By George Christie
Most of us in the northeastern United States have heard the story of the chestnut tree (Castanea dentata). How it was a dominant tree of the hardwood forests the Europeans found when they arrived in the 1600s and 1700s. How it was light, strong, and easy to work as a building material and how its chestnuts fed people, wildlife, and livestock alike. How a blight swept through the forests in the early 1900s and the once dominant tree was reduced to saplings arising from the stumps of giants, only to succumb themselves to the disease as they reached twenty-plus feet in height.
But that isn’t my story today. My story involves what the chestnut tells us about our definitions of native and non-native plants. In researching native plant use in permaculture, I discovered a fascinating range map for the American chestnut. It turns out that, based on pollen records, prior to the arrival of Europeans, the chestnut had been expanding its range north and east for some 10,000 years, following the retreating glaciers. Meaning, range maps, when drawn, were not windows into a static world, but snapshots of a dynamic process.
Further meaning, if the chestnut can move north, why not other plants? What on earth is wrong with facilitating that which the plants themselves do all the time? Of course, the counterargument is the range extension of the chestnut was “natural” whereas me planting a Hydrangea arborescens is “assisted migration” where I’ve co-opted Gaia’s role and moved a plant that could never have made the jump without me.
Welp, sure. I am bringing plants north and east. Bee balm (Monarda didyma) is probably not native to Rhode Island, nor is Alleghany spurge (Pachysandra procumbens). I could go on. So, I agree to the assisted migration part of the counterargument, but I am very suspicious that the northward movement of chestnut was as naturally pure as the mythologists wish it.
Here is my line of reasoning. Everywhere researchers look, humanity has been shaping the world around themselves for millennia. One of the prime ways they shape the environment is by favoring plants which furnish them with food, shelter, medicines, and other useful items over plants that don’t. We know that maize followed essentially the same path as the chestnut, albeit much faster, being an annual crop. So, do we really believe that chestnut seeds weren’t traded northward? Sure, they grow slowly and harvests might not become useful for decades, but we know that many eastern woodland tribes routinely thought in terms of generations when making future plans. Johnny Appleseed didn’t expect to see the results of his seeds for many years, so how hard is it to believe that some young woman planted a chestnut seed in a new location, hoping to gather its nuts someday, granddaughters by her side?
My point is this. Plants themselves have been moving around for a very long time. People have been helping them move for probably 10,000 years or more. Can I prove that the chestnut’s range is at least in part due to indigenous people’s actions? No. But I can sleep comfortably believing it is so.
Does this mean we can move anything anywhere without thought or planning? I don’t think so. Logic remains a guiding force. Introducing a plant native to Long Island into Rhode Island can be thought to mimic an expected pattern of migration. Stuffing our gardens full of exotic plants from Europe and Asia cannot. As Toby Hemenway writes in Gaia’s Garden (2nd edition, page 15):
“It would be foolish to deliberately introduce a species known to be locally opportunistic [=invasive]. Permaculturalists use a hierarchy of safety for choosing plants. First, use a native to fill the desired role if at all possible. If no natives for that niche exist, then use a tested exotic. Only after a great deal of research would a person then consider a small-scale introduction of a new exotic.…”
Whether or not indigenous peoples aided the chestnut in its northward journey, the fact remains, when we choose wisely, we can use plants that European botanists did not find when they first documented Rhode Island’s flora.
As it turned out, the chestnut’s migration did not save it from catastrophe, a cautionary tale to which we should pay heed, but in this age of warming, the chestnut has shown us a logical path forward as we seek plants to withstand and mitigate the vagaries we have brought upon ourselves. It is a path we would be wise to explore.