Dendrochronology:
A fusion of science and history.
Jason S. Chambers, Senior Biology Major, Dr. Daniel Druckenbrod, Assistant Professor, Longwood University, Farmville, Virginia
Skeleton Plotting and Measuring
Introduction
Study Site
This study utilized the foundations of dendrochronology in order to date the
construction of a supposed pre-Civil War structure. Core samples and crosssections were obtained from Oak, genera Quercus, building logs and analyzed
to either confirm or refute the date of construction.
The structure under scrutiny is located on a farm purchased in 2003 by Doctors
Clifford and Rebecca Ambers located in Amherst County, Virginia. A deed
search on the property can trace ownership back to the year 1770; however it is
unclear as to the exact date the structure was built on the property (See Fig 2).
According to Dr. Neiman, an
architectural archeologist at
Monticello, structures such as
these that dot rural landscapes
in this state are difficult to
impossible to date using
building style alone. This is due
to the simplicity of one building
style and availability of supplies
during pre and post Civil War
rural America. Thus, this is
(Fig 2)Back of structure in Amherst County, Virginia
why dendrochronology is
the dating method of choice, for structures such as these. The structure has
undergone several additions and modifications over the generations. Samples
then were taken only from foundation and primary construction logs, to limit
erroneous dating.
Definitions
Following are several definitions that are pertinent not only to our study
but to the field of dendrochronology itself; as defined by *Fritts (2001).
• Dendrochronolgy: The science that deals with the dating and study of
annual growth layers in wood
• Ring-width chronology: The averaged standardized ring-width indices
from a number of trees sampled from a particular site which can be
used for cross-dating and deducing past climate.
• Crossdating: The procedure of matching ring-width variations and
other structural characteristics among trees that have grown in nearby
areas, allowing the identification of the exact year in which each ring
was formed.
• Signal: A detectable quality, pattern or variation in a time series such
as ring widths which can be attributed to meaningful information on
climate, environment, or biological conditions of trees, as opposed to
the background variations or noise which provide no information about
the trees and their environment.
• Earlywood: The wood produced in the annual ring during the early
part of the growing season, characterized by large thin-walled cells.
Earlywood is more porous the latewood and often lighter in color.
Sometimes referred to as springwood. (See Fig. 1)
• Latewood: Dense and often dark wood produced in the annual ring
during the later part of the growing season, characterized by small,
thick-walled cells. Also referred to as summerwood. (See Fig. 1)
(Fig. 1)Cross-section of an oak log under a microscope; early and late wood labeled
(Fig.5)A skeleton plot of a core sample
The next step was skeleton plotting. In this process a core or a crosssection is viewed through and microscope and each ring is evaluated on its
width relative to rings located around ten rings away. A skeleton plot is
made by marking a longer vertical line for more narrow rings and a “B” for
very wide rings on the corresponding year on the plot (See Fig.5). Once
several samples have been plotted the plots can be aligned in hopes of
creating a master chronology for the sample site. Once several cores and
cross-sections were plotted using this method, the samples were then
measured using a Velmex measuring station, to an accuracy of 1000ths of
a millimeter. The ring width indices were then loaded into statistical
programs in order to verify that the skeleton plots were correctly
crossdated.
Results
Coring and Sample Preparation
The first process that was performed at the site was the identification of ideal
sample logs. Questions that were assessed include: 1) is the log part of the
primary structure, 2) is the end of the log visible to obtain the orientation of the
log and its center, and 3) is there bark on the outside of the log or does the
outer surface appear intact (or
does it appear to have been split).
Once an ideal sample log was
identified the next step was
coring. Core samples were
obtained by using a power drill
and a specialized hollow bit. The
drill bit allowed for much more
efficient sampling than hand
corers would due to the hard dried
(Fig.3)Core sampling using a drill and specialized bit
wood of the structure (See Fig.3).
Cross-sections were obtained using a chainsaw. Once back in the lab the
samples were mounted and then sanded extensively. Sanding was done in a
stepwise fashion down to a grit size of nine microns (See Fig.4)
(Fig.4)A mounted and sanded core sample
(Fig.6)Ring width indices showing sensitivity and crossdating
Acknowledgments
The authors of this poster would like to thank the following people and
departments for all of their help and support: Clifford and Rebecca Ambers,
The Longwood University Faculty Research Grant, Dr. Neiman, and the
Department of Natural Sciences at Longwood University.
*Fritts, H.C. (2001). Tree Rings and Climate. The Blackburn Press. Caldwell, New Jersey.