A Camellia Grows in Boston

November 26, 2002
By PETER DEL TREDICI
NY Times.com

BOSTON
If there's one trait that gardeners have in common, it's a
desire to grow plants that experts tell them they shouldn't
be able to grow. Be it bamboo in Boston, evergreen
magnolias in New York or tree ferns in Atlanta, the urge to
cultivate something that nobody else in the neighborhood
has runs deep. Whether this passion comes from a need to
compete, to experiment or just to be different is
irrelevant. What counts is pushing the limits of
possibility and proving the experts wrong.

But what happens when the limits of possibility are pushed
not by gardeners but by climate change? Some of the joy
leaves the enterprise; ambivalence seeps in. At least it
has for me.

The arboretum where I work has given me a special vantage
point from which to witness - and react to - the shift in
growing patterns brought on by a world that's getting
warmer. The Arnold Arboretum was founded in 1872 for the
purpose of scientific research. Its charter specifies that
it cultivate "as far as practicable, all the trees, shrubs,
and herbaceous plants, either indigenous or exotic, which
can be raised in the open air."

It's a concept that has its origins in the passion for
collecting that characterized the Victorian era in America,
and it's one to which the arboretum has remained true
throughout its history. We gather plants from all over the
world, grow them outdoors in Boston and see how they fare.
For the first 114 years, observations were recorded on
index cards; since 1986 they've been fed into a computer.

The process of testing a plant's adaptability to any given
climate is essentially one of trial and error, with the
results defying predictability. It is possible, though, to
draw a couple of conclusions from the arboretum's
experiments. First, plants from parts of the world that
have a climate similar to Boston's (in terms of rainfall
and temperature) have a greater chance of surviving than
plants that come from areas with very different climates.

Second, there are always exceptions to this rule, most of
them attributable to the effects of glaciation, which long
ago transported cold-tolerant plants into some very warm
climates. Identifying these vestigially hardy plants is one
of the most rewarding aspects of my job. It's also one of
the most challenging, because a wide variety of
environmental factors can influence the survival of a given
plant. A series of warmer or wetter years, for example, may
allow us to grow something for a time. It's not until a
fatal act of nature comes along - a summer drought or a
winter ice storm - that the true extent of a plant's
hardiness is revealed.

Climate change has complicated this enterprise. To see how,
one need only review the arboretum's "dead files," the
records of plants that were planted on our grounds but that
are no longer living. Take, for example, the Chinese tulip
tree, Liriodendron chinense. We first imported this tree
from China in 1908. It lived for 11 years. We imported the
species at least seven more times over the next 70 years,
and the tree never survived more than 15 years and never
flowered.

Last year, two trees we raised from seed imported from
China in 1980 flowered for the first time in the history of
the arboretum at the age of 22. What does this mean? Simply
that this species, which has always been considered
marginally hardy in Boston, has finally survived long
enough to bloom.

Another example is Magnolia grandiflora, the famous
evergreen magnolia so characteristic of the Deep South.
We've been growing this species at the arboretum since
1932, but it has always suffered winter injury and seldom
flowered. Since 1984, however, our efforts have been much
more successful. Now, our plants bloom almost every year,
produce viable seed and make it through the winter with
very little damage, except for the breakage of limbs caused
by the buildup of ice on their evergreen leaves.

And finally there's Camellia "Winter's Star," which has
survived the past four winters in our outdoor nursery. It's
the first camellia ever to make it out onto the grounds,
and it's in full bloom right now.

What's curious about all these observations is my personal
reaction to them. At first there is a flush of pride, and
even triumph, at being able to accomplish something that
hasn't been done before. This is the gardener in me. But
then comes the letdown when I realize that I am staring at
hard evidence that our climate today is not the same as it
was when the arboretum was founded. What should be a
horticultural triumph turns out to be a hollow victory -
one that has less to do with skill than it does with a
changing climate (and, I imagine, America's love of fossil
fuel).

But this is not the end of the story, for something else is
happening to our plants. As the winters have been warming
in Boston, the summers have been getting drier, especially
over the last decade. This has led to problems with
viburnums, umbrella-leaf magnolias and many other plants
that have never struggled here before. While a serious
drought can kill some plants outright (particularly the
very young and the very old), it can also weaken healthy
plants, making them more susceptible to insects and
disease. Based on my observations, our longstanding concern
about the cold hardiness of plants is being trumped by
concerns about their tolerance of summer drought. What
nature gives with one hand, it takes away with the other.

Certainly the effects of global climate change are
unpredictable. All we really know is that the weather is
going to be different than it has been in the past.
Unheralded species of plants, waiting in the wings like
Broadway understudies, may become dominant over time, while
old favorites decline. From the garden where I work, the
plants seem to be telling us something we may not want to
hear: the world is changing.


Peter Del Tredici is director of living collections at
Harvard University's Arnold Arboretum.

http://www.nytimes.com/2002/11/26/opinion/26DELT.html?ex=1039339865&ei=1&en=34ab3b47584d93e5