Paleo Slide Set: Tree Rings: Ancient Chronicles of Environmental Change
Cutting cross-section from subfossil huon pine (Lagarostrobus franklinii) log, Tasmania.

Sometimes it is more useful to have a full cross section of the tree for analysis, 
but scientists do not want to destroy living trees and so take full cross sections 
only from dead trees, logs, or stumps. This "remnant" material can remain intact 
on the ground or buried for hundreds to thousands of years under certain conditions 
(cold and/or dry, under water, or in peat bogs), and can provide very valuable 
information about variations in climate beyond the span of living trees. 
If these samples overlap in time with living trees, they can be crossdated 
and incorporated into a live tree-ring chronology. A European oak chronology 
has been developed from subfossil oak buried in peat bogs and river gravel 
that spans over 7 millennia (Baillie, 1995). This photo shows a sample being cut 
from a subfossil huon pine that died around AD 1200. The sample was later used 
to help extend the huon pine chronology back to 200 BC.

Photo Credits:
Edward Cook
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY: slides