[tt] Nature: Colin Tudge: The twentieth century in a nutshell

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Colin Tudge: The twentieth century in a nutshell
Nature 450, 169
7.11.8, published 11.7

A sad and salutary tale of success, commerce, hubris, 
razzmatazz and scientific heroism.

BOOK REVIEWED
-American Chestnut: The Life, Death, and Rebirth of a Perfect Tree
by Susan Freinkel

University of California Press: 2007. 294 pp. $27.50, £16.95

Prominent among the many riches that successive waves of human beings 
discovered in North America was Castanea dentata, the American chestnut. 
This tree could be relied on to produce an enormous crop of edible nuts 
every year, unlike the oak and beech. It was also huge — more than 5 
metres in diameter — and, although not as strong as oak or as pretty as 
walnut, it supplied timber for anything from telegraph poles to coffins 
and even, at a pinch, for pianos. The tannin in the wood stopped it 
rotting or could be extracted to treat leather, leaving fibre for making 
paper.

The American chestnut grew abundantly. It was said that a squirrel could 
jump from chestnut to chestnut without touching the ground, all the way 
from Georgia to Maine. And, as Susan Freinkel remarks in American 
Chestnut, it "would pass over 1,094 places along the way with 'chestnut' 
in their names". In the Appalachian mountains, the tree's main stronghold, 
it supported an entire economy and culture. People ate the nuts and let 
their pigs and cattle loose to feed on them. They sent trains full of nuts 
and timber to the eastern cities. Ten million wild turkeys gorged on the 
Appalachian chestnuts. And the trees supported the now-extinct passenger 
pigeon — so numerous in the late nineteenth century that single flocks 
took several hours to pass overhead.

Unfortunately, European Americans from the early nineteenth century 
onwards have tried to improve on the native chestnut. They introduced 
other species of Castanea that had bigger and fleshier nuts. Former US 
President Thomas Jefferson favoured the European species; others went for 
Asian types. And with the Asian trees came the blight. These trees were 
resistant, but the American species was not. The fungus was originally 
identified as the genus Cytospora, then reascribed to Diaporthe, then to 
Endothia. In 1978 it wound up in Cryphonectria, where it remains as 
Cryphonectria parasitica.

The first signs of disease appeared in 1904 in what is now the Bronx Zoo: 
dying leaves, then canker, then death. The Bordeaux fungicide mixture that 
had worked so well in French vineyards was of no use. By 1908 the disease 
was out of hand, and by 1911 it had spread to more than ten states. One of 
these, Pennsylvania, created a 'firewall' by destroying all of its 
chestnuts in an unsuccessful attempt to contain the disease, spending 
$275,000 (about $5 million in today's money) and inflicting much misery. 
They may even have signed the American chestnut's death warrant by wiping 
out those trees that might have founded a resistant generation. By the end 
of the 1920s, the wild trees had all but gone.

Ever since, various enthusiasts and professional institutions have been 
trying to stage a chestnut come-back by means of three strategies. One is 
conventional breeding — crossing native American and resistant Asian trees 
to combine the best of both, or backcrossing resistant hybrids with pure 
Americans to produce second-generation hybrids that are 75% American and 
25% Asian, hoping that the Asian contribution includes the genes for 
resistance. Hypovirulence is another approach, infecting the blight fungus 
with a virus (discovered by chance in Italy) that greatly reduces its 
vigour, so that even American trees recover from its attacks. 
Blight-ridden American trees have been saved by infecting the active 
fungus with virus-ridden fungus. The third approach is to use genetic 
engineering to introduce genes for blight resistance — including synthetic 
ones. This is difficult because chestnuts — in contrast to, say, poplars — 
grow poorly in culture. Like the giant panda, these trees seemingly resist 
the efforts of conservationists.

The story of the American chestnut encapsulates the history of the 
twentieth century. We began the century with a tree that could do 
everything, and all we had to do was to treat it with respect. Instead, 
the entrepreneurs undertook an exercise in hubris, trying to improve on 
the unimprovable with sublime disregard for the complexity of nature. Then 
came the political razzmatazz: much posturing and rhetoric, and 
significant consignments of public money — all well intended but, in the 
end, horribly misguided. It would have been better to have done nothing 
(which is difficult for politicians). Then there have been decades of 
scientific enterprise by heroic individuals, some of whom sacrificed 
careers and income for chestnut breeding.

The result? To celebrate Arbor Day in 2005, President George W. Bush 
planted a hybrid chestnut outside the White House that was 75% American; 
it may have enough resistance to fend off blight but probably not the 
genetic wherewithal to grow to American size. The president told us that 
planting trees "is good for the economy and good for the environment". 
Latest reports indicate that the White House tree is not thriving.

American Chestnut is a parable for our time: a sad and salutary tale, 
beautifully told by US science journalist Susan Freinkel. Parables lend 
themselves to different interpretations. Freinkel says, "The American 
chestnut, successfully restored, would confirm that we have the power to 
make things right." A potentially dangerous conclusion, as only with large 
slices of luck do we get away with our excesses. The lesson to be learned 
from this majestic tree, I suggest, is that we should aim to leave well 
alone.


Colin Tudge is the author of The Secret Life of Trees and 
Feeding People is Easy.