by Richard Gardner
As an ecologist, I’m accustomed to testing paradigms that have become science doctrine to determine whether they’re true. This spring and summer, I surveyed the American chestnut tree (Castanea dentata) along the Appalachian Trail (AT) and other parts of Blue Mountain in central Pennsylvania to see whether there was any truth to the generally believed story of the American chestnut being extinct (or almost so) from the chestnut blight. I decided to do this survey based on a few casual observations, gut instinct, and intuition. As an invasive plant ecologist, I dispel myths in my field by walking and following my instincts and intuition. So naturally I decided to walk, look, and photograph the AT and related trails in central Pennsylvania using a camera with a GPS. I chose the stretch of AT from the Rausch Gap Shelter to Lehigh Gap, as well as related trails from Pennsylvania Route 501 to Hawk Mountain Road. Instead of finding a tree going extinct, I found the American chestnut thriving.
I walked over 80 miles of the AT and many more miles of trails, dirt roads, and fields connecting to the AT on Blue Mountain. What I found is that the AT and other trails have thousands of American chestnut trees of every age class from seedling to reproducing adults. Admittedly, I did not find the giant, disease-free trees from long ago, but I did find healthy, disease-free adult trees producing fresh generations of offspring in addition to diseased trees producing seeds. Every generation means increasingly disease-resistant trees are growing.
The chestnut blight has been in Pennsylvania since a few years after its discovery in New York City in 1904. Since the disease was introduced to the American chestnut, it ripped across the landscape, killing vast numbers of trees. However, it did not kill all the American chestnuts. Salvage logging destroyed most of the survivors. The AT, because of its remoteness and policy of minimal ecological and environmental disturbance along its length, became a refuge for these survivors. My understanding is that it takes 5 years for an American chestnut tree to go from nut to mature adult. Since the founding of the AT, there have been at least 15 potential generations of American chestnut trees, with 21 possible generations since the start of the blight in Pennsylvania. Using basic evolution as a model, I realize that the healthiest and most resistant trees mature to larger adults that then produce the most pollen and seeds. Therefore, as my walking suggests, there is ongoing improvement in the resistance of the American chestnut to the blight. The trees are simultaneously changing growth habits to accommodate the blight. In addition, pathogens often lose virulence through successive generations.
Among the most interesting discoveries is that the AT along the Blue Mountain ridgeline is a corridor for the spread of the American chestnut tree. Birds during the fall migration use the AT, especially along its wider spots, as an easy, friction-free corridor over which to fly; turkeys and mammals also use the trail. All this use of the AT helps spread seeds. This is obvious when looking at the general linearity of the location of individual trees and groves. Over the length of the AT, the southward spread of seeds during the fall crow migration and northward spread of pollen during the spring pollinator migration are among the most important ways for the American chestnut to maintain its genetic heterogeneity while spreading disease resistance between naturally occurring groves.
Another interesting discovery ties in with what’s been found in the forest around the Hamburg Reservoir, near Port Clinton. Having not been logged since the late 1800s, this forest serves as a refuge for blight-surviving American chestnut trees. The AT helps move seeds and pollen out from refuges like this stepwise. Once these trees mature and reproduce, their seeds and pollen in turn are spread further along the trail. I found 4 substantial refuges on the AT, with several smaller ones nearby. These refuges have been protected from logging because of their remoteness or status as protected land. The forest around the Birdsboro reservoirs, protected since the late 1800s, confirms these findings.
What can we do to further help the American chestnut tree? One is for trail maintainers to know what the American chestnut tree looks like to avoid cutting down or pruning back young trees. Another is recognizing and protecting groves of trees. If I can find 4 groves in 80 miles, over the remaining 2,000 miles there must be many more. We can also provide corridors for seeds to be spread by birds and mammals.
If anyone is interested in walking with me to see the American chestnuts on Blue Mountain or in looking at the metadata, please contact me at rtgardner3@yahoo.com.