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Absent rings are rare in Northern Hemisphere forests outside the American Southwest

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Background/Question/Methods  ...

Background/Question/Methods 
Under environmental stress, boreal and temperate trees will occasionally form a discontinuous layer of wood about their stem, a condition described as a locally-absent (or “missing”) growth ring. Absent rings can potentially cause errors in tree-ring dates and dendroclimatic reconstructions but the frequency, distribution and controls of these features are not well understood at large spatial scales. Furthermore, the recent claim that the Northern Hemisphere tree-ring network contains multiple chronological errors caused by widespread but unrecognized locally-absent rings has been difficult to evaluate because it is not known where or when absent rings have occurred across boreal and temperate forests or what environmental factors cause the development of spatially-extensive absent rings. Here we present a synthesis of locally-absent rings across the Northern Hemisphere during the last millennium based on 2,359 publicly-available tree ring-width records.

Results/Conclusions 
Over the entire dataset, one locally-absent ring was observed for every 240 visible rings. More than half of all records (1,296 of 2,359) did not contain a single absent ring. Absent rings were extremely uncommon at high latitudes; poleward of 50°N, the absent:visible ratio increased from 1:240 to 1:2,500. Absent rings were not widespread during the growing seasons that followed the four largest stratospheric sulfate aerosol injection events of the last millennium, including A.D. 1259 and the “Year Without a Summer” in A.D. 1816 or during the coldest year in the Northern Hemisphere in the last 1,500 years. Because these features have occurred so rarely in high-latitude and high-elevation tree ring-width records, the argument that paleotemperature estimates based on these data contain chronological errors due to unrecognized absent rings is not consistent with field observations. If however the rate of absent-ring formation were to increase in forests outside of the American Southwest, that behavior would represent a response to environmental stress that is without precedent over the last millennium.

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    Absent rings are rare in Northern Hemisphere forests outside the American Southwest Absent rings are rare in Northern Hemisphere forests outside the American Southwest Presentation Transcript

    • Source: Stones 55
    • Source: Intergovernmental Panel on Climate Change, 2007 Tree rings are one of the main proxy archives used to estimate past changes in regional and global climate.
    • narrow growth ring a “missing” ring
    • ‘LOCALLY-ABSENT’ RING
    • The cambium of trees of many species may be locally dormant, in the sense that no new cells are produced, throughout one or more growing seasons. “ ”Edmund Schulman Ecology, 1941
    • The 1815 eruption of Mount Tambora was one of the the largest volcanic events of the last millennium.
    • Michael Mann and colleagues used numerical simulations of climate and tree growth to show that when temperatures fall abruptly for one or two growing seasons, trees in these regions undergo li le or no growth. “ ” Nature Geoscience press release February 2012
    • ? COULD THE GLOBAL TREE-RING NETWORK CONTAIN WIDESPREAD (BUT UNRECOGNIZED) ‘ABSENT’ RINGS?
    • Picea Pinus Pseudotsuga Quercus Larix a 18ºN 36ºN 54ºN 72ºN 90ºN 120ºW 60ºW180ºW 0º Source: St. George et al., Geophysical Research Le ers (2013)
    • 60ºE 120ºE 180ºWSource: St. George et al., Geophysical Research Le ers (2013)
    • Picea Pinus Pseudotsuga Quercus Larix a c #records %records b 18ºN 36ºN 54ºN 72ºN 90ºN 120ºW 60ºW 0º 60ºE 120ºE 180ºW180ºW 2000 1000 0 0% 12% 6% 0º How o en have locally-absent rings occurred across the Northern Hemisphere tree ring-width network? Source: St. George et al., Geophysical Research Le ers (2013)
    • TDF0
    • ? WHERE AND WHEN HAVE ABSENT RINGS OCCURRED ACROSS BOREAL AND TEMPERATE FORESTS?
    • ? WHAT ENVIRONMENTAL FACTORS CAUSE THE DEVELOPMENT OF WIDESPREAD ABSENT RINGS?
    • Absent rings are rare in tree-ring records. 1
    • 1 : 240 absent rings visible rings ALL RECORDS
    • 1,063 RECORDS HAD AT LEAST ONE ABSENT RING. 1,296 RECORDS DID NOT HAVE A SINGLE ABSENT RING.
    • 2Absent rings form quite o en in some regions (and tree genera) and very rarely in others.
    • 0% 2% 4% 6% 8% 20°N 40°N 60°N 80°N Latitude Percentage of locally-absent rings b Picea Quercus Pinus Pseudotsuga Larix Other genera Source: St. George et al., Geophysical Research Le ers (2013)
    • 8% 60ºE 120ºE 180ºW Frequency of locally-absent rings
    • 120ºW 60ºW180ºW 0º 18ºN 36ºN 54ºN 72ºN 90ºN Frequency of locally-absent rings
    • 1005 1090 1258 1475 1542 1580 1685 1729 1904 20% 40% 60% 80% 100% 0% Intensity of locally-absent rings During the last millennium, widespread absent rings have been observed  only in the southwestern United States. Source: St. George et al., Geophysical Research Le ers (in press)
    • 3Absent rings are extremely rare in temperature-limited environments.
    • Source: Mirko Thiessen
    • 1 : 2,500 absent rings visible rings ABOVE 50°N
    • PICEA LARIX (spruce) (larch)
    • 134 881TREE-RING ‘YEARS’
    • 134 881TREE-RING ‘YEARS’ ZERO CASESWHERE A GROWTH RING WAS MISSING FROM EVERY SPRUCE TREE AT THE SAME SITE.
    • 1816THE “YEAR WITHOUT A SUMMER”
    • 1816 1259 1453 20% 40% 60% 80% 100%0% Intensity of locally-absent rings During the “Year Without A Summer”, there are almost no cases where even one tree was missing a ring for that year. Source: St. George et al., Geophysical Research Le ers (2013)
    • ? COULD THE GLOBAL TREE-RING NETWORK CONTAIN WIDESPREAD (BUT UNRECOGNIZED) ‘ABSENT’ RINGS?
    • EVERYWHERE ANYWHERE
    • ‘LOCALLY-ABSENT’ RING
    • ±0
    • Source: Phil Camill DROUGHT STRESS?