Editing Dendrochronology (section)

=== Growth rings ===
{{Redirect-distinguish|Tree ring|Tree ring (landscape feature)}}
{{Further|Wood}}

[[File:Tree secondary growth diagram.svg|thumb|left|Diagram of [[secondary growth]] in a [[tree]] showing idealised vertical and horizontal sections. A new layer of [[wood]] is added in each growing season, thickening the stem, existing branches and roots, to form a growth ring.]]
Horizontal [[cross section (geometry)|cross sections]] cut through the [[trunk (botany)|trunk]] of a [[tree]] can reveal growth rings, also referred to as '''tree rings''' or '''annual rings'''. Growth rings result from new growth in the [[vascular cambium]], a layer of cells near the [[bark (botany)|bark]] that botanists classify as a [[lateral meristem]]; this growth in diameter is known as [[secondary growth]]. Visible rings result from the change in growth speed through the [[season]]s of the year; thus, critical for the title method, one ring generally marks the passage of one year in the life of the tree. Removal of the bark of the tree in a particular area may cause deformation of the rings as the plant overgrows the scar.

The rings are more visible in trees which have grown in [[temperate zone]]s, where the seasons differ more markedly. The inner portion of a growth ring forms early in the growing season, when growth is comparatively rapid (hence the wood is less dense) and is known as "early wood" (or "spring wood", or "late-spring wood"<ref>"Early wood" is used in preference to "spring wood", as the latter term may not correspond to that time of year in climates where early wood is formed in the early summer (e.g. [[Canada]]) or in autumn, as in some [[Mediterranean region|Mediterranean]] species.</ref>); the outer portion is the "late wood" (sometimes termed "summer wood", often being produced in the summer, though sometimes in the autumn) and is denser.<ref>{{Cite book |last=Capon |first= Brian |title= Botany for Gardeners |year=2005 |pages=66–67 |edition= 2nd |isbn=978-0-88192-655-2 |publisher= Timber Publishing |location=Portland, OR}}</ref>{{better source needed|date= November 2014}}

[[File:Tilia tomentosa coupe MHNT.jpg|thumb|[[Silver lime]] cross section showing annual rings.]]

Many trees in temperate zones produce one growth-ring each year, with the newest adjacent to the bark. Hence, for the entire period of a tree's life, a year-by-year record or ring pattern builds up that reflects the age of the tree and the climatic conditions in which the tree grew. Adequate moisture and a long growing season result in a wide ring, while a drought year may result in a very narrow one.

Direct reading of tree ring chronologies is a complex science, for several reasons. First, contrary to the single-ring-per-year paradigm, alternating poor and favorable conditions, such as mid-summer droughts, can result in several rings forming in a given year. In addition, particular tree species may present "missing rings", and this influences the selection of trees for study of long time-spans. For instance, missing rings are rare in [[oak]] and [[elm]] trees.<ref>The only recorded instance of a missing ring in oak trees occurred in the year 1816, also known as the "[[Year Without a Summer]]".{{cite web |url=http://www.ltrr.arizona.edu/lorim/good.html |title= Useful Tree Species for Tree-Ring Dating |author= Lori Martinez |year= 1996 |access-date= 2008-11-08 |url-status= live |archive-url=https://web.archive.org/web/20081108094321/http://www.ltrr.arizona.edu/lorim/good.html |archive-date=2008-11-08 }}</ref>

Critical to the science, trees from the same region tend to develop the same patterns of ring widths for a given period of chronological study. Researchers can compare and match these patterns ring-for-ring with patterns from trees which have grown at the same time in the same geographical zone (and therefore under similar climatic conditions). When one can match these tree-ring patterns across successive trees in the same locale, in overlapping fashion, chronologies can be built up—both for entire geographical regions and for sub-regions. Moreover, wood from ancient structures with known chronologies can be matched to the tree-ring data (a technique called 'cross-dating'), and the age of the wood can thereby be determined precisely. Dendrochronologists originally carried out cross-dating by visual inspection; more recently, they have harnessed computers to do the task, applying statistical techniques to assess the matching. To eliminate individual variations in tree-ring growth, dendrochronologists take the smoothed average of the tree-ring widths of multiple tree-samples to build up a 'ring history', a process termed replication. A tree-ring history whose beginning- and end-dates are not known is called a 'floating chronology'. It can be anchored by cross-matching a section against another chronology (tree-ring history) whose dates are known.

A fully anchored and cross-matched chronology for oak and pine in central Europe extends back 12,460 years,<ref>{{cite journal |last1=Friedrich |first1=Michael |last2=Remmele |first2=Sabine |last3=Kromer |first3=Bernd |last4=Hofmann |first4=Jutta |last5=Spurk |first5=Marco |last6=Felix Kaiser |first6=Klaus |last7=Orcel |first7=Christian |last8=Küppers |first8=Manfred |title=The 12,460-Year Hohenheim Oak and Pine Tree-Ring Chronology from Central Europe—A Unique Annual Record for Radiocarbon Calibration and Paleoenvironment Reconstructions |journal=Radiocarbon |date=2004 |volume=46 |issue=3 |pages=1111–1122 |doi=10.1017/S003382220003304X |bibcode=2004Radcb..46.1111F |s2cid=53343999 |url=http://physics2.fau.edu/~wolf/BasicScience/Friedrich_Dendro_RC04.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://physics2.fau.edu/~wolf/BasicScience/Friedrich_Dendro_RC04.pdf |archive-date=2022-10-09 |url-status=live }}</ref> and an oak chronology goes back 7,506 years in Bohemia, 7,429 years in Ireland and 6,939 years in [[England]].<ref name="kyncl" /><ref>{{cite book |chapter-url= https://books.google.com/books?id=1rYCjUzMM3UC&q=northern+ireland+dendrochronological&pg=PT145 |chapter= 5.2.3 Dendrochronological Series |first= Mike |last= Walker |title= Quaternary Dating Methods |publisher= John Wiley and Sons |year=2013 |isbn= 9781118700099 |url-status= live |archive-url= https://web.archive.org/web/20161128050944/https://books.google.co.uk/books?id=1rYCjUzMM3UC&pg=PT145&lpg=PT145&dq=northern+ireland+dendrochronological&source=bl&ots=-83vqIKmdt&sig=gvKAhREENtGBCdVV2TK7131y92I&hl=en&sa=X&ved=0ahUKEwjR65yEzcnQAhXKCsAKHUP_CG84ChDoAQgqMAM#v=onepage&q=northern%20ireland%20dendrochronological&f=false |archive-date=2016-11-28}}</ref> Comparison of radiocarbon and dendrochronological ages supports the consistency of these two independent dendrochronological sequences.<ref>{{cite journal |last1=Stuiver |first1=Minze |last2=Kromer |first2=Bernd |last3=Becker |first3=Bernd |last4=Ferguson |first4=C W |title=Radiocarbon Age Calibration back to 13,300 Years BP and the {{chem|14|C}} Age Matching of the German Oak and US Bristlecone Pine Chronologies |journal=Radiocarbon |date=1986 |volume=28 |issue=2B |pages=969–979 |doi=10.1017/S0033822200060252 |bibcode=1986Radcb..28..969S |doi-access=free |hdl=10150/652767 |hdl-access=free }}</ref> Another fully anchored chronology that extends back 8,500 years exists for the bristlecone pine in the [[Southwestern United States|Southwest US]] ([[White Mountains (California)|White Mountains]] of California).<ref>{{cite journal |last1=Ferguson |first1=C. W. |last2=Graybill |first2=D. A. |title=Dendrochronology of Bristlecone Pine: A Progress Report |journal=Radiocarbon |date=1983 |volume=25 |issue=2 |pages=287–288 |doi=10.1017/S0033822200005592 |bibcode=1983Radcb..25..287F |hdl=10150/652656 |hdl-access=free |doi-access=free }}</ref>