Lamarche on Treelines #2

Here is Lamarche’s diagram of altitudes at the key bristlecone sites of Sheep Mountain and Campito Mountain (as noted below, when wood erosion is allosed for, the post-MWP decline is placed after 1500.)

The other diagram of treeline elevations that I’ve seen is at the Polar Urals site, which I’ve shown here and here. The really odd coincidence – and I don’t believe in coincidences – is that bristlecones and Polar Urals ring width chronologies are the "active ingedients" in showing a low 11th century relative to the 20th century in MBH99, Jones et al [1998] and Crowley and Lowery[2000] – the mainstays of IPCC TAR. Now I think that 11th century Polar Urals site chronology is screwed up (and there is no valid chronology until at least 1100), as discussed before, but that’s a different issue.

Shiyatov aobviously thought that the MWP had the most substantial growth at Polar Urals within the last millennium. Here is an extended excerpt from Lamarche [1973], showing that there’s no indication that he thought the MWP was a period of reduced growth at Sheep Mt or Campito Mt.

In passing, Lamarche attributed the aridity of the White Mountains to it being in the lee of the Sierras for Pacific moisture and being at a great distance from the “monsoon”à rains of southwestern U.S. He refreshed the observation that Sheep Mountain bristlecones were on the east slope on dolomite substrate, while Campito bristlecones were on the NW slope on sandstones. He observed that seedlings and saplings at Sheep Mt were abundant below the treeline but scarce above it, with many fewer seedlings and saplings at Campito Mt. The oldest living trees at Sheep My were established between 850 and 1050, with relatively few trees between 1450 and 1850. All saplings sampled had pith dates from 1865 to 1948 (younger ones were present but were not sampled due to their small size) . The upsurge in reproduction at Sheep Mt commenced about 1850 or 1860 and has continued. At Campito Mt, there were trees established from 500 through 1500, when reproduction rates declined. There were no survivors, which started between 1700-1900. The saplings were smaller and younger than Sheep Mt (only 3 from the period 1920-1950) . Lamarche:

“the decline in reproduction beginning about 1500 and lasting until 1850-1900 is a striking feature of both areas. ..The decline was most pronounced at high altitudes, where there are no living trees between 13 and 50 cm radius corresponding to the period from about 1250-1850….

Although the dating is not exact, the death of large numbers of trees in both localities at upper treeline a few centuries ago indicates an abrupt climatic deterioration. Since both areas were affected, the climatic change seems to have involved both temperature and precipitation…Reproduction was at a minimum between 1700 and 1850, whereas most of the trees died before 1600."

Lamarche said that his Figure 17 (shown above) shows the minimum altitudes., noting that, between 4000-2500 BP, trees grew at the highest possible altitudes on Campito Mountain and the climatic treeline probably lay above the altitude of the summit.

Lamarche notes that the actual treeline between 1100 and 1500AD was also amost certainly higher than shown in Figure 17. He observed:

“bark persists only 10-20 years after death. The sapwood is probably removed within 100-200 years of study. ..sapwood is outer 20-150 (avg 75) rings….

[for the medieval subfossil trees] , the outside rings of the best preserved of these dead trees give dates shortly after AD1500. Weathering and consequent loss of wood could account for [apparent] outside dates of 1100-1200 on many of these trees, which may have died in the interval 1300-1600….

The oldest specimens have been greatly reduced in size since death. Several hundred years of growth may be missing from the inner and outer parts of such specimens.

I try to keep an eye on comments about 19th century human impact – other than CO2. Lamarche observes that loggiing and grazing are unlikely to have had an impact, but then says:

There are very few young trees in established stands at lower altitudes [LaMarche 1969] whereas areas cleared by logging and fire have abundant seedlings and saplings.

I’m interested in the footprint of small 19th century mines in this area. I started posting up some information on bristlecone sites about 6 months ago and have information in inventory, which I should post some time. I’m also interested in the potential impact of sheep grazing. In other parts of the southwest, a "pulse" of conifer growth is attributed to 19th century sheep eating up ("mining out") herbs and grasses that were in competition with the conifers. The possibility of this has not been excluded in bristlecone sites. Lamarche says:

Large numbers of sheep are said to have grazed in this region during the latter half of the 1800s and cattle graze seasonally in the subalpine meadows. This activity does not seem to have caused reduced reproduction at upper treeline but in fact coincides with a period of high reproduction rates.

Lamarche then discusses the relationship of changes in treelines to glacier activity, pointing our inconsistencies, showing the need to attend to changes in precipitation, which proximately affect glacier acumulation.

Trends in treeline altitude in the White Mountains are opposite to trends inferred by Richmond 1972 from relative altitudes of glacier termini during successive periods of glacial advance during the past several thousand years….In many cases, glacier termini reached early Neoglacial limits that were only slightly higher in altitude than those reached in late Neoglacial time. ..The discordant response of the Sheep Mountain and Campito Mountain treelines may mean that the early Neoglacial cooling was also associated with increased precipitation. Such conditions would be favourable for growth of mountain glaciers.

It sure is hard to read these observations and come away with an impression that these trees are telling you that the 20th century was unequivocally warmer than the MWP. Lamarche wrote a famous paper in which he argued that there was a warm MWP, and, this together with Lamb’s reconstruction of CEng from documents, buttressed the former concept of a MWP.

Reference:
Lamarche, V., 1973. Holocene climatic variations inferred from treeline fluctuations in the White Mountains, California. Quat. Rese 2, 632, 660.


2 Comments

  1. TCO
    Posted Sep 21, 2005 at 1:53 PM | Permalink

    Very nice summary.

  2. Posted Aug 13, 2009 at 2:54 PM | Permalink

    There is a new study on the response of treelines to climate change reported here.

One Trackback

  1. […] areas. Medieval treelines in California were higher than at present, discussed here and here. Post-medieval lakes have even submerged medieval trees. Miller (2006) discussed here and here […]

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