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Lesson Plans

Dendrochronology Field Study

Introduction:

In this activity, you will be coring several trees and analyzing the tree rings. You will be looking for correlations between the growth rate (tre ring width) and local rainfall data as well as determining the ages of your specimens.

Materials:

Increment borer
Straws
Masking tape
DBH tape
Colored flagging

Procedure: Field Work

Seelect two trees to core according to your intructor's directions.
Put the increment borer together and remove the core extractor.
Have one member of the team hold the extractor.
Core at a very slightly upward angle.
When you judge tht you have reached the center of the tree, insert the extractor, convex side up (push it straght through but do not bang on it.)
Turn the increment borer one half turn counterclockwise, then carefully pull out the core extractor and core (have a group member stand by with cupped hands in case any pieces fall apart.)
Carefully use a straw to remove the core from the extractor.
Note which end of the core is the outside (bark) and which is inside.
Use masking tape to seal ends and label the tape to indicate the tree number and species as well as which end is which.
Measure the diemeter (dbh - diameter at breast height) of the tree and record. Divide by two to find the radius and record.
Mark the tree with a piece of flagging so no other groups core it.
Find a second tree of the same species and repeat the procedure.

Procedure: Lab Work

Carefully remove one core from its straw container, being creful not to lose track of which end is which.
Use a hand lens if needed to count the rings from the outermost to the center, and record this number as the tree's age.
If you don't have a complete core sample, count as many rings as possible and measure ( to the nearest tenth of a centimeter) the width of the segment counted. Multiply this number of rings/cm X the radius of the tree to get an estimate of its age. Record the estimated age and show your work in the data section.
Find two of the widest rings in your core sample, and identify the years they represent. Record in the data section.
Identify a section of the core sample with the narrowest rings. This may be about a centimeter wide, slightly more or slightly less. Recored the years represented by this section.
Use the rainfall data provided to calculate the average rainfall for the widest ring years.
Use the rainfall data provided to calculate the average rainfall for the narrowest ring years segment of your core.
Find the growth rate for your tree by dividing the diameter by the age of the tree and record.

Data:

Tree #1:

                Species: _______________________

                DBH: ________cm               Radius: ________

                Age: ______ years                  Actual or estimated? ______________

                If age is estimated, show calculations here:

                Year of first widest ring ______________      rainfall: ______in.

                Year of second widest ring: ___________       rainfall: ______in

                Narrowest ring years: _________ to ________

                Average rainfall for narrowest ring years: _______in

                Show your calculations for growth rate here:

                Growth rate of tree #1: ________cm/yr

Tree #2:

Questions:

Describe the general relationship between tree ring width in your cores and amount of rainfall:
Describe why the trees you selected should or should not be sensitive to the amount of precipitation (in other words, why would their ring widths match well or not match the rainfall data).
Explain the difficulties that your group encountered during this field experience. Be specific.
Propose a tree investigation we could perform other than correlating ring width with rainfall data: