I’ve been starting to dismantle the fallen oak that I wrote about a few days ago. I’m pretty certain that it’s a Northern Red Oak (Quercus rubra) but need to look at it a little closer to be sure.

UPDATE - Glenn confirmed it.

I haven’t yet gotten out the chainsaw to cut through the trunk closer to what used to be the ground, but I have cut through a tertiary and secondary branch to look at the tree rings. The saw marks the secondary branch cut:


The tertiary branches, already sawed, are about 3.6" diameter, and the secondary branch is about 5.8" diameter. Here’s the tertiary branch; it seems to be about 28 years old:


I did a little dendrochronology on this thinner branch, but decided to go for the thicker one. One relevant piece of information that I’ll refer to below is that the thinner branch has about 24 annual rings per inch, or 1mm per ring, and the thicker branch below has about 14 annual rings per inch, or 1.8 mm per ring. Strangely to me, the lower thicker branches grow faster than the upper thinner ones. Here we’re at 36 years old.


This branch shows many of the characteristics that you note in a woodcut. You first notice the lighter colored cylinder of wood around the darker core. The lighter is called sapwood, and the inner is heartwood. The branch converts xylem (because that’s what wood is, xylem - pulling water up the tree to hydrate the leaves) into heartwood for storage of organic materials, and the cutoff here seems to be about 1997. Younger xylem is sapwood; older xylem is heartwood. Glenn says the heartwood smells wonderful.

The second thing you might notice is that the rings are not fully symmetric; they might bulge outward on one side or inward. Tighter rings on one side show that that side is under mechanical stress, perhaps the bottom of the branch supporting more of the weight of the branch than the opposite side. This is tension wood. The relative sizes of the rings stay the same though.

The third thing you notice (or maybe it’s the first thing - but it’s the third thing I *want* you to notice) is the light and dark rings. The light rings, which are thinner, are supposed to be springwood, or earlywood. The cells here grow in the springtime when water is plentiful and temperatures are benign. The cells are large and have thin walls, giving the light color. As temperatures increase in the summer, and water becomes less abundant, the next set of cells are smaller with thick walls, dark fiber, and appear darker in color. This band of dark ring is summerwood, or latewood. This constitutes an annual ring; alternating light and dark.

Here’s how it works. The first panel below shows a three-year-old branch. The green layer on the outside is the vascular cambium. This is the meristematic tissue that makes trees get bigger around. It’s called bifacial, because it produces two types of cells; xylem toward the center, which is the wood; and phloem on the outside. Phloem is living tissue which carries sugar to all parts of the tree (I’ve omitted the phloem here - it’s doesn’t produce substantial rings; it gets crushed by the expanding xylem every year and has to be renewed).

The second panel shows that the springwood has been laid down, pushing the vascular cambium outward. The third panel shows that the darker summerwood gets laid down later in the summer. The last panel shows that in the following year a new layer of springwood will be laid down, and you get those nice alternating ring patterns.


Here’s a cutaway of the older secondary branch, with the left side the youngest and the center on the right side. I’ve numbered the years and measured both the light and dark ring widths. This branch started in 1969; it was 36 years old when the tree fell.


And here I’ve plotted the numbers for springwood and summerwood:


A few interesting things that I’ll get more into later, perhaps. First, the linear rate of growth of summerwood slows down as the branch ages, although the correlation coefficient is pretty low. Nonetheless there are years in which late summergrowth can be as extensive as in earlier summergrowth. The annual springwood growth, on the other hand, is pretty constant over the 36 years, although there’s still a lot of variation. I suspect that the growth of the summerwood doesn’t actually decrease with age so much as that our summer temperatures have been getting warmer in the last 36 years, and warmer temperatures means more stress and less growth in the summer.

Take a look at 1983-1984: Very little summerwood growth that year, although springwood growth was considerable. 1982-1983 was the most intense El Nino every recorded, and it was followed by a La Nina in which we tend to have drought here.

Here’s the trunk itself:


It measures 73" around at approximately “breast height”. That’s roughly a diameter of 24". If we go by the secondary branch annual ring width of 1.8mm per ring, (and this may be an incorrect assumption) it suggests that the tree was about 160 years old.

One thing that falls out from that kind of age is that the creek and surrounding bank that this tree grew near has been at about the same level for over a century. I had assumed much of the carving out had been done relatively recently, perhaps even by cotton farmers, but our long hollow may actually be quite old.

Gotta get out that chainsaw!