geog5839.06, the principle of cross dating
TRANSCRIPT
Source: Baillie (1982)
September 20
The principle of cross-dating
GEOG5839FROM LIMITS TO PATTERNS
h!p://esp.cr.usgs.gov/data/atlas/li!le/
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Isolated populations
Extinct populations
MAIN RANGE DISCONTINUOUS RANGE
TEMPORARYPOPULATIONS
Individual adults (not reproducing)
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h!p://esp.cr.usgs.gov/data/atlas/li!le/
Source: Elroy
Source: Bryant Olsen
Source: Phil Camill
Growth is controlled by the scarcest resource (limiting factor), not the total amount of resources available
LAW MINIMUMTHE OF THE
Average temperatures are remarkably consistent at treeline locations around the world.
Source: Körner and Paulsen, Journal of Biogeography, 2004
temperature water day length
h!p://esp.cr.usgs.gov/data/atlas/li!le/
“COMPLACENT”
“SENSITIVE”
Weather and climate act to synchronize growth rates at the level of the cell, the tree, the forest and beyond.
RINGS IN THE BRANCHES OF SAWED TREES SHOW
THE 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
Same environmental forcings
Similar growth pa!erns
GEOG5839CHRONOLOGY
THE PRINCIPLE OF CROSS-DATING
Matching pa!erns in tree-ring widths or other ring characteristics (such as ring density) among several trees allow the identification of the exact year in which each ring was formed.
Photograph: Dan Gri"n
3Di!erent approaches
T H E ‘ L I S T ’ M E T H O D
1900 1910 1920 1930
Two Douglas-fir cores from Eldorado Canyon, CO
Source: Je# Lukas, INSTAAR
THE PRINCIPLE OF CROSS-DATING
S K E L E T O N P L O T T I N G
Compare rings to their neighbors.
R I N G M E A S U R E M E N T
Source: Hughes and Brown, 1992
GEOG5839PROBLEMS WITH DATING
Why can’t you just count the rings back in time?
COMPLICATION #1
“Micro” rings
Source: Peter Brown
Ponderosa pinePinus ponderosa
COMPLICATION #2
Partial rings
Limber pinePinus flexilis
COMPLICATION #3
Missing rings
Picture not available.
A “missing ring” is a term used to describe the phenomenon where 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
Source: Peter Brown
Ponderosa pinePinus ponderosa
Source: Peter Brown
Arizona cypressCupressus arizonica
Falsering boundary
Annualring boundary
gradual
sharp
Why can’t you just count the rings back in time?
GEOG5839PUZZLES IN TIME
Widespread drought caused narrow rings to form across the southwest USA during 1748 and 1750.
Source: Kurt Kipfmueller
COMPLICATION #5
No outer date
Bur oak (Quercus macrocarpa) is a common tree along rivers in Minnesota and the upper Midwest.Select trees of this species can live for up to 450 years.
Photo: Erik Nielsen
68Photo: Erik Nielsen
69
What kind of trees have rings that can be dated?
• 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.
Tucson AZ
‘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.
Source: Baillie (1982)
September 20
The principle of cross-dating
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