide. To date, we've found only eight butternuts that meet our strict standards and show signs of significant resistance to the disease. From those 'super trees' we have established a one acre seed orchard at the state forest nursery in Boscawen and a smaller orchard at the Fox Research Forest in Hillsboro. We graft approximately 50 scions a year with a success rate of about 50%. That's an excellent success rate for hardwoods such as walnut and butternut. The oldest grafted trees (grafted in 1997) are four feet tall now, and we expect to hand pollinate and produce seed in five to ten years.
We are always looking for new super trees, and help from the public is critical. If you know of any butternut tree that is over ten inches in diameter, growing naturally, not planted, has little or no sign of disease, and has dead and dying butternut nearby, please call. We'd be happy to do a site visit to inspect the tree for disease and determine its suitability for this project.
NH State Record: Largest Butternut tree found in Loudon.
The black lesion area shown is the Butternut canker disease. Cross section of severely diseased Butternut.
Butternut canker lesion on a branch. .
Tree climber collecting scion material. Grafting scions to walnut root stock.
Grafted scion that has survived in the greenhouse. Scion that has grown into a small tree located at Fox State Forest.