AP Biology Dendrochronology Tree Dating Lab

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.

TREE TREE SAMPLING TREE SLICE SAMPLING Increment 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? 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 shows annual tree growths close to tree pith. PithBark UNDER THEMICROSCOPE

PithBark

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. PithBark 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