PRINCIPLES OF DENDROCHRONOLOGY Set of principles or scientific

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 CO 2 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

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 variation can 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 samples to establish building sequences

Ecological Amplitude • Tree growth more sensitive to environmental factors at edge of species range • Altitudinal: – Pine sensitive to moisture at lower elevational 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 rainfall totals

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 1900 s calibrated with rainfall records from 1900 s – 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 Mac. Donald 1994: Agedependent 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