Butternut: An Urban Species at Risk?

January-February 2009

MANY OF YOU ARE FAMILIAR with the butternut tree. It can be a large beautiful specimen with the bark’s interesting diamond-shaped, flat topped ridges and its large spreading crown. The nuts of course are a dead giveaway – those oval, sticky, green orbs that thankfully aren’t produced as often as black walnuts – at least from a homeowner’s point of view. You may also have heard about butternut canker, the fungal disease that is threatening this species. It kills areas of the cambium on twigs and branches, spreads to the main stem and as the cankers spread, the tree is eventually killed. The symptoms include dead branches in the sunlit part of the crown (shaded dead branches are normal for butternut which is very intolerant of shade), and sooty black patches on the bark.

In Ontario, butternut canker has been on tree folk’s radar for almost 15 years. The Forest Gene Conservation Association (FGCA) first started working on it in the early 1990s, alerted to the problem by the Eastern Chapter of the Society of Ontario Nut Growers. Their American colleagues had been dealing with it for a few decades longer.

Nut growers were concerned about the effects on their breeding programs, as butternut is our most northern, cold-hardy, edible nut species. In the States, foresters were also concerned about the loss of butternut, also called white walnut, which can be more common in their forests and is an important mast species and valued for fine wood products.

Beacons of Hope
As we further researched the situation, we learned a lot from American forest managers and scientists. Butternut canker is a very virulent disease of unknown origin and was causing a lot of tree mortality south of the border.

We also learned that there was hope – people were finding vigorous trees amidst dead and dying ones. These trees were the beacons for recovery programs. But first, word had to get out that it was not game over for butternut. We didn’t want to lose any trees to the attitude “cut it now ‘cause it’s going to die anyways.”

Don’t Cut Prematurely
Since about 1992, FGCA has been promoting butternut conservation and recovery with landowners, recommending that they:

1. keep all butternut around as long as possible – simple yet crucial
2. remove only those trees that are dead or dying
3. report butternut information
a. to increase our knowledge about where and how quickly it is dying and where is it regenerating, and
b. to help locate vigorously surviving trees that may be showing genetic resistance. The Recovery Team is developing a program to take samples from these trees to screen for resistance and establish in a breeding orchard (a very long term program).
4. plant butternut with hope, though not expectation, on good, open sites using seedlings grown from the seed of locally-adapted, vigorous trees. Many of the seedlings will likely die from the canker yet some will survive to help to maintain the local gene pool.

New Trees on the Block
One aspect of recovery that we hadn’t realized would be such a concern is that of hybrids. There are records of exotic walnuts being planted in eastern North America as early as the mid 1800s, and people seemed to have a penchant for breeding and moving nut trees around in the landscape.

For now we are concentrating only on the native, pure Juglans cinerea. There may come a time when hybrids, due their apparently better resistance to the canker, could be considered an option to help restore this species’ niche and function in our forests. That begs the question of not only what is butternut’s niche, but can hybrids fill it? They may survive the canker but can they regenerate in our forests and not cause disruption in forest communities?

So we are accumulating field tips on how to tell the native butternut from several hybrid varieties that appear to be common in cities and other long settled areas in southern Ontario. See the sidebar at the end of this article.

Researchers have developed DNA tests that can help when field tips are inconclusive. Staff at the Ontario Ministry of Natural Resources’ Ontario Forest Research Institute (ORFI) have developed this expertise. It helps us determine which of the most vigorous trees we find are pure butternut so that we don’t spend precious resources planting or cloning hybrids.

Now Officially Endangered
In Ontario, butternut recovery efforts have been impacted by its recent official status as an endangered species. It was listed nationally (Ontario, New Brunswick and Quebec) under the Species at Risk Act (SARA) in July 2005, which prohibits its cutting on federal lands and spurred the development of a National Recovery Strategy (still a draft as of December 2008). The biggest and most recent impact comes from Ontario’s new Endangered Species Act (ESA, 2007) which prohibits the cutting of butternut on all lands, unless a tree assessment determines that it is not vigorous enough to be retained.

The FGCA developed a tree assessment manual and course to help develop consistency in how trees are being assessed. This work is the basis for certifying Butternut Health Assessors under the ESA. Those qualified can assess butternuts as retainable or not, and reports must be submitted to the landowner and OMNR. Workshops will be held next summer to train more people such as arborists, forest and ecological consultants and tree markers. Non-retainable trees may be removed. Retainable trees might also be removed upon application for a 17(2) permit. If a permit is granted, certain activities would have to be carried out such as planting butternut seedlings in lieu of the tree to be removed. If the tree is especially vigorous or showing signs of overgrowing the cankers, then that tree must be cloned before it can be removed. Contact your local OMNR office and talk to the Species at Risk Biologist for more information on butternut and the ESA (2007).

Landowner Assistance
Butternut is found largely on private land and the Ontario Butternut Recovery Team has been fortunate to have the assistance of several local landowner contact programs. Through these programs, landowners can find out about butternut and the canker and how to manage their trees. The Recovery Program benefits greatly as retainable trees are located and monitored for seed collection to help support planting programs. Most importantly, such trees can then be monitored and may be cloned and added to a butternut archive such as the one being developed in eastern Ontario with the Rideau Valley Conservation Authority, OMNR and the Ferguson Forest Centre.

In this way, we can bring together vigorous, possibly resistant trees to study, screen for resistance and possibly develop into a seed orchard. This is a long term proposition that hopefully will result in disease resistant trees to reintroduce to our forests. The lessons we learn along the way can likely help us with other tree species that are being threatened by insects and diseases such as ash, beech, and flowering dogwood – as the butternut program has benefited from the work of the University of Guelph Arboretum’s Elm Recovery Program.
— Email Barb at barb.boysen@ontario.ca


Pure Butternut
• leaves flush late in the spring and yellow and drop early in the fall
• pith in 2nd year or older wood is narrowly chambered and dark chocolate brown
• male flowers are short, 10 to 15 cm
• female flowers are fewer (4 to 7)
• large seed crops every 3 to 4 years
• leaves, buds and new growth twigs are not excessively hairy
• leaf scars are not as large as hybrid
• tend to be found in rural and woodlot settings

• leaf drop is not until a heavy frost in October/November
• pith is widely chambered and a lighter brown
• leaves, buds and new growth twigs are excessively pubescent
• male flowers are very long, 15 to 30 cm
• female flowers are numerous
• large, frequent seed crops
• leaf scar is large
• tend to be found in urban settings


Stormont, Dundas & Glengarry, Leeds & Grenville, Lanark Counties
Rose Fleguel, rose.fleguel@rvca.ca
Rideau Valley Landowner Resource Centre, 613-692-3571 ext. 1128 or ext. 1132

Frontenac, Lennox & Addington, Hastings, Prince Edward Counties
Dave Sexsmith, sexsmith@kingston.net
Upper Canada Woods Cooperative, 613-373-9334 or

Steve Pitt, steve.pitt@ontario.ca
Lennox & Addington Stewardship Council, 613-531-5723

Northumberland County
Glenn McLeod, glenn.mcleod@ontario.ca
Stewardship Council, 705-755-3298

Peterborough County
Peter Mabee, peter.mabee@ontario.ca
Peterborough County Stewardship Council, 705-755-1951

City of Kawartha Lakes
Doug van Hemessen, doug.vanhemessen@ontario.ca
Victoria Land & Water Stewardship Council

Dufferin County
John Osmok, john.osmok@ontario.ca
Land Stewardship Network

Simcoe County
Al Winters, al.winters@ontario.ca
North Simcoe Private Land Stewardship Network, 705-725-7557

Halton & Peel Regions
Greg Bales, greg.bales@ontario.ca
Halton-Peel Woodlands and Wildlife Stewardship, 905-713-7410

Huron & Perth Counties
Steve Bowers, steve.bowers@ontario.ca
Huron Stewardship Council

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