Trees – As Thermometer Or As Sun Gauge?

I have 2 California Bay Laurel trees ( or Oregon Myrtle… same tree different names) that volunteered in the back yard a few years back (about 2014 or maybe a bit earlier). They are roughly on a line from North East to South West. This means that the one NE gets a bit of morning sun (but that is partly blocked by a fence and a neighbors tall bush) then is shaded into the afternoon.

The result as been that the tree “up sun” is much larger while the one shaded is not so big. They will have the same number of growth rings as they arrived at the same time…

So IF you came back in 400 years and looked at the growth rings of the smaller one (assuming some catastrophe befell the larger, like me about to remove it…) and looked at the growth rings, it would look like the first decade of it’s life was “terribly cold” IF you presume the rings measure temperature. Yet they both have had the same rain, the same fertile soil, the same climate and weather. The only thing different is one shades the other.

In natural forests, there are always some trees shading others, and there are always old trees falling over and letting sun get to the struggling ones. On that grounds alone tree rings as an indicator of temperature are highly suspect.

Here’s a photo looking more or less into the morning sun, at about 9 AM. The 1/2 cinder block is there as a size reference.

Two Same Age Calif. Bay Laurels – One shades the other

So what does one tree in Yamal tell us? Not much…

The larger tree has now started putting limbs in front of the smaller one to capture even the morning sun. These trees can grow to about 80 cm trunk size and 30 M tall so eventually the faster tree will completely shade the smaller one, that is now runted and acting like a shrub in the shade.

As I don’t have room for 2 x 30 M trees (about 100 feet tall and 2.5 foot diameter trunks) I’ve decided they both need to be removed. When they first “volunteered” I didn’t know what they were, only later finding out. They have medicinal properties and a very interesting clove like fragrance, so I let them grow. Then spent a couple of years on contract in Florida and came back to “minor trees”… The bigger one is presently about 10 M / 30 feet tall and would likely add another 5 to 10 feet this summer if I let it grow. I’ve decided that, as much as I like the things this tree can provide in the way of medicinals and pest control, it’s gotta go. Otherwise I’ll have a “1 tree yard” and no garden to speak of.

The good news is that it has shaded out a big enough area that I’ll have some clear garden space again once it is down ;-)

After they are down, I’ll take close up photos of the stumps (hopefully the rings will be clear even with a Sven Saw cut) and add them here. That will be a few days (today was triage of the space, decisions, and pruning some other overgrowth.)

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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8 Responses to Trees – As Thermometer Or As Sun Gauge?

  1. Bill in Oz says:

    This observation about trees growth rings being effected by shading by adjoining trees is an important one.

    It makes the whole idea of estimating temperature from growth rings unviable. In other words poor & shonky science.

    But maybe that is to be expected as one of the pioneers of this ‘technique’ was some silly bugger named Mann ?

  2. H.R. says:

    wOw! Great to see the pictures of those trees, E.M. You described the situation a week or two ago, but those trees are waaay bigger than I gathered from you describing them as only a few or 5 or so years old.

    That is some serious growth compared to anything around my neck of the woods. Closest thing we’d have that grows fast is Silver Maple, and I still don’t think a Silver Maple would keep up with your tree.
    Learning about Liebig’s Law of The Minimum several years ago disabused me of the notion that tree rings were good for anything but telling how old a tree is.

  3. oldbrew says:

    So what does one tree in Yamal tell us? Not much…

    Indeed. An average from a ‘significant’ (insert definition here) sample is a minimum requirement.

  4. Gary says:

    Most of the trees used in climate research are fairly isolated so shading isn’t a problem. And it’s relative ring size in the same tree that indicates slow and fast growth periods. Data are standardized so multiple trees can be averaged. Age of tree also makes a difference and formulae have been developed to account for it.

    That said, trees can’t tell temperature very well because too many other factors contribute to growth — rainfall, nutrient regime, insect and other chewers, physical damage, etc.

  5. E.M.Smith says:


    That “fairly isolated” is exactly the problem. Fairly isolated now but what about 300 years ago? You just do not know if some other tree, older and nearing EOL or just the same age but unlucky in a fire, was then suddenly gone leaving your tree “fairly isolated”.

    Then, you are looking at relative sizes of rings in the same tree that vary in size as it starts growing big fat ones in all that sun.

    Averaging is good, sort of. It does take out the “one shaded tree” problem, but what happens when a forest fire runs through, lots of young ones start, then slowly die off as some grow faster than others and shade them out or rainfall changes in a cycle and the more shallow rooted die. now you have a set of fat rings at the start, then small as competition hits and water is scarce, then large again when rains return and the survivors are the best competitors. You are measuring rain and competition more than temperature.

    I’m not saying it is impossible to see temperature effects in tree rings; I’m saying it is fraught with confounders and perils and that “one tree in Yamal” is “exactly wrong” in terms of how to do it.

    The basic problem is that you don’t know what happened to the rest of the context of that tree over the history of the place.

    I think of it as “The bear shat in the woods where?” problem.

    Recently it was figured out that bears shit in the woods on or near their “favorite tree” after eating a lot of salmon. This delivers a load of nitrogen to said tree and it grows very well.

    Now what happens when that bear dies off (hunter, other bears, old age, new territory) and some other bear chooses some other “favorite tree”? Eh? How do you know which tree was the favorite of a bear and when?

    I can see a way to test for that using isotope ratios (sea critters have slightly different ratios of some things so a minor undertone of that will end up in the tree) but does anybody DO that? And is it enough to work?

    BTW, we’ve hunted out most of the bears and fished out as much of the salmon as possible so right now, over the entire PNW region (where this was ‘discovered’) the average forest nitrogen is way lower than it was before we got here with guns and trawlers. That ought to show up in the average tree rings being smaller from low nitrogen. This signal will be blended with the drought cycle signal of larger and smaller (we have cyclical rainfall patterns). Then we also have CO2 fertilization pushing the other way, to faster growth. Just where in that set of confounders will the temperaure signal stand out?…

    So my little back yard experiment has controlled for same water, same air temperature, same CO2, same lifetime, same soil and soil fertility, same… Just the relative positions to the sun are different. And growth is dramatically different.

    Hmmm…. Maybe I ought to just cut down the big one, let the little one grow another year or two THEN cut it down and show how “relative growth ring size” expands when the competitor dies off… Will I be here long enough for it to show? Do I want to keep one of the trees that long?

  6. cdquarles says:

    That’s right. All tree rings tell you, relative to the quadratic growth curve, is how close to optimal any particular year was; given a dozen (more) major contributory factors, of which any one may have be the limiter that particular year. Then there are years where you get ‘double’ rings, because there was a period of stress inside of a year with good conditions either side of it.

  7. Bill in Oz says:

    E M Thanks for the comments about trees and all the confounding factors for tree rings..Very clear & to the point.

    Pretty clear to me that using tree rings as a measure of temperature is just dopey non science.

  8. Gary says:


    I should have been clearer. The ancient, slow-growing trees are the target and they tend to live in marginal areas (mountain top, arctic tree line) where their distribution is sparse (many feet between individuals). We trust (yeah, I know, but what can you do?) that researchers avoid obvious contaminants such as shading and special fertilization. Steve McIntyre found that sampling of strip-bark bristlecone pines might have ignored mechanical stress responses, so not everything gets caught. Tree-ring analysis started out as dendro-chronology where timbers in ancient structures such as the abandoned southwest pueblos and European buildings could be dated by matching ring patters to standard chronologies for the region derived from living and fossil trees. It was quite useful for that purpose. Then I suspect someone got to wondering about the the causes for deviations, speculated, and opened the floodgates for non-biologists (I blame physicists) to run with the false premise that all trees everywhere predominantly record a temperature signal.

    As for your experiment, I say go for it if it doesn’t impact the shading you desire.

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