9BTimeandTreeRings

Dotreeringstellastory?

Ifyoulookatthecross-sectionofa tree,youwillsee treerings.Treerings tellastoryaboutthegrowing conditionsofthe tree.Thenumberof ringsthat atree hasequalsitsage.

Carefulexaminationoftreeringscangivedetailed informationabouttheageofapieceofwoodandthe growingconditionsatree experiencedduringitslife time.Scientistscomparetreerings toacatalogoftree ringhistory tofigureout theageofcertainwooden objectslikeoldships,logcabins,and archeological artifacts. Inthisinvestigation, youwilldeterminethe ageandgrowingconditionsofseveralsamplesofwood

byexaminingtreeringsandtreecoresamplesyourself.

Howdotreesgrow?

Materials

•Microscopeslideofatree cross-section

•Treecrosssection

•7 paperstripsrepresentingtree cores,a setof 4andasetof 3(includedas a graphicinthe lab)

•Two blank pieces of paper

•Graphpaper

•Scissors

•Tape

•Ruler

•Coloredpencils

•Magnifyinglens

Eachyear,atreegetslargerbyonering.Itiseasytocounttree

ringsbecauseeachringhasalightandadarkband.

Treeringsvaryin widthdependingonthe growingclimate.Wet,warmyearsallow formoregrowththancool,dryyears.A wideringmeansthetree grewduringa wetyear.A narrowringbandmeansthetreegrew duringacool,dryyear.

a.Notice: Lookatthemicroscopeslideofthetreecross-section.Use themagnifyinglenstohelpyouseethedetails.Record your descriptive observations:

______

b.Wonder: What information, about events and conditions present when the tree was alive, could be gathered from the tree rings?

______

c.Lookingattheslide,howmanytreeringsdoyousee? ______

Investigatingtreerings

1. Treecross-section:

Now,lookatthetreecross-section.Useamagnifyinglenstohelpyouseetherings. Noticethewidthofthebands.Notice the bark, the outside of the cross-section, and the pitch, the very center of the cross-section. In your group, determinetheageofthetree.Rememberthatonering(oneyear’sgrowth)includesalightband andadarkband. Thepithandbarkare notcountedindeterminingtheageofasample.Theyoungestwoodisunderthebark.

Age of this tree: ______

2. Treecores – Population #1:

Cut out sample tree core strips.Thestripsrepresent treecoresfromfourdifferenttrees.Thetreesarethesamespeciesandgrewinthe samewoodland.

3. Determinetheageofeachtreebycountingtherings(oneringincludesawidelight bandanddarkline).RecordyouranswersinTable1.

4. Lookforpatternsintherings.Lineupallthesamplesbymatchingthepatterns beforetapingthemontoablankpieceofpaper.Colortheoverlappingsectionssoyou don’tlosetrack.Figureouttheageofeachtreeandrecordthisinformation,andthe yearsthatthetreesbegangrowingandwerecutinTable1.

Table1:Treecoredata

Sample / Age ofTree / YearCutorCored / YearGrowthBegan
1
2
3
4

c.Did this woodland have more years of drought or plentiful rainfall? Use data to support your answer.

______

5. Moretreecores – Population #2:

Nowlookat thethreenewtreecores(seenextpage).Writedowntheageof eachcore.

Sample / Age
A
B
C

6. Measurethewidth ofthering foreach yearlistedbelow.Twoyearshavealreadybeendonefor you:2006and2005.Recordthe datainTable2.

Table2:Treecoredata

YearTreeringwidth
(mm)
200610mm
20058mm
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994

Investigation9BTimeandTreeRings

7. Makeagraphofthistreecoredata.Plotthering-widthdata(onthey-axis)against time(onthex-axis).Oneringincludesawidelightbandanddarkline.Labelthe graphappropriately.

Thinkingaboutwhatyouobserved:

a.What does your graph show about the three cores from Population #2 and the climate?

______

b.How do the growing conditions compare between the two populations?

______

______

c.Trees are like history books of a forest. What other natural objects or organisms can we observe and measure learn about certain environments?

______

d.How do tree core models help us understand Earth’s history?

______

Extend:

Global warming, caused by an increase of carbon dioxide in the atmosphere, is a current environmental topic. One result of global warming is an increase in Earth’s average temperature. Due to global warming, what differences would you expect to see between tree rings today and those 100 years from now?