geog5839.06, the principle of cross dating

Source: Baillie (1982)

September 20

The principle of cross-dating

GEOG5839FROM LIMITS TO PATTERNS

h!p://esp.cr.usgs.gov/data/atlas/li!le/

xx

x

Isolated populations

Extinct populations

MAIN RANGE DISCONTINUOUS RANGE

TEMPORARYPOPULATIONS

Individual adults (not reproducing)

**

*

**

* *

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

GEOG8280NEXT CLASS