Tree rings   Colby Rucker
  Monday, October 21, 2002 11:17 PM


About a week ago I had a visit from a classmate of mine whom I last saw in
the late 1940's. He's a retired engineer, well-traveled and well read, with
an interest in most everything, and has a country place in the woods in
western Maryland.

He forwarded a xerox of a draft of a chapter from a book that an associate,
Richard L. Phipps, at the Tree-ring Laboratory at the U. S. Geologic Survey
is writing, and sent to him for review. The chapter, Crossdating, Measuring
and Standardization, is most interesting, and emphasizes the difference
between counting rings and crossdating. The matter of false rings and
missing rings may make trees in certain stands, or different situations
within the stand nearly impossible to date. The matter of selecting useful
trees, utilizing the most reliable group of rings within that tree, and
correlating that sequence with a resource of reliable material is essential.
Such determinations often require specialized equipment and rather complex
mathematical formulas.

Although reliable sequences can be constructed, and numerous structures have
been accurately dated, certain species are more difficult to date. Phipps
mentions two in particular; Taxodium distichum and Nyssa sp. He states
that Nyssa and other diffuse-porous species from certain habitats can be
nearly impossible to work with. Discontinuous rings and false rings are
common in Taxodium, and trees in some areas could not be crossdated at all.

In reading Fowells (1965), I see a reference to a study by Beaufait &
Nelson. They found that false rings were common in three second-growth
stands of Taxodium, and "conventional ring counts averaged 1.6 times the
actual age." Phipps states that "Correctly crossdated material produces
absolute dates for each ring...It is not possible to know how many missing
or multiple rings will be found in material of a given species in a given
habitat until a number of collections of material from an area have been

Locally, I have found that trees are usually not nearly as old as people
make them out to be. The immense southern red oak at Cedar Park was less
than 200 years old, not 350. The Wye Oak was probably 325, not 460. The
Liberty Tree was probably 375, not 600 plus. As a creator of stumps, I've
counted rings in chestnut oaks to 160, sour gum to 175, and a mockernut that
was 211. Judging from limb structure and bark contours, I believe a few
trees in Chase Creek Woods may be older, especially sour gum.

Of course, none of my ring counts were cross dated. It appears that we
should be aware that simple ring counts can be inaccurate - as inaccurate as
some of the claims for tree height. For that reason, we may want to be a
bit more cautious regarding some of the exceptional counts taken from black
gum, bald cypress, white cedar and other material.