Philadelphia Reflections

American Chestnut Trees

American Chestnut tree

RECENTLY, John Wenderoth of the Tyler Arboretum visited the Right Angle Club of Philadelphia, bringing an astounding account of the triumph, near-extinction, and revival of the American Chestnut tree. The Tyler Arboretum, and this man, in particular, is at the center of the movement to rescue the tree, although the modern Johnny Appleseeds of the movement seem to be a Central Pennsylvanian named Bob Leffel, and a geneticist named Charles Burnham. Together, they had the vision and drive to enlist a thousand volunteers to plant seedlings in Pennsylvania; and there are many other volunteer groups in other states within Appalachia. About 45,000 Chestnut hybrids have been planted, surrounded by wire fencing to protect the new trees until they grow too tall for deer to reach the leaves. Here's the story.

In 1904 it was estimated that a fourth of all trees in the Eastern United States were American Chestnuts. The tree typically grew to eighty feet before permanent branches took over, so the shading and tall pillars of tree trunks gave the forest a particular cathedral-like distinctiveness, much celebrated by such authors as James Fennimore Cooper. The wood of the American Chestnut tree is rot-resistant, so it was favored by carpenters, log-cabin builders, and furniture makers. It once was a major source of tannin, for leather tanning. The nuts were edible, but it has been a long time since they were available for much eating. The chestnuts you see roasted by sidewalk vendors are primarily Chinese Chestnuts, which actually come to us from South Korea. The Buckeye, or horse chestnut, produces a pretty and abundant nut but is too bitter for most tastes. For whatever reason, a fungus was first discovered to infect the chestnuts of the Bronx Zoo in 1905, attracting the attention of Teddy Roosevelt and his Progressive naturalist friends, but to little avail. The fungus (Cryptomeria parasitic) enters the tree through cracks in the bark, flourishes in the part of the tree which is above ground, leaving the roots undisturbed. Ordinarily, when this sort of thing happens, the roots send up shoots which keep the tree alive and flourishing. Unfortunately, the abundant deer of this area quickly nipped off the shoots as they appeared, and finally, the trees died. It took only a decade or so for this combination of natural enemies to wipe out the species, and today it is unusual to see lumber from this source. The forests of Chestnuts have been replaced by other trees, mostly oaks. The Chinese chestnut, however, proved to be resistant to the fungus, even though it does not grow to the same height.

Chinese Chestnuts

After many futile but well-meaning efforts to save the trees by foresters, friends of the American Chestnut tree turned to geneticists. The goal was to transfer the fungus resistance gene from the Chinese Chestnut to a few surviving American Chestnuts. It took six or seven generations of cross-breeding to do it (four generations of seedlings, then crossing the crosses, then weeding out the undesirable offspring), but eventually, the Tyler Arboretum was supplying truckloads of seedlings to the volunteers to plant in likely places. It's going to take many years for the seedlings to grow in sufficient numbers to make an impact on our forests, and eventually on our carpenters, but that effort is underway with gusto. If anyone wants to volunteer to join this effort, there appears to be room for plenty more people to help.

Originally published: Friday, November 30, 2012; most-recently modified: Monday, May 13, 2019