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GEOG3839_6_CrossDating

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  • 1. How do we know tree rings are annual?
  • 2. The “pinning” method Photograph: Keith Weston
  • 3. Band dendrometer
  • 4. Photograph: Baillie (1982)
  • 5. P R I N C I P L E S O F C R O S S - DAT I N G
  • 6. Scots pine Pinus sylvestrisPhotograph: Fritz Schweingruber
  • 7. temperature water day length
  • 8. Climate acts to synchronize growth rates at thelevel of the cell, the tree, the forest and beyond.
  • 9. “ RINGS IN THE BRANCHES OF SAWED TREES SHOWTHE NUMBER OF YEARS AND, ACCORDING TO THEIR THICKNESS, THE YEARS WHICH WERE MORE OR LESS DRY. ” Leonardo da Vinci
  • 10. Tree-ring width is not just a function of wet and dry
  • 11. THE PRINCIPLE OF LIMITING FACTORS The rates of biological processes in trees, including the formation of woody cells, are constrained by the primary environmental variable that is most limiting.
  • 12. temperature water day length
  • 13. Same environmental forcings Similar growth pa erns
  • 14. THE PRINCIPLE OF CROSS-DATINGMatching pa erns in tree-ring widths or other ring characteristics(such as ring density) among several trees allow the identificationof the exact year in which each ring was formed.
  • 15. How cross-dating works.
  • 16. Photograph: Dan Griffin
  • 17. When was the outer ring formed?
  • 18. Why can’t you just count the rings back in time?
  • 19. COMPLICATION #1 “Micro” rings
  • 20. Ponderosa pine Pinus ponderosaPhotograph: Peter Brown
  • 21. COMPLICATION #2 Partial rings
  • 22. Limber pinePinus flexilis
  • 23. COMPLICATION #3 Missing rings
  • 24. Picture not available.
  • 25. A “missing ring” is a term used to describe the phenomenonwhere a tree does not form wood around its trunk during a single growing season.
  • 26. A “missing ring” is a term used to describe the phenomenonwhere a tree does not form wood around its trunk during a single growing season. At the position where the tree-ring sample was collected!
  • 27. COMPLICATION #4 False rings
  • 28. Ponderosa pine Pinus ponderosaPhotograph: Peter Brown
  • 29. Arizona cypress Cupressus arizonicaPhotograph: Peter Brown
  • 30. Falsering boundary sharp gradual Annual ring boundary
  • 31. COMPLICATION #5 No outer date
  • 32. Photo: Erik Nielsen
  • 33. 47Photo: Erik Nielsen
  • 34. 48
  • 35. THE PRINCIPLE OF CROSS-DATING 1900 1910 1920 1930 Two Douglas-fir cores from Eldorado Canyon, COGraphic: Jeff Lukas, INSTAAR
  • 36. THE ‘LIST’ METHOD
  • 37. S K E L E TO N P LOT T I N G
  • 38. Photograph: Baillie (1982)
  • 39. Ring width Tree age
  • 40. Compare rings to their neighbors.
  • 41. Marking tree-ring specimens for dating decade half-century century millennium
  • 42. RING MEASUREMENT
  • 43. Source: Hughes and Brown, 1992
  • 44. Widespread drought caused narrow rings to form across the southwest USA during 1748 and 1750.Source: Kurt Kipfmueller
  • 45. What kind of trees have rings that can bedated? • They have distinct and detectable rings. • Their rings must be reliably annual. • The formation of their rings must be sensitive to environmental conditions. • That sensitivity must cause the rings to vary from year to year. • Several trees must share common pa erns in tree-ring width, wood density or some other wood variable.
  • 46. ‘Complacent’
  • 47. ‘Complacent’ tree-ring series: • exhibit very li le year-to-year variation. • grow in se ings where the limiting growth factor doesn’t change much. • are tough to cross-date.
  • 48. ‘Sensitive’
  • 49. ‘Complacent’ tree-ring series: • exhibit very li le year-to-year variation. • grow in se ings where the limiting growth factor doesn’t change much. • are tough to cross-date.‘Sensitive’ tree-ring series: • have wide and narrow rings that are intermixed through time. • Found in environments where the limiting factor is highly variable year to year • Matching ring pa erns across trees is easier.
  • 50. Tucson AZ
  • 51. PRE-WORK ASSIGNMENTBefore next class, try cross-dating online
  • 52. h p://www.ltrr.arizona.edu/skeletonplot/introcrossdate.htm or google ‘LTRR skeleton plot’
  • 53. P R I N C I P L E S O F C R O S S - DAT I N G

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