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.

-BDon

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..

Ed Frank

I like the "stacked cones" description, that works fairly well.

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