How to Visualize Tree Rings?
One of the forestry classes I took at Humboldt State U. prepared
me well, to answer your question...it was called Stem Analysis
(pretty dry title, prof was lucky to get anyone to sign up!). Great
class! I think there were 4 groups of four students...we each went
out and cut down an entire tree (about 5-6" dbh, a white fir, I
think). We brought them back into our lab...using a chain saw, we
cut 'cookies' out of the 20+ foot tall tree at every growth node,
and mid-way between grown nodes. We planed a face of each cookie and
then counted the number of growth rings.
To make a long story shorter, we ended up with the visualization of
a tree as a series of embedded cones (conical 'cylinders' or
'pyramids', if you will). With white fir, in our neck of the woods,
that meant that each cone (growth ring) was about a foot taller than
the one that grew inside of it. Sure enough, each whorl of limbs
represented a new years growth, and on average were about a foot
above the previous one.
As a general rule (barring all kinds of natural events like deer
browse, etc.), it took the average white fir 6-7 years to grow to a
height where a dbh could be taken. To be conservative we'd add seven
years to whatever increment coring we got at breast height. If that
white fir had damage sufficient to cause it to fork at breast
height, but not set the growth back, then that fork started
developing 'conical cylinders' at year 7, and 'subsequent growth
years' or 'conical cylinders' or as seen by an increment core,
'growth rings' would add to that.
For deciduous trees, I suspect it varies alot from species to
species, and site to site on how long it takes a tree to get to
breast height. But in general, the same conical cylinder scenario
would play out.
The limbs have rings also. The center of the limb - the zero
point - is the point at which the limb sprouted. Large lower limbs
are younger than the tree itself, but do from the time they sprouted
have annual rings. So the difference in the age shown by the limb
and the age of the tree is simply the time between the sprouting of
the tree and the start of growth of the branch. Many trees develop
hollow trunks. The center protin of the tree is missing so a good
age can't be determined by ring counts/ coring. Lower limbs on the
otherhand may still be solid. These are not as old as the trunk
itself, but may have counts greater than those you can get from the
hollow portion of the trunk. Depending on the species and height of
teh limb, the count from a fat low branching limb may be ten years
or less different from the total age of the tree.
if you look at old wolf trees in some species, ones that grew in the
open before being surrounded by younger forest trees, yu will often
see the dead banches forming a ring around the trunk every few feet
up the trunk. These collars of limbs represent the amount of annual
growth of the tree. Each spring a new set of branches would be put
out at the new tree height and form another collar. So by counting
the branch collars f present you can get some idea of the age of the
tree prior to the sprouting of a lower level branch..
I like the "stacked cones" description, that works
It is pretty incredible when you realize that about 97% of a redwood
tree is "dead" at the cellular level and yet at the
organism level the "system" is alive. The cambium couldn't
live on its own without the rest of the tree.
There are many analogies here, all the way from our own bodies to
the biosphere, which according to the Gaia Theory says that the
biosphere is a living SYSTEM. Whether or not certain components of
the biosphere are "alive" or "living" becomes a
matter of definitions and application of systems theory. Also
whether one is driven by reductionism or systems theory.
Gary A. Beluzo