A look at treemometers and tree ring growth

peanuts_treemometerSince 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.”

Leibigs_barrel

Liebig's barrel - The growth potential of a plant or tree is like a barrel with staves of unequal length. Each stave might represent different factors; light, water, nutrients. The capacity of the barrel is limited by the length of the shortest stave (in this case, water), and can only be increased by lengthening that stave. When that stave is lengthened, another becomes the limiting growth factor.

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.

 \frac{dO}{dt} = min \left( \frac{I}{k_{I} + I}, \frac{N}{k_{N} + N}, \frac{P}{k_{P} + P} \right)

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:

Forest_dynamics_page65

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.

Forest_dynamics_page71

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?

Forest_dynamics_page72

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.

99 thoughts on “A look at treemometers and tree ring growth

  1. Pardon me for saying this, but I rather trust the men of Fort York to read a thermometer than a tree ring proxy. Just sayin’ ….

  2. I read a book sometime ago that discussed the idea that tree rings give you an age and the highest altitude you find such trees (possibly dead) tells you that the climate was suitable there. This would give some estimate of temperature at a certain point in the past. I cannot see though that it would be that accurate and also all life is quite adaptive. I have never accepted that if there is more than one factor that you can say it was temperature.

  3. Of course the dendros will argue that site choice can eliminate precipitation as a significant variable in the mix, etc. All well and good. The main point here, as AW stresses, is the parabolic nature of the temperature response curve. Now there is a pretty point–how do you whittle that one away? Doesn’t (or couldn’t) that stick a fork in the whole dendro concept? Plus, even in you find trees whose growth ring variation mirrors local measured temperatures over the same time period, we do not know if this “mirroring” was true back before there were measured temperatures. And, to get really picky about it, we need some good statistical analysis of ALL trees cored in the area in order to tell us whether this alleged mirroring is statistically probable or whether the trees selected are merely mirroring coincidentally/randomly. Always have to be on the lookout for the post hoc, ergo propter hoc fallacy.

  4. Seeing this article and the effects of variables on tree growth I wonder if anyone has used an operations research approach to describe tree ring growth as a minimum function subject to the growth-limiting factors. This is the first thing that sprung to mind when Liebwig’s Law was mentioned.

    Then again, I know how much you guys like models ;)

  5. Excellent article, Anthony. It gives me much food for thought. I didn’t think all of this tree-ring stuff was so complicated, but your ultimate point is the most important one: how can anyone really know for sure to what degree tree-ring proxies are a reliable indicator of climate?

    REPLY: They might be a good indicator of the sum of climate, meaning amounts of sunlight, rainfall, and temperature, but separating one from the others accurately is difficult, if not impossible, without something to calibrate against. – Anthony

  6. Thank you for these invaluable posts as of late!

    To Mann, Kaufmann, and others…

    The tree does what it does.

    It is a living organism with a billion variabilities.. not unlike our own species.

    How an entire world and scientific policy decisions…can be based upon a few flawed tree-ring measurements…is beyond me.

    Better off using the actual wood for REAL hockey sticks…and save us from all this mess.

    Trees are great. They eat up CO2 and give us oxygen. And they don’t lie.

    But they aren’t merely open books to “temperature”.

    The trees….and the world in which they reside..are MUCH more complex than that.

    But all of you erring humans….Mann et al….and all of those who ride blindly on his feeble “peer reviewed” consensus coattails…leave the trees out of this.

    They just do what they do…and they don’t lie.

    Only if we as a species could aspire to the same amount of honesty.

    The truth is out there. It just probably does NOT rest in any political, religious, or pseudoscientific orthodoxy…no matter how forceful the dogma.

    As of now I predict (lol) the dogma of CRU will continue to grow more shrill.

    Or will they evolve and admit their mistake?

    Time will tell.

    Chris
    Norfolk, VA, USA

  7. And let’s not forget supposed higher current CO2 levels than a century ago. Just another factor that would change tree rings if all other factors were the same. It makes the mix just that much more interesting.

  8. “It seems to me that dendroclimatology has a lot of uncertainty.”

    Good research with a beautifully understated conclusion….

    Dendroclimatology has always activated my bullshit detectors….
    Now I know why….

  9. But, I am amazed at the nonlinearity and interactivity of all limiting growth factors, and especially the parabolic response to temperature.

    That’s pretty well known. What is also interesting, is that different plants have different ideal temperature ranges where they grow the best. Grasses are different from legumes, and even within grasses and legumes there are differences in temperature response, so, even that isn’t cut and dried.

    Also, I believe that this passage is a mistake. “The trees response to Nitrogen is the same whatever the level of Phosphorus.” This simply isn’t true. When something is yield limiting, that means that it is YIELD LIMITING. If Phosphorus, or Boron, or Potassium, or whatever, is yield limiting then, yes, you will get a response from adding Nitrogen. However, you won’t get the same response per unit of N than if Phosphorus or Boron, or Potassium, or whatever had NOT been limiting. This is why we try to look for yield limiting factors, and correct for as many as we can as economically as we can as quickly as we can. Also, if moisture is limiting, you can dump on all the N you want, and all you have is a really High N, sick plant.

  10. Excuse my ignorance; but the thought occurs, having examined a number of felled trees and the timber therefrom in some quite old English buildings, is that tree rings, even in very tall straight growing species, are very rarely symmetrical. So taking a ‘core’ from the xylem to the heartwood. which is I believe the current method for establishing the amount of tree growth occurring in any one year, cannot be reliably used as a ‘proxy’ for anything but highly local environmental factors like slope, shade, rainfall, branch growth, damage and disease.

    If as observed, tree rings are generally asymmetrical in width and a sample core is only taken from one side of the tree, how can said core be said to form a reliable proxy for temperature and / or climate in the first place? The growth rings would have to be measured across the entire cross section of the tree and some kind of averaging formula used to give an approximate value for any given year.

    Just an anecdotal observation you understand. Please delete this comment if I have stated the blindingly asinine or obvious.

  11. Ok I need to exert a little trademark action.

    From the same guy who brought you “free the code” and the Piltdown Mann, and “Tammy” I’m claiming priority on “treemometer”

    made up oct 13 2007 on CA thread.

    http://www.climateaudit.org/?p=2183#comment-147933

    hehe. Back then my hair was on fire.

    REPLY: Trademark granted in perpetuity. I suggest using less VO5. – Anthony

    Reply 2: The Morgan County WV tree planting board beat you to it. ~ ctm

  12. Imagine you have a tree growing in alkaline soil. A volcano erupts down wind a few hundred miles. Rain becomes a little more acid, the tree is able to absorb more nutrients, maybe for several years. Or maybe a heard of elk get caught in an early storm and freeze to death. Or maybe there is a massive battle between two clans of humans leaving hundreds of dead scattered on the ground. Or maybe a skunk dies in the root zone of that tree. Maybe a nearby tree to the south of the target tree fell over giving the target tree more sunlight or maybe a tree grew upwind causing more snow to drift at the target tree resulting in more water in Spring. Or maybe there is a long period drought such as happens in California which can experience droughts that last centuries.

    There are just too many variables and there are too many ways they can vary. Maybe one year the constraining factor was phosphorus. Maybe the next year it was water, maybe the next it was temperature, maybe the next it was pH and the next it was nitrogen.

    Or maybe the increase in atmospheric CO2 is causing plants to grow better and so you have a feedback loop where increased CO2 causes better growth but is interpreted as higher temperature and yet more CO2 is released and you get even better growth again misinterpreted as temperature increase.

    Its just plain nuts, the whole mess of it.

  13. “But, I am amazed at the nonlinearity and interactivity of all limiting growth factors, and especially the parabolic response to temperature.”

    I believe this is due to photorespiration. When the temperature is too high for some plants (those of the C3 photosynthesis variety; most plants) they close off their stomatal openings to prevent heavy water vapor losses. Unfortunately for the plant, this also shuts off the CO2 supply that is used for photosynthesis. At this point the plant will begin consuming the sugars it has made (respiration) to make CO2, thereby continuing photosynthesis. Not very efficient and largely responsible for the parabolic response. Sort of how the government wants to do things; break some windows so they can be rebuilt.

  14. REPLY: They might be a good indicator of the sum of climate, meaning amounts of sunlight, rainfall, and temperature, but separating one from the others accurately is difficult, if not impossible, without something to calibrate against. – Anthony

    Which is why the instrument records are vital. You need those old records preserved, and if you suspect they have been altered or expunged, find the originals, dig through old newspapers, etc. and get them safe from the weather record monsters.

  15. I have to agree with many commenters here. The big missing link here is how does CO2 increases change tree growth?

    That’s the study I want to see.

  16. While there are undoubtedly many factors that contribute to tree-ring growth, not all of these factors are necessarily independent. Some variables are strongly correlated (say, following a large volcanic eruption that causes a lack of sunlight, increased rainfall, and lower temps).

    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.

  17. This is a fascinating area of research, it would be interesting to hear from the Dendrochronologists themselves (retired or otherwise) to see how they arrive at a temperature,and,what degree of confidence they have in their figures.

    If a pine lasts for thousands of years in difficult soil at the edge of the tree line with fluctuating rainfall then everything in its makeup points to its survival as paramount over simple growth. In other words optimal temperature alone will not make the tree grow rapidly.The only assumption to be made for a thicker ring is to assume that ALL factors (sunlight,temperature,soil and air nutrition,trace elements and water) were optimal for that particular period. How do you clearly separate temperature from that mix?

    Surrounding Canberra are commercial P Radiata plantations. The climate,rainfall etc, apparently are suitable but without the trace element Boron, there is no growth. Our clay soils are deficient in Boron so it is added,by helicopter I believe.

    Great topic Anthony!

  18. Has anyone modelled the energetics, to see if the irradiance capable of raising land temperature (say) 1 deg C., is adequate to make an observable difference in photosynthesis and hence growth ring thickness of threes such as those studied? Remember that there are commonly 10 or more degrees difference between summer and winter, to produce the ring effect. So what does 1 degree do in controlled experiments?

  19. Back 40 years ago, my friend told me trees have souls. I wouldn’t go that far out on a limb, but I do consider trees and vegetation have a sort of communication mechanism. Through their DNA, maybe they resonate a calling to mother Earth for sustenance. On a human level it would be called praying. On another level the whole Earth may call to the stars for something it needs. When vast areas of deforestation take place due to natural or man made causes, a dryness and desertification occur upon the land due to a lack of calling. Evidence, due to the call no longer being there?

    Something different to ponder for variety, bookmark for when you get time.
    The last 20 minutes of this movie give a good explanation of the proces.
    The Calling – Full HD Version

    http://www.in.com/videos/watchvideo-the-calling-full-hd-version-3690289.html

  20. Fascinating stuff, this. Thanks for posting it.

    I would add another variable (as if there are not enough already): wind.

    Having traveled quite a bit, I noted that trees in very windy places have stunted growth. Having done no research on the matter, I wonder if there exist any studies. It would appear to me that a tree might grow quite well in years when the wind was moderate, but not so well when the wind was howling.

  21. Am I really the first to notice the irony of how applicable “Lie Big’s Law” is to the work of climate “scientists”?

  22. “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.

  23. 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.

  24. 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.

  25. 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

  26. 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 ?

  27. 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.

  28. 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.)

  29. 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

  30. 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.

  31. 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

  32. 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!

  33. 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

  34. 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

    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.

  35. 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?”

  36. 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??

  37. 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.

  38. 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.

  39. 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.

  40. 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!

  41. 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.

  42. 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?

  43. Dave Wendt (02:55:14) :

    Your scenario is called “peer pressure” and “finding a postdoc for the student pressure”.

    I agree that it is a fascinating subject that has been swept under the rug by the consensus team.

  44. There would appear to be abundant literature available that enables anyone with an open mind to question the validity of tree ring data used to produce estimates of temperatures. In addition, many of the contributors to this thread (most of whom, I would guess, are not professionals in the field) have highlighted additional factors.

    The question that arises in my mind is why the peer review process has failed to raise all these very valid doubts. This would appy not only to Mann’s use of tree ring proxies in his (peer reviewed) works but also the authors of studies which Mann used to justify his use of temperature proxies.

    I am not a scientist, so don’t fully appreciate how peer review works, but I would expect it to raise questions and demand answers before publication is permitted. How can all these undoubtedly intelligent people fail to ask such pertinent questions?

  45. OT but worth a laugh – the UK Met Office is predicting that this winter will be milder that last. I must remember to order my thermal underwear.

  46. Are these tree rings from larches growing in permafrost? Wouldn’t the depth of the active layer of permafrost be a big factor in amount of growth?

    An interesting article is “The Effect of Permafrost on the Northern Treeline” by V. V. Kryuchkov presented about 1973. Larches have some interesting growth patterns that maybe some botanists reading here could explain better than I (if indeed these rings are from Siberian Larches).

  47. Nice book find. This was discussed in depth by many people at Climate Audit several years ago including the “parabolic response” to growth factors, the mathematical product model for growth, and the fact that tree ring growth is not symmetrical around the circumference of the tree. Somewhere in CA archives there’s a very funny annotated photograph of Michael Mann holding up a section of a tree that demonstrates asymmetric growth perfectly.

  48. It’s good to see this technical but very clear enumeration of the the biological factors involved. The climatologists frequently enter the field with little if any appreciation for biological principles. Besides what has been presented here, there are influences on individual trees that cause them to produce different responses to their environments: 1) genetic variation, 2) mechanical damage (eg, strip-bark bristle cone pines), 3) tree anatomy (individual roots translocate nutrients vertically very well but not so well horizontally in some species which causes the trunk to grow unevenly if that root should tap into a pocket of minerals or water).

  49. Given that trees have leaves which photosynthesise with CO2 ……. I guess its possible that they grow better with higher concentrations of it in the air. Which as a fact just by itsellf, makes a mockery of the idea that the growth was caused by the temperature …. which happened to have been caused by the CO2 ….

    …..even if there was any correlation …. which there doesn’t appear to be …..

  50. Given that trees have leaves which photosynthesise with CO2 ……. I guess its possible that they grow better with higher concentrations of it in the air. Which as a fact just by itself, makes a mockery of the idea that the growth was caused by the temperature …. which happened to have been caused by the CO2 ….

    …..even if there was any correlation …. which there doesn’t appear to be …..

  51. I have said Douglas Fir as an example, on the west side of the Cascades, it is a primary
    Tree,in the Forest succession. Look at the tree rings of a 40-year old Doug Fir, and for the most part,wide,healthy, growth. Over here, on the east side of those cascades,that same 40 year old Doug Fir would be a fair Christmas tree.Moisture is the key…

  52. I am just speechless as to how an entire field of researchers can look at a mountain of data, pick the 10 pieces they like while ignoring the copious volume of data they don’t like, make a graph, have that graph reviewd and published without anyone saying a damn thing. And they are PROUD of this workd and call it “science.”

    I would have failed my 8th grade science project if I pulled a stunt like that.

    Repeat after me: the chronologies that DO NOT correlate with temperature are JUST AS VALID as the ones that do. You DO NOT get to ignore them just because you feel like it.

  53. Gary (06:07:03) wrote:

    “…..there are influences on individual trees that cause them to produce different responses to their environments: ….. 3) tree anatomy (individual roots translocate nutrients vertically very well but not so well horizontally in some species which causes the trunk to grow unevenly if that root should tap into a pocket of minerals or water).”

    I have noted in the lower trunk of some dead poplar trees that the wood discolored differently in various “zones” across the cross-section of the trees, and there was often a black “line” separating the zones. It appeared that the zones were determined by the root that fed that zone.

  54. I am just speechless as to how an entire field of researchers can look at a mountain of data, pick the 10 pieces they like while ignoring the copious volume of data they don’t like

    That’s why it’s called Climate “Science”.

  55. Upon reflection, perhaps the method of tree ring data collection could be improved. Perhaps some improved variant of a UDD (Ultrasonic Decay Detector) see link below, might improve the quality of the source data by allowing non invasive and more comprehensive tree ring mapping.

    http://www.treesearch.fs.fed.us/pubs/4429

    Such a method of data collection might go some way to preventing future misinterpretations.

  56. I worked on a similar model a few years ago. We looked at net productivity at all latitudes for forages and foraging lifeforms.

    What we found was that the forage produced was the same regardless of latitude given the same growing degree days – but the parabola was taller and skinnier the higher in latitude one went. The brix (and related higher quality content) in the forage was much more sustained at higher latitudes, due to the constant solar insolation, leading to a much faster growth curve for the forager. The other thing we discovered was that the growth at higher latitudes was more efficient because it did not have to stop and start every day especially during the Boreal day which was almost constant. This meant that the forage needed less resources per unit of growth.

  57. Very good read. I know that temp was only one factor in growth, but this sheds alot of light on the many veriables. I found it very interesting that a small tree ring, among other things, may indicate either cold or hot temperatures.

    Maybe a better way of doing tree ring analysis is for each year to see what spiecis of tree grows the best, then look at those parabola tables to see what temp that spiecis grows best at.

  58. Perhaps you know this, but Professor Botkin is a rather interesting fellow. I corresponded with him briefly regarding an hysterical column on climate by Paul Krugman, of the NYTimes. If you visit Botkin’s website, you will find an article he wrote about his skeptical attitude on AGW.

    In our exchange, he made one excellent point relevant here as well. Computer models are great for gaining understanding of systems, how things may change if some other things change. They are not good for making predictions, unless the system is totally defined, like the orbit of a satellite, for example!!

  59. If you start with the assumption that climate was constant within a narrow range and then hindcast the temperture and rainfall readings, using a temperature and rainfall profile from the 1800’s, for the period before records, then you get what you look for. That way, you know that if you don’t get the expected results from one sample, its obviously flawed, so you choose another one that is more compliant to your hypothesis.

    Its far more difficult to explain why your original hypothesis was wrong than it is to ensure that your study comes up with the “correct” answer. The denro people aren’t the first, nor last, group to fall into this experimental fallicy. And its very difficult for most of us to admit that we were wrong, especially if there was great fanfare given to what we did, its easy to climb the tree, much more difficult to climb down.

    Living things respond to a miriade of environmental conditions, they are not computer programs that operate in a controlled manner reliably time after time.

    I have often wondered why they don’t look at O2 and CO2 isotope ratios in the tree rings (if that’s possible) to determine a better temperature proxy.

  60. jnicklin (08:55:40) – I’m sure that changes in air pressure allows gases to move through wood, so there are not many gases trapped in trees. Carbon-14 dating is based upon carbon in solid form, which does not migrate.

    Anthony – Maybe we keep thermometers away from trees because the trees set such a bad example of how to measure temperature. :-)

  61. Anonymoose

    I agree that wood is not so solid as it may seem, but I was considering the O2 and C bound up in the cell structures, not the air spaces. In either case, it may not be possible.

  62. Quote Tenuc (00:11:29) :

    “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.”

    I absolutely agree that using a few trees from a few regions will not provide conclusive results on global temperature trends, and I wasn’t advocating doing only that. As important as the large- and long-scale trends are the uncertainties associated with them. I believe a careful scientist would try to estimate these uncertainties by (a) taking tree-ring samples from many places around the world as an attempt to piece together the more global picture, (b) taking many samples from the same location to investigate how much variation there is in that particular location, and (c) doing related experiments on the side, as you described doing.

    I my view if tree rings can provide a useful proxy for historical temperature, then that would be exceedingly useful, and is worth trying to see if it can work. But quantifying the uncertainties in the measurement is an important piece of that work, and needs to be done with care.

  63. Great description of forest growth factors – very instructive.

    I think there still may be some temperature information to be gathered from tree ring data, once we get past the species growth curve standardization and the problems of defining the actual diameter of an asymmetrical tree ring.

    Assume you have a valid growth curve for the species you’re studying. Identify three points on the curve: the ‘max growth value’ (MGV), a ‘smaller value’ (SV), and a ‘larger value’ (LV) at the same height on the curve as the smaller value.

    If the tree ring you’re examining has a diameter exactly on the MGV, then the temperature can be determined directly from the curve, since no factor is the limiting factor. This condition is extremely unlikely.

    If the tree ring has a diameter exactly as high as the SV, then we can determine a minimum value for the temperature, since a lower temperature would have produced a narrower ring. But the actual temperature may have been as high as the LV, which would limit the ring diameter to the same value, according to the standardized growth curve.

    We can’t tell which factor was the limiting factor, but if it was the temperature, it can’t be any lower nor any higher than the SV or LV. If another factor is the limiting one, the temperature would fall somewhere in between.

    So, tree ring data should be able to provide a temperature range which could have produced the given tree ring, even though a definitive, specific temperature reading can’t be determined.

  64. Supercritical (01:04:09) : “…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.)”

    I prefer “dendrophrenology.”

  65. You wrote: “I was surprised to see that photosynthesis is not linear with temperature, but parabolic!”

    Do you not live in or near wine country? I’m told many hot summer area vineyards use mist systems on auto-control to moderate the temperature as it approaches that point in the curve where photosynthesis would rapidly drop. Next time you need a break from the computer screen go have a talk with a winegrower and taste a few samples – it sooths the soul.

  66. Jon:
    “Tilo … in order for a plant to process more co2 it needs more water:

    6CO2 + 6H2O + Energy ® C6H12O6 + 6O2″

    Jon, I’m not an expert on this, but it seems to me to be important that this is not a test tube reaction we are talking about. In order for the reaction to occur, these molecules have to find each other. Sorry, about the “find each other” but I’m not sure of the right way to describe the problem. Anyway, let’s say that you keep the amount of water constant, but you increase the amount of CO2. This would not increase the total number of possible reactions, but it could increase the number of actual reactions because more of these molecules could find each other. The same priciple would apply if there were more CO2 but slightly less water.

    Does that make sense, or am I completely out to lunch here. In any case, I didn’t make up the assertion that CO2 makes plants more drought resistant. I picked it up from a paper that I read some time ago on the subject of CO2 fertilization.

  67. Very very interesting post, specially for a botanist and plant physiologist.
    I have learned and teached that there was 3 kinds of response curves for different growth limiting factors.

    1) For N, P, K … and water a curve with a plateau, and perhaps a toxicity but never encountered in true ecological situation.
    2)For temperature an upside down quadratic response as said McInt at CA on october 10th 2005. A +/- 5°C around optimum leads to a loss of about 15% of growth.
    3) For CO2 a near straight line without optimum or plateau only a slight bent at high doses between 0 and 1000 ppm or higher. The range of growth beeing 3 to 4 folds between 200 and 1000 ppm (300 to 400%).

    I think that for trees in their optimal growth area the rings which vary, in mean over 10 years and about 30 trees, from 100 to 200% around the mean between Mediev Th Opt and LIA, the main factor governing tree ring groxth is partial CO2 pressure.

    So I propose to call tree ring width proxies treebarometer or treebarco2meter.
    Is it a joke? Or does it match with ice cores CO2 ?

  68. What about a lofty plastic greenhouse, (maybe inflated using CO2) to test a bunch of variables on trees. I had heard that someone in Arizona I believe had done this to an orange grove to see if growth rates and fruiting were increased with CO2 concentrations (sorry no link)

  69. Jim B in Canada (22:47:09) : The big missing link here is how does CO2 increases change tree growth? That’s the study I want to see.

    It would be nice to have a guest post from the Idsos here.

    Now look at this Google map with all the site locations from a poster at CA. Just fly up there over the Russian trees and zoom in. I think the landscape itself (plus ground pics like in the Hantemirov Yamal paper have highly suggestive evidence that microclimate changes happen, moisture is a major factor, tree areas are sharply bounded (why?) and the watercourse meanders change often enough to show in the aerial photos.

    A river course 2km wide in which the meanders change constantly: trees grow thick up to the edge of this “valley” but they end suddenly and beyond is dead naked tundra. There are many rivercourse changes (natural with meanders like these). Microclimates caused by different balances between permafrost levels, river levels, groundwater levels, small banks, and neighbouring trees.

  70. When you are talking fractions of a degree up or down to demonstrate global warming or cooling, (the anomaly) it seems ludicrous that tree rings as indicators of temperature could have anything like the precision needed (even without all the interesting complications revealed in this blog). I don’t believe they know what they are doing. I think the same is true of the paucity of temperature measurement sites. I can see several degrees difference between New York and my yard 25 miles away. So what does a measured temperature mean for me if it is measured 1000 miles away? Millions of accurate temperatures taken simultaneously around the world would be needed to convince me that anyone knows the”global average temperature” to within a degree or so. And what about sea bed core samples. They say they can tell the temperature by which fossils are found in a sample representing a given period because certain ones prefer a particular temperature range. I just don’t believe these tiny creatures could live at T degrees, but not at T plus or minus 1 degree or so. This whole AGW construction is such a house of cards that it seems incredible that reputable scientists go along with it.

  71. Retired BChe

    You have a point! Most organisms are able to withstand a fairly wide temperature range, definitely more than +/- 1 celcius degree. Most terrestrial organisms experience wider temperature swings between midnight and noon every day. Aquatic creatures also experience swings greater than 1 degree over the year, especially in temperate climates.

    Does seem strange that all of this panic is over a few possible degrees of warming that could happen maybe, someday, someplace. Yet with nothing but this kind of shoddy evidence, AGW/CC proponents accuse skeptics of treason against humanity and forcast the destruction of the planet.

  72. jon (04:39:27) :

    Nic … you could add insect defoliants, parasites, disease, herbivores and competition etc. to your list.

    Jon – I was only trying to grasp the point that a bad growing season might be due to many factors.

    Now you suggest that optimum growing conditions (which should produce a “warm” ring) might give a “cold” ring because ;

    a.The caterpillars thrived and ate all the leaves.
    b. The increased cow/sheep/reindeer population in the benign/optimum/warm conditions ate all the bark making the tree suffer.
    c. No one has yet mentioned lichen/fungus/algae – thriving in the warm but having a parasitical effect.
    d. Which leads me to mistletoe (a true parasite).= Parasite thrives in good conditions but host does not.

    Oooh Eck. Um. Perhaps there is not a direct correlation between ring thickness and aveage annual temperature. There seem to be number of factors at play here.

    What a fascinating area for study by those who know better.

  73. Being an agronomist I’ve always been of the opinion that dendroclimatology is a little bit of voodoo and hocus pocus blended with science. Anybody who understands plant physiology knows that there are a great number of factors, and combinations of factors, that influence plant growth. As an example, you can have a cooler than normal year with ample moisture or a year that is warmer than normal with limited moisture and yet have the same size tree ring at the end of each year.

    To further confuse the issue… a cool year with ample moisture and an abundance of sunshine can produce a ring the same size as a warm year with ample moisture and limited sunlight. There are simply too many variables to be able to reliably use a tree as a treemometer. This has been demonstrated with the “divergence” problem seen in the later half of the 20th century. Rather than admit to the obvious, dendroclimatologists have developed half-baked theories such as co2 fertilization in order to explain away this obvious stumbling block. I think the dendro community is due for a rude awakening.

  74. Patrick Davis (23:39:58) :

    “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).”

    yes, my cousin, Dr Andrew Lorrey of the U of Aukland’s climate dept, did a study of subfossil Kaori recovered from bogs to extend the NZ dendro record back thousands of years: http://hol.sagepub.com/cgi/content/abstract/16/2/188

    You all may remember him from his cave speleotherm ring study (similar to dendro work) put out last year that covers a 5000-odd year period and helped put out solid peer reviewed evidence that the MWP was in fact a global climate effect, not limited to northern europe and north america:

    http://wattsupwiththat.com/2009/01/03/4000-year-o18-histories-of-new-zealands-north-and-south-islands/

  75. Another limiting factor for tree rings as a proxy for temperature is whole concept of biological growth and sexual reproduction. Organisms that reproduce sexually ‘grow’ physically in size only up to a point that reproduction can occur. This is a bit like us, where in human males, maximum Femur length is reached at about 22 years of age. Height is more or less maintained throughout life and biological ‘energy’ is then devoted to reproduction. Trees are basically no different, the size they reach is the ‘correct’ size necessary for the next stage of the life cycle of the tree,namely, reproduction. Tree rings are laid down after reproductive maturity but at a slower rate and only enough to maintain the framework. The tree itself is mealy a living ,somewhat static scaffolding, that enables reproduction .
    To assume that a tree will burst in to life and record its progress with a fat growth ring every time the temperature is optimal for 1000’s of years is simplistic in the extreme.
    A tree existing for 1000 years in one location and not outstripping its resources must be doing something right, and growth for growth’s sake is not one of them.

  76. “”” J. Peden (17:33:33) :

    Is ring width or surface area even a valid proxy for the volume of each tree’s yearly growth? “””

    Jim, the core boring tree ring method suffers from sampling errors, since the rings aren’t constant thickness all around or up and down the tree, so it depends on sheer luck as to where a core is drilled.

    So is your Dory Still out on the water, or are you mothballing it for the ice season ?

    George

  77. As a gardener, Liebig’s barrel makes a lot of sense. On occasion, I will supply a garden or individual plant with as much as I can give but I don’t alway have control over the conditions after I’ve gone. Some people don’t appear to understand that compost and fertilizer become functional only in the presence of water, relative to the specific requirements of the plant. Seems pretty simple to me.

  78. Internode length is also a relative measure of annual tree growth. Whether it can be detected in very old wood is another matter. Probably not.

  79. “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.”

    Maybe Anthony’s just being conservative here, but I don’t think he’s going far enough in saying that the task is “very difficult” or “uncertain”. Frankly, the parabolic response curve alone makes it IMPOSSIBLE to divine temperature from tree ring width.

    When a function is parabolic, you can easily determine the value of Y for any given value of X (in this case, X is temperature and Y is ring width). However, for any given value of Y, there are TWO values of X. So, if you know the width of the ring, even if you have accounted for all the other factors that have a hand in determining ring width, you still have two possible values for temperature. How do you know which one to pick? It’s IMPOSSIBLE. Unless, of course, you’re Michael Mann, in which case, you simply pick the lower temperature, because you KNOW temperatures could not have been higher at any time in the past than they are right now.

  80. To be honest, what’s new with Liebig’s barrel, if we look at our selfes we function the same way. If our food contains to little of of one component we can’t even out that by eating more of something else, common sence! A well mixed diet is the best way to health!
    What do dendroclimatologists eat?

  81. George E. Smith:

    “Jim, the core boring tree ring method suffers from sampling errors, since the rings aren’t constant thickness all around or up and down the tree, so it depends on sheer luck as to where a core is drilled.”

    Yeah, I know.

    Btw, I’m not Jim who has a dory, but I do admire your thought.

  82. MITSCHERLICH’S LAW OF PHYSIOLOGICAL RELATIONS is the response most physiologists acknowledge is a better fit to the data. Liebig is obsolete.

    Some others questioned interactions, this is a general response from an abstract (my copy of the paper is behind a paywall), I’ll get others later:

    Light and temperature-response curves and their resulting coefficients, obtained within ecophysiological characterization of gas exchanges at the leaf level, may represent useful criteria for breeding and cultivar selection and required tools for simulation models aimed at the prediction of potential plant behaviour in response to environmental conditions.

    Leaf-scale gas exchanges, by means of an IRGA open-flow system, were measured in response to light intensity (8 levels from 0 up to 2000 μmol m−2 s−1), CO2 concentrations (ambient—350 μmol mol−1 and short-term enriched—700 μmol mol−1) and air temperature (from 7 up to 35 °C) on three Vicia faba L. genotypes, each representing one of the three cultivated groups: major, equina and minor. The net assimilation rate response to light intensity was well described by an exponential rise to max function. The short-term CO2 enrichment markedly increased the values of light response curve parameters such as maximum photosynthetic rate (+80%), light saturation point (+40%) and quantum yield (+30%), while less homogenous behaviour was reported for dark respiration and light compensation point. For each light intensity level, the major and minor genotypes studied showed assimilation rates at least a 30% higher than equina.

    The positive effects of short-term CO2 enrichment on photosynthetic water use efficiency (WUE) indicate a relevant advantage in doubling CO2 concentration. In the major and minor genotypes studied, similar assimilation rates, but different WUE were observed.

    The optimum leaf temperature for assimilation process, calculated through a polynomial function, was 26–27 °C and no relevant limitations were observed in the range between 21 and 32 °C.

    Analysis at the single leaf level provided both rapid information on the variations in gas exchange in response to environmental factors and selection criteria.

  83. The reason Stratevarius violins sound so good is because he picked trees with tighter tree rings that grew at higher altitudes during the last little glacial (Maunder Minimum). The global warming idiots do not even hear the violins playing their death song.

  84. Er, I was struck by the idea that temperature was derived from ring growth thickness. That tree growth is affected by a variety of factors was nicely illustrated by the article by the guest writer about trees showing response to fertiliser. So I was struck by the problem of isolating one factor from all the others.
    Thus, in fact, Liebigs law of Minimums actually clarifies and provides a foundation for the proposition that tree rings can be temperature proxies.

    This is because, as presented here, the tree growth will depend not on all factors but on the minimum.
    On Dr Briffa’s web information (http://www.cru.uea.ac.uk/cru/annrep94/trees/) we see he claims that for high altitude trees that minimum is temperature…. so we could accept the idea that high altitude tree growth is linked to temperature.

    It isn’t, in fact, the ring width that is measured but oxygen isotope ratios, according to the Science Daily article (http://www.sciencedaily.com/releases/2008/06/080611135100.htm) that discusses the new study suggesting that tree leave temperature is largely self regulating.
    The article says:
    “….scientists studying climate change have measured the oxygen isotope ratio in tree-ring cellulose to determine the ambient temperature and relative humidity of past climates.”

    “The assumption in all of these studies was that tree leaf temperatures were equal to ambient temperatures.

    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.”

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