Comments on: A Weird Jacoby-D'Arrigo Series

By: Steve McIntyre

Steve McIntyre — Sun, 16 Apr 2006 02:48:58 +0000

#9. Each core was standardized by fitting a “generalized negative exponential” i.e. a negative exponential with an asympotote to each core following usual procedures. I did this in R, but I’ve verified the algorithm against ARSTAN.

The bottom graphic where the red chronology is somewhat similar to my emulation of Jacoby is from Schweingruber and is archived rather than calculated. The inability to replicate Jacoby-D’Arrigo is odd, but D’Arrigo said that the chronology needs to be withdrawn (but has not done so.) The chronology is used in a number of studies.

By: TP

TP — Sat, 15 Apr 2006 21:12:00 +0000

Dear Steve,

I am curious as to why your blue curve in the upper half of the last figure [the second Figure 1], while standardized, still has a long, downward trend in ring index from the late-1700s until 1950?

You are aware of the well-documented phenomenon of narrower ring-widths as trees get larger, right? It is simple geometry: if a tree has a constant rate of growth, raw ring widths must decline as the stem expands. Therefore, a constant raw ring width or increase in raw ring width as the stem increases in diameter indicates increased tree growth rates. Allometric equations, used in forestry to predict the amount of aboveground biomass [wood], support this line of thinking. This is a primary reason as to why ring widths are ‘standardized’.

So, the long downward trend in ring index since the 1700, when the trees were smaller, until the 1950s, when the trees were undoubtedly much larger, can be explained if the geometric growth trend described above is not removed. I am curious at to your standardization method. You say it is standard, but that is rather vague. Can you elaborate?

Thanks,
Terrence

By: jae

jae — Mon, 10 Apr 2006 16:34:55 +0000

Getting much clearer: you can pick a set of tree rings to construct ANY type of curve you wish.

By: mark

mark — Sun, 09 Apr 2006 17:06:58 +0000

Lots do. PCA is used primarily for image processing where the cause and effect is known. It also is used in situations where the weights are applied to data with stationary statistics for noise. I.e. just because the weighting is valid in the 20th century does not mean it is valid for the 18th because the noise in the samples is not known to be the same then as now.

Mark

By: JerryB

JerryB — Sun, 09 Apr 2006 15:52:02 +0000

Re: “The ability to pick and choose which samples to use is an advantage unique to dendroclimatology.”

I sometimes wonder whether some practices, that might be valid in dendrochronology, got carried over to dendroclimatology in which they would be invalid.

By: Steve McIntyre

Steve McIntyre — Sun, 09 Apr 2006 14:39:51 +0000

#3 – they both started numbering from 1, but the samples are not the same where the numbers coincide. They seem to be from different programs.

By: CasualBrowser

CasualBrowser — Sun, 09 Apr 2006 07:08:56 +0000

Although they report different total core numbers, is there any way to compare Jacoby and Schweingruber cores to see which cores Jacoby left out?

Were the cores Jacoby left out, and Schweingruber used, reported by Jacoby (but not used)?

By: Steve McIntyre

Steve McIntyre — Sun, 09 Apr 2006 05:14:58 +0000

#2 – there’s something else going on besides cherry picking. In the top panel, I’ve benchmarked my emulation of Jacoby’s chronology calculations on another data set, where I can replicate very closely. Here I’ve worked with the cherry picked measurements (if indeed they have been picked) and still get a different answer. I think that there might be something wrong with the calculation. We already know that D’Arrigo asked the chronology be withdrawn from WDCP.

I’m not sure that I’ll be able to locate other overlaps, but I’m definitely going to look.

By: TCO

TCO — Sun, 09 Apr 2006 02:23:23 +0000

I think wiggle matching theory would imply that the high frequency agreement would be reasonable for trees from the same population. But low may not be (not sure why…competition?) Anyhow, if there is some effect of people creating series that bias result by leaving out the “apples”, that might be the effect one would see.

By: Nicholas

Nicholas — Sat, 08 Apr 2006 23:14:25 +0000

The blue and black graph shows remarkably good correlation in the high frequencies (eyeballing it) over pretty much the whole chronology, but has two significant divergences from 1700-1750 and 1920-1970. I wonder what that means? Perhaps we’re seeing the “divergence” problem happening in earlier parts of the chronology as well as in the 20th century? Or perhaps some other biasing local factor.

Either way it doesn’t look good for those trying to extract a meaningful low-frequency signal from them. Which one is correct? The high frequency signals seem much more reliable.