PRINCIPLES OF DENDROCHRONOLOGY

• Set of principles or “scientific rules”

• Some are specific to dendrochronology

– Tree selection

• Others are basic to many disciplines

– Replication

Crossdating

• Matching of ring patterns across trees

– Widths, density, other features

• Allows year date of formation to be assigned to each ring

• Critical to dendrochronology

Limiting Factors

• Liebig’s Law of the Minimum

– Rate of a process is limited by most limiting factor

– Interactions between nutrients

– Other factors: water?

Limiting Factors

• Tree Growth

– Cannot proceed faster than is allowed by most limiting factor

– Degree and duration of a limiting factor change from year to year ring variation

– Could be different limiting factors relative to various frequencies of growth

Limiting Factors

• Sheep Mt bcp: moisture/temperature limited at high-frequency

• Decadal ramp evidence of CO2 limitation?

Aggregate Tree Growth

• Ring variation is a function of

– Age or size

– Climate

– Endogenous disturbances

– Exogenous disturbances

– Leftover

Aggregate Tree Growth

• To focus on one of these factors, others must be accounted for

– To study past climate:

– Sample trees without past disturbance

– Remove age effect

Aggregate Tree Growth

• Age or size effects removed by detrending

0

2

4

1800 1850 1900 1950 2000

Rin

g W

idth

(m

m)

RW = 2.68 • e(-0.02 • time) + 0.26

(a)

0

1

2

1800 1850 1900 1950 2000

Year

Inde

x

(b)

Site and Tree Selection

• Select a site to maximize effect of an environmental factor on tree growth

• Eliminate or equalize other factors

• Isolate the single factor of interest

• Edaphic variationcan be below surface

Site and Tree Selection

• Not random sampling in true ecological sense

• Ramifications for inference

– Instead of saying: Climate affects tree growth in such a way …

– We might say: Past climate at this site has been such and such …

Replication

• Multiple radii to estimate tree growth

• Multiple trees to crossdate, estimate site patterns

• Multiple sites to estimate regional tendencies

• Multiple samplesto establish building sequences

Ecological Amplitude

• Tree growth more sensitive to environmental factors at edge of species range

• Altitudinal:

– Pine sensitive tomoisture at lowerelevational limit

Ecological Amplitude

• Latitudinal:

– Trees may occupy wide variety of microsites in center of range, not limited by single factor

– Trees may occupy narrow variety of microsites along margins of range

Ecological Amplitude

• White oak is classic

– Enormous range

– Gentle topography

– Itrdbfor: “In the East … tree sensitivity to climate increases from the range center out toward the range edge.”

Ecological Amplitude

• Might affect age of trees:– Schulman, Ferguson 1956 (Science 1954, v.

119, pg. 396, 883)– “Young” bcp in

east– Old bcp to west– Corresponds to

average rainfalltotals

Ecological Amplitude

• Currey 1964:

– Found oldest bcp on Wheeler Peak, NV

– “The simple hypothesis of Schulman and Ferguson is … no longer tenable.”

Uniformitarianism

• Physical and biological processes that link current environmental processes with current patterns of tree growth operated similarly in the past

• “Present is key to past” (Hutton 1785)

Uniformitarianism

• Tree rings from the 1900s calibrated with rainfall records from 1900s

– Annual precipitation

• Past rings indicate past precipitation

Uniformitarianism

• Have current environmental conditions existed in past?

• Do past environmental conditions exist currently?

• Young trees vs. old trees?

– Szeicz and MacDonald 1994: Age-dependent tree-ring growth responses of subarctic white spruce to climate. CJFR 24:120-132.

Uniformitarianism

• Paleo twist: Past is key to future– This is why we do what why do