This is the first installment of Disease!, planned to be a semi-regular series of diaries about a category of overlooked epidemics -- plant and animal diseases. While they rarely make the news, these epidemics, often caused by invasive pathogens, have had and continue to have enormous ecological and economic impact. And in a world with changing climate and blending borders, we can only expect more to come.
Let's pretend, just for a moment, that you could play God and were tasked to design a perfect tree. What features might it have? Obviously, it would be a tall and stately shade tree, because we value those highly. It should be valuable for the timber industry, too, growing tall and straight, with wide trunks. Its wood should be straight-grained, easily worked, and resistant to rot and exposure. Because we want our timber industry to be a sustainable one, it should grow quickly, too, so that it will always be plentiful and so that managed forests never fall prey to overharvest. But because this is supposed to be a perfect tree, that's not far enough. It should bear some sort of edible fruit, maybe a nut of some kind, and should produce them in bountiful crops, consistently, year after year. That way, those nuts can be a dependable cash crop for people as well as an important food source for wildlife. Why not have its bark and wood scraps -- the cast off leavings of that timber industry -- able to be processed into some useful industrial chemical, too? Sure, that doesn't seem very realistic, but this tree is borne of our imagination. To top it off, let's give it a deep and powerful root system, and the ability to grow back from its roots, even decades after the tree itself has been felled by illness, axe, or fire.
Of course, trees aren't created by Intelligent Design. And there's no such thing as a perfect tree in nature. Until the early 20th century, though, a tree exactly like the one I described above was one of the dominant components of the Appalachian forests.
But it wasn't a perfect tree, because it had a perfect murderer.
Most of the diaries I have planned for this series are about epidemics where the end of the story hasn't been written yet: diseases where we're trying to stop the spread, or save the plants or animals that are the victims. But it isn't really possible to discuss these epidemics without starting here, with one of the greatest ecological and economic disasters in human history, even though the ending -- at least for now -- has already been written. It is against this benchmark that all later plagues, for better or worse, have been compared.
This is the story of the American Chestnut, and the blight fungus that has destroyed it.
If you stepped back in time to any year before 1900, the Appalachian mountains and the forest that surrounded them would look very different than they do today, for a reason totally unrelated to mining or urban sprawl. Perhaps as many at 25% of the trees would be a species that most readers of Daily Kos have never seen before. Tall and stately, with yellow-flowered catkins in the spring and crops of nuts in the fall, the American Chestnut defined the woodlands of Appalachia. There were, by all estimates, some four billion of the trees at any given time, from as far north as Maine to the Deep South.
It was everything I described above the fold. The American Chestnut was one of the most commercially important timber trees in our country's history. Trees with a diameter of 3 or 4 feet were commonplace. Trees 6 feet around across and larger were by no means rare. And the American Chestnut grew straight and true, allowing for board-lengths that are unheard of in modern lumber. The light, rot-resistant wood built barns and split-rail fences, was used for shingles and telephone poles, found purpose as plywood and piers. And the byproducts of the timber industry were used to make tannic acid, used to tan and prepare leather. Once, southern Appalachia saw the leather industry, and the timber operations they had bought out to support their needs, as one of its primary sources of revenue. At its peak, somewhere between half and two-thirds of the tannic acid used by the American leather industry came from the chestnut. The nuts were a cash crop, too. If you've ever wondered about those "chestnuts roasting on an open fire" sung about every Christmas, wonder no longer: they were American chestnuts.
But it was not to last. In the late decades of the 19th century, there was a fashion for planting gardens and city spaces with exotic, foreign species, especially those from the Far East. Thousands of Japanese Chestnuts, a related tree with a smaller, branching trunk, were imported by a nurseryman in Queens and another in New Jersey. Somewhere along the way, at least one, and likely many, of those trees brought with it a murderer.
In 1904, Hermann Merkel, chief forester at the New York Zoological Park (now the Bronx Zoo), noticed that the chestnuts on the property were dying. They suffered from a strange disease that made their bulk bulge and split, eventually girdling the tree. Infected plants suffocated and starved to death, their ability to transport nourishment up and down the trunk forever destroyed. He brought the disease to the attention of W. A. Murrill, a New York Botanical Garden mycologist, who identified it as a fungal disease, and named it Endothia parasitica (since renamed to Cryphonectria parasitica). Murrill was concerned, but there was no way to foresee how rapid and devastating the condition's spread would be.
The next year, chestnut blight was a topic of concern for the USDA, who had been receiving reports of tree declines and death across New York. Another year passed, and in 1906, it was reported from New Jersey, Maryland, and Virginia. 1907, Ohio. 1908, Pennsylvania. Infected trees all suffered the same fate -- killed back to the ground by the relentless fungus. It was clear that a crisis was unfolding. But then, as now, public interest in plant disease was low, and resources were slow to deploy. It wasn't until 1909 that experiments were performed by Pennsylvania Department of Forestry researcher John Mickleborough and nurseryman Isaac Hicks, showing that the disease was native to Japanese Chestnut and had indeed invaded on the imported trees. And it wasn't until 1911 that the U.S. Congress approved emergency funds to research and combat the epidemic.
The Pennsylvania research team tried antifungal injections, sprays, and corrective tree surgery. They failed. Additional money from Congress in 1912 and 1913 helped pay for a control of last resort. A giant swath of forest was cleared across the Appalachians of North Carolina, a firebreak against the spread of the fungus. The northern forests were already lost, but the hope was that the blight's range could be restricted and the tannin industry of the south could be saved.
Perhaps the firebreak needed to be larger to prevent the spread of the chestnut blight's airborne spores. Perhaps, by 1913, it was simply already too late. Late in the year, blighted trees were identified in Georgia. The quarantine was broken, and there was no hope of establishing another one. Nor would there have been money to do so, because in 1914, declaring the fight against the disease futile and the need for additional war funding paramount, Congress discontinued its emergency funding of blight research. A little over a decade later, the Appalachian tanning and leather industry collapsed, the trees that sustained it dead to the blight. Nothing has ever filled the economic void left behind.
All told, it took less than four decades for chestnut blight to destroy an estimated four billion -- with a b -- trees. The disease eradicated a major industry and reduced the estimated commercial value of the eastern hardwood timber stands by half. By the time people started singing that song about roasting chestnuts, they would have been hard-pressed to find any for sale. The ecological impact was crippling as well. In the short-term, a quarter of the forest cover in the Appalachian mountains died. The loss of those trees, and the plentiful nuts they provided as winter food for animals, has been blamed for the decline of wild turkeys, wood ducks, grouse, and black bears throughout the eastern United States. Seven species of moths fed exclusively on the American Chestnut and have gone extinct. Forty-nine more moth species had other food sources and so have survived, with their numbers reduced. Erosion of the thin mountain soils has increased, because the remaining tree species do not have root systems that bind the soil as strongly as the chestnut did.
Unlike the way things work in the movies, there was no last-minute reprieve, no miracle cure, no happy ending. The blight won.
But ... there is still a glimmer of hope. The American Chestnut is not extinct. It's not even endangered. Many of these trees, felled by illness now a century ago, resprout from their still-living roots every few years. The blight never left, and they die quickly, but every now and then, one lives long enough to reproduce. Mature trees still survive, too. Stands exist far outside the natural range, where the blight never reached. There are American Chestnuts up and down the Pacific Coast, and some in Canada. And there are a handful of carefully guarded trees from Michigan to Georgia that survived the blight by luck or by genetics.
Congress may have given up on stopping the blight in 1914, but scientists have never surrendered to its advance. The American Chestnut Cooperators Foundation has been breeding those rare survivors, trying to develop a blight-resistant selection. The American Chestnut Foundation and the United States National Arboretum have been producing American/Chinese Chestnut hybrids, attempting to back-cross with pure American Chestnut stock to create a blight resistant variant that retains the American trees' important features. Early experiments with direct genetic engineering have begun. And researchers in Europe have discovered that a non-lethal, hypovirulent strain of the blight exists, which may be able to outcompete and displace its fatal relative.
It is too soon to know whether the American Chestnut will ever return to our eastern forests, much less whether it will ever return to its position of dominance. But no matter what the future holds, the introduction and spread of the chestnut blight -- and its four billion casualties in 40 years -- should serve as a reminder that diseases which don't infect humans can still affect us. Unfortunately, although Congress passed the Plant Quarantine Act in 1912, expanded and strengthened in the Plant Protection Act of 2000 (also known as the Agriculture Risk Protection Act), that's a lesson we seem doomed to relearn over and over and over again, as we'll see later in this series...