Introduction To Tree Rings & Dendrochronology

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DETECTING GLOBAL WARMING:In the recent past, we use the “INSTRUMENTALRECORD” based on actual Thermometerreadings from around the globeTemperatureTrends FromDire Predictions, p 36

We looked at some of these during thisIndicator Interlude . . . Remember thesetime series “anomaly” plots?But what about what happened longbefore the Industrial Revolution?Don’t we really need to look at temperaturesfrom a LONG time ago to assess the severityof the recent temperature observations ofwarming?These temperature records and graphs are available online at the NationalClimatic Data Center (NCDC) of NOAA (The National Oceanic & AtmosphericAdministration): 45

To make an incontrovertible case aboutthe role that humans play in globalwarming, what do scientists need?1) a long-term temperature record, i.e., centuries2) over a large part of the globe3) To be able to say . . . . .“What's the average been for several hundredyears, & is this a significant departure from that?”“And that's very difficult to do.”(James Trefil, physicist)Review: p 17

Trees and stoneswill teach you thatwhich you cannever learn frommasters. St. Bernard of Clairvauxp 51

“PROXY” DATA orNATURAL ARCHIVES of CLIMATECoralsIce coresPollenLake, bog &oceansedimentsTree rings!


Dendrochronology is the datingand study of annual rings in trees: dendros: from trees, or morespecifically the growth rings oftrees chronos: time, or morespecifically events in past time ology:the study of . . .

The current year’sactively growingcells are justunderneath the barkPartialcross-sectionof a coniferoustreeHow old is it?(in completeyears) count ‘em!7 years old(now in 8th yearof growth)P 51

With 7 rings inthe crosssection,Is this thetree’s age?It depends onthe height ofthe sampleP 51

With 7 rings inthe crosssection,Trees grow from the topFewerringsIs this thetree’s age?It depends onthe height ofthe Identification/Wood&Charcoal Part2.htm

Clicker Question:Given what you just learned about how trees grow,what is wrong with this picture?A. Trees grow up, not out,so this is clearly a photoshopped image.B. In 99 years of treegrowth, the bicycle wouldbe much higher up in thetree.C. In 99 years of treegrowth, the bicycle wouldstill be on the ground, butthe tree would have startedto grow around it.

Why we can see the rings: cell size & thicknesschanges during the growing seasonConifer Tree Ring(cross-section view)

Earlywood: Cells: thin walls, large diameter Appears light in color Latewood: Cells: thick walls, small diameter Appears dark in color

Ring Porous Angiosperm Tree Ring(cross-section, view) Earlywood: Cells: large diameter vessels Latewood: Cells: small diameter vesselsButnot alltreeshaverings!

The image below shows a conifertree-ring sample with about thirtyrings (every tenth ring is marked)– growing from left to right.The rings display much variation:Tree growth (adding new cells) is this way PithBark (center of tree)(outside of tree)

Variation in tree rings is due tovariation in environmentalconditions when they wereformed. dry or moist soil conditions cold or warm temperatures frost rings from tissue damage even insect outbreaks, fires, andother non-climatic factorsStudying this variation gives usinformation about past environmentalconditions and is the basis for manyresearch applications ofdendrochronology.

How do we get thetree rings withoutkilling the trees!Extractcores withanincrementborer

If the tree isalready dead orcut down, wecan take crosssections fromthe tree or itsstump Notice how widethe rings in thecenter are– this was whenthe tree wasyoung andgrowing faster!

KEY PRINCIPLES OFDENDROCHRONOLOGYUNIFORMITARIANISM –“The present is the key to the past”(this is a key principle for many other naturalarchives used in the geological sciences as well)KeyPrinciplesp 51

LIMITING FACTORS –growth can occur only as fast as allowedby the factor that is most limiting, e.g. “too dry” – the amount rainfall is the limitingfactor “too cold” or “too hot” – the temperature isthe limiting factor NOTE: the limiting factor can vary from siteto site, even in the same species of tree!KeyPrinciplesp 51

SITESELECTION -sites are selectedbased on criteriaof tree-ringsensitivity to anenvironmentalvariable(temperature,precipitation, etc.)KeyPrinciplesp 51

ComplacentSensitivep 52

Crossdating: The Central Premise 7018801890 “Bridging” the record back in time KeyPrinciplesp 51

CROSSDATING –matching patterns in rings of severalsensitive tree-ring series allowsprecise dating to exact yearTo Crossdateyou need a lot ofrings tocompare, usually50 ringsminimum to becertain of datingKeyPrinciplesp 51

Now, back to the principles:REPLICATION –“noise” minimized by sampling many trees ata site more than one core per treeKeyPrinciplesp 51

Ring width measurements showing asimilar pattern of growth

ECOLOGICALAMPLITUDE –trees are moresensitive to theirenvironment atlatitudinal andelevational limitsof the treespecies’ rangeVery old tree on Mt Graham,SE Arizonainner ring date: A.D. 1101KeyPrinciplesp 51

KEY SCIENTIFIC ISSUES Missing rings & false rings (to identifythese, need a “master chronology”) Species limitations (some trees have norings, non-annual rings, or poorly definedrings) Trees must crossdate! (can’t develop achronology or link to climate without this)Today’s class activityTop ofp 52

Geographical limitationstropics, deserts and othertreeless areas, oceans, etc.)p 52

Agelimitationsold trees hardto findoldest livingtrees BristleconePines 5,000 years oldwhy don’t weknow for certain?Because sampling the baseof a live tree is difficultp 52

Value of precise dating(long chronologies, climatereconstructions, archaeology,radiocarbon dating)p 52

Now on to the G-3Tree-Ring “Wood Kit”ASSIGNMENT!

Goals of Assignment G-3:(1) To see “inside” different species oftrees and woody shrubs(2) To classify the wood samples in a“wood kit” into categories :Trees that are:(1) Suitable or(2) Unsuitable. . . for crossdating and subsequentdendrochronological analysis.


Then, for each specimenin your box, fill out reasonsFOR using it and reasons for NOTusing it in a dendrochronological studyStart by matchingeach wood specimenwith a PHOTO,using LABELS on thewood to guide youSouthwestern white pine(Pinus strobiformis))Example:SEGI Giant redwood

1) Match the wood specimens in yourbox with the right tree photo2) Fill our the chart for the specimensin your box3) SWAP boxes4) REPEAT for second box5) All who participated, sign the form& return the folder with yourcompleted G-3 form inside


TIME TO WRAP UP FORTODAYPlease clean up your areaand put chairs back inplace

Missing rings & false rings (to identify these, need a "master chronology") Species limitations (some trees have no rings, non-annual rings, or poorly defined rings) Trees must crossdate! (can't develop a chronology or link to climate without this) Top of p 52 Today's class activity

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