Great Momentsin

Dendrochronology

Paul Sheppard

Forestry Major

Humboldt State University, California

Forestry Major

• Tree identification

• Forest ecology/biogeography

• Silviculture

• Production

• Dendrochronology

Dendrochronology = tree-ring science

UA Tree Rings

Dating

Climate

Fire

Geology

Water

Chemistry

• Eternal question

– Why do you do what you do?

• Eternal question

– Why do you do what you do?

• Eternal answer

– Put modern times in context of deep past

• Eternal come back

– Yea, yea, but give examples!

– Great Moments in Dendro

Bridging the Gap

AndrewEllicott

Douglass

2014

1050

The Gap

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Floating Ruins Chronology

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Dated Tree Chronology

Show Low

• Buried log

Universal Accolades

• “most valuable contribution ever made to American archaeology”

• “most important thing ... thus far in American prehistory”

• “your contribution … is singularly outstanding”

• “tree-ring approach has been the single greatest contribution ever made to American archaeology”

Bridging the Gap

• Interesting, hard problem

• Huge data set

– Thousands living trees, Sky Islands

– Hundreds beams, dead trees

• Took 20+ years of work

• Multidisciplinary

– Dendro, archaeo, geogr

• First great moment

Radiocarbon Date Check

14N

14C

14N

into plants, animals

they die half-life =5730 yrs

Obvious Experiment

• Try C14 dating of wood already dated by dendrochronology

• Should result in a 1:1 line in a scatter plot

• If not … ?

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C1

4 D

ate

Tree-Ring Date

• Irish oak: 9,000 years

• US bristlecone pine: 8,700 years

• German oak-pine: 12,500 years

6000 BC AD 2000

800 years!!!C14 vs dendro

of wood

Electromagnetic strength

Radiocarbon Date Check

• Interesting, hard problem

• Huge data set

– Hundreds of trees, living dead

• Took tens of years of work

• Multidisciplinary

– Dendro, phys, chem, astro

• Spectacular moment!

Colorado River

Colorado River Compact, 1922

• 4th from left?

• WY, CO, UT, NM – Upper Basin

• AZ, NV, CA – Lower Basin

• 7.5 maf for each basin per year

• Extra 1 maf for Lower Basin (CA)

• Total: 16 maf every year

Colorado River Compact

Colorado River Watershed

• Abundant, long-lived trees, Sky Islands

• Statistical relationship ring width and gauge record river flow

• Past 450 years:

– Average: 13.5 maf

– Range: 4.4 – 22 maf

– 1922 was high!

Reality Check

Updated recently•15 maf•1920s still high•1100s?

Testimony to State Govt.(March 3, 2003, AZDS,

Drought in West may last decades)

• Expert: The current drought in Arizona could conceivably last for 20-30 years.

• Agency official: “We hope all this stuff about the ocean [and our rainfall] turns out to be wrong.”

Colorado River

• Interesting, hard problem

• Huge data set

– Thousands of living trees

• Took tens of years of work

• Multidisciplinary

– Dendro, hydro, geogr, stats

• Compelling great moment

Other Great Moments

• Forest fire history

– Profound ecological change, Sky Islands

• Drought atlases

– North America, Asia, Europe

• Dating, discovering past earthquakes

– San Andreas fault

• Dating past volcanic eruptions

– Sunset Crater, Arizona

Potential GM: Global Warming

Global Warming?

• Instrumental record shows warming

• Ocean or land

• Now: warmest years are 1.8 °F above coolest years

• Is this unusual in the long term?

Paleo Temperature

• Worldwide temperature reconstruction

• Tree rings, ice,pollen, corals

• Last 1300 years: Current warming is unusual

Paleo Temperature

Potential GM: Global Warming

• Interesting, hard problem

• Huge data set

– Thousands of trees, living & dead

– Ice, pollen, corals, sediments

– Weather data worldwide

• So far: decades of work

• Multidisciplinary

– Dendro, ocean, neo-paleoclime, policy

• Tree rings on global warming: Great?

Questions, comments?