History Among The Trees
February 14, 2003--
What most people call a tree, Dan Druckenbrod calls history.
stands in the forest below Monticello, the home of Thomas Jefferson,
looking for old trees.
because a tree is big, it doesn’t mean it’s as old as
a smaller tree nearby,” he said. “White oaks grow slow,
so they can be much older than the faster growing red oaks.”
spots a white oak that looks like it has seen some years, with missing
and gnarled branches near its canopy. He begins coring the tree,
seeking its center with a hand-cranked boring device. Soon, he will
know how old the tree is and where its place is in the land-use
history of a famous American’s property.
trees have different climate responses,” Druckenbrod said.
“They have different life spans and growth rates. They are
affected by the amount of light and moisture they get. Reconstructing
their life history is somewhat of an art, but it’s rationale-based.”
a University of Virginia doctoral student in environmental sciences
who will be graduating in May, has been comparing the weather records
kept by James Madison and Thomas Jefferson with the climate history
stored in the trees surrounding the old plantations at Montpelier
and Monticello. He’s curious about the history of the forest,
how old the trees are, what the climate has been like during the
lives of the trees and how the land has been used — whether
the forest has been logged and replanted, or if it came back naturally.
is 300 years of land use at Madison’s Montpelier,” he
said. “I’m interested in how the use of the land there
has impacted the environment. I’m looking for lessons in land
use from the past.”
28, recently published his first scientific paper — in the
Bulletin of the American Meteorological Society — detailing
his reconstructions of precipitation patterns at
Montpelier in the late 18th century. The first chapter of his doctoral
dissertation on forest responses to climate, the paper is eloquently
written, a fascinating combination of human and natural history.
more than a year Druckenbrod and colleagues cored dead trees in
the old growth forest around Montpelier and analyzed the long, thin
plugs for climate history in the time of Madison. Madison kept extensive
weather diaries for seven years while living on the property, and
Druckenbrod has compared the natural archive from the trees with
Madison’s carefully logged observations.
agree well,” he said.
Madison saw heavy rainfall, Druckenbrod found accelerated tree growth,
a “signal” of moisture. Where Madison recorded drought,
Druckenbrod found indications of slow growth, a sign of low moisture.
What he found that surprised him, though, was that over a tree’s
long life, 200 or more years in some cases, the moisture signal
shifted from May in Madison’s time, to June in succeeding
may be a physiological response to climate by the tree as it ages.
It may be because of a shift in land use patterns, such as land
clearing which may have impacted the seasonal precipitation in the
area. Or it may be that the summer peak of rainfall has actually
shifted one month later,” Druckenbrod said.
also found that a drought Madison recorded in 1792 shows up in the
tree rings from the Montpelier forest and corresponds with an El
Nino event now known to have occurred at the time. El Nino, a periodic
warming of surface water in the tropical-Pacific Ocean, often causes
a lowering of precipitation in the eastern United States.
has now turned his attention to the forest below Jefferson’s
Monticello. Archaeologists at Monticello are interested in reconstructing
the forest history there, and they hope to determine the age of
timbers from a log cabin that existed during Jefferson’s lifetime.
This information can provide a clearer picture of how the plantation
operated and how the land was used. Druckenbrod is again comparing
the history he finds in the trees and timbers with the detailed
weather diaries kept by Jefferson.
also is, as a matter of curiosity, trying to determine the age of
his parent’s farm home in rural Pennsylvania, the house where
he grew up. A large timber from the house rests on a table in his
lab along with cores and the cross-sections of trees from Montpelier
spent a lot of time in the woods growing up,” he said. “I
grew up in a house that dates back to the 1780s, and my parents
always collected antiques. I’m interested in both natural
and human history.”
co-authors include U.Va. environmental sciences professors Michael
Mann and Hank Shugart, and University of Arkansas researchers David
Stahle, Malcolm Cleaveland and Matthew Therrell. The paper can be
found at: http://ams.allenpress.com/amsonline/?request=get-toc&issn=1520
Samarrai, (434) 924-3778