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Tree stems contract and expand as stem water is depleted and replaced. Band
dendrometer studies suggest that such daily changes are small (<0.2 mm diameter),
and they are ignored in most growth measurements. However, several studies using
other approaches note larger changes (even >1 cm diameter), suggesting that
significant biases are possible. An exploratory study examined the pattern and
magnitude of daily stem changes and whether commercial band-dendrometers were
able to reveal them. A method involving multiple precision measurements on eight trees
in a Bornean hill dipterocarp forest revealed daily shrinkage and expansion of girth of
around 1 mm. Fluctuations were greater in bright weather. Band-dendrometers detected
these changes but revealed less than a tenth of their magnitude. An analytical model
for dendrometer error is presented that predicts how measurement biases can be
reduced. Tropical trees can fluctuate appreciably in stem diameter over the day. These
reversible changes are of sufficient magnitude to merit concern in growth studies.
Influential biases seem especially likely when measurement intervals are short and
involve systematic differences in timing and weather. Further study is required to gauge
the more general influence of these measurement problems.