Tree cores were extracted from 25 trees within five different genuses - oaks (Quercus), hickory (Carya), maple (Acer), red cedar (Juniperus), and ash (Fraxinus). In particular, cores were taken from white oak, red oak, chestnut oak, shagbark hickory, bitternut hickory, sugar maple, red cedar, and white ash. We examined average annual ring widths in millimeters, annual basal area increment growth(%), and species sensitivity.

An increment borer, also known as a tree corer, is a metal, T-shaped instrument used to drill into the trunk of a tree and extract a tree core.  To use the borer, press the drill-like tip into the tree. Make sure to hold the borer securely and perpendicular to the trunk of the tree. Then PUSH! Grab the handles of the insturment and rotate it clockwise. Do not wiggle the borer. Wiggling damages the core and impairs the readability of the tree rings. Continue drilling into the tree until the the borer has cored through the approximate center of the tree. Insert the extraction rod through the hole in the middle of the handles. Rotate the borer handles counter clockwise to release the tree core. Pull out the extraction rod. Be careful to preserve the bark end of the tree core. Place core into a drinking straw for storage. To withdraw the borer from the tree, continue turning the borer handles counter clockwise.

The core is taken back to the laboratory, thoroughly air dried, and permanently mounted. It is then carefully sanded in order to make it easier to read the tree rings. Under a microscope, we can magnify the tree rings and measure the width of each growth year with an ocular micrometer. An ocular micrometer is a tiny ruler which is located in the eyepiece of the microscope. By turning the eyepiece, we can line up the ruler with the tree core and take tree ring measurements.

Cranking in increment borer	Withdrawing tree core	Removing increment borer	Storing core in soda straw

Drawings by Anne Osborn

Basal Area Increment (BAI)

Ring width measurements in millimeters were used to calculate basal area increments. Basal area is the cross-sectional area of a tree taken at breast height diameter measurement (1.37 meters above the ground). 

To calculate basal area, tree diameter is divided by two to get the radius; square the radius, and then multiply by 3.14 (Pi). This is the basic equation for finding the area of a circle. To find the annual growth in terms of basal area increment for Year X, the following equation is used:

X-(X-1) 

(X-1) 

where X is the basal area at year X and X-1 is the basal area of the tree measured the year previous to X. (units are cm and cm2). 

Basal area increment gives us one year's basal area growth. This value was then expressed as a percentage of the overall basal area up to the previous year. This allows standardization of growth rates and allows comparisons among trees and between sites 

Sensitivity is calculated in order to determine the responsiveness of each tree to changes in its’ environment. The more a tree's rate of growth has been limited by such environmental factors, the more variation in ring to ring growth will be present. This variation is referred to as sensitivity and the lack of ring variability is called complacency. 

Sensitivity is calculated using the following equation: 

(X1 – X2)        +   (X2 – X3)     +     . . . . 
(X1 + X2)/2         (X2 + X3)/2 

where X1 is the most recent years growth (in cm.), X2 is the previous years growth, and X3 is the growth which occurred the year previous to X2. This process is continued until all years have been accounted for (X25 in our analysis). 

To Tree Ring:

• Introduction
• Methods
• Data Analysis