in Plot 1, which is only about twenty-five hundred feet higher.
Silman first laid out the plots in 2003. His idea was to keep coming
back, year after year, decade after decade, to see what happened. How
would the trees respond to climate change? One possibility—what might
be called the Birnam Wood scenario—was that the trees in each zone
would start moving upslope. Of course, trees can’t actually move, but
they can do the next best thing, which is to disperse seeds that grow into
new trees. Under this scenario, species now found in Plot 4 would, as the
climate warmed, start appearing higher upslope, in Plot 3, while Plot 3’s
would appear in Plot 2, and so on. Silman and his students completed the
first recensus in 2007. Silman thought of the effort as part of his long-
term project and couldn’t imagine that much of interest would be found
after just four years. But one of his postdocs, Kenneth Feeley, insisted on
sifting through all the data, anyway. Feeley’s work revealed that the
forest was already, measurably, in motion.
There are various ways to calculate migration rates: for instance, by
the number of trees or, alternatively, by their mass. Feeley grouped the
trees by genus. Very roughly speaking, he found that global warming was
driving the average genus up the mountain at a rate of eight feet per year.
But he also found the average masked a surprising range of response. Like
cliques of kids at recess, different trees were behaving in wildly different
ways.
Take, for example, trees in the genus Schefflera. Schefflera, which is
part of the ginseng family, has palmately compound leaves; these are
arrayed around a central point the way your fingers are arranged around
your palm. (One member of the group, Schefflera arboricola, from Taiwan,
commonly known as the dwarf umbrella tree, is often grown as a
houseplant.) Trees in Schefflera, Feeley found, were practically
hyperactive; they were racing up the ridge at the astonishing rate of
nearly a hundred feet a year.
On the opposite extreme were trees in the genus Ilex. These have
alternate leaves that are usually glossy, with spiky or serrated edges. (The
tuis.
(Tuis.)
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