Method of dating based on the analysis of patterns of tree rings
The growth rings of a tree atBristol Zoo,England. Each ring represents one year; the outside rings, near the bark, are the youngestA "tree cookie" cross-section of aCoast Douglas-fir tree displayed in theRoyal Ontario Museum. The tree was over 500 years old when it was cut down inBritish Columbia in the 1890s. The markings indicating historical events were added in the 1920s.
Dendrochronology (ortree-ring dating) is thescientific method ofdating tree rings (also called growth rings) to the exact year they were formed in a tree. As well as dating them, this can give data fordendroclimatology, the study of climate and atmospheric conditions during different periods in history from the wood of old trees. Dendrochronology derives from the Ancient Greekdendron (δένδρον), meaning "tree",khronos (χρόνος), meaning "time", and-logia (-λογία), "the study of".[1]
Dendrochronology is useful for determining the precise age of samples, especially those that are too recent forradiocarbon dating, which always produces a range rather than an exact date. However, for a precise date of the death of the tree a full sample to the edge is needed, which most trimmed timber will not provide. It also gives data on the timing of events and rates of change in the environment (most prominently climate) and also in wood found inarchaeology or works of art and architecture, such as oldpanel paintings. It is also used as a check in radiocarbon dating tocalibrate radiocarbon ages.[2]
New growth intrees occurs in a layer of cells near the bark. A tree's growth rate changes in a predictable pattern throughout the year in response to seasonal climate changes, resulting in visible growth rings. Each ring marks a complete cycle ofseasons, or one year, in the tree's life.[2] As of 2023, securely dated tree-ring data for Germany, Bohemia and Ireland are available going back 13,910 years.[3][4][5] A new method is based on measuring variations in oxygen isotopes in each ring, and this 'isotope dendrochronology' can yield results on samples which are not suitable for traditional dendrochronology due to too few or too similar rings.[6] Some regions have "floating sequences", with gaps which mean that earlier periods can only be approximately dated. As of 2024, only three areas have continuous sequences going back to prehistoric times, the foothills of theNorthern Alps, the southwestern United States and the British Isles.Miyake events, which are major spikes incosmic rays at known dates, are visible in trees rings and can fix the dating of a floating sequence.[7]
The Greek botanistTheophrastus (c. 371 – c. 287 BC) first mentioned that the wood of trees has rings.[8][9] In his 1651Trattato della Pittura (Treatise on Painting),Leonardo da Vinci (1452–1519) was the first person to mention that trees form rings annually and that their thickness is determined by the conditions under which they grew.[10] In 1737, French investigatorsHenri-Louis Duhamel du Monceau andGeorges-Louis Leclerc de Buffon examined the effect of growing conditions on the shape of tree rings.[11] They found that in1709, a severe winter produced a distinctly dark tree ring, which served as a reference for subsequent European naturalists.[12] In the U.S.,Alexander Catlin Twining (1801–1884) suggested in 1833 that patterns among tree rings could be used to synchronize the dendrochronology of various trees and thereby to reconstruct past climates across entire regions.[13] The English polymathCharles Babbage proposed using dendrochronology to date the remains of trees in peat bogs or even in geological strata (1835, 1838).[14]
During the latter half of the nineteenth century, the scientific study of tree rings and the application of dendrochronology began. In 1859, the German-AmericanJacob Kuechler (1823–1893) used crossdating to examineoaks (Quercus stellata) in order to study the record of climate in western Texas.[15] In 1866, the German botanist, entomologist, and foresterJulius Theodor Christian Ratzeburg (1801–1871) observed the effects on tree rings of defoliation caused by insect infestations.[16] By 1882, this observation was already appearing inforestry textbooks.[17] In the 1870s, the Dutch astronomerJacobus Kapteyn (1851–1922) was using crossdating to reconstruct the climates of the Netherlands and Germany.[18] In 1881, the Swiss-Austrian forester Arthurvon Seckendorff-Gudent (1845–1886) was using crossdating.[19] From 1869 to 1901,Robert Hartig (1839–1901), a German professor of forest pathology, wrote a series of papers on the anatomy and ecology of tree rings.[20] In 1892, the Russian physicistFedor Nikiforovich Shvedov [ro;ru;uk] (1841–1905) wrote that he had used patterns found in tree rings to predict droughts in 1882 and 1891.[21]
Diagram ofsecondary growth in atree showing idealised vertical and horizontal sections. A new layer ofwood is added in each growing season, thickening the stem, existing branches and roots, to form a growth ring.
Horizontalcross sections cut through thetrunk of atree can reveal growth rings, also referred to astree rings orannual rings. Growth rings result from new growth in thevascular cambium, a layer of cells near thebark that botanists classify as alateral meristem; this growth in diameter is known assecondary growth. Visible rings result from the change in growth speed through theseasons 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 intemperate zones, 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"[22]); 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.[23][better source needed]
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 inoak andelm trees.[24]
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,[25] and an oak chronology goes back 7,506 years in Bohemia, 7,429 years in Ireland and 6,939 years inEngland.[3][26] Comparison of radiocarbon and dendrochronological ages supports the consistency of these two independent dendrochronological sequences.[27] Another fully anchored chronology that extends back 8,500 years exists for the bristlecone pine in theSouthwest US (White Mountains of California).[28]
A typical form of the function of the wood ring width in accordance with the dendrochronological equationA typical form of the function of the wood ring (in accordance with the dendrochronological equation) with an increase in the width of wood ring at initial stage
The dendrochronological equation defines the law of growth of tree rings. The equation was proposed by Russian biophysicist Alexandr N. Tetearing in his work "Theory of populations"[29] in the form:
where ΔL is width of annual ring,t is time (in years),ρ is density of wood,kv is some coefficient,M(t) is function of mass growth of the tree.
Ignoring the natural sinusoidal oscillations in tree mass, the formula for the changes in the annual ring width is:
wherec1,c2, andc4 are some coefficients,a1 anda2 are positive constants.
The formula is useful for correct approximation of samples data beforedata normalization procedure. The typical forms of the function ΔL(t) of annual growth of wood ring are shown in the figures.
Dendrochronology allows specimens of once-living material to be accurately dated to a specific year.[30] Dates are often represented as estimated calendar yearsB.P., for before present, where "present" refers to 1 January 1950.[30]
Timber core samples are sampled and used to measure the width of annual growth rings; by taking samples from different sites within a particular region, researchers can build a comprehensive historical sequence. The techniques of dendrochronology are more consistent in areas where trees grew in marginal conditions such as aridity or semi-aridity where the ring growth is more sensitive to the environment, rather than in humid areas where tree-ring growth is more uniform (complacent). In addition, some genera of trees are more suitable than others for this type of analysis. For instance, thebristlecone pine is exceptionally long-lived and slow growing, and has been used extensively for chronologies; still-living and dead specimens of this species provide tree-ring patterns going back thousands of years, in some regions more than 10,000 years.[31] Currently, the maximum span for fully anchored chronology is a little over 11,000 years B.P.
IntCal20 is the 2020 "Radiocarbon Age Calibration Curve", which provides a calibratedcarbon 14 dated sequence going back 55,000 years. The most recent part, going back 13,900 years, is based on tree rings.[32]
European chronologies derived from wooden structures initially found it difficult to bridge the gap in the fourteenth century when there was a building hiatus, which coincided with theBlack Death.[33] However, there do exist unbroken chronologies dating back to prehistoric times, for example the Danish chronology dating back to 352 BC.[34]
Given a sample of wood, the variation of the tree-ring growths not only provides a match by year, but can also match location because climate varies from place to place. This makes it possible to determine the source of ships as well as smaller artifacts made from wood, but which were transported long distances, such as panels for paintings and ship timbers.[citation needed]
Miyake events, such as the ones in774–775 and993–994, can provide fixed reference points in an unknown time sequence as they are due to cosmic radiation.[35] As they appear as spikes incarbon 14 in tree rings for that year all round the world, they can be used to date historical events to the year.[36] For example, wooden houses in theViking site atL'Anse aux Meadows in Newfoundland were dated by finding the layer with the 993 spike, which showed that the wood is from a tree felled in 1021.[37] Researchers at the University of Bern have provided exact dating of a floating sequence in aNeolithic settlement in northern Greece by tying it to a spike in cosmogenic radiocarbon in 5259 BC.[7][35]
Frost ring is a term used to designate a layer of deformed, collapsedtracheids and traumaticparenchyma cells in tree ring analysis. They are formed when air temperature falls below freezing during a period ofcambial activity. They can be used in dendrochronology to indicate years that are colder than usual.[38]
Dendroclimatology is the science of determining pastclimates fromtrees primarily from the properties of the annual tree rings.[40] Other properties of the annual rings, such as maximumlatewood density (MXD) have been shown to be better proxies than simple ring width. Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous.[citation needed]
Dendrochronology has become important to art historians in the dating ofpanel paintings. However, unlike analysis of samples from buildings, which are typically sent to a laboratory, wooden supports for paintings usually have to be measured in a museum conservation department, which places limitations on the techniques that can be used.[41]
In addition to dating, dendrochronology can also provide information as to the source of the panel. ManyEarly Netherlandish paintings have turned out to be painted on panels of "Baltic oak" shipped from theVistula region via ports of theHanseatic League. Oak panels were used in a number of northern countries such asEngland,France andGermany. Wooden supports other than oak were rarely used by Netherlandish painters.[42]
A portrait ofMary, Queen of Scots, determined to date from the sixteenth century by dendrochronology
Since panels of seasoned wood were used, an uncertain number of years has to be allowed for seasoning when estimating dates.[43] Panels were trimmed of the outer rings, and often each panel only uses a small part of theradius of the trunk. Consequently, dating studies usually result in aterminus post quem (earliest possible) date, and a tentative date for the arrival of a seasoned raw panel using assumptions as to these factors.[44] As a result of establishing numerous sequences, it was possible to date 85–90% of the 250 paintings from the fourteenth to seventeenth century analysed between 1971 and 1982;[45] by now a much greater number have been analysed.
A portrait ofMary, Queen of Scots in theNational Portrait Gallery, London was believed to be an eighteenth-century copy. However, dendrochronology revealed that the wood dated from the second half of the sixteenth century. It is now regarded as an original sixteenth-century painting by an unknown artist.[46]
While dendrochronology has become an important tool for dating oak panels, it is not effective in dating the poplar panels often used by Italian painters because of the erratic growth rings in poplar.[48]
The sixteenth century saw a gradual replacement of wooden panels by canvas as the support for paintings, which means the technique is less often applicable to later paintings.[49] In addition, many panel paintings weretransferred onto canvas or other supports during the nineteenth and twentieth centuries.
The dating of buildings with wooden structures and components is also done by dendrochronology;dendroarchaeology is the term for the application of dendrochronology in archaeology. While archaeologists can date wood and when it was felled, it may be difficult to definitively determine the age of a building or structure in which the wood was used; the wood could have been reused from an older structure, may have been felled and left for many years before use, or could have been used to replace a damaged piece of wood. The dating of building via dendrochronology thus requires knowledge of the history of building technology.[50] Many prehistoric forms of buildings used "posts" that were whole young tree trunks; where the bottom of the post has survived in the ground these can be especially useful for dating.
The burial chamber ofGorm the Old, who died c. 958,[54] was constructed from wood of timbers felled in 958.[50]
Veliky Novgorod, where, between the tenth and the fifteenth century, numerous consecutive layers of wooden log pavement have been placed over the accumulating dirt.[55]
There are many different file formats used to store tree ring width data. Effort for standardisation was made with the development of TRiDaS.[57][58] Further development led to the database software Tellervo,[59] which is based on the new standard format whilst being able to import lots of different data formats. The desktop application can be attached to measurement devices and works with the database server that is installed separately.[60]
Bard et al write in 2023: "The oldest tree-ring series are known as floating since, while their constituent rings can be counted to create a relative internal chronology, they cannot be dendro-matched with the main Holocene absolute chronology. However, 14C analyses performed at high resolution on overlapped absolute and floating tree-rings series enable one to link them almost absolutely and hence to extend the calibration on annual tree rings until ≈13 900 cal yr BP."[61]
Herbchronology is the analysis of annualgrowth rings (or simply annual rings) in the secondary rootxylem ofperennialherbaceous plants. Similar seasonal patterns also occur inice cores and invarves (layers ofsediment deposition in a lake, river, or sea bed). The deposition pattern in the core will vary for a frozen-over lake versus an ice-free lake, and with the fineness of the sediment.Sclerochronology is the study ofalgae deposits.
Some columnarcacti also exhibit similar seasonal patterns in the isotopes of carbon and oxygen in their spines (acanthochronology). These are used for dating in a manner similar to dendrochronology, and such techniques are used in combination with dendrochronology, to plug gaps and to extend the range of the seasonal data available to archaeologists andpaleoclimatologists.
^The term "dendrochronology" was coined in 1928 by the American astronomerAndrew Ellicott Douglass (1867–1962).Douglass, A.E. (1928).Climatic Cycles and Tree Growth. Vol. II. A Study of the Annual Rings of Trees in relation to Climate and Solar Activity. Washington, D.C., USA: Carnegie Institute of Washington. p. 5. From p. 5: "One can see that in all this we are measuring the lapse of time by means of a slow-geared clock within trees. For this study the name "dendro-chronology" has been suggested, or "tree-time." "
^Holliday, Trenton (2021).Cro-Magnon: The Story of the Last Ice Age People of Europe. New York: Columbia University Press. p. 44.ISBN978-0-231-20497-2.
^Theophrastus with Arthur Hort, trans.,Enquiry into Plants, volume 1 (London,England: William Heinemann, 1916), Book V,p. 423. From p. 423: "Moreover, the wood of the silver-fir has many layers, like an onion; there is always another beneath that which is visible, and the wood is composed of such layers throughout." Although many sources claim that Theophrastus recognized that trees form growth rings annually, this is not true.
Studhalter, R. A. (April 1956). "Early History of Crossdating".Tree-Ring Bulletin.21:31–35.hdl:10150/259045. (Condensed from:Studhalter, R. A. (1955). "Tree Growth I. Some Historical Chapters".Botanical Review.21 (1/3):1–72.doi:10.1007/BF02872376.JSTOR4353530.S2CID37646970.
Studhalter, R. A.; Glock, Waldo S.; Agerter, Sharlene R. (1963). "Tree Growth: Some Historical Chapters in the Study of Diameter Growth".Botanical Review.29 (3):245–365.doi:10.1007/BF02860823.JSTOR4353671.S2CID44817056.
James H. Speer,Fundamentals of Tree-ring Research (Tucson, Arizona: University of Arizona Press, 2010), Chapter 3: History of Dendrochronology, pp. 28–42.
Leonardo da Vinci,Trattato della Pittura ... (Rome, (Italy): 1817),p. 396. From p. 396:"Li circuli delli rami degli alberi segati mostrano il numero delli suoi anni, e quali furono più umidi o più secchi la maggiore o minore loro grossezza." (The rings around the branches of trees that have been sawed show the number of its years and which [years] were the wetter or drier [according to] the more or less their thickness.)
Sarton, George (1954) "Queries and Answers: Query 145. — When was tree-ring analysis discovered?",Isis,45 (4): 383–384. Sarton also cites a diary of the French writerMichel de Montaigne, who in 1581 was touring Italy, where he encountered a carpenter who explained that trees form a new ring each year.
^du Hamel & de Buffon (4 May 1737)"Observations des différents effets que produisent sur les végétaux les grandes gelées d'hiver et les petites gelées du printemps"Archived 2015-05-09 at theWayback Machine(Observations on the different effects that the severe frosts of winter and the minor frosts of spring produce on plants),Mémoires de l'Académie royale des science, in:Histoire de l'Académie royale des sciences ..., pp. 273–298. Studhalter (1956), p. 33, stated that Carl Linnaeus (1745, 1751) in Sweden, Friedrich August Ludwig von Burgsdorf (1783) in Germany, and Alphonse de Candolle (1839–1840) in France subsequently observed the same tree ring in their samples.
(Anon.) (1835)"Evening meeting at the Rotunda"Archived 2015-05-14 at theWayback Machine,Proceedings of the Fifth Meeting of the British Association for the Advancement of Science held in Dublin during the week from the 10th to the 15th of August, 1835, inclusive, pp. 116–117.
^J. T. C. Ratzeburg,Die Waldverderbniss oder dauernder Schade, welcher durch Insektenfrass, Schälen, Schlagen und Verbeissen an lebenenden Waldbäumen entsteht. [The deterioration of forests or lasting damage that arises from feeding by insects, debarking, felling, and gnawing on living forest trees.], vol. 1, (Berlin, (Germany): Nicolaische Verlag, 1866),p. 10.Archived 2015-10-01 at theWayback Machine From p. 10:"Die beiden, auf Taf. 42, Fig. 6 (mit dem Durchschnitt Fig. 7) und Fig. 1 (mit dem Durchschnitt Fig. 2) dargestellten Zweige hatten in dem Frassjahre 1862 einen doppelt so starken Jahrring als in dem vorhergehenden angelegt, und auch der (hier nicht abgebildete) Ring des jährigen Triebes war bei den gefressenen stärker as der eines nicht gefressenen." (Both branches that are presented in plate 42, fig. 6 (with the cross-section in fig. 7) and fig. 1 (with the cross-section in fig. 2) had produced, in the defoliation year of 1862, a growth ring that was twice as strong as in the preceding one, and so was the ring of the year-old shoot (not illustrated here) stronger in the case of the defoliated tree than one that was not defoliated.)
Seckendorff, Arthur von (1881) "Beiträge zur Kenntnis der SchwarzföhrePinus austriaca Höss" [Contributions to our knowledge of the black pinePinus austriaca Höss],Mitteilung aus dem forstlichen Versuchswesen Oesterreichs [Report from the Austrian Department of Forestry Research] (Vienna, Austria: Carl Gerold Verlag, 1881), 66 pages.
Шведов, Ф. (Shvedov, F.) (1892) "Дерево, как летопись засух" (The tree as a record of drought),Метеорологический Вестник (Meteorological Herald), (5) : 163–178.
Speer (2010), p. 37.
^"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 someMediterranean species.
^Capon, Brian (2005).Botany for Gardeners (2nd ed.). Portland, OR: Timber Publishing. pp. 66–67.ISBN978-0-88192-655-2.
^"WM Trædatering" [WM Tree dating].skalk.dk (in Danish). Archived fromthe original on 21 December 2014. Retrieved15 May 2015.
^abAndrej Maczkowski et al, "Absolute dating of the European Neolithic using the 5259 BC rapid 14C excursion", Nature Communications, 2024doi:10.1038/s41467-024-48402-1
^Spronk, Ron (1996). "More than Meets the Eye: An Introduction to Technical Examination of Early Netherlandish Paintings at the Fogg Art Museum".Harvard University Art Museums Bulletin.5 (1):1–64.JSTOR4301542.
"Tree Ring Science", the academic site of Prof. Henri D. Grissino-Mayer, Department of Geography, The University of Tennessee, and the Laboratory of Tree-Ring Science
Briand, Christopher H.; Brazer, Susan E.; Harter-Dennis, Jeannine M. (December 2006). "Tree Rings and the Aging of Trees: A Controversy in 19th Century America".Tree-Ring Research.62 (2):51–65.doi:10.3959/1536-1098-62.2.51.hdl:10150/262645.S2CID162884050.
.jpg)
