Finding history among the trees
by Fariss Samarrai
researcher and graduate student Dan Druckenbrod extracted
and examined samples from trees at Monticello. He will continue
his research at Jeffersons historic home following graduation.
By Fariss Samarrai
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 doesnt mean its 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 Americans 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 its rationale-based.
a U.Va. doctoral student in environmental
sciences who will be graduating May18, compares 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. Hes 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.
are 300 years of land use at Madisons Montpelier,
he said. Im interested in how the use of the land
there has impacted the environment. Im looking for lessons
in land use from the past.
28, published his first scientific paper in the Bulletin
of the American Meteorological Society earlier this year
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
and offers 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 Madisons carefully logged observations.
They 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 trees long life, 200 or more years in some cases,
the moisture signal shifted from May in Madisons time, to
June in succeeding decades.
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 Niño event now known to have occurred at the time.
El Niño, a periodic warming of surface water in the tropical-Pacific
Ocean, often causes a lowering of precipitation in the eastern
also turned his attention to the forest below Jeffersons
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 Jeffersons
lifetime. This information can provide a clearer picture of how
the plantation operated and how the land was used. Druckenbrod
again compared the history he found in the trees and timbers with
the detailed weather diaries kept by
also has been, as a matter of curiosity, trying to determine the
age of his parents farm home in rural Pennsylvania, the
house where he grew up. A large timber from the house rested on
a table in his lab along with cores and the cross-sections of
trees from Montpelier and Monticello.
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. Im 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: