Friday, September 23, 2016

A Lesson in Dendrochronology

Date published: 2016 September 23
Source material: 2016 August 19

          Dan has many old trees around his garden with signs detailing their estimated age along with a brief history of the tree and how he acquired it. The trees on display in his garden on the younger end of the age spectrum are mostly those he personally has grown from seed over the past 40-50 years. The vast majority of the rest of his trees are centuries old that he has collected from some rocky mountaintop or growth-inhibiting bog. Frankly, Dan has so many multi-centarian trees that the layman, who is not informed as to the extent of such available specimen in the US, often is suspicious that Dan overstates the age of his trees. The scrutiny of the masses is enough to make Dan be more conservative with his labeled ages. Despite that conservatism Dan's oldest tree is said to originate from 300 BC. As astounding as that is, he often tells me he suspects the tree to be a thousand years older, but does not label it as such because those without his knowledge and experience in forestry would think him guilty of gross exaggeration. There is a clear discrepancy between what the public is familiar with and what Dan is familiar with; this discrepancy is a major motivating factor behind Dan's collection and displaying of old deadwood snags in his garden because most people will never see these ancient artifacts of amazing trees in person anywhere else.
This is Dan's oldest tree in his garden, sometimes referred to as "Methuselah." I assume it was so-named after the man of the same name who was reported to live to 969 years old in the Hebrew Bible. Dan has kept this tree for years in its natural state - without any styling - out of respect for the 2000+-year-old tree as well as to show visitors something they might find in the wild. This photo was taken in early April of 2016, however, since then Dan has put some approach grafts of Shimpaku juniper foliage onto this tree. Rocky mountain juniper foliage reportedly does not do well in our wet PNW climate and that fact is the main suspected cause for the slow decline this tree's health has observed in recent years. 
        Dan has a background in forestry and a great skill for telling the stories of what happened to trees before he came across them. That being said, he still is limited to only estimating the age of his collected trees, as opposed to being able to elucidate their true age. There are only two methods to get a true age of a tree: 1) cut the tree down at the base and count the total rings, or 2) take a core sample of the tree by boring a hole through the center. These methods are both unsuitable for bonsai. The first method would kill the tree, and the second method is aesthetically unpleasing as it leaves a noticeable hole behind. Dan's alternative age estimation method is to take a cross-section of a large branch or root he has cut off from the tree of interest, sand and polish the cross-section, use various degrees of microscopy to find the average growth rate of the tree over some distance (sometimes with extremely slow growing trees, the rings are too close together to be counted unless via Scanning Electron Microscope (SEM), which can magnify up to 30,000x), and then (assuming the center is in tact and not eroded away) Dan will multiply the age/radial distance by the total radius of the tree's widest base area to get an estimate for the total age of the tree.
          It occurs to me now that in some cases, this method may be unreliable or have to be modified due to Andy Smith's trunk-hammer hypothesis. based on mimicking wild circumstances of a tree growing in a crack with no ability for lateral roots to stabilize against the wind (I hope to do my own hammer experiment in the coming years). The hypothesis states that - particularly for pine trees grown naturally in this condition, the wind will knock the tree around and the tree's only available method to stabilize itself is to lay down an extremely thick base of the trunk. For this reason, Andy (who's professional job is estimating the age of trees in South Dakota for the forest service) conducts his estimates a few inches above the base. I don't think Dan has run into this issue, as none of his collected pines that I can think of have the characteristically extreme taper that Andy has observed in this phenomenon. Anyways, I hope my distracting tangent was at least enjoyable if not productively enlightening as to these tree aging nuances.
          Since I am a "sciencey type of guy" (Dan's words), he enlisted me to help him estimate the age of a tree he recently used for a carving demonstration back in July for the Evergreen Bonsai Association. The tree was a Sierra Juniper that Dan collected from Nevada. Dan doesn't have his own SEM, but in the past, he has sent some samples to Weyerhaeuser, a local timber company, to use theirs to get estimates. I don't have one either, but through my connection to the University of Washington, I was hoping to gain access to one.
The product of Dan's July carving demonstration. Also the source of our branch cross-section (the branch used to be alive and supported a relatively large canopy). Unfortunately, at the time I did not have the foresight to take a complete before picture.
Aside from the carving, Dan has taken the styling of this tree very gradually. There's a branch he wants to reduce severely on the left, but he is concerned that the small amount of foliage that would remain would not be enough to sustain the small strip of live bark to that branch. His decision was to leave the rest of the styling for later while the foliage he wants to preserve grows and is bolstered in vigor.
Dan doesn't use lime sulfur solutions to bleach his deadwood; instead, he prefers to let the sun naturally do it. In a few years his freshly carved regions which currently show the different colors of the interior wood will become the gray-white color of the natural deadwood in the front, thanks to a process known as photobleaching. Photobleaching occurs as the pigments (molecules) which give the wood its color break down over time by exposure to the sun. The dead wood will not produce new pigments to replace damaged ones, and the white exterior color should be sustained thereafter.
"Bonsai Man Dan" is the nickname I've given Dan when talking to friends. Yes, I shamelessly Snapchat about my bonsai experiences to all my friends.
This is from the academic paper on SEM use in dendrochronology that I linked previously. Note the sample seems to have one or two rings per 400 MICROmeters. This converts roughly to 25 years per  radial centimeter, or 63 years per radial inch.
I lack access to a SEM, however, I do work in a lab with some other useful tools. I am trying to talk the university into letting me use one of their SEMs to recount this sample as well as for other trees Dan has worked on this past year that he wants to age.

          From an artistic standpoint, bonsai is more about the appearance of age than the tree's actual age of the tree. That being said, such ancient yamadori (naturally occurring) bonsai have great stories to tell through their many years of existence and that alone carries great weight to viewers.


  1. One thing that really intrigues me is how to estimate age of tree without observable damage.
    Dan's method can be unreliable since the age distance is greatly affected by the climate of that year ( good years have wider distance). The average growth rate which is estimated from branches only reflects the rate within a specific time period. That's to say, a tree with longer life span grew in a more unstable environment, this method is less convincing. However we are not doing science, this method is a good alternative.
    Besides, it's hard to tell the actual age of bonsai by naked eyes and the artificial sculpture would age the appearance of bonsai. Is it still important to know the "true age"?

    1. Yeah, it's an interesting problem. I have been working further with people at my school involved in SEM and dendrochronology on getting more data since this post and may offer a sequel someday.

      I have learned a few things lately: apparently roots are more variable than branches, and wild naturally stunted trees have more variability than average in the rings, but when talking about trees that are hundreds or thousands of hears old, the uncertainty margin is relatively low. I think it's not a necessity to know the true age of a tree that we collect, but it can add context to the tree's stories in my mind and makes for an interesting side detail aside from their natural or imposed design.