Comments on: Tornetrask #2

By: TCO

TCO — Sun, 18 Sep 2005 06:39:25 +0000

Here is a type of diagram which I often do on tree ring data. I’ve never seen anything like this in the tree ring literature, but some of you may be interested.

Why not share this with the community by publishing.

By: Steve McIntyre

Steve McIntyre — Sat, 02 Apr 2005 03:54:49 +0000

Dave – I’m going to post up something about NA values, which are more of a problem at Polar Urals than Tornetrask. In doing densitometric studies, Schweingruber’s group broke the cores and, if you can imagine, did not measure ring widths. Jones said that they counted the missing rings. I asked a specialist about this – he said that there should never be more than 1 broken ring and, if you have more than 1 break, the core is at a tangent. At some of the Urals cores, there are 7 breaks and up to 59 years missing at a break. Some of the cores definitely seem to be at a tangent. I’m not sure whether this has a material effect. The same specialist said that the data collection appeared to be hit-and-run, which may explain why there don’t seem to be any sampling maps.

John Bell, I’ve seen a report discussing modern sampling bias of a quite extraordinary type, which I’m going to post up. When they do samples, the cut-off point seems to be a 10 cm (or sometimes 8 cm tree). Also it seems that once trees get to a certain size, they are more prone to die. Sites have both fast-growing and slow-growing trees. So the cutoff point will not pick up slow-growing modern trees, whereas the fossil trees do not have the same bias. This has an effect on Briffa’s RCS method, but would not affect standardization with individual effects. The issue may be very serious.

By: John G. Bell

John G. Bell — Fri, 01 Apr 2005 19:25:16 +0000

Might a person extracting cores select from among the healthier live trees with the thought that they will more accurately record the weather, but in fact introduce a bias in that earlier cores from dead trees included trees in their decline with with smaller RWs in their last years? Could the AD1500 to 1600 gap be a result of so many 500 or so year old trees fitting into that category? AD1600 is not quite a light switch for live/dead cores but almost. conservatively 5/45 to 13/14. Keep in mind that this is by eye and I am proven subject to optical illusions

By: John G. Bell

John G. Bell — Fri, 01 Apr 2005 14:09:02 +0000

Dave – Exactly right. It was an optical illusion. A good one I think.
Steve – I wondered about the total lack of juvenile growth spurts in cores after 1600 and think it might be caused by drilling orientation on live trees so often missing their true centers. That would make me think those trees older and at a later stage of their life. Perhaps only by decades. Just a guess.

By: Dave Dardinger

Dave Dardinger — Fri, 01 Apr 2005 13:46:35 +0000

So how do they measure the distance between rings? Do they rotate the core until the rings are parallel in the microscope first or do they just measure the distance from ring to ring even if there’s a tilt in the rings? if the latter they’re off by a factor of Cos(tilt angle). Of course at low angles it doesn’t matter much, but if they indeed aren’t aimed directly at the center of the tree it will make the younger rings look increasingly wider as you approach the center.

By: Steve McIntyre

Steve McIntyre — Fri, 01 Apr 2005 05:52:10 +0000

NA- not available. The core in question is horizontal over the NA values; the impression of a negative slope is either an optical illusion or the plot is slightly tilted for some reason. I think that it’s an optical illusion. I haven’t determined the reason for the prolonged NA values. I have sorted out some NA issues in Polar Urals. There were two cores with archived values of 0 for over over 400 years (the life of the Polar Urals trees is usually only a couple of hunder years.) After many inquiries, it turned out that they had mistakenly assigned the same id number to two different cores (in 2 cases). They never explained to me how they handled this in RCS calculations as presumably the relatively high values of “700″ year old trees would affect the RCS calibration. I suspect that it’s posssible that there are different cores with the same ID number.

One unusual feature of the Polar Urals dataset (and to a lesser extent Tornetrask) is the many cores with some NA values. After many inquiries, Phil Jones said that they broke the cores for densitometric studies, resulting in rings being unavailable for measurement but not actual “missing” – if you follow the distinction. He said that they counted the rings, but did not measure them before breaking them. I asked a specialist about this and he said that numerous breaks show that the core is not oriented right and is proceeding at a tangent; also that cores break cleanly and no more than one ring should be lost. So there are many remaining quality control issues at these sites.

By: Dave Dardinger

Dave Dardinger — Fri, 01 Apr 2005 04:05:45 +0000

Re Comment 8.

Unless he’s already corrected what you mentioned, I think you’re being taken in by an optical illusion. When I hold a paper to the screen the line looks flat, not negative. But with all the other lines trending upward, that one flat one looks like it’s declining.

By: John G. Bell

John G. Bell — Fri, 01 Apr 2005 00:13:14 +0000

Steve,
The updated “grass” diagram now has one core with some years of negative RW values. That’s not raw data, it’s bloody . What is a NA value? Not available? The core I speak of lasts from AD900 to 1450 or so. A negative slope is unexpected, right? Perhaps, an unavailable ring width is indicated by a negative value in the data? Sounds like a standard programing trick to me . Better to replace the negative RWs with zero. Not right but not so wrong.

By: Steve McIntyre

Steve McIntyre — Thu, 31 Mar 2005 13:46:36 +0000

I amended the “grass” diagram as the first one (which I’d prepared fresh for the website) didn’t show values after an NA value. The amended one has more detail, although anyone’s impressions are unlikely to be altered. Steve

By: Steve McIntyre

Steve McIntyre — Thu, 31 Mar 2005 02:24:47 +0000

Larry, I haven’t quantified the effect of the “alpha” tree. The “robustness” of various dendro standardization methods is an interesting question – in fact, all the statistical methods involved in dendro “chronology” calculations need a big housekeeping. I’ve spent a lot of time on this in the past year and have a lot of thoughts in inventory but haven’t worked up much yet.

I’ll post up some info on the Polar Urals site in a day or two to give more food for thought.

One would really like to see maps of where the samples were taken. If geologists were doing this, they would be much more methodical and everything would be better documented (I haven’t seen any evidence that dendro people routinely make proper sampling maps, but I don’t know that they don’t either.)

I think that I’ve read somewhere that the Tornetrask Scots pine are to the north of their modern range and are a relict (like some other long-lived sites), which would toe them to the Finnish oaks, but I don’t recall the reference.
Regards, Steve