Mt Almagre and the “Divergence Problem”

1. Mt Almagre and the “Divergence Problem” 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 PP51C-0665 Stephen McIntyre and Peter Holzmann www.climateaudit.org • 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. • 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.) • 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. Modern portion of Almagre Tree #30 showing narrow recent ring widths Panorama of Graybill site on Mt Almagre 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. Two cores from Almagre strip bark tree #31Black –middle of strip; red – towards edge Two cores from Upper Wright foxtailLloyd’s field notes confirmed strip bark. Further Information Contact: Stephen McIntyre www.climateaudit.org Email: stephen.mcintyre@utoronto.ca Acknowledgements U.S. Forest Service; Jenny Franks of the University of Guelph; Leslie Holzmann, Nola McIntyre, Leslie Thomas, Tori Bommarito, Rebecca Lee. Combined chronology without power transformation Combined chronology with power transformation of 0.375