1. Mt Almagre and the
“Divergence Problem”
Stephen McIntyre and Peter Holzmann
www.climateaudit.org
Acknowledgements
U.S. Forest Service; Jenny Franks of the University of Guelph; Leslie
Holzmann, Nola McIntyre, Leslie Thomas, Tori Bommarito, Rebecca
Lee.
Methods
Sampled 64 cores (36 trees), of which 38 cores (20 trees) at or near Graybill site with other cores at lower sites;
Measurement and cross-dating by U of Guelph (J. Franks). Thus far 38 cores (23 trees) cross-dated
WinDendro used for measurement (see example below)
Measurement data and meta-data online within 3 months of sampling (www.climateaudit.org/data/colorado). ITRDB archive to follow. Meta-data includes: 5-digit co-
ordinates, altitude, aspect; strip bark, heart rot, compression.
Comprehensive photo gallery with pictures of all trees (picasaweb.google.com/Almagre.Bristlecones.2007) and panoramas (www.gigapan.org keyword: Almagre).
Analysis is in progress as measurement data received only recently and more cross-dating appears possible.
Average ring width is only 0.41 mm
Strip Bark
Strip bark forms said to be problematic (North et al, 2006)
Major differences between individual cores in strip bark trees
Not obvious how to model error structure statistically
Lloyd (pers. comm.) confirmed strip bark at similar foxtail core.
(see UWL132 at right)
Chronologies
Chronologies calculated using generalized negative exponential or line through mean
Chronology from new samples reconciled closely to Graybill in overlap period. Further crossdating may affect results,
Extreme non-normality with positive skew. Power transformation is effective in mitigating non-normality (but not autocorrelation.)
Further Information
Contact: Stephen McIntyre
www.climateaudit.org
Email: stephen.mcintyre@utoronto.ca
Identifying the
Graybill Site
Individual trees were identified from online photos and tags. We located 16
tagged trees of which 8 have been sampled. We reconciled the tags to the
ITRDB archive (thanks to C. Hallman). Only 3 of the 8 sampled trees had
been archived. It appears that Graybill sampled 42 trees, of which only 21 are
archived, although additional measurement data exists in Tucson.
Mt Almagre, Colorado
Updating the Mt Almagre bristlecone pine chronology offered an opportunity to
test several hypotheses:
• It was a classic Lamarche and Graybill site that had not been updated
since 1983;
• it is a treeline site. Indeed it was the highest (3,600 m) chronology at
ITRDB going back to AD1000;
• It was a bristlecone site, used as an individual proxy in Crowley and
Lowery 2000 and as a component of Mann’s PC1 in multiple studies;
• It was very close to Colorado Springs (and Boulder)
• No location map but believed to be near a Forest Service road and
accessible by 4-wheel drive;
• It was a “southern” chronology in Cook et al (2004) terms and could
test the hypothesis that “divergence” was limited to northern sites.
Discussion
Almagre is a bristlecone treeline site that has been used as a
“temperature sensitive” site in reconstructions;
on geographic grounds, it should be more temperature limited than
California bristlecone sites: it is about 90 miles north and 125
meters higher than the Sheep Mountain CA bristlecone site (about
120 miles north and 80 meters higher than the Upper Wright CA
foxtail site);
Under the hypothesis (Mann et al 1998, 1999, 2003, 2007) that
bristlecones are “teleconnected” to global “climate fields”, Almagre
ring widths would be expected to increase in the warm 1990s and
2000s.
Instead, Almagre has the “divergence” problem characteristic of
northern sites: ring widths have declined in the 1990s and 2000s
from high levels in the late 19th and mid-20th century.
The site has an extremely arid appearance and it appears likely
that growth is moisture limited even at treeline;
Growth suppression in the 1840s is very distinctive. Woodhouse et
al (BAMS 2002) reported a mega-drought from 1845-56 in eastern
Colorado and the Colorado Front Range and the growth
suppression at Almagre may be related. Growth suppression in the
1840s is characteristic of other Colorado Front Range bristlecone
sites and can even be perceived in California bristlecone
chronologies.
Developing a proper statistical model for strip bark presents
formidable difficulties since the growth pulses appear to exceed
climatic effects and combine extreme non-normality and
autocorrelation. Under the circumstances, it was encouraging that
we were able to obtain similar results to Graybill from a different
sample. However, the effect of cross-dating selection has not yet
been evaluated.
The existence of unarchived Graybill measurement data at the
University of Arizona was identified. Archiving of this data is
encouraged.
Left – Location map showing Mt Almagre to west of Colorado Springs;
Right – Google Earth image of Mt Almagre with Forest Service access road.
Left – Original Graybill photograph (84-55; ALM16).
Right – the same tree (#30) being cored by Pete Holzmann.
Tree rings dated back to AD 1126
Combined chronology without power transformation Combined chronology with power transformation of 0.375
PP51C-0665
Two cores from Upper Wright foxtail
Lloyd’s field notes confirmed strip bark.
Two cores from Almagre strip bark tree #31
Black –middle of strip; red – towards edge
Panorama of Graybill site on Mt Almagre
Modern portion of Almagre Tree #30 showing
narrow recent ring widths
