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The need for new theory in global dendroclimatology

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Interdisciplinary Tree-Ring Research | European Geosciences Union General Assembly | April 10, 2018
THE NEED FOR
NEW THEOR...

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Source: Niklas Torberg
LATE-HOLOCENE TEMPERATURES

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Source: Schneider et al, Geophysical Research Le ers, 2015
RECONSTRUCTION OF SUMMER (JJA) TEMPERATURES
IN THE NORTHERN HEM...

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The need for new theory in global dendroclimatology

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So much of what we know about the Earth’s climate during the past two millennia comes from tree rings. Information gleaned from the physical or chemical properties of growth rings in trees have allowed us to extend hemispheric-scale temperature records back by several centuries, construct annual maps of drought severity that span several continents, and generate proxy estimates for many of the leading modes within the climate system. The theoretical foundation that underpins these products — and most others in dendroclimatology — was fully mature by the early 1990s and set out in detail by Cook and Kairiukstis in their seminal book, ‘Methods in Dendrochronology’. Most of the core analytical methods used to infer past climate from tree rings that appear in this reference (as well as prior works) depend on two concepts in particular: first, the idea that patterns common to many trees at many sites are more likely to be related to synoptic-scale climate variability (the principle of replication), and second, the notion that the most useful tree-ring records are found in forests where growth is particularly sensitive to a specific aspect of local climate (the principle of site selection). But because of (i) the gradual expansion, extension, and in-filling of the global tree-ring network and (ii) the emphasis given to atypical or even unique site-specific signals by some novel reconstruction methods, it is a point of debate within our community, at least implicitly, whether these principles remain valid. This presentation will review several recent studies that illustrate the possible advantages offered by a disregard for the usual ‘rules’ of dendroclimatology but will also discuss the potential pitfalls of placing too much emphasis on apparently optimal records. We hope this talk will encourage the sharing of ideas on how best to extract climate information from the ever-expanding network of tree-ring records across our planet and help open a discussion on the relevance of our standard theoretical framework to contemporary global dendroclimatology.

So much of what we know about the Earth’s climate during the past two millennia comes from tree rings. Information gleaned from the physical or chemical properties of growth rings in trees have allowed us to extend hemispheric-scale temperature records back by several centuries, construct annual maps of drought severity that span several continents, and generate proxy estimates for many of the leading modes within the climate system. The theoretical foundation that underpins these products — and most others in dendroclimatology — was fully mature by the early 1990s and set out in detail by Cook and Kairiukstis in their seminal book, ‘Methods in Dendrochronology’. Most of the core analytical methods used to infer past climate from tree rings that appear in this reference (as well as prior works) depend on two concepts in particular: first, the idea that patterns common to many trees at many sites are more likely to be related to synoptic-scale climate variability (the principle of replication), and second, the notion that the most useful tree-ring records are found in forests where growth is particularly sensitive to a specific aspect of local climate (the principle of site selection). But because of (i) the gradual expansion, extension, and in-filling of the global tree-ring network and (ii) the emphasis given to atypical or even unique site-specific signals by some novel reconstruction methods, it is a point of debate within our community, at least implicitly, whether these principles remain valid. This presentation will review several recent studies that illustrate the possible advantages offered by a disregard for the usual ‘rules’ of dendroclimatology but will also discuss the potential pitfalls of placing too much emphasis on apparently optimal records. We hope this talk will encourage the sharing of ideas on how best to extract climate information from the ever-expanding network of tree-ring records across our planet and help open a discussion on the relevance of our standard theoretical framework to contemporary global dendroclimatology.

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The need for new theory in global dendroclimatology

  1. 1. Interdisciplinary Tree-Ring Research | European Geosciences Union General Assembly | April 10, 2018 THE NEED FOR NEW THEORY IN GLOBAL DENDRO- CLIMATOLOGY
  2. 2. Source: Niklas Torberg LATE-HOLOCENE TEMPERATURES
  3. 3. Source: Schneider et al, Geophysical Research Le ers, 2015 RECONSTRUCTION OF SUMMER (JJA) TEMPERATURES IN THE NORTHERN HEMISPHERE EXTRATROPICS FROM WOOD DENSITY
  4. 4. Source: Svein-Magne Tunli COLORADO RIVER DISCHARGE
  5. 5. Source: Meko et al, Geophysical Research Le ers, 2007 TWELVE CENTURIES OF PALEODISCHARGE ESTIMATES FOR THE UPPER COLORADO RIVER BASIN
  6. 6. Source: NASA JET STREAM POSITION
  7. 7. Source: Trouet et al, Nature Communications, 2018 ESTIMATING PAST VARIABILITY IN THE LATITUDINAL POSITION OF THE NORTH ATLANTIC JET FROM TREE RINGS
  8. 8. Source: Emile-Jeay et al, Scientific Reports, 2017 TREE RINGS ARE THE MOST NUMEROUS PROXY IN THE PAGES 2K DATABASE AFTER CE 1200, AND DURING THE LAST SIX CENTURIES CONSTITUTE A SOLID MAJORITY. Our contribution
  9. 9. THEORY
  10. 10. WHENEVER ANYONE MENTIONS THEORY TO A GEOMORPHOLOGIST, HE INSTINCTIVELY REACHES FOR HIS SOIL AUGER. “ ” Richard Chorley Bases for theory in geomorphology (1978)
  11. 11. Source: Chad King
  12. 12. NORTH AMERICAN TREE-RING NETWORK
  13. 13. ? DO WE AGREE AS A COMMUNITY, THAT THESE PRINCIPLES ARE STILL VALID OR DO THEY REQUIRE REVISION?
  14. 14. PRINCIPLE OF REPLICATION PRINCIPLE OF SITE SELECTION
  15. 15. PRINCIPLE OF REPLICATION
  16. 16. COLLECTING DATA FROM MORE THAN ONE RADIUS PER TREE, MORE THAN ONE TREE PER SITE, AND MORE THAN ONE SITE PER REGION MAXIMIZES THE ENVIRONMENTAL SIGNAL AND MINIMIZES THE AMOUNT OF ENVIRONMENTAL NOISE.
  17. 17. ATHABASCA RIVER COLORADO RIVER
  18. 18. Source: Svein-Magne Tunli COLORADO RIVER, USA
  19. 19. Source: Meko et al, Geophysical Research Le ers, 2007 THE RECONSTRUCTION MODEL USED BY MEKO AND COLLEAGUES WAS COMPLEX IN EXECUTION BUT SIMPLE IN DESIGN.
  20. 20. FCOLORADO=aX+b(i) All tree-ring chronologies were used to predict F (ii) Principal components analysis gave more emphasis to variance shared among all chronologies (iii) All chronologies had a positive association with river flow water-year total natural flow tree-ring width chronologies
  21. 21. ATHABASCA RIVER COLORADO RIVER
  22. 22. ATHABASCA RIVER, CANADA Source: Sarunas Burdulis
  23. 23. 16 CHRONOLOGIES 5 LAGS & LEADS 1-3 TREE-RING VARIABLES 80-240 POSSIBLE PREDICTORS
  24. 24. AthabascaRiver - Latewood is more narrow when discharge is high Latewood is wider when discharge is high + NEIGHBORING CHRONOLOGIES DEVELOPED FROM THE SAME SPECIES
 SHOW THE OPPOSITE RESPONSE TO RIVER FLOW.
  25. 25. ? HOW DO WE EVALUATE WHETHER RARE SIGNALS THAT ARE ANALYTICALLY USEFUL TO US REFLECT REAL RELATIONSHIPS BETWEEN CLIMATE AND TREE GROWTH?
  26. 26. TOTAL RING-WIDTH EARLYWOOD WIDTH LATEWOOD WIDTH MAXIMUM LATEWOOD DENSITY 𝛅13C 𝛅180 𝛅D TRACHEID SIZE
  27. 27. PRINCIPLE OF SITE SELECTION
  28. 28. DENDROCHRONOLOGISTS SHOULD APPLY THE PRINCIPLES OF LIMITING FACTORS AND ECOLOGICAL AMPLITUDE TO DETERMINE WHICH TREES ARE MOST LIKELY TO PROVIDE INFORMATION ABOUT A SPECIFIC ENVIRONMENTAL SIGNAL.
  29. 29. Source: Wikipedia user Brambleshire LOWER FOREST BORDER SOUTHWESTERN USA
  30. 30. Source: Daniel Case ARCTIC/ALPINE TREELINE YUKON CANADA
  31. 31. CORRELATION BETWEEN TREE-RING WIDTHS AND SUMMER (JJA) TEMPERATURE Modified from St. George, Quaternary Science Reviews, 2014
  32. 32. CRATER LAKE
  33. 33. CRATER LAKE NATIONAL PAKK
  34. 34. LTS 0 .2 2 -0 .2 4 -0 .3 8 -0 .4 1 -0 .4 2 -0 .3 6 -0 .3 5 -0 .3 4 -0 .1 9 -0 .3 0 -0 .4 7 -0 .5 0 -0 .4 7 -0 .3 8 -0 .3 4 -0 .3 4 -0 .2 0 0 .3 1 -0 .2 1 0 .3 0 0 .2 0 0 .2 1 -0 .2 3 -0 .2 7 -0 .3 7 -0 .4 3 -0 .4 1 -0 .3 4 0 .2 7 -0 .2 5 LLR PMP PSD MTS CTR PNC 0 .2 7 0 .1 8 -0 .2 5 -0 .2 8 -0 .2 9 -0 .2 4 -0 .2 2 -0 .1 8 0 .2 1 -0 .2 3 -0 .3 3 -0 .3 8 -0 .2 5 -0 .2 3-0 .3 5 -0 .2 9 Precipitation (three-month total) pAug pSep pOct pNov pDec Jan Feb Mar Apr May Jun Jul Aug Sep Source: Appleton et al, in review DESPITE GROWING IN (DRY SUMMER) SUBALPINE CLIMATE, HEMLOCKS RETAIN A FAIRLY GOOD (NEGATIVE) PRECIPITATION SIGNAL.
  35. 35. ENSOEL NIÑ0-SOUTHERN OSCILLATION PDOPACIFIC DECADAL OSCILLATION AMOATLANTIC MULTIDECADAL OSCILLATION NAONORTH ATLANTIC OSCILLATION PNAPACIFIC-NORTH AMERICAN PATTERN SAMSOUTHERN ANNULAR MODE
  36. 36. Source: Stahle et al, Bulletin of the American Meteorological Society, 1999
  37. 37. FOREST STAND OCEAN BASIN 2.5 HECTARES 50,000,000 KM2 — 80,000,000 KM2
  38. 38. PACIFIC DECADAL OSCILLATION
  39. 39. CORRELATION BETWEEN TREE-RING WIDTHS AND THE PACIFIC DECADAL OSCILLATION (OCT-MAR) Modified from St. George, Quaternary Science Reviews, 2014
  40. 40. ? IN WHAT GEOGRAPHIC LOCATIONS AND ECOLOGICAL POSITIONS SHOULD WE EXPECT THE IMPRINT OF REMOTE TELECONNECTIONS TO BE MOST EVIDENT?
  41. 41. THE GLOBAL TREE-RING WIDTH NETWORK Source: St. George, Past Global Changes Magazine, 2015
  42. 42. 50,000,000 KM2 — 80,000,000 KM2 OCEAN BASIN FOREST STAND 2.5 HECTARES
  43. 43. Source: Chad King
  44. 44. @sco stgeorge

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