Laboratory Methods in DendrochronologyLaboratory Methods in Dendrochronology

• Now, let’s take our wood samples back to the laboratory:

• Pre-process our cores:

1. Lay out all cores in their straws so they can air-dry.

2. Once dry, select a core and write its ID on a core mount (both sides).

3. Carefully remove the core from the straw – there’s a right way and a wrong way to do this.

4. If the core is in pieces, ensure that all pieces are in their correct order and in their correct alignment!

5. Lay the core alongside the core mount and place glue in the groove of the mount the length of the core.

• Mount your core properly!

1. The core must be mounted with its cells vertically aligned, i.e., straight up and down, similar to how they were positioned originally in the tree.

2. If the core is mounted improperly, you may have ruined any chance of the sample being used, because…

3. …if the core is mounted with the cells at an angle or horizontal, the ring boundaries will not be distinct.

4. First, inspect the core and find the “shiny sides.” These are the sides of the core. Why does a core have shiny sides?

“Shiny side”!

“Shiny side”!

Individual wood cells

• Mount your core properly!

5. Second, inspect the ends of the core to verify your evaluation. The ends of the core will clearly show the alignment of the cells.

6. Press the core into the groove. Excess glue is no problem.

7. Tape the core down onto the mount firmly at both ends and in the middle of the core.

• What if your core is twisted?

1. The sample must be mounted with the cells vertically aligned. Some samples, however, may be twisted. This is common.

2. If the core is only slightly twisted, you can simply break the core into two or three pieces and mount these correctly.

3. If the core is badly twisted (many turns), you have to steam the core while simultaneously untwisting it gently. Don’t have to do this too often.

• All wood samples have to be precision sanded!

• Sand progressively beginning with 80-grit, then 100, 120, 150, 180, 220, 320, then finish with a 400-grit.

• The wood should look like polished furniture when done!

Before After

• Measuring the ring widths:

• Preferably should be done after you have crossdated your samples.

• If the rings are not problematic, you can measure your cores first and then crossdate them statistically.

• Total ring width is only one physical property of a tree ring we can measure. What others can we measure?

• Measuring the ring widths:

• Four parts to a basic measuring system

• Movable stage micrometer with trigger

• Digital display

• PC running measurement software

• Stereozoom boom-arm microscope with crosshair reticule and light source.

• This is NOT cheap. Basic system = $3,000 + $2,000 + $1,500 + $200 = $6,700.

Movable stage

Digital display

Microscope

Light source

21” TV monitor

CCD camera

Advanced measuring system:

Advanced Measuring system:

•Simple system below uses CCD camera to reduce eye strain

• Measuring the ring widths:

• Crosshair guides you from one ring boundary to the next.

• Note! Everybody’s eyes are different. If you can’t see the crosshair, you can manually adjust the lens by removing the ocular and turning the lens up or down!

• Make sure you measure perpendicular to the ring boundary, always!

• Turn the handle on the stage from one boundary to the next.

• Hit the trigger to record the measurement.

• MeasureJ2X most popular software for measuring. Java based, requires Pentium PCs or Macs.

• Measures to the nearest 0.01 mm or 0.001 mm (preferred).

• Sometimes you have to physically move or relocate the core to ensure that you measure the width of the ring perpendicular to the ring boundaries.

• Imaging Systems = the future of dendrochronology.

• Enter WinDendro, $20,000 system that automatically detects and measures ring widths: EW, LW, and TRW

• Measurements must be archived in several locations.

• First, all tree-ring data are deposited with me and archived on an external drive.

• Second, all tree-ring data are archived at the International Tree-Ring Data Bank of the World Data Center for Paleoclimatology (part of the National Climatic Data Center) in Asheville, North Carolina.

• Finally…

• Consumes the majority of time learning about tree-ring dating.

• The more you do it, the better you become.

• Revolves around pattern recognition.

• Three basic techniques:

• Graphical techniques… then

• Statistical techniques, which lead to…

• Memorization

• All experienced dendrochronologists have mastered the art of memorizing some of the more important ring patterns for certain years in their geographic areas of study.

• You will do the same, starting with the 20th Century!

• Crossdating tree rings

• Graphical techniques

• Two techniques:

• Skeleton plots (favored in the SW U.S.)

• Crossdating tree rings

Quick. Would you consider this a good match?

Quick. Would you consider this a good match?

• Graphical techniques

• Two techniques:

• Alignment plots, favored in Europe and SE US

Norris Dam and Swaggerty Blockhouse Chronologies

Swaggerty Norris

• Crossdating tree rings

• Remember the ultimate goal: you must start memorizing which rings are particularly narrow or which have noteworthy properties.

• Other properties:

• very wide rings• frost rings• thin latewood rings• light rings• rings with excessive resin ducts (called

traumatic resin ducts or TRDs)• false rings, double rings

• Crossdating tree rings

• Let’s try crossdating via skeleton plots by visiting Dr. Paul Sheppard’s excellent educational web site at the Laboratory of Tree-Ring Research, University of Arizona in Tucson …

• Note! You’ll be learning this technique in later labs, so please spend some time to do this on your own. The more you do this, the better you become.

• Crossdating tree rings