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Castanea

Imagine we hike up to High Point on a humid summer day. We walk through a varied landscape in a dance with life. In the flood plain, we find sycamores and tulip poplars four to five feet in diameter. We cannot help but investigate every summer bloom, and, in the process, we become entranced by the unique echoing of birds' songs amplified as they reflect off and reverberate through the small gap in the mountain while deflecting down from the towering canopy of trees. After losing ourselves in a swift, cold stream teaming with darners, minnows, shiners, and brook trout, we try to decipher sights and sounds that are coming faster than our senses can discriminate.

Immediately after departing one treasure, our ascent brings us to coves, hollows, and gentle eastern slopes that all appear to be molded by herbs and defined by 130-foot red oaks, white oaks, bitternut hickories, and white ashes. These pockets of vegetative lushness swoop in and out like lines drawn in the sand. On one side we have barren acidic chestnut-oak/heath and pine-oak/heath communities that have been scarred by fire; on the other side, rich basic oak hickory forests that appear unburnable. We plunge our hands into the soil to see if it holds the answer to this boundary dispute. Standing under a large hickory we meticulously grind the mineral components through our hands and find a dark loam with some sand and clay. We than jump the line and rip through five inches of heath root mass to find sand, rock, and charcoal. We study the topographical differences between the lines and try to make sense of the pattern. We snap to as we remember our quest for the top and resolve that every answer just spawns another question.

When we reach the ridgeline, we gorge on blueberries and huckleberries that thrive in a diffuse understory, thinned from burning. We enter an extensive stand of pitch pines. Their trunks bear clusters of short, needle-loaded branches that give them an unshaven look. Their deeply fissured bark scales seem engineered to resist fire as they effectively burn like hairs on a hand, far from the life-giving cambium. The scene melts into a pure stand of weathered table-mountain pine, whose lower branches droop gracefully and are loaded with squat cones composed of large scales that once open, expose large, stout, strongly hooked spines. We obtain our first view off the western precipice of quartzite, a rock that seems to lounge and dangle simultaneously, with roots pointed sharply to the east and heads sloughing off, creating huge boulder fields to the west.

Our mouths gape as we enjoy an endless view of the series of mountains and foothills laid down before any life on land. As we join the human struggle to find a consistent thread in this world, we reflect back on our journey, only to stumble upon the fact that one type of tree "sows" this mountain together: Castanea dentata, the American chestnut. In the bottomlands these trees sky to 150 feet and have six-foot diameters; in the mid-slopes they are dominant in many of the hardwood communities; on the ridge they are a sub-dominant in all of the hardwood communities. In fact we never were out of sight of a chestnut on the entire hike.

This is what a naturalist would have found in the Bull Run Mountains for thousands of years. Today, most of the elements in the mountain communities are intact, but the thread that was part of almost every hardwood community in all of Appalachia, the American chestnut, is nothing but a ghost, with only rootstock sprouts to remind us of what used to be a constant.

In 1904, the first signs of the fungus blight, Cryphonectria parasitica, were witnessed in the trunks of American chestnuts. H.W. Merkel, a forester working at the Bronx Zoo, is credited as the fungi's first observer. Within a year after he first noticed it, he valiantly began doctoring the infected trees. Unfortunately, the blight had the head start it needed. It was later surmised that it had been introduced around 1890 with a nursery shipment of Asian chestnuts.

The fungi's threadlike mycelium spreads like an inkblot effectively girdling the tree and cutting off the flow of water and nutrients through the thin cambium layer as it breaks down the chestnut's tissues. Sunken cankers speckled with small, orange, spore bearing dots began to show up outside New York City as early as 1909, and by 1915 Connecticut's chestnuts were disappearing fast. New England was devoid of chestnuts by the 1920s, and as early as 1918 the blight reached the Peaks of Otter region of Shenandoah National Park. The blight arrived in the Smokies in the mid-1920s and by 1938 the majority were dead. By the 1940s everything had ended except the mourning. The American chestnut was completely eliminated, as a defining component to any North American hardwood forest community, in less than 40 years.

Spores from the cankers spread by wind, insects, birds, and rain. Scientists once washed a billion blight spores from the legs of one woodpecker. If one spore among billions lands on a chink in a chestnut's bark, it will quickly invade and encircle the tree in four or five years. The only saving grace is that the fungus cannot survive under the soil; thus chestnuts in drier, more open forests continually send up root sprouts. Some of the sprouts reach 20 or so feet before the fungus finds them. Once infected, the tree flowers profusely in one last-ditch effort to reproduce.

In the 1950s, the world looked to Europe, where the same blight was having a similar effect on the native chestnuts, Castanea sativa. An Italian plant pathologist, Antonio Biraghi, noticed that some of the blight cultures he grew were white instead of the normal orange. Curiously, when he added the white strain to a culture dish of the orange strain, the orange strain lost its ability to kill chestnut trees. Biraghi's discovery was first met with disbelief, but it was soon proven correct. A virus had latched onto the blight fungus and altered it enough to make it less virulent or "hypovirulent." The hypovirulent fungus can still infect the chestnut, but the tree can survive if the new strain supplements the old, deadlier variety. In the decades since, Europe has successfully saved its chestnut orchards with this hypovirulent strain.

In Europe, where there were only a few blight fungus strains, natural blight suppression has occurred, but the myriad of blight strains has been a core obstacle in the Appalachians. American chestnut is highly susceptible compared to European chestnut. This has led to a much higher biomass of blight fungus and greater sexual reproduction within the blight fungus. The diverse blight fungus strains that were created from these sexual fruiting bodies differ from each other in compatibility and have prevented the transfer of viruses between strains. Recently, molecular biologists have genetically engineered the virus that causes hypovirulence, permitting the virus to be transferred from fungus to fungus during mating--something that does not happen in the naturally occurring hypovirulent strain. This potential will take time to develop because it uses recombinant DNA technology and thus must pass through a stack of federal regulations.

The American Chestnut Foundation has taken over where the USDA left off and is attempting to hybridize American chestnut with the desirable characteristic blight resistance of the Chinese chestnut (Castanea mollissima) using a technique known as "backcrossing." Basically, the idea is to cross Chinese and American trees, resulting in a generation that is half Asian and half American. Then those hybrids are crossed with American trees, producing chestnuts that are only one-quarter Chinese. Each new generation is again crossed with American trees, eventually swamping all of the Asian characteristics except the blight resistance and ultimately producing a tree that is virtually indistinguishable from the American chestnut. Of course the problem lies in the fact that as Asian genes are lost with crossing, the chances of bumping out the blight resistance increases, which is compounded by the length of time one has to wait for the hybrids to grow up before blight resistance is clearly demonstrated. With genetic mapping techniques advancing, breeders will soon be able to tell quickly the breeds with blight resistance from those that lack it without waiting for lengthy field trials.

Current restoration efforts, on the part of the American Chestnut Cooperator's Foundation, focus on grafting more resistant surviving American chestnuts in conjunction with artificial inoculation of hypovirulent strains to create seed stock. The seedlings are then planted in appropriate habitats and forest management techniques are used to artificially reduce local flora competition.

With the advances in genetic research, perhaps an engineered hypovirulence will allow treatment of surviving rootstock--the ideal solution from an ecological standpoint, because it would preserve pure American chestnuts and their geographically specific diversity within all natural habitats. If this were to happen, with the speed at which American chestnuts can grow, we could see the transformation of the Appalachian hardwood forests within a human lifetime. Instead of the usual story line of loss and destruction, the American chestnut offers the hope of renewal and resurrection.

We are offering a program entitled "The American Chestnut" this November. Please see our program calendar for more information.