Since there has been a huge amount of interest in Steve McIntyre’s recent discovery of what happens to the “hockey stick” when all of the Yamal tree ring data is used rather than a special subset of 10, I thought it might be a good time to talk about how tree rings are grown.
Several readers have correctly pointed out that trees don’t respond just to temperature. The also respond to available water, available nutrients in soil, and available sunlight. For example, the only time in modern history where some trees did not produce summer growth rings occurred in the year 1816, also known as the Year Without a Summer:
Many consider the Year Without a Summer to have been caused by a combination of a historic low in solar activity (The Dalton Minimum) and a volcanic winter event; such as the powerful Mount Tambora eruption in 1815 which had four times the power of the famous Krakatoa eruption and hurled huge amounts of aerosols into the atmosphere.
Obviously, sunlight was a limiting factor for tree growth then, reduced temperature also figured in.
I touched on the idea of trees used for dendroclimatology being rain gauges before: Bristlecone Pines: Treemometers or rain gauges ? There has obviously been years of drought when trees also did not grow as much, so how do we separate temperature and moisture in the growth analysis?
But, right now what I really want to introduce readers to is Leibig’s Barrel.
While I don’t like to use Wikipedia that much, this page doesn’t seem to be controversial so appears safe enough:
Liebig’s Law of the Minimum, often simply called Liebig’s Law or the Law of the Minimum, is a principle developed in agricultural science by Carl Sprengel (1828) and later popularized by Justus von Liebig.
It states that growth is controlled not by the total of resources available, but by the scarcest resource (limiting factor). This concept was originally applied to plant or crop growth, where it was found that increasing the amount of plentiful nutrients did not increase plant growth. Only by increasing the amount of the limiting nutrient (the one most scarce in relation to “need”) was the growth of a plant or crop improved.This principle can be summed up in the aphorism, “The availability of the most abundant nutrient in the soil is as available as the availability of the least abundant nutrient in the soil.”
Liebig used the image of a barrel—now called Liebig’s barrel—to explain his law. Just as the capacity of a barrel with staves of unequal length is limited by the shortest stave, so a plant’s growth is limited by the nutrient in shortest supply.
Liebig’s Law has been extended to biological populations (and is commonly used in ecosystem models). For example, the growth of an organism such as a plant may be dependent on a number of different factors, such as sunlight or mineral nutrients (e.g. nitrate or phosphate). The availability of these may vary, such that at any given time one is more limiting than the others. Liebig’s Law states that growth only occurs at the rate permitted by the most limiting. For instance, in the equation below, the growth of population O is a function of the minimum of three Michaelis-Menten terms representing limitation by factors I, N and P.
It is limited to a situation where there are steady state conditions, and factor interactions are tightly controlled.
In the book: Forest dynamics: an ecological model, 1993, Oxford University Press, By Daniel B. Botkin the relationship between all of the different growth factors is modeled per Liebigs Law. In Chapter 3, page 64 the author talks about Liebigs Law and how it operates on forest populations. He then goes no to describe a model of forest growth.
Page 65 has a very interesting passage which I’ve highlighted:
For our readers reference, JABOWA is his forest modeling software, now in version 3 which you can read about here and download a free trial. It was designed for a specific region, the Northeastern United States. From JABOWA another similar forest growth simulator FORET was derived, which has been adapted for modeling diverse forests of the southern United States. Obviously modeling different forest regions requires specific model programming.
The point I’m making with all this is: If “the total growth response of a tree is the product of all environmental factors”, and forest modelers have to separate temperature and precipitation diameter increments, plus create different models for different forest regions, how can then one accurately divine temperature over millenia from width analysis of tree ring growth from trees in a single region?
The task is huge.
It seems to me that temperature is intertwined with so many other factors that it can’t easily be separated without at least knowing how they also changed over time. Further on in the book the author goes on to talk about other limiting growth factors, such as soil moisture, available light, nutrients etc, but a couple of pages, 71 and 72, really described how temperature (as degree days) is figured into forest growth estimates. I was surprised to see that photosynthesis is not linear with temperature, but parabolic! I’ve excerpted the pages below.
Another interesting thing I learned was that to accurately gauge forest growth, you should have nearby weather records. Missing that, you can estimate the temperature profile from January and July average temperatures. OK but how do you do that for 200, 500, or 1000 years ago?
Barring having any temperature information from the region at all, the possibility exists for doing lab growth experiments, though I don’t recall seeing anything about that in MBH98 or similar papers.
I make no claims of being an expert in either forest growth or dendroclimatology. I’m simply presenting interesting information here for discussion.
But, I am amazed at the nonlinearity and interactivity of all limiting growth factors, and especially the parabolic response to temperature.
Thus in my opinion, it seems rather difficult to estimate forest growth when parameters are known, and even then the outcome is uncertain.
Imagine trying to reverse engineer temperature from forest growth (using tree rings) with all of the simultaneously acting growth factors, population density and shade limiting, the parabolic response curves, and you realize that divining the temperature out of trees over millenia is a very difficult, nonlinear, and uncertain task.
If you see a wide tree ring, you can safely conclude the tree had a good year. If you see narrow rings you can conclude a poor growth year. But was that poor year a product of an unfavorable temperature range alone? Or was it due to lack of moisture or lack of sunlight or both? Not having local records for those, how would you know?
It seems to me that dendroclimatology has a lot of uncertainty.
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“I have to agree with many commenters here. The big missing link here is how does CO2 increases change tree growth?”
It’s an interesting question. Actually, the Graybill North American series that was used by Mann and that was so heavily weighted by Mann was actually produced by Graybill to investigate the effect of CO2 fertilizing. Graybill got what he was looking for (although it looks like he also cherry picked his data) – CO2 fertilization; and Mann got what he was looking for out of the same data. Except that Mann interpreted it as temperature increase.
Nevertheless, CO2 does seem to have a fertilizer effect on most plants. It also makes many of them more drought resistant. In theory, this should mean that trees could grow better with less water. And the bristlecone pines that were used live in an area that is very water limited.
Though ‘irony’ might be the wrong word…
I know of a place where one can study 500+ year old tress, right now, today. New Zealand. Kauri and Totora trees are natives (So too are Pohutukawa trees, though I don’t think they live anyway near as long).
Tane Mahuta (The Father of the Forest) is supposed to be upto 2500 years old, with a trunk girth of 13m. It’s a remarkalble tree, and site, and scared to Maori. It is also interesting that most of the Kauri forest was plundered long ago in the 19th century, but some, very young trees still survive and are being preserved.
Totara trees mature in about 250-500 years, and “my” tree just north of Wellington will jsut about it’s teen by the time I snuff it!
I recall from a trip to the region that there are examples of “swamp” Kauri which is supposed to be 4-5million years old. There are also examples of these trees recording the great Lake Taupo erruption (Soot etc). Anyone in that part of New Zealand should go.
Quote: MDR (22:54:56) :
“…Granted, not everything is correlated, but if groupings of variables can be shown to be largely dependent, then it seems to me that one may in fact be able to learn something about longer-term trends in the weather from the historical tree-ring record.”
Reply: Don’t agree. Some time ago I dabbled in hydroponics and to maximise growth the list of things which have to be right is legion. In addition to the well known macro factors which influence growth, minor factors like the balance of trace elements and the amount of light play a big part – even the wavelength of light can effect growth.
I also found that within a population of plants all growing under the same conditions, the rates of growth were not the same. Some did very well, while others didn’t – used to drive me mad.
So I don’t think using a few trees from a few areas can give any useful information about temperature, and will at best only give a very broad and unquantifiable indication about climate, even when well calibrated to actual climate conditions.
steven mosher (22:05:59) :
made up oct 13 2007 on CA thread.
http://www.climateaudit.org/?p=2183#comment-147933
hehe. Back then my hair was on fire.
Nice rant, I ran out of breath just reading it, did you pass out after writing it? :o)
Cheers
Mark
Trees both individually and in forests tend to alter temperature towards their own optimum, and as this study shows, individual leaves control their own temperature,
http://www.sciencecentric.com/news/article.php?q=08061131
which means as the article says that a reappraisal of proxy temperatures from tree cores is required.
Jim B in Canada, CO2science.org has much information on CO2’s effect on plant and tree mass production, from memory it is as high as 40% for some species.
Michael, somewhere recently a study found that trees communicated a fungus threat ahead of its spread and altered resistance to it favourably, if I can find it again I’ll post URL
So if I understand this correctly;
(apologetically being very simple about this)
A thick ring denotes an optimal year for growth.
A thin ring denotes a lack of one or more “nutrients, etc.” (delivered at the desired steady state I assume), including but not limited to;
a. Water
b. Sunlight (which could be degraded by dust or cloud)
c. Ground based nutrients
d. Air based nutrients (CO2)
e. Optimum ambient temperature
f. Temporary presence of “poisons” such as sea-salt. (I understand that un-harvested lemons if left lying on the ground around the tree will be detrimental to the lemon tree.)
So a thick ring probably denotes a warm year. A thin ring could be caused a number of reasons including low temperature but could it also be caused by excessive ambient temperature ?
As I understand the first quoted passage from Botkin’s book, after briefly describing Liebig’s law and explaining how it would be applied to tree growth, the remainder of the discussion casts that law aside as being incorrect and instead argues that the most constrained nutrient in fact does not limit the rate at which a tree grows due to an increase in other variables. Rather, the partial derivative of tree growth per season with respect to each variable is posited to be independent of the others.
On intuition, I would guess that neither approach is strictly correct. The partial derivative with respect to each nutrient is also likely a function of the amount available of other nutrients (i.e. nutrients do not act independently as modeled by Botkin) but there would not be a point where increasing any one nutrient while holding the others constant would not produce any tree growth (not strictly Liebig’s law either). That’s just a hunch, though.
Regardless, the conclusion of the post is accurate. Whether a tree grows according to Botkin’s model or Liebig’s law, trying to correlate the net growth in a season to any one of the influencing factors seems nearly impossible unless you know the state of all other factors except what you are trying to correlate.
Bill Sticker and Roger Sowell point to two additional non-linearities that to my mind will absolutely have to be taken into account; i.e the radial variation in ring thickness on the same tree caused by all sorts of temporal factors such as wind, proximity to other trees, and so on.
If these assymetries in the same tree are not somehow averaged out, then the dendro-information of one core cannot be of any significance. For example the SAME tree will produce wildly different cores. It also seems an impossible task to do the averaging without taking a complete set of radial cores all round the trunk … i.e. to cut it down … even for the ‘perfect specimen’ … else how do you know there are no radial assymetries.
Personally, I am amazed that the whole Climate Chage/Carbon thing is reliant on this somewhat wispy science. (I would prefer it were called Dendro-haruspication.)
you forgot to mention that co2 also effects plant growth and we only know what co2 did historically at the poles.
If a tree is fighting for light than the surrounding trees disapear the tree ring growth can increase significantly as it is no longer limited in growth. Just an example of how an unknown event could create a hocky stick when temps remain consistant which could misconstrued by a climatologist
I think Anthony is being very polite.
It strikes me that trees just cannot be used for temperature reconstructions and that an attempt to do so is … well never mind.
But that then brings me to a question.
Has anyone published a multi proxy temperature reconstruction that specifically excluded TreeMometers.
Plants do send chemical signals to each other when under insect, and other, attack. As for rainfall and trees, that seems to me to apply in areas where rainfall is linked to convection air currents, less so where rainfall is dominated by the interation of cold and warm fronts.
Chemical signalling in plants:
http://www.physorg.com/tags/chemical+signal/
http://www.uky.edu/~garose/link100.htm
http://www.nature.com/nature/journal/v410/n6828/full/410530a0.html
I just want to thank you so much for this website and the discussion it prompts. I am not a scientist and sometimes I really struggle to follow the information and the arguements, but just because it’s hard to understand does not mean that we shouldn’t try. Without people like you, most of us ordinary bods would be totally at the mercy of the spin doctors and pseudo-scientists, who treat us like sheep.
So keep up the good work!
Re
Tilo (23:36:12) :
“Nevertheless, CO2 does seem to have a fertilizer effect on most plants. It also makes many of them more drought resistant. In theory, this should mean that trees could grow better with less water.”
This is an interesting comment relative to the increase in woody vegetation cover in semi-arid and arid rangelands, as e.g outlined in:-
http://www.snr.arizona.edu/people/archer
Steve has an on-line bibliography of this, but I need an updated contact for it
Really good post this. I need to read it all properly later. The “liebig barrel” effect was a new one on me. That’s an interesting take on things.
It’s always been obvious to me (and many others) that tree ring growth could not be used as a direct proxy for temperature. At best, the data might indicate the temperature ‘contribution’ to ring growth. This would explain the lack of variability in tree-ring based climate reconstructions (e.g. MBH), and why Briffa (2000) and Cook (2004??) found that tree rings significantly under-estimated warming in the late 20th century.
See here
http://www.ncdc.noaa.gov/paleo/pubs/briffa2001/plate3.gif
Note the divergence in the late 20th century. In fact the only time there is any agreement with observations is during the calibration period (~1900 to ~1980). Before that, in the mid 19th century, observations and proxies are actually heading in different directions.
This means one of 2 things, i.e.
1. The late 20th century (& mid 19th century) record is wrong (I don’t think it is)
2. Tree-mometers are junk.
anna v (23:29:21) :
What about this?
http://www.nature.com/news/2008/080611/full/news.2008.884.html
J Braggins (00:14:21) :
Trees both individually and in forests tend to alter temperature towards their own optimum, and as this study shows, individual leaves control their own temperature,
http://www.sciencecentric.com/news/article.php?q=08061131
I’ve had a minor fascination with this paper since I first became aware of it through a post here, back when it was published. It seemed at the time to be a veritable stake through the heart of tree ring temp proxies, since if a tree’s only active interface with the atmospheric environment was maintaining itself within a much narrower range than the ambient temperature there would seem to be no conceivable means for the tree to record anything meaningful about that temp. Since, by the time the paper appeared, the extent that Mann’s hockey stick had incestuously and pervasively spread it’s tentacle’s throughout the IPCC’s entire AGW hypothesis had become apparent, it also seemed to be at least a potential contradiction of the whole concept. Given the potentially momentous quality of its hypothesis I fully expected the publication to generate at least a minor firestorm of controversy. Instead, if you Google “tree leaves maintain own temperature” or some variation what you find is several dozen cites of the paper which all appeared within about a week or so of its publication, then, if you venture down through the other 350,000 hits that come up, there is nada. At least for the couple of thousand cites on Bonsai culture and Peach orchard maintenance that I’ve had the patience to review. I’ve found this incredibly curious and really had a hard time accounting for the resounding indifference to something I perceived to have such significance. Then the other day as I was looking for a link to post in a comment on the QOTW thread, I stopped to reread the press release that UP had put out to announce the paper’s publication and a possible scenario presented itself. http://www.upenn.edu/pennnews/article.php?id=1404
If you read the release, after several more or less objective paragraphs describing the methods and results of the study, you come to this paragraph
The study also presents a new hypothesis for why certain trees grow in certain climates and provides a new theory for how and why trees in the north will suffer from global warming, by overheating due to the mechanisms they have evolved to keep their leaves warm.
which obviously provides the GW spin folks were meant to draw from this work, since it’s a couple more paragraphs before this appears
Researchers at Penn, using measures of oxygen isotopes and current climate, determined a way to estimate leaf temperature in living trees and as a consequence showed this assumption to be incorrect. This is an unfortunate finding for the potential to reconstruct climate through tree-ring isotope analysis but a boon to ecologists because it creates potential for the reconstruction of tree responses to both average climate and climate change over the last couple of centuries.
Your “Where’s Waldo” assignment for today is to locate the buried lede in that para.
I admit that the scenario I now present is mere paranoid conspiratorial speculation, but see what you think.
As I see it, as reports of the dozens of citations come in, the folks at UPenn are momentarily excited by the interest their little paper is generating, but excitement quickly turns to chagrin as they come to realize that everyone has glided seamlessly by their intended spin and latched like ticks on a coon hound on their buried lede. I see the poor unsuspecting biology professor and his doctoral candidate assistant, who produced the work, summoned before their superiors and told Speaking of This in the Future is Unwarranted. I admit I have absolutely no evidence for any of this, but as the alarmists always say when discussing CO2 as the sole cause of everything, “What else could it be?”
Have any studies been done taking 10 cores from the same tree on different sides at different heights then examining the spread in the ‘temperature record’ from one tree to get an idea of error bars??
Nice summary post. I agree with the thrust of the post — having looked into it myself.
I think one cannot develop accurate global temperature anomalies from tree rings. Heck, I seriously doubt it can be done with the historical thermometer data — at least not accurately enough to support AGW claims and trillion dollar taxes.
Steven Mosher, I liked the Pilttdown Mann.
But then skeptics are just Neanderthal.
But tis better to be a Homo neanderthalensis than an Eoanthropus dawsoni.
Don’t forget that trees also respond to competition for light (especially here in Australia). In such cases factoring out that competition will be impossible for reconstructions. Also eucalypts are notoriously impossible to age via growth rings as they are adventitious species i.e. they do not put down annual rings, rather they grow when conditionas are suitable.
Tilo … in order for a plant to process more co2 it needs more water:
6CO2 + 6H2O + Energy ® C6H12O6 + 6O2
This whole tree ring, hockey stick, climate scam is ripe for the picking (cherries included). All it needs is one well written MSM article.
I challenge any forward thinking (go get em) journalist to cover this story. Period!
What I find really interesting, is that despite all these climate variables acting ins multi-faceted ways, the Mannian’s still come out with an unchanging proxy over a thousand years.
Really weird.
Nic … you could add insect defoliants, parasites, disease, herbivores and competition etc. to your list.
When I bought the house at my present location 8 years ago, there was a small tangerine tree in the front yard. It was not well cared for, thin, not very healthy and only produced small amounts of fruit which was bitter. I cleared the weeds from around the base and started using the proper combination of fertilizer and water. The tree has responded over the years with increased growth and fruit bearing. I also stressed the tree by trimming it back slightly each year causing increased fruit production. Now the tree is large and healthy and I have a bumper crop of fruit. All this happened without change in average annual temperature. If one were to check the tree rings years from would they conclude that there was a temperature step increase in 2001?