AMERICAN CHESTNUT TREE RESTORATION AT THE GARDEN

New England Botanic Garden recently became part of an American chestnut tree restoration effort that is different from many others. Led by the American Chestnut Cooperators’ Foundation (ACCF), a Virginia-based nonprofit, the effort aims to restore the iconic American chestnut tree (Castanea dentata) to its native range in eastern hardwood forests with trees that are naturally blight resistant and 100% pure American chestnuts.

That such trees even exist may come as a surprise to those familiar with the story of the American chestnut. In the early twentieth century, chestnut blight (Cryphonectria parasitica), a pathogenic fungus introduced through the nursery trade, destroyed more than 3.5 billion American chestnut trees from Georgia to Maine. The ecological, cultural, and economic fallout from losing this valuable species is hard to overstate. While the blight was catastrophic and continues to persist across the landscape snuffing out non-resistant chestnuts that make new attempts at growth, some trees did survive the original outbreak. ACCF discovered a surviving population in Virginia in the 1970s, and since then developed a traditional backcross breeding program that successfully reinforced blight resistance in new generations of American chestnuts. These trees are now ready to be tested in natural forest settings.

The Garden is currently serving as ACCF’s largest site for reforestation, with 160 ACCF seeds and 20 seedlings planted in a section of forest north of the Garden’s core property. This area offers perfect American chestnut habitat — sloping, rocky hillsides and a mature, mixed oak forest complete with an understory of witch hazel and mountain laurel. A heavy presence of blighted American chestnuts offers further proof of their historic presence in the area.

The planting includes American chestnut trees representing eight distinct genomes. The slightly different genetic makeup of the trees means different genomes may have better tolerance for environmental conditions, things like seasonal temperatures, precipitation, pests. The Garden will regularly collect data on how the trees perform and share this with ACCF to support the organization’s continued research and the ongoing evolution of their breeding program. How well the Garden’s trees do over time, in response to blight and other environmental factors, has the potential to inform future reforestation efforts across the Northeast. It’s a thrilling prospect that, thanks to ACCF, has already been decades in the making. We look forward to sharing more about this important work in the months and years to come.

The American chestnut is a broadleaf deciduous tree that once inhabited mountainous areas and sloping terrain in eastern forests from Georgia to Maine. It’s hard for people alive today to grasp the full impact of the American chestnut’s loss nearly a century ago. Trees whose presence was felt for thousands of years were gone within a single human lifespan. Though not quite as dominant in their range as once believed, American chestnut trees played an outsized role in the cultures of both indigenous people and European settlers. Chestnuts provided medicines and dyes, firewood and fence rail. Because of their immense size — roughly 100 feet tall and five to eight feet wide — they served as witness trees on land surveys. Their rot-resistant wood fueled an economy of lumber for homes and furniture, and their massive annual mast of nuts provided high-protein forage for wildlife, livestock, and people.  

Chestnut blight (Cryphonectria parasitica) is a fungal pathogen native to Asia. It is believed to have been brought into the U.S. accidentally as early as the late 1800s through Chinese chestnut (Castanea mollissima) and Japanese chestnut (Castanea crenata) nursery stock. It was first documented in the Bronx Zoo in 1904.  

Wind spreads the fungal spores of chestnut blight enabling it to travel quickly and far. In only a few years after introduction, chestnut blight spread to impact American chestnuts across their entire range — roughly 300,000 square miles of eastern North America.  

Chestnut blight attacks the cambium of susceptible trees, the part responsible for new cell growth, and causes cankers around trunks and limbs that cut off nutrients and ultimately kill trees in as little as three years. There is no known cure for this pathogen.

Where can I find American chestnut trees at the Garden? 
Small trees, called stump sprouts can be found in the Inner Park, The Ramble and along the Summit Trail. Look for canoe-shaped leaves with coarsely-toothed edges. ACCF American chestnuts are planted in an area of the Garden known as the Kim property, a 26-acre parcel that features ideal chestnut habitat — sloping, rocky hillsides and a mature, mixed oak forest complete with an understory of witch hazel and mountain laurel. Seedlings can be spotted from the North Woods Trail that extends through this property from the Summit to the Inner Park, as well as in The Ramble, Wildlife Garden, and Inner Park. 

Can I get ACCF blight-resistant American chestnut trees to plant at home?
ACCF provides seeds to member growers, also known as cooperators. Individuals are encouraged to learn more about ACCF and their program, and then connect with them if interested in becoming a cooperator. Growing ACCF seeds involves participating in ACCF’s ongoing research by monitoring trees and reporting annually on their conditions. 

I’ve seen small American chestnut trees growing in the forest. Are these trees resistant to chestnut blight?
The short answer is, probably not. The American chestnut is incredibly good at sprouting from its stump. This ability led to chestnut proliferation in specific areas of the eastern U.S. during the heavy logging of the nineteenth century. When we see young stump sprouts in the forest, we can assume larger chestnut trees once grew there, but died or were cut down due to blight. 

American chestnuts are sometimes described as “functionally extinct” because blight attacks the cambium layer of trees, girdling upper trunks and limbs with cankers. Before trees reach a reproductive age, the affected areas die back, but the stump remains alive and new sprouts grow. 

Luckily, ACCF discovered a naturally blight resistant population of American chestnuts in Virginia. Through a backcross breeding program, resistance stemming from these survivors has been improved in new generations of ACCF trees. This work demonstrates that, instead of being “functionally extinct,” the American chestnut as a species has the potential to be restored. 

Does this mean the Garden’s ACCF trees won’t get chestnut blight?
Blight resistance is not the same as total immunity from chestnut blight. Because chestnut blight remains active across our landscape, the Garden’s ACCF trees may come in contact with it. The resistance these trees possess makes it less likely that they will succumb to the blight. If infected, ACCF trees quickly recognize the fungus and initiate protective measures to prevent it from entering into their cambium layer where it can do the most damage. Though cankers may form, these are typically restricted to the outer bark layer of the tree.

  • “Did American Chestnut Really Dominate the Eastern Forest?” by Edward K. Faison and David R. Foster, published in Arnold Arboretum’s journal Arnoldia in 2014, takes an interesting look at sources that suggest the American chestnut was not as naturally dominant in forests as commonly believed but rather stewarded into dominance because of its cultural and economic value.  
  • The American Chestnut Cooperators’ Foundation, the Virginia-based science and education organization the Garden collaborates with on this conservation initiative, is dedicated to restoring the American Chestnut tree to its former place in our Eastern hardwood forests. Priorities include the development of blight-resistant all-American chestnuts and economical biological control measures against chestnut blight in the forest environment.   

A hand holds a chestnut seed
Leaves of an american chestnut tree
Land Steward Robert Graham plants a chestnut seed