Saturday, September 27, 2014

Cutting up an old friend: the life and times of a suburban tree.

I'm back in the northeast for a bit. My parents had to have an old white oak (Quercus alba) removed from our yard, as it hung over the driveway and the house and dropped a big branch on my dad's car last year. The two trunks stood less than a meter from the driveway and it was shaded on one side by tall white pines (Pinus strobus), the other side by the house and sheltered an understory of pokeweed and poison ivy. Notably, in the mid-90's, I spent considerable time in a rickety treehouse between the two trunks. More recently, I'd watch migrant warblers in the spring and fall and chickadees, nuthatches and creepers in the fall on it - for awhile a suet feeder hung which we watched from the kitchen windows.

The author in the tree "house", 1993. The author is 5, the tree ~ 90.
I only know the history of the tree since ~1991 (and those early years, I don't actually remember). But the removal of the tree offered the opportunity to see its history. What had it seen? How old is it? Did the building of a house/driveway next to it cause it any harm? It was obvious from the start that this "tree" started as two individual oaks, which then joined (inosculated is apparently the correct term for this - see some striking examples here)

Days before its demise. 2014. 
Chainsaw marks had made reading the rings difficult, so I sanded a line on each side of the stump and tried to make out the rings.

In progress. The far right side of this photo actually is asphalt, though hidden under debris - the tree was only 

What I found, indicated that I needed to do more work. A set of really thin lines occurred in the early 1970's on one trunk and late 1970's on the other. So clearly I couldn't delineate them accurately. What caused those really lean years, I figured initially must have been the construction of the house and the building of the asphalt driveway practically on the tree.

Something is wrong here! Blow this up to see better. 
Therefore, my dad and I planed the whole stump (until the planer broke, ~50% done). This allowed us to also see clearly the junction of the two trees.

So what caused that big set of lean years, now correctly dated as 1976-1982? The house was built in 1982... the driveway a few years later - that certainly didn't cause the lean years as I had initially hypothesized. So what happened?

Now, a couple hours later, they line up!

Let's construct the history of the tree. Because the planer broke before I could get to the very center, I actually don't have good resolution the first couple years. The left trunk (father from the driveway), looks to have put down its first ring in ~1900, the other a few years later, ~1904. What was happening in Wrentham at that time? In 1870, Wrentham had 2202 people, 1900 - 2720 and 1910 - only 1748 people. I suspect that loss of populations corresponded with the degradation of farmland, and increased exports of agriculture from the great plains (at least this is what I remember from a New England environmental history course in college). A large dairy farm up the road - Birchwold Farm, now a great conservation area (best place to find black racers around Wrentham) - folded at about the same time.

Had the tree been paying attention to world events, it might have noticed these (a smattering of things I could think of
no rhyme or reason to them). 
So these trees took root - not a meter apart, in the first decade of the century or slightly before on what was likely fallow farmland reverting to mixed deciduous forest - what most of New England has gone through at one point or another. They then grew steadily through the next few decades until 1944-1946, when growth slowed to an inchworm's pace for both stems. Many factors could slow a tree's growth in this way including drought, this hurricane, an abnormally short growing season, an ice storm (leading to loss of healthy limbs), or insect outbreaks, to name but a few. Which ones contributed to this, I don't know, nor can I find any information on anything abnormal happening in that period (but do let me know if you do!).

The next big hit the trees took was in the late 1970's - 1980's. At first glance, the cause is obvious: the two trees hit. When this happened, they seem to have put much effort into wood building at the junction - perhaps as a form of competition - as the lines are quite wide at the junction, but get infinitesimally small around the other 3/4 of the trunk. This period is why I didn't get equal counts from the two trees. Even with a hand lens, I couldn't make out the lines accurately on the first area I sanded. In the center of the junction a crack is visible - this is where vascular tissue never grew, I suspect the soft material in the center is old, compacted outer layers of bark which had nowhere to go when the fusion happened around them.

A branch with some sort of rot - I presume fungal
But I suspect that is not the whole story. 1981 was the worst year for both trees - they put on pretty negligible growth even in the usually fat junction area. I suspect this was due to the worst ever infestation of gypsy moths, an invasive caterpillar which defoliated almost 13 million acres of oak and other deciduous trees in this area that year. Because these caterpillars can almost entirely defoliate a tree, that tree won't have much photosynthetic tissue that season and will suffer reduced growth, and if this repeats, as another invasive, the winter moth, often does, it can kill trees.

Since that time, the trees had been growing steadily... gaining a tree "house" in 1993 and losing a limb here or there in a storm, possibly pre-weakened branches because of fungal infection or physical injury.

Two days of this before the fun (the tree rings and research) began.
Now that my parent's house has a wood-burning stove, a tree will have to be taken out every year or so. Will that upset the ecology of the area? It probably won't have a huge effect, but it may midly benefit it by creating a rare microhabitat in the area. Because our neighborhood is suburban, most snags (dead trees) are removed quickly and probably not left on the ground. The stumps and leftover wood which could not be split and used as firewood will lie around, food for insects (perhaps horntails!) or fungi, which will of course attract other insects or birds and continue on up. And for curiousity's sake, the next tree will give us a better idea of what happened in 1944-1946 and the 1970's and 1980's. If we see that the 70's and 80's cruised by without a single hitch, the reduced growth in these trees is probably competitively-caused. If 1981 was a bad year for the new tree - gypsy moths are the likely culprit. If the whole period is bad for the other tree as well, then the microclimate may have been unfavorable. Perhaps before the house was built construction or other land use change occurred, which was unfavorable to the trees.

While it is a little sad to see an old friend go, it was necessary for safety of the house, cars and inhabitants, useful for heating, and the history was exciting and informative. Next time you see a tree down, check it out - much can be learned from it!