www.carbon14.pl

www.carbon14.pl

AP Biology

DendrochronologyTree Dating Lab

http://web.utk.edu/~grissino/

Want to understand climate?Ask a tree who was there!

• Dendrochronologist study annual growth rings of old trees to learn about past environmental changes.

• By combining living and dead wood scientists can extend tree-ring paleoclimatology records back hundreds to thousands of years. 

What are tree-rings?

• Trees expand in width by the division of cells in a thin layer underneath the bark

• Some cells add to the bark, but most add to the wood

• These “xylem” cells carry water and minerals from the roots

• Only one ring grows each year• Age of a tree can be determined by analyzing

rings

Why does ring width vary?

• Environmental factors will cause rings to be narrower or wider. These include:– Drought or abundant rainfall– Saturated soils– Insect, fungus, or other diseases– Volcanic eruptions, earthquakes, or other

natural disasters

Human activities may also affect ring width

For example, the impact of solution-brine mining in the Finger Lakes region of New York State is preserved in these tree rings.

http://ny.usgs.gov/pubs/fs/fs05797/html2/FS057-97.html

TREE TREE SAMPLINGTREE SLICE SAMPLING

Increment borerIncrement borer

Collection of the tree slice

Tree core

TREE CORE SAMPLING

Principle of Limiting Factors

• The rates of plant processes are constrained by the primary environmental variable that is most limiting.

• Most often this is precipitation. But at higher latitudes, it may be temperature.

• One illustration of this principle is shown in the next slide.

The tree on the right shows greater impact from variations in rainfall than the one growing on flatter ground where rain collects.

INSIDE THE TREE

• Tree ring width varies of tree ring width and climatic conditions

• Seasonal patterns: – Early wood Large, thick-walled cells – Late wood Small, densely-packed, thin-walled

cells – Together = an annual growth ring

• Mean width of rings dependant on: tree species, age, availability of stored food, & climate

Cross-section of the tree trunk.

How old is this tree?

1

2

3

4

5

6

7

• 7 Years old!• Year 5 was

very dry• Year 3 was

very rainy• If this three was

cut down in 2006,it was planted in 1999

Microscope view of pine (Pinus Sylvestris) slice. This part showsannual tree growths close to tree pith.

PithPith BarkBark

UNDER THEMICROSCOPE

PithPith BarkBark

UNDER THE MICROSCOPE

In some cases tree growths are very thin (e.g. during the drought). In this picture annual growths

with very small width 0.3 – 0.8 mm are shown.

PithPith BarkBark

UNDER THE MICROSCOPE

Use tree bore samples

• You will use two tree bore samples for the last part of this lab

• Tree bores provide data without cutting down the tree

• If you have more than one bore (or beam), you can overlap them to see where growth ring patterns match

Principle of Cross-Dating

Matching patterns from several trees increases the ability to identify the year in which a tree started to grow or died.

You are now ready to try dendrochronology on

your own!•The tree ring photos for the lab are online in the chapter 35 resources

•Tree bore sample are on your desk