Woodend Restoration Watch: American Chestnuts

A majestic American chestnut standing tall in Mitchell County North Carolina.

We have partnered with the Maryland Chapter of the American Chestnut Foundation to help restore our once majestic American chestnuts (Castanea dentata). Standing at 100 feet tall and numbering in the billions, this tree was once considered the finest chestnut tree in the world, but times have changed. Following the introduction of an invasive fungus from China, this species quickly became functionally extinct in the wild. But all hope is not lost as a few trees did survive. These survivors are now the key to restoring this keystone species.

Left: American chestnuts were once an important source for timber. Right: American chestnut seeds were once an important food source for the Appalachian area.

 

Historically a crucial part of the ecosystems and economies in the eastern US, the loss of this tree is broadly felt. The chestnut blight is caused by the fungus Cryphonectria parasitic and was introduced when Japanese chestnut trees were imported in the late 19th century. Asian chestnut species have natural resistance to the fungus while American chestnut’s do not. Following the first observation of infection on American chestnuts in New York in 1904, over three and a half billion trees had succumbed by 1940. Despite this scale of loss, the species is not considered to be extinct. The USDA considers the species functionally extinct because the blight does not kill the tree’s root system underground. The American chestnut has survived by sending up stump sprouts that grow vigorously in logged or otherwise disturbed sites, but inevitably succumb to the blight and die back to the ground before they are able to bear fruit. The American chestnut has also survived because there are some remaining individuals that do still produce fruit. These individuals are the key to restoring this once majestic species. 

Left: Chestnut blight affects the main truck of the chestnut trees. Right: The blight kills chestnuts by girdling the trunk, cutting off the tree’s vascular system.

 

To revive this iconic species, The American Chestnut Foundation (TACF) is working diligently to produce blight-resistance American chestnuts. This is primarily being done through a transgenic breeding program, otherwise known as traditional breeding. The first step is to breed surviving wild type American chestnuts with pure Chinese chestnuts. This introduces the blight resistance to the American species and the resulting offspring is 50% American and 50% Chinese. Next, backcrosses with pure and hybrid American chestnuts are done to increase the genetic dominance of the American species. The end result of the breeding program are ‘American’ chestnuts that are 94% American and 6% Chinese that will hopefully be blight-resistant.

Left: A chestnut seedling two months after planting. Middle: Chestnuts were planted in tree tubes for structural support and protection from herbivory. Right: This effort was the result of a partnership with the Maryland Chapter of the American Chestnut Foundation.

 

The next step is to test the blight resistance ability of these bred ‘American’ chestnuts. This is where the Audubon Naturalist Society comes in. At Woodend, in an area once dominated by bamboo, 24  ‘American’ chestnut seeds were planted. We will monitor the survival of these individuals and denote any presence of the blight. If any individual survives and reaches fruit bearing age, their seeds will be collected and planted in their native range.

 

Definitions:

Functionally extinct: The reduced population no longer plays a significant role in ecosystem function; or; The population is no longer viable.

Transgenic: relating to or denoting an organism that contains genetic material into which DNA from an unrelated organism has been artificially introduced.

Backcrossing: crossing of a hybrid with one of its parents or an individual genetically similar to its parent, in order to achieve offspring with a genetic identity which is closer to that of the parent. 

 

Sources:

Chestnut Blight: Cryphonectria parasitica – Cornell University. (n.d.). Retrieved June 19, 2019, from http://plantclinic.cornell.edu/factsheets/chestnutblight.pdf

Saving the American Chestnut Tree. (n.d.). Retrieved June 11, 2019, from https://www.acf.org/

Get the latest updates on Woodend restoration on our new blog @ Woodend Sanctuary – Nature Forward

About Bradley Simpson

Bradley is a Restoration Fellow working for the Restoration department at ANS from August 2019 - August 2020. He is a recent graduate from the University of Maryland, College Park with a B.S. in Wildlife Ecology and Management and hopes to pursue a graduate degree this fall.
Bookmark the permalink.

Comments are closed.