North American Upper Treeline #2

In our continued search for evidence supporting the IPCC 4AR SPM claim that “”Studies since the TAR draw increased confidence from additional data showing coherent behaviour across multiple indicators in different parts of the world”, I am reviewing upper treeline North American site chronologies specifically mentioned in the short Wilson and Luckman 2003 survey of such chronologies excerpted yesterday here. Their short survey began: “Dendrochronological studies at upper treeline in the southern Canadian Cordillera have focused on either Vancouver Island (Smith and Laroque, 1998; Laroque and Smith, 1999)… ”

Yesterday I discussed Laroque and Smith 1998, which reported 4 Vancouver Island mountain hemlock chronologies up to 1994, yielding a composite chronology with mutlidecadal variation since 1500 but no 20th century upward trend and no strong positive response in ring widths to recent warming, providing no support for the SPM statement.

Laroque and Smith 1999 url is a report on 4 high-elevation Vancouver Island yellow cedar chronologies also up to 1994. Laroque and Smith 1999:

Yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach, Cupressaceae) trees are common associates of high elevation stands in the Pacific Northwest (Dobrའet al. 1996). They are the oldest known coniferous trees in Canada… Yellow-cedar is abundant on Vancouver Island at sites where the climate is hypermaritime and where the soil is moist and derived from base-poor igneous rock (Klinka 1992). At sites with deep fertile soils, yellow-cedar trees are uncommon, as they are unable to compete with fastergrowing tree species such as western hemlock (Tsuga heterophylla (Raf.) Sarg.) and grand fir (Abies grandis Dougl. Lindl.)…first dendrochronological investigation of yellow-cedar trees at montane sites on Vancouver Island and considers the effects of climate on the radial growth of yellow-cedar…

The dominant tree species at all study sites was mountain hemlock, with a minor constituent of yellow-cedar and amabilis fir. … Three of the sites share similar topographic characteristics (elevation, slope angle, and aspect): Mount Cain; Mount Washington; and Mount Arrowsmith (Table 1). The Milla Lake site was steeper …

Their Figure 4 shows the resulting chronologies as follows:

Laroque and Smith 1999 note strong positive autocorrelation on the chronologies, from which they conclude that:

yellow-cedar growth in this region was strongly conditioned by factors in preceding growth years. Similar relationships have been noted within amabilis fir (Dobrའand Klinka 1998), mountain hemlock (Wiles et al. 1996), and subalpine fir (Ettl and Peterson 1995) trees in the Pacific Northwest.

They conclude by reporting that there was a strong common signal to the chronologies, which they interpreted as evidence of climatic control as follows:

Our discovery of a common growth signal within high-elevation stands of yellow-cedar on Vancouver Island connotes a relationship with strong similarities over a broad regional area. Our efforts to identify the role climate plays in this relationship were successful …

These chronologies were mentioned in passing once before on a previous thread. I noted that Rob Wilson’s Gulf of Alaska chronologies included a yellow-cedar site. Ever since Gaspé, I keep my eyes open for cedar sites and I posted the figure excerpted above as a comment to the Gulf of Alaska thread, observing:

I find the distinctive HS shape hard to discern as well as the linear positive response to 20th century temperature increases.

Rob Wilson wrote to me offline stating that this was an instance of misinformation – I had challenged him for instances of supposed “misinformation” – saying that, although he would have to dig the paper out, he was sure that these data “were never used to reconstruct climate” and, accordingly, my presentation of these chronologies was a “confusing” reference that was not relevant to the thread except that I “like showing TR series which show no increasing trends.”

I think that we can all agree then that these chronologies are upper treeline chronologies, that they do not show an increasing trend, that they are not “additional data showing coherent behaviour across multiple indicators in different parts of the world” – and that the study was cited by Wilson and Luckman 2003 in their short survey of prior upper treeline studies.

Rob justified his reproach to me on the basis that these chronologies had not been used “to reconstruct climate”. Although Laroque and Smith 1999 said that the common yellow-cedar signal was attributable to climate, they did not present a reconstruction of either temperature or precipitation obtained by inverting the chronologies.

However, to borrow a phrase from Clinton, it depends on what the meaning of “used” is. These upper treeline chronologies were clearly canvassed and assessed in the attempt to reconstruct upper treeline temperature. They were disregarded – but they were touched in the collective search process of the dendro community and became part of the sampling program. In my opinion, the situation is parallel to Jacoby’s “few good men”: Jacoby said that he used the 10 most “temperature-sensitive” chronologies out of 36 and discarded the rest because they didn’t provide a story. These yellow-cedar chronologies were part of a collective search process and were even cited by Wilson and Luckman. It’s entirely relevant to show that these yellow-cedar chronologies did not have HS-shape as part of a survey of upper treeline populations.

I might add here: if my ongoing survey of these chronologies is deficient in some particulars relative to an ideal survey by dendroclimatological specialists, I apologize. However, to my knowledge, there is no such survey; IPCC AR4 failed to cite or commission such a survey and, if any dendroclimatologist wishes to bring our attention to such a survey, I will gladly re-focus my attention on that survey. In the mean-time, I’m going to go through the articles mentioned by Wilson and Luckman 2003 one by one and see what they say.

Laroque, C.P. and Smith, D.J. 1999: Tree-ring analysis of yellow cedar (Chamaecyparis nootkatensis) on Vancouver Island, British Columbia. Canadian Journal of Forest Research 29(1), 115—23.


  1. JerryB
    Posted Apr 6, 2007 at 9:52 AM | Permalink

    Steve M,

    It seems that some odd bits and pieces of statments, starting with:

    “standard chronology of the radial growth behaviour of high-elevation yellow-cedar trees on Vancouver Island (Fig. 5).”

    are floating around near the end of that post.

  2. jae
    Posted Apr 6, 2007 at 10:27 AM | Permalink

    I wish someone would update these samples. It would be interesting to see what the ’98 El Nino did to growth in 1998-1999.

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