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

This study utilized the foundations of dendrochronology in order to date the construction of a supposed pre-Civil War structure. Core samples and cross sections were obtained from Oak, genera Quercus, building logs and analyzed to either confirm or refute the date of construction.

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.

Study Site

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 why dendrochronology is (Fig 2)Back of structure in Amherst County, Virginia 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. (Fig.5)A skeleton plot of a core sample The next step was skeleton plotting. In this process a core or a cross section 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

• 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)

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 (Fig.3)Core sampling using a drill and specialized bit 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 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.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.

(Fig. 1)Cross-section of an oak log under a microscope; early and late wood labeled (Fig.4)A mounted and sanded core sample