Living historical records in tree ring details

By James L. Cummins
Conservation Corner
In our last article we talked a little about how tree rings form. Here will talk about how trees
serve as living historical records and how studying the rings can be used to determine climate
events.
Tree Rings as Historical Records – By aging the trees of an area, a time reference can be
established to determine climate/environmental conditions for that area. For example, trees can
indicate: 1) a timeline for when farmland was abandoned or no longer cultivated; 2) a minimum
length of time since new land surfaces were created (i.e., flooding, glaciers, landfills, road cuts,
etc.); and 3) a reference of time since a land surface first became suitable for germination and
growth of tree seedlings.
If the tree rings can be dated, then the exact year during which a tree was damaged can be
determined. This would make it possible to date the event responsible for the damage. Also, if a
patch of bark is damaged, the date of damage can be determined by counting the number of
rings in an adjacent undamaged area. This method has been used in identifying catastrophic
events such as ice storms, forest fires, and even hurricanes.
Identifying such events is possible even in partially tipped trees. Terminal shoots of trees
generally grow upward. When a tree is tipped over, new shoots emerge and grow vertically at
an angle to the axis of the bent‑over trunk. Therefore, the event that caused the damage can
be dated by counting the number of rings in the new shoots that are now growing vertically from
the trunk.
Use of Tree Ring Studies – Tree ring dating has been perfected to the point of being used to
date events and conditions. Calibrated records have been used to classify past conditions into
two categories: cool and wet or hot and dry.
The Water Resources Division of the U.S. Geological Survey maintains a Tree Ring Laboratory
near Washington, D.C. There, research is conducted relating tree growth with hydrology.
Currently, studies are being conducted to help hydrologists determine conditions in areas where
no records exist. They have also been successful in expanding records into periods of time
before information was collected.
It has been discovered that tree ring records in humid areas can be successfully cross dated
enabling researchers to calibrate tree ring records with hydrologic records. This will allow for
estimation of yearly variation in stream flow of small streams and water‑level variation in
wetland areas.
Tree ring studies have proven that information about past environmental conditions may be
reconstructed and have revealed the many ways in which environmental factors affect the
growth of a tree. Therefore, trees serve as natural recorders of their environment.

These articles only touch the surface of all the fascinating things that can be derived by studying
tree rings. Take the time to look up how tree rings are used in various studies to fully appreciate
the importance of tree rings.
James L. Cummins is executive director of Wildlife Mississippi, a non-profit, conservation
organization founded to conserve, restore, and enhance fish, wildlife, and plant resources
throughout Mississippi. Their web site is www.wildlifemiss.org.

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