The study of annual growth rings on
trees for dating the recent geological past. This field is closely
related to dendroclimatology, which is the study of the sizes
and relative patterns of tree growth rings to yield information
about past climates. Tree rings are most clearly developed in
species from temperate forests but not well formed in tropical
regions where seasonal fluctuations are not as great. Most
annual tree rings consist of two parts—early wood, consisting
of widely spaced thin-walled cells, followed by late wood,
consisting of thinly-spaced thick-walled cells. The changes in
relative width and density of the rings for an individual
species are related to changes in climate such as soil moisture,
sunlight, precipitation, and temperature, and they will also
reflect unusual events such as fires or severe drought stress.
The longest dendrochronology record goes back 9,000
years, using species such as the bristlecone pine, found in the
southwestern United States, and oak and spruce species from
Europe. To extend the record from a particular tree, it is
possible to correlate rings between individuals that lived at
different times in the same microenvironment close to the
same location.
See also PALEOCLIMATOLOGY.
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