New life from an old chestnut

One morning this past May, on the second of our two annual point counts for the Bald Eagle Ridge Important Bird Area, I was pleased to run across a couple of these brown, porcupiney things in the middle of our Laurel Ridge Trail. American chestnut husks! We looked around for the tree of origin, but we were in a hurry, and I had to return the next day and find it. It wasn’t more than fifteen feet off the trail — a forty-foot-tall tree, to all appearances still healthy, about five inches in diameter at breast height. The ground around it was littered with the tell-tale husks.

The day before yesterday I went for another look. Despite the absence of obvious lesions on its bark, it clearly had the blight; all the leaves had turned brown with the exception of those on the new sprouts that were already clustered around its base. (You can see the lowest branch in the above photo; none of my photos of the crown of the tree were worth sharing.) Like every other American chestnut on our mountain — and well over 99.9 percent of all native chestnuts in the eastern United States — this individual will never again be able to grow an above-ground stem for more than a couple of decades before succumbing to the introduced Asian fungus, Cryphonectria parasitica.

But unlike most of the other spindly chestnuts on our ridges, this stem lived long enough to produce one crop of nuts before it died. There’s a slight — very slight — chance that they were fertile, cross-pollinated with some other rare tree that happened to flower in the spring of 2006 somewhere in the vicinity. And there’s an even slighter chance that one of those fertile nuts was spared by the squirrels and managed to sprout in a favorable location. Do you believe in miracles? But it is upon just such miracles — and/or the intervention of geneticists — that the future of this totemic species depends, because it is only through sexual reproduction that the American chestnut will be able to evolve resistance to the blight.

I know: you thought the purpose of sex was reproduction, didn’t you? But many plants can reproduce vegetatively, too; Castanea dentata is a great example. “King of the coppice,” biologist Joe Schibig calls it. Who knows how the hell old some of these ridgetop rootstocks might be? It’s eerie to stand among the twisted chestnut oaks and the mountain laurel (now also dying en masse due to a blight of unknown origin) and realize that 100 years ago, the woods here would have been dominated by straight, soaring trunks, and that 200 years ago — before the first clear-cutting of Plummer’s Hollow around 1815 — the forest primeval would’ve been an almost unimaginably full cornucopia, with a deep carpet of chestnut burrs every fall. Even on years when the acorn and hickory crops failed, chestnuts, having bloomed well after the last frost, were still available to fill the bellies of squirrels, deer, raccoons, mice, chipmunks, and a host of other creatures. Evolution called the vast flocks of passenger pigeons into existence in part as a response to this superabundance of chestnut mast. One out of every four trees in the Appalachians was an American chestnut. Its wood was straight-grained, easy to split, rock-hard, and virtually impervious to rot.

It’s a bit of an irony, I guess, that trees so resistant to the common agents of decay would fall victim to a fungus. First spotted at the Bronx Zoo in 1904, the airborne disease spread at a rate of about fifty miles a year, wiping out in excess of three billion trees over the next half-century. A half-century after that, what’s the prognosis for the species? As Schibig notes,

Some chestnuts have repeatedly died and sprouted again from their root collars for the past 70 years, but the vigor and number of these sprouts have been declining. After all, they can’t be expected to forever battle the blight, other diseases such as root rot, ravenous insects, browsing by deer, competition from other trees, unfavorable weather conditions and habitat destruction by humans. It was hoped that in some parts of its natural range there would be pockets of chestnuts that would have resistance to the disease and would be reproducing successfully from their nuts, not just by sprouting. To my knowledge, such populations, sometimes called the “holy grail” by American chestnut fans, have never been found. It appears that human intervention will be necessary to restore the American chestnut to the forests of the eastern U. S.

The remainder of Schibig’s brief essay describes the effort to resurrect the American chestnut. I’m most familiar with the efforts of the American Chestnut Foundation, whose quarter-century-long experiment began by crossing American chestnuts with blight-resistant Chinese chestnuts, then crossing the resulting hybrids with more American Chestnuts, and so on: crossing each new generation with pure C. dentata stock until they get a tree that has all the attributes of an American chestnut, but with the disease resistance of its scrubbier East Asian ancestor. The main site for this research in Pennsylvania is at the Penn State Experimental Forest in Stone Valley, less than 25 miles away from our mountain as the pigeon flies.

The passenger pigeon and the American chestnut were almost certainly both examples of what ecologists call keystone species: species without which basic ecosystem functions such as carbon cycling and nutrient storage are fundamentally altered. Without a steady supply of chestnut mast, many wildlife populations have probably become a great deal more unstable, with repercussions up and down the food chain. Without passenger pigeons — which were on the way out well before the introduction of the chestnut blight, due to market hunting and widespread clear-cutting — our forests have lost a major, periodic source of fertilizer and a disturbance regime as natural and necessary as the once-in-a-century wildfire.

It’ll be great if the American Chestnut Foundation’s back-crossing scheme works and we can restore at least one of these two species. But in order to do so, we will also have to be mindful of a third keystone species: the white-tailed deer. Here in Plummer’s Hollow, as I’ve noted before, a number of years of good hunting have brought the deer herd down to reasonable levels, allowing a few of the chestnut sprouts to survive. But we can never quite relax: one year of poor hunting combined with a mild winter could change all that. Eternal vigilance, it seems, is the price not only of liberty but of healthy forests as well.

I know I will never see a fully mature American chestnut tree in my own lifetime — just as I will never see a large, old-growth mixed-deciduous landscape in the East outside of the Porcupine Mountains, way over on the Upper Peninsula of Michigan. A recent article from the Christian Science Monitor on the American Chestnut Foundation’s research sounds a hopeful note, projecting enough nuts for a large-scale replanting effort to commence by 2015. Hope is good. But I do think a consciousness of just how much we’ve lost is also important if we really want to overcome public complacency and rally support for protecting and restoring what we have left.
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Don’t forget to submit links for the upcoming Festival of the Trees #15 by Thursday at the latest. See the details here.