On 01/06/2016 9:34 AM, dpb wrote:
....

The US FPL Wood Handbook --
http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=100


See chap 3 for botany lessons. Short version is, in temperate climates
such as most of the US, there is an annual growth and dormant season and
so the growth rings can be associated with that yearly cycle. How
prevalent they are is basically determined by the variety of the tree
itself, spacing is related to environmental and local conditions. But it
makes note that this is a temperate-zone characteristic and so to refer
them as "annual rings" isn't necessarily accurate; use the term "growth
rings" or "growth increment" instead.

OTOH, in many tropical woods it's essentially impossible to visually
detect growth rings altho I note in the 2010 edition it includes the
following: "... continuing research in this area has uncovered several
characteristics whereby growth rings can be correlated with seasonality
changes in some tropical species (Worbes 1995, 1999; Callado and others
2001)."
....

First sentence 2nd paragraph is garbled -- I changed horses in
midsentence on what was planning on writing and didn't get all the first
outta' there that shoulda' been --

What was intended to say was impossible had to to with associating
growth rings with a necessarily annual cycle in tropical regions, not
that the growth increments are not visible.

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