Comments on: "Modern Sample Bias", RCS and Briffa’s "Adjustment"

By: TCO

TCO — Sun, 18 Sep 2005 17:07:09 +0000

How much extra work (or environmental damage or economic loss) would it be to actually cut the live trees down to get disc samples?

By: John G. Bell

John G. Bell — Thu, 07 Apr 2005 14:02:53 +0000

Schweingruber, F.H. 1988. “Tree Rings: Basics and Applications of Dendrochronology”. Kluwer Academic Publishers, Dordrecht, Netherlands

By: John G. Bell

John G. Bell — Tue, 05 Apr 2005 17:21:00 +0000

Re Schweingruber’s book
I’ll go down to my library and try to get it via ILL. I can find a huge list of articles he published but not his book. Do you recall the title? But, more relevant is how the cores and sections that became the data in these articles were prepaired. I’ll just have to RTFA .

When I google, poor signal to noise ratio!, I come up with all sorts of preparatory methods.
One had wet cores put in 95% alcohol for days at high temperature to extract the resin, then dried in telephone books before being glued into a shallow straight groove gouged in the upper surface of a plank. The next step is to sand down the mounted core to expose the rings. Obviously you can’t get MXDs from a core fixed by this method. Another site had the cores refrigerated. Perhaps they were confused with polar ice? They didn’t mention why this was done. It seems RWs from dead trees can come from disk-like sections. For some reason they don’t want to do this to live trees. Perhaps stumps are harder to hug. It does seem that
RWs taken from dead trees vs live trees are prepaired quite differently. They are sure different before they are prepaired. So …

Do the different initial condition of these samples, different methods of acquisition, and different methods of preporation before data extraction introduce a bias in data from live trees relative to that taken from dead trees?

I would like to see a chart showing percent of data from live trees in Tornetrask vs year above a plot of the difference of the Tornetrask RW and MXD chronologies. A strong match in data rich years would be interesting.

By: John G. Bell

John G. Bell — Mon, 04 Apr 2005 18:45:33 +0000

Steve, how do I find out how cores taken from live trees are desiccated so that they are in a like state with cores taken from long dead, cured timber? This has to take place before RWs and MXDs are taken, right?. Does this desiccation shrink the outer RWs of a tree more than the inner RWs? How does it effect the relationship between RWs and MXDs if at all? I ask because I understand the outer rings of a tree are by far the most biologically active and carry the substantial portion of water and nutrients.
I also wonder if in identically cured cores, one taken from the same tree decades later, the later core will show any shrinkage in the RWs that correspond to the earlier cores outer rings. This due to some other effect. Lessened use atrophy? Hydrostatic pressure gradient effects?

Steve: My understanding is that they treat the wood, but I don’t know how. Probably the best text to check on would be Schweingruber’s.

BTW along these lines, I recall seeing an article mentioning very long-term changes in wood density in samples from the early Holocene. I don’t remember the reference and I’ve googled all conceivable combinaitons without success to try to retrace my steps. If anyone runs across any references to wood density in the early Holocene, I’d much appreciate the information.

By: Peter Hartley

Peter Hartley — Mon, 04 Apr 2005 01:01:26 +0000

Further to the last post – I apparently had an error in my html, since I also referrred to a reference I found at CO2science.org that claimed to find in experiments with loblolly pine that CO2 increases ring width more than wood density. Hence, the CO2 fertilizer effect might indeed help explain a bias like you referred to above.

By: Peter Hartley

Peter Hartley — Sun, 03 Apr 2005 18:34:15 +0000

Has anyone studied what CO2 fertilization would do to maximum density and ring width? Presumably, one could examine trees from a FACE experiment an measure this directly. There is a FACE experiment using loblolly pines at Duke University

By: Dave Dardinger

Dave Dardinger — Sun, 03 Apr 2005 13:12:32 +0000

I was reading the early part of the thesis and one thing I was struck by was the reliance on ‘curve fitting’ to decide what adjustments to the raw data were to be made as a first step. I’m not saying this is necessarily wrong, but I’d feel happier with a bit more justification. I believe that the theory is that any error induced in the record of an individual tree will be washed out since there are many overlapping trees. But he does have some discussion of problems there can be when filtering, in essence, throws out the signal with the noise, in a slightly different context, so I wonder if the same thing can happen with the curve fitting? Can we assume there will be no bias introduced by ‘curve fitting’?