Here’s a Gazprom aerial photo which illustrates this better than 1000 words. (Yamal is the location of some huge Gazprom natural gas fields.) From the colors, I presume that the picture is taken in fall as the larch have changed color. Spruce do not appear to be in evidence here – they have a more southerly treeline. The remarkable relationship between the rivers and the larch “forest” is not discussed in Briffa (2000) or Briffa et al (2008).
Climate Audit 
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Mr. McIntyre, I’m not getting it. Yes the “forest” of larches are but a row of spectators as the parade of rivers flows by. So? Please elaborate as to the significance of this. “Inquiring minds want to know.”
Re: Shallow Climate (Apr 28 09:58),
I have the same question. Is there some issue with spatial distribution of the samples, perhaps?
It is clear from the image that the Larch population is responding to the stream as a critical environmental element. That in turn means that the critical growth factor is directly linked to water in some manner. It could still be that climate changes have lead to an earlier thaw, which in turn would make water available earlier (and longer) in the year. But that is not what was proposed by Briffa. They argued for a direct growth to temperature response. The picture simply shows that the situation is more complex.
The larches for dendrochronology were collected at the upper parts of the rivers. They are proxy for summer temperatures only. They can’t grow in any other time of the year.
Trees growing in close proximity to rivers/lakes are much less prone to atmospheric influences impacting their growth/tree rings due to water shortages and temperature changes.
A highly significant fact not elaborated on by any Team members could mean they have never taken a basic course in Fluvial Geomorphology or they left out the information as it didn’t support the desired. conclusions.
My personal opinion all global warming is really caused by meandering thalwegs.
“My personal opinion all global warming is really caused by meandering thalwegs.”
Hilarious!
I would assume from the photo that water is not a limiting factor to growth since they appear to be growing in an alluvial, river bed soil. The soil should also be fairly fertile as well. It sure looks like they have a better chance of being tree-mometers that the Colorado bristlecones.
Or not. Perhaps the absence of trees only a few tens of meters from the river indicates a high sensitivity to water availability. Until somebody actually tests an hypothesis on these trees in situ, its speculation in either direction.
Based on tree position the river meanders slowly. But it meanders – it’s what rivers do. When it picks up its banks and moves on old trees disappear and new trees replace them. Trees don’t appear in equivalent numbers where avulsion has isolated them. The tree life cycle is then highly dependent upon the river course and what ever affects that. The stands move with the river or disappear.
What might a 1000 year slow-motion video show as the river bed wanders around plain?
Meandering rivers like those in the picture may change course over time. Is there any evidence that the water environment of the old trees has been the same all along?
DP posted a comment at 10:23 while I was writing mine of 10:25. Both point to the same issue.
And I was reading the comments before I was about to post the same thing. 🙂
It seems to me that any environment where the “envelope of life” is very narrow would be subject to potentially many factors affecting growth. It seems obvious that this fact should at least be noted.
It all rather reminds me of one of WUWT’s “exposés” of a rural monitoring station, at the edge of a parking lot next to an air conditioning unit.
The idea of scientific research performed through direct observation is rather more multi-level than one might at first think when considering the irrelevance of climate models. No?
The revealing fact is that you cannot collect tree rings remotely, and the growth environment of the tree is a critical factor in analyzing the rings. The fact that such an easily made observation was left out is at best poor science. Worst case, the authors, confident of their conclusions decided to omit confounding elements. They decided not to “confuse the reader” with the facts.
It’s quite possible that rainfall and river path changes, rather than temperature drove tree rings?
Seems like when I water my trees they unexpectedly grow.
Chuckle !!!
I thought my trees were growing because I was exhaling my CO2 on them !!!!
I will try the “water” method !!!!!
Assuming the above isn’t a new growth forest (after a fire, etc), the trees have a range of sizes in close proximity to each other. To me that says a large variability why some trees grow faster than others, within a small spatial area. The size variability shouldn’t correlate with climate, because they are close enough to experience the same climate.
Which trees do you select?
Let me clarify: “the trees have a range of sizes in close proximity to” should have read “the trees have a range of sizes while in close spatial proximity to”
I’m not suggesting that this photo is any sort of smoking gun – just that it’s interesting.
So, if I am reading you correctly, what you’re saying is that the “remarkable relationship” between rivers and larch location is something that Briffa needed to have taken up somehow, but didn’t; that he needed to address the river proximities as (allegedly) unimportant/insignificant with respect to using/selecting these trees as treemometers. Am I at all on the right track with your thinking here?
I asked my neighbour who is a retired forest ranger here in Manitoba about American larch (commonly called tamarack) in Canada. He told me that, besides stunting and other growth features exhibited near the tree line, it also has different growth features between swamp and uplands below the tree line. He said that the forest rangers refer to swamp growth as “red tamarack” because of its different appearance but, in fact, it is all the same species.
Note the evidence of the meandering, with filled in but depressed oxbow lakes, and with oxbow lakes with water still in them. A question to ask is if it is necessary for this species of larch to have roots in both aerobic and anaerobic soils. American cypress has a specific niche dependent on this phenomena. In which case growth could be effected by both dry and too wet conditions. It also calls into question that the Irish oaks could not be used for temperature per Ballie as claimed, but contested in a post below. The real question is the double standard, especially if larch responds differently whether the roots are mostly aerobic or mostly anaerobic.
It is hard to tell, but it looks like the trees are growing on the elevated banks of the river. Flooding rivers as they overtop the banks drop sand (and gravel, but unlikely in such a meandering river where such meanders mean slow moving). An elevated sand bar will not develop permafrost or water-logging. Better for tree growth. In some other pictures of the area we have seen the trees appear to be in a valley but the valley may not be the deciding factor but rather the soil. What does this have to do with hockey sticks? A very small change in drainage at one site could lead to a sudden change in growth unrelated to temperature. That is, a spurious signal is easy to obtain in such a habitat.
According to Hantemirov, the valleys were crucial locations, because there the trees were a bit protected from the frost and wind on the plains. And they collected the standing trees on the higher alluvium – I think there were some 3-4 meters mentioned.
If CO2 is the only factor limiting growth why are the trees clustered around the river, should they not be growing everywhere on that pic.
No…. because they are limited by water…which changes over 1000 years.
And the trees get smaller in the distance 😉 obviously it’s hotter nearer the photographer!
Nonsense.
The RIVER gets smaller in the distance, limiting water, resulting in smaller trees!
🙂
Craig, meandering may be normal at normal flow. This is not the same as flooding at flood stages. It could be that the river floods from first melt, and then slows and becomes more sluggish as fall approaches. The american cypress, IIRC, has this ability. Other species that are anaerobic tolerant cannot compete well with cypress in slow brackish areas that flood and stay anaerobic for long periods from spring floods. This allows the cypress a microniche. The pictures appear to be fall.
Larch and black spruce also tolerate waterlogged soils, but the consequence is extreme stunting, with a 50 year old tree maybe 8 feet tall. Good growth (as also with cypress) occurs with less waterlogging. This can be the deciding factor at treeline, not just the temperature. The waterlogging is also related to permafrost. As another example, as study I saw showed white spruce in canada on sandier hills (small hills) but with some warming the permafrost drops and the water table falls and the sand hills become dry and the spruce suffer. In areas south of the permafrost, spruce grow on medium soils with lodgepole or jack pine on sand hills, but this is a long term effect, vs the transient effect I discuss above. None of these systems should be assumed to be in equilibrium if you change the hydrology like a site in Pennsylvania is.
The thing that interests me most is the long “apron” on the most prominent curve of the river. How come there aren’t smaller trees toward the river? I suspect it’s because between the time the larger trees were seeded and the present it’s been too cold for new seedlings to occur. The question is just how old the big trees are. I’d guess they’d be from the Medieval Warm Period. Rather ironic if that’s the case.
In sites close to the treeline seedlings will only survive to grow into trees in rare cases when there is a series of good years. Thus trees tend to belong to a few distinct age-classes. This is well known to foresters in Scandinavia. It is extremely difficult to re-plant forest close to the treeline, the plantings usually fail, again and again.
The following is hopefully generally on point to this discussion:
A controlled experiment in the Amazon, where trees on one hectare were starved of water while surrounding trees (obviously expsosed to the same temperatures) were not.
“The fact that drought interfered with the tree growth isn’t surprising. What is surprising, says Nepstad, is where in the tree this slow-down occurs … It turns out that wood production is the most sensitive to drought stress. Trees just stop growing in diameter …”
– from a NASA article on the experiment.
http://earthobservatory.nasa.gov/Features/AmazonDrought/stealing_rain4.php
This might help:
The habitat pictured looks like Arctic tundra, too cold to be able to sustain many trees. It is not taiga, boreal forest.
The trees grow near rivers that provide provide water for the growing season and may renew riverbank soil with silt.
Trees seem to huddle near rivers, presumably for survival. Do roots stretch deep enough to obtain underground water, year around, beneath frozen soil?
Dave Dardinger said “How come there aren’t smaller trees toward the river?”
It is because of high water level variation, the trees will not be able grow under water from time to time. They grow along the river because of milder climate near the river. Larix sibirica may be 200-250 years old.
Larry Huldén
Finnish Museum of Natural History
Thanks for the post, Larry. Do you know if Larix sibirica’s root are anerobic tolerant?
Spring floods vary from year to year and thus may carry different amounts of fertilizing sediments over time. Perhaps the variations in tree ring widths represent variations in soil fertility. A core of the soil layers might be helpful.
“A core of the soil layers might be helpful”.
Yes, one would think that such an approach would be advisable prior to declaring these trees temperature proxies.
After they used 12 trees from this area, it must have looked like it was clear-cut. 😉
Yes, rivers can have a huge variance of shape in surprisingly short amounts of time.
http://earthobservatory.nasa.gov/IOTD/view.php?id=6887
Not sure the relevance here, but rivers erode bank on the outside of the oxbow and deposit sediments on the inside. As you can see in the picture, all the growth is in the recent river deposits on the inside of the oxbow.
That is an interesting observation. The trees tend to occupy higher ground along the crests of natural levees on the inside of the oxbows. I think they need to keep their roots dry by preference and the erosion along the outside of the oxbows probably limits the potential lifespan of seedlings.
Also, the insides of the oxbows are surrounded on 3 sides by water, and hence have a more stable temperature and water table?
I see what steve is getting at. It’s interesting because perhaps the treemometers are really soil hydrometers. “A hydrometer analysis is the process by which fine-grained soils, silts and clays, are graded. Hydrometer analysis is performed if the grain sizes are too small for sieve analysis. The basis for this test is Stoke’s Law for falling spheres in a viscous fluid in which the terminal velocity of fall depends on the grain diameter and the densities of the grain in suspension and of the fluid. The grain diameter thus can be calculated from a knowledge of the distance and time of fall. The hydrometer also determines the specific gravity (or density) of the suspension, and this enables the percentage of particles of a certain equivalent particle diameter to be calculated.” So the larch trees rings are just the historical record of grain densities in liquid.
huh? Tensiometers maybe, i.e., dependent on availability of moisture in the soil. Clearly its a mobile river system (look at the cut off oxbows, etc..highly meandering with a large tortuosity)…so the obvious major influence is proximity to the river over time….seems this would indeed drown out any climactic temperature signal due to a few tenths of a degree change.
A meandering river will occasionally undercut trees, leaving their neighbors suddenly in the sun to undergo a growth spurt. The Yamal 12 are characterized by recent sudden growth spurts. Hmm.
Of course we don’t know that the Yamal sample came from a site that looked like this — this is just Gazprom’s photo of one spot in Yamal.
Subtitle for this thread — Yamal and the Night Visitors? 😉
Another intersting aspect of this is temporary dredging for roads. It does not have to be in the immediate area, but close enough to effect hydrology. In botany we went on a field trip to see succession caused by a recent road where the stream was put into a culvert that caused periodic flooding, most notably in the spring. Certain tolerant species at the edge dies as the saturated zone was raised. You could see the dead trunks and the new growth further upslope.
In a taiga boreal forest, the climate is hospitable enough to support many trees, both near and far from rivers.
But in the harsh cold of the Yamal, the hardy Siberian larch can only eke out an existance situated on one side of meandering rivers. These trees owe their lives to the rivers.
Even if, hypothetically, the volume of water rivers were to owe to and be a perfect indicator of prevailing temperature, rivers may still alter course and thereby alter tree growth rates.
OK, now I’ve got it figured out. Starting in the lower left corner of the photo, follow the line of trees on the left bank of the river, moving on up the bank towards the center of the photo where the line of trees curves sharply to the left and then seems to terminate. What you see is the rough outline of a hockey stick.
YIKES! OXBOWS!
Any schoolchild knows what oxbows do over time: they change course continually, and suddenly. They flood and move channels. Dramatic alterations can occur that change availability of water on and under the ground. The movement of an oxbow can alter motions of browsing animals and thus drastically change the outcome for plant life.
There’s so much tree-growth background noise in this environment, they might as well have selected trees from Central Park in NYC.
Well, every schoolchild should know that it is the river channel that moves. Oxbows are remnants of old abandoned “paleochannels” and as such do not move anywhere.
More pictures from Yamal here:
http://englishrussia.com/index.php/2010/03/25/yamal-peninsula/
Nice photos. There are not a lot of larches in the Yamal. Those that exist must be to the south and huddle along summer rivers. The Siberian larch must be one tough tree.
Here are some additional photos from the same site.
http://englishrussia.com/index.php/2007/08/26/some-sceneries-of-yamal/
This one
looks like it shows some of the fallen trees in the area. Most the pictures are very treeless.
For some additional pictures of Larch in the Yamal area, check http://www.arcticphoto.co.uk/results.asp?W=4&F=0001&Step=1
Re: Keith W. (May 3 17:10),
Look at RY.0232-19. Another possible confounding factor: reindeer! I know reindeer are noted for eating mosses, but might they also eat Larch seedlings or young trees? If so, after they grow above the browse line, there could be a sudden spurt in growth.
White-tailed deer have a history of actually feeding off the lower branches of spruce trees during winter, going as far as to strip small branches. It is certainly possible that reindeer might do something similar, resulting in strip bark type wounds on some trees. This could lead to anomalous growth patterns.
A study by Dulamsuren et al. (http://www.ncbi.nlm.nih.gov/pubmed/19203936) showed that stomatal opening, and hence photosynthesis, in Larix sibirica at the taiga margin in Northern Mongolia can be severely limited by water availability. However, this limitation to photosynthetic production and growth is relieved where trees have direct access to the water table:
http://www.ncbi.nlm.nih.gov/pubmed/19203936
The confinement of trees in this photograph (Are they L. sibirica or L. gmelini?) to riverside locations suggests that they are phreatophytic, i.e., that their survival depends on root contact with the water table, the accessibility of which may vary sharply with precipitation and stream flow. In that case, the photosynthetic production of the trees, and hence xylem ring widths, may largely reflect year-to-year variation in water table depth, which may not be closely correlated with mean summer temperature.
Looks similar to the Thelon River valley in Nunavut, which flows across the tundra/transitional forest for most of its length, tho’ the Thelon valley itself is steeper and perhaps a warmer micro-climate than Yamal.
Here’s Briffa’s Yamal map
Now here’s Google Earth imagery from the same area. I’ve added red dots in the same places that the dots appear on Briffa’s map.
From the imagery, it appears that vegatation follows the rivers and drops off steeply as a function of distance from the rivers.
Also note its a very stange place.
Re: mpaul (Apr 28 14:51),
Thanks, very informative.
Briffa got his tree cores from a Russian group, who actually did the field work, ims.
Did the Russians comment on the trees’ environment and growth patterns?
Thanks, Pete Tillman
It is entirely possible that Dr Briffa has no idea what the local conditions are. Would he care?
The Russians did a lot of work concerning various aspect of these larch growths. Unfortunately, except for that Shiyatov paper, all of it is in Russian papers or in Theses. Hantemirov according to that short Thesis content calculated also the wood mass during the centuries and similar forestry things.
Its also interesting to note that the ‘lakes’ don’t have vegetation around them, its only the rivers.
Flowing water in its limited way can be a source of heat and given sufficient flow rate would resist freezing over better than ponds.
Well what the photo says to me as a hydrogeologist is that there would probably be a shallow watertable near and some distance away from the river channel(s) with tree roots deriving their water uptake from that source rather than just rainfall.
That seems to be the reason for the accelerated grow. But you would have drill some monitoring holes to confirm all that including a study of root depths etc.
Hey, all you contributors here!: IMHO you offer interesting and valuable insights–thanks! Now for me this is a fine example of “Internet Peer Review”, with even some humor thrown in–how can you beat that? Frankly, I think it’s great. I like the questioning, probing spirit and the contributions from people with knowledge in several different fields. Briffa, next time, post your paper here first.
Re: Shallow Climate (Apr 28 16:21),
That’s what we strive for here. Little sideshows like ClimateGate can be a distraction, but the members of this community care deeply about good science.
For an example of the kind of contextual data we’re hoping to see, check out the Almagre collection, and in particular the data/metadata spreadsheet.
Of course, that’s just an “internet amateur” effort; we would hope the full time professionals will soon be sharing much more complete data than this.
(Please remember that expectations must be much lower for data from the past, because most dendro data was collected for chronology rather than ecological analysis.)
Am I dumb, or is it that obvious? Trees grow taller (and wider) near water, no matter what the air temperature might be. So, how can a tree’s growth tell you how hot or cold it was at any given time if you don’t know what it was dipping its roots in during any particular growing season? A time machine will be helpful but I don’t think Mr Gore has finalized its construction yet.
How were the Briffa samples collected? As you said several months ago, there was an obvious relationship between rivers and many Yamal samples in another paper. From “More Yamal tree ring temperature data: this data is flat as roadkill” where you mention Rashit M. Hantemirov and Stepan G. Shiyatov: “Small boats were then used for locating and collecting cross-sections from wood exposed along the riverbanks.”
IIRC wasn’t the core expedition in Yamal by boat via the River? I seem to recall seeing some expedition photos taken at river level, looking up banks and trees that had been or were about to be sampled.
It may be that Briffa and others never saw an aerial photo at the time the papers were written, only photos taken from the riverbed looking upslope.
They may have never gotten the idea that the trees never propagated much past the river meander zone, and thus they were sampling a unique “river population” and not a broader forest.
I certainly didn’t realize it until I saw the Gazprom photo, and then the lightbulb with Liebigs law written on it illuminated brightly over me.
Trees are a proxy for the available growth factor. If records exist of the river flow/stages, correlations might be found.
I found the photo of the Yamal core sampling expedition I was thinking of. Here’s how they got many of the tree samples using a rubber boat:
The authors (Hantemirov- Shiyatov) write:
The nature of the expedition transportation almost guaranteed cherry picking. It was probably not intentional, as field work is often a matter “get what you can” and not often “get what you want”. Though, it would have been instructive to whomever read their paper if they had put some aerial photos of the helicopter flight over the trees during the initial spotting run.
The paper is here:
A continuous multimillennial ring-width chronology in Yamal, northwestern Siberia (PDF) by Rashit M. Hantemirov and Stepan G. Shiyatov
Did they sample the downed ‘wood’ embedded in the river bank deposits? If so, they don’t know where that ‘wood’ grew. Looks like the river is actively eroding what appear to be flood deposits in which the downed trees are embedded.
Perhaps there is a parallel to the situation in northern Alberta, where there is a well-understood differential rebound from the most recent substantial depth (and weight) of ice.
In the Alberta case, the erosion of a river channel means less weight in the surface layers localized along the river. Deeper layers, still compressed from the weight of glacial ice removed less than 10,000 years ago, then rebound faster, relatively, immediately under the river valley than in adjacent areas. The result is narrow ribbons along each side of the river valley that are higher, and better drained, than the broader swaths of muskeg further from the river. So, river, then river bank (as per Anthony’s photo), then a narrow band of high well-drained well-wooded land, then wet muskeg (which cannot drain through the high ridge near the river, so always but tends to stay wet.
Not sure what that implies for tree selection and tree sampling. But it is an explanation for the form of the forest in the photo.
Once the trees establish for whatever reason, they can also be sustained near a river because of the (usually) greater incidence of fog. Trees can trap fairly amazing amounts of water that runs off the needles/leaves to the roots if theres a high incidence of fog.
JC
That photo of Anthony’s clearly shows a hockey stick just above the boat.
Proof!
None of the above posts mention the permafrost in the tundra. It is a major factor if we look at the maps. The tree roots and pattern do not spread in frozen soils. Near the river, there was melt, precipitation and some thawing from soaking near the river banks. Now the huge hypothesis killer can be flowing water and not the air at all. If the temp by reason of water flow effects the habitat for tree growth, it may have nothing to do with land temps 1/2 mile away.
As Doctor_d and Duster note, the Gazprom photo shows the trees along the INNER oxbow loops, NOT on the OUTER oxbow loops. This suggests trees grow in the soft wet sediment left by the advancing meanders.
However, Anthony’s photo of the trees sticking out of the bank shows an OUTER oxbow loop where the tree had fallen, been covered up, and is now exposed by the advancing meander. This seems to indicate trees formed in previous meanders that were under cut and fell into the river. They may have moved and then may have caused and been covered over by a sandbar. Later an advancing meander again exposed the tree.
Furthermore, as “Henry chance” notes, the trees may only grow near water, not into permafrost. This suggests the tree temperature may be controlled by the river’s upstream temperature conditions, not the growth locality.
These factors suggest that neither the original location of the tree is known, nor the hydrological conditions of its growth, nor temperature influencing the growth could be identified. i.e. all the major parameters of Liebigs law are unknowable in these exposed Yamal tree trunks.
snip – editorializing
Click to access Frost.pdf
The aerial photography suggested a terrain that was deficient in one or more essential nutrients, ones that were carried by rivers and removed by rivers. Sulphate could be a candidate because of its solubility, but this is clearly a guess with no supporting information. Time-wise, it could also correspond with increased industrial activity.
With each post the complexity of the area increases, to show how naive is the blind assumption that tree rings reflect temperature in a simple way.
It also shows a lack of customary, preliminary, probing experiments that can either kill or admit more ordered development of an emerging new method. I’ve been caught this way and it hurts.
“Time-wise, it could also correspond with increased industrial activity.”
So, the Downsteam UHI effect?
Perhaps in this “Sacred Grove” the “vodoo science” takes place?, a most unusual place.
Could I suggest some hypothesis to the stand for the siberian larch ?
Tree roots don’t like permanent water, so they can survive only above the water line in the river banks. The other fact to consider is also how deep the soil stays frozen. The larch finally can only colonize a band along the river, above the water line et where the perfrost melt early et for the minimum growing season for the larch.
The older trees seem to follow the ancient banks, not the youngest and non stable ones.
“Tree roots don’t like permanent water, so they can survive only above the water line in the river banks.”
This is not so in the case of many species, which are either facultative or obligate phreatophytes, i.e., stimulated in growth by or dependent for survival on access to the water table. As I noted above, Larix sibirica is, apparently, one such a species (http://www.ncbi.nlm.nih.gov/pubmed/19203936). See also comment by John in L du B on red tamarack.
Alluvial groundwater levels adjacent to stream banks can vary greatly with precipitation, melt water, changes in the stream course, obstructions to flow, etc. (http://treephys.oxfordjournals.org/cgi/content/abstract/23/16/1113). One would expect, therefore, that there would be substantial variability in the growth of riparian larch stands quite independently of any variation in temperature.
i find the whole idea of using tree ring data to measure temps a bit silly
i live in aust and the rivers here are not where thay were 1000 years ago and i imagine the same would be true there all you need is a tree to fall into the river debris gathers around and forms a dam and the river finds another way just for one example. floods thunderstorms can all affect one tree or lots soil types soil p/h nutrient animals will often sleep under a certain favorite leaving there droppings there as fertiliser and so on and on to put this data up a proxie well!
That is interesting. One look at the picture does yell Oxbows. I would think that from sedimentation it should be possible to age the oxbows and perhaps reconstruct when the bites were bypassed? Is there a time correlation wrt typical age of oxbows and events in tree rings, or correlation of actual events with bites in the river being bypassed?
Point of clarification — is the assertion that these trees are THE trees from the sample?
I don’t see how you could assert a correlation to temperature without proving an ability to factor our hydrology and soil factors from the river… I would think the remaining uncertainty would still be so great it would make more sense to just look for trees in more stable geology.
Annual erosion along the riverside precludes seedlings from establishing too close to the river independently of average water level. That’s why the river slope lacks growing trees. Old subfossil trees can be found along the slope because erosion will redirect the river from time to time and trees fall closer to the river.
Larry Huldén
Finnish Museum of Natural History
This would seem to seal the deal, as far as the credibility of several dendro proxy hypotheses is concerned.
snip – overeditorializing
OK, reword. What major research supporting AGW is credible? No sarcasm, no editorializing, just a question…
I little project that would be right up Steve’s street would be to try to get hold of some river flow data (say summer seasonal runoff) from a river in the region and actually do some correlations with contemporary tree ring and temperature data. I make it sound easy but the biggest problem might be getting hold of the hydrological data.
Max Beran,
perhaps downstream of an hydro-dam would be a good place to look for tree-ring thikness vs water flow?
The pictures shown here certainly warrant a closer look at this (obvious) influence on the tree-ring data.
I thought that the Ingoing assumption was the the only rate-limiting factor growth was temperature. These photos seem to suggest a sensitivity to water availability. As to the question of man-made variations in local conditions that might affect tree growth patterns, see
Click to access GubarkovAA2010_yamal_tal100408.pdf