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.”

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.

“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.

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.

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

“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/

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.

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.