American Chestnut

Castanea dentata

by John Brouwer

“Chestnuts roasting on an open fire . . .”

Haven’t had any chestnuts lately? Don’t know what chestnuts are? You are not alone.

The American chestnut effectively disappeared from the North American Carolinian forest by the 1950’s. In 1904 a blight introduced on nursery stock from Asia was observed killing trees in New York city. It quickly spread across the whole Carolinian zone, infecting and killing all chestnuts. By 1950 the American chestnut was reduced to the status of a threatened species.

Up until the 1900’s chestnut was one the most important hardwoods in the Carolinian forest, making up 25% of its trees. Pure chestnut standards were found in the drier upland sites. Trees were routinely around 100 feet tall, 6 feet in diameter, and branchless for the first 50 feet. In southern Ontario millions of trees were present on sandy and well-drained soils, concentrated in Norfolk county and the region around Dundas.

Early settlers found the tree one of the best for timber. It was straight-grained, lighter and more easily worked than oak, and as rot resistant as redwood. Log homes, barns, shingles, telegraph poles, fine furniture and musical instruments were all made from chestnut. Today old barns are scoured by salvagers to find old chestnut boards and beams and paneled chestnut boards can be found in a couple of old country churches.

Chestnuts were a staple food of settlers who gathered the glossy dark brown nuts in the fall and stored sacks full in attics. Worm eaten nuts were a primary feed for livestock. Wildlife, from birds to bears, depended upon the abundant nuts.

All this ended with the blight introduced from Asia. Ten million years of chestnut evolution was terminated by human progress.

The blight is a fungus which attacks the tree by forming cankers on the trunks that enlarge and completely encircle the tree and eventual kill it by destroying the inner bark layer which carries nutrient from the roots to the leaves. The roots will then send out new shoots but as these grow to sapling size they are also infected and die.

Over the last thirty years various research organizations, public and private, have been working to introduce a blight resistant chestnut. Efforts have focused on three strategies.

  1. Finding surviving trees

There are a few sites in southern Ontario where mature chestnut trees still survive. The sites are available only to researchers. There are a couple of hundred sites where saplings are still fighting infection.

These few mature trees provide the nuts used in Ontario chestnut re-introduction programs, as it is assumed that these trees have some internal resistance to the blight.

Nova Scotia has some thriving chestnuts which were introduced by loyalists familiar with the tree. Because Nova Scotia is outside the chestnut’s natural range it is also outside the natural range of the blight. The Nova Scotia trees are considered to be a valuable source of genetic material in developing blight resistance in the United States.

  1. Developing a blight-resistant chestnut

Breeding efforts to develop a blight-resistant chestnut in the 1960’s were unsuccessful. A new program underway in Vermont has now cross bred trees through six generations and is expecting the seedlings growing now to exhibit resistance. If successful this program will be distributing seed stock within eight years.

  1. Decreasing the potency of the blight

European chestnuts are regenerating because the blight fungus was attacked by a virus which decreased its potency (hypovirulence). Hypovirulence isolates have also been found in Ontario but is not spreading as effectively as it did in Europe. The university of Guelph is hosting research to foster this naturally occurring chestnut blight hypovirulence.

American chestnut could not be planted twenty years ago because there was no seed stock and no strategies for blight control. With seed stock from surviving species and promising blight control strategies, the best time to plant a chestnut is now.

This spring workday two American chestnut seedlings were planted in the co-op – one in the area between block ten and the driveway and one behind the retaining wall of the playground pathway.

May 2008