A website from UGA Cooperative Extension

by Carole MacMullan, Fulton County Master Gardener Extension Volunteer

This article is part of Garden Buzz, a series from Appen Media and the North Fulton Master Gardeners, where rotating columnists explore horticulture topics like herbs, insects and wildlife conservation. Find all Garden Buzz articles here.

As a result of the COVID-19 pandemic, the word “pandemic” became a household word. But did you know, over the last one hundred years, the Appalachian Mountain Forest has experienced several pandemics or transformative events that have reshaped the eastern United States forests.  

If we could step back in time, back to the early 1900s, the Appalachian Mountain Forest would look different from the Appalachian Forest in 2023. The dominant hardwood forest trees in Georgia today are the oaks, and their acorns sustain directly or indirectly a significant population of forest organisms, making them a keystone plant. 

One hundred years ago, the dominant keystone tree was the American Chestnut (Castanea dentata) tree. You might ask, have I ever seen an American Chestnut tree and where are they now?  During the late 1800s, wealthy Americans began to import exotic plants to create eye appealing gardens along with their stately homes to highlight their wealth and social status. Bringing in foreign grown plants had its peril!  In 1904, newly identified cankers appeared on some of the American Chestnut growing in the Bronx Zoo.

From left: Map of Eastern US showing where American chestnut trees once grew. Photo by Penn State Extension; American chestnut seed with seed coat opened to show the chestnut. Photo by Penn State Extension; This picture, taken in the mid- to late 19th century, gives an idea of just how large and profuse the American chestnut tree was in Eastern U.S. forests. There are now only 100 or so that remain. Photo by American Chestnut Foundation. 

Botanists identified the blight as a fungal disease (Cryphonectria parasitica) originating from imported Japanese Chestnut trees. Japanese Chestnut trees have a natural immunity to this fungal disease, but the American Chestnut does not! Within a 30-year period, the lethal fungal disease spread throughout the entire Appalachian Mountain chain from Maine to North Georgia. As the American Chestnuts died out, the entire ecosystem changed. If you look at pictures of American Chestnut trees, you will be mesmerized by their size. Many of the forest animals were dependent on the nutritious chestnuts that covered the forest floor. The timber was highly prized for its durability and resistance to rot. Not only did the chestnuts serve as a food supply for the forest animals but also for human consumption. Chestnut Ridge, near my former, western Pennsylvania home, was named for this ecologically, culturally and economically valuable tree that until the mid-1930s covered the mountain ridge.

The rapid spread of this fungal disease was possible since fungi reproduce by airborne spores. When the wind carries spores to the American Chestnut host tree, the spores germinate and begin to divide. The fungus cells, in turn, form root-like hyphae. These hyphae branch out and penetrate the bark of the tree. Over time cankers grow and interrupt the internal flow of water and nutrients to the tree’s branches, leaves and roots resulting in the death of the tree. 

Two factors contributed to their extinction.  As American Chestnut trees began to die in astoundingly large numbers, lumber companies stepped in and quickly cut down any remaining Chestnut trees.  The result was the complete loss of vast swaths of forest, creating erosion and in some cases, flooding and changing the Appalachian Mountain Forest ecosystem forever!

With the loss of a tree that could stand 100 feet tall and produce over 6000 chestnuts at maturity, there has been a desire to see these trees returned to our eastern forests. How can the goal to create a genetically, blight resistant tree be accomplished?  The solution is complicated!

The American Chestnut Foundation was organized in 1989 to achieve this goal. Fortunately, Chinese Chestnut trees have a genetic resistance to the chestnut blight. As a result, the two chestnut species have been crossbred, but the resulting first-generation hybrids have only 50% of the desired genetic characteristics of the American Chestnut. Over the last four decades, the most blight-resistant hybrids have been crossbred with the American Chestnut in an attempt create a chestnut tree that is as genetically close to the American Chestnut as possible. Currently, a hybrid has been created that contains 94% of the genes of the American Chestnut. Another group has used modern genetic engineering techniques to create a hybrid with 99% of the American Chestnut genes plus genes to provide immunity from the fungus blight. With the cooperation of federal, state and local forest services, as well as research scientists and private citizens, hybrid trees are being grown throughout the American Chestnuts’ former Appalachian Mountain habitat to find the most resistant hybrid. 

Pilot research projects have been established in several locations in the Atlanta area. There are 18 hybrid Chestnuts growing in the Atlanta History Center orchard, and 13 of them have prospered and 5 are too weak to grow to maturity.  In 2019, Big Trees Forest Preserve in Sandy Springs next to the UGA Extension office, planted several dozen young, hybrid Chestnuts. Both locations hope their young, hybrid trees will mature and produce chestnut seeds to help the American Chestnut Society reach their goal of re-introducing healthy, blight resistant, American Chestnut trees into the Appalachian Mountain Forests.

Wishing success to the combined efforts of everyone working on the American Chestnut restoration project!

Happy Gardening!

About the author

This week’s “Garden Buzz” guest columnist is Carole MacMullan, a master gardener and a Milton resident. She taught biology for 35 years in the Pittsburgh area. In 2012 after moving to Milton, Carole completed the Master Gardener training program and joined the North Fulton Master Gardeners (NFMG) and the Milton Garden Club.  Carole uses her teaching skills to create a variety of presentations on gardening topics for the NFMG Lecture Series and Speakers Bureau. She also volunteers weekly at the Assistance League of Atlanta (ALA) thrift store and acts as chair of their Links to Education scholarship program. Her favorite hobbies are gardening, hiking, biking, and reading.

North Fulton Master Gardeners, Inc. is a Georgia nonprofit 501(c)(3) organization whose purpose is to educate its members and the public in the areas of horticulture and ecology in order to promote and foster community enrichment.  Master Gardener Volunteers are trained and certified by The University of Georgia Cooperative Extension. Learn more at nfmg.net