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GEOG3839_6_CrossDating
 

GEOG3839_6_CrossDating

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    GEOG3839_6_CrossDating GEOG3839_6_CrossDating Presentation Transcript

    • How do we know tree rings are annual?
    • The “pinning” method Photograph: Keith Weston
    • Band dendrometer
    • Photograph: Baillie (1982)
    • P R I N C I P L E S O F C R O S S - DAT I N G
    • Scots pine Pinus sylvestrisPhotograph: Fritz Schweingruber
    • temperature water day length
    • Climate acts to synchronize growth rates at thelevel of the cell, the tree, the forest and beyond.
    • “ 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
    • Tree-ring width is not just a function of wet and dry
    • 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.
    • temperature water day length
    • Same environmental forcings Similar growth pa erns
    • 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.
    • How cross-dating works.
    • Photograph: Dan Griffin
    • When was the outer ring formed?
    • Why can’t you just count the rings back in time?
    • COMPLICATION #1 “Micro” rings
    • Ponderosa pine Pinus ponderosaPhotograph: Peter Brown
    • COMPLICATION #2 Partial rings
    • Limber pinePinus flexilis
    • COMPLICATION #3 Missing rings
    • Picture not available.
    • 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.
    • 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!
    • COMPLICATION #4 False rings
    • Ponderosa pine Pinus ponderosaPhotograph: Peter Brown
    • Arizona cypress Cupressus arizonicaPhotograph: Peter Brown
    • Falsering boundary sharp gradual Annual ring boundary
    • COMPLICATION #5 No outer date
    • Photo: Erik Nielsen
    • 47Photo: Erik Nielsen
    • 48
    • THE PRINCIPLE OF CROSS-DATING 1900 1910 1920 1930 Two Douglas-fir cores from Eldorado Canyon, COGraphic: Jeff Lukas, INSTAAR
    • THE ‘LIST’ METHOD
    • S K E L E TO N P LOT T I N G
    • Photograph: Baillie (1982)
    • Ring width Tree age
    • Compare rings to their neighbors.
    • Marking tree-ring specimens for dating decade half-century century millennium
    • RING MEASUREMENT
    • Source: Hughes and Brown, 1992
    • Widespread drought caused narrow rings to form across the southwest USA during 1748 and 1750.Source: Kurt Kipfmueller
    • 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.
    • ‘Complacent’
    • ‘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’
    • ‘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.
    • Tucson AZ
    • PRE-WORK ASSIGNMENTBefore next class, try cross-dating online
    • h p://www.ltrr.arizona.edu/skeletonplot/introcrossdate.htm or google ‘LTRR skeleton plot’
    • P R I N C I P L E S O F C R O S S - DAT I N G