Dendrochronology

Dendrochronology

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Dendrochronology or tree-ring dating is the scientific method of dating based on the analysis of patterns of tree-rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year. This has three main areas of application: paleoecology
Paleoecology
Paleoecology uses data from fossils and subfossils to reconstruct the ecosystems of the past. It involves the study of fossil organisms and their associated remains, including their life cycle, living interactions, natural environment, and manner of death and burial to reconstruct the...

, where it is used to determine certain aspects of past ecologies
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

 (most prominently climate); archaeology
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...

, where it is used to date old buildings, etc.; and radiocarbon dating
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

, where it is used to calibrate radiocarbon ages (see below).

In some areas of the world, it is possible to date wood back a few thousand years, or even many thousands. In most areas, however, wood can only be dated back several hundred years, if at all. Currently, the maximum for fully anchored chronologies is a little over 11,000 years from present.

History


Dendrochronology (word derived from Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 , dendron, "tree limb"; , khronos, "time"; and , -logia) was developed during the first half of the 20th century originally by the astronomer A. E. Douglass
A. E. Douglass
A. E. Douglass was an American astronomer. He discovered a correlation between tree rings and the sunspot cycle....

, the founder of the Laboratory of Tree-Ring Research
Laboratory of Tree-Ring Research
The Laboratory of Tree-Ring Research was established in 1937 by A.E. Douglass, founder of the modern science of dendrochronology. The LTRR is a research unit in the College of Science at the University of Arizona in Tucson, Arizona...

 at the University of Arizona
University of Arizona
The University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...

. Douglass sought to better understand cycles of sunspot activity and reasoned that changes in solar activity would affect climate patterns on earth which would subsequently be recorded by tree-ring growth patterns (i.e., sunspots → climate → tree rings).

Growth rings


Growth rings, also referred to as tree rings or annual rings, can be seen in a horizontal cross section
Cross section (geometry)
In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc...

 cut through the trunk
Trunk (botany)
In botany, trunk refers to the main wooden axis of a tree that supports the branches and is supported by and directly attached to the roots. The trunk is covered by the bark, which is an important diagnostic feature in tree identification, and which often differs markedly from the bottom of the...

 of a tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

. Growth rings are the result of new growth in the vascular cambium
Vascular cambium
The vascular cambium is a part of the morphology of plants. It consists of cells that are partly specialized, for the tissues that transport water solutions, but have not reached any of the final forms that occur in their branch of the specialization graph...

, a lateral meristem, and are synonymous with secondary growth
Secondary growth
In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length. As long as the lateral meristems...

. Visible rings result from the change in growth speed through the season
Season
A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...

s of the year, thus one ring usually marks the passage of one year in the life of the tree. The rings are more visible in temperate zones, where the seasons differ more markedly.

The inner portion of a growth ring is formed 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". The outer portion is the "late wood" (and has sometimes been termed "summer wood", often being produced in the summer, though sometimes in the autumn) and is denser. "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
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

) or in autumn, as in some Mediterranean species.

Many tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

s in temperate zones make one growth ring each year, with the newest adjacent to the bark. For the entire period of a tree's life, a year-by-year record or ring pattern is formed that reflects the climatic conditions in which the tree grew. Adequate moisture and a long growing season result in a wide ring. A drought year may result in a very narrow one. Alternating poor and favorable conditions, such as mid summer droughts, can result in several rings forming in a given year.
Missing rings are rare in oak and elm trees—the only recorded instance of a missing ring in oak trees occurred in the year 1816, also known as the Year Without a Summer
Year Without a Summer
The Year Without a Summer was 1816, in which severe summer climate abnormalities caused average global temperatures to decrease by about 0.4–0.7 °C , resulting in major food shortages across the Northern Hemisphere...

.
Trees from the same region will tend to develop the same patterns of ring widths for a given period. These patterns can be compared and matched ring for ring with trees growing in the same geographical zone and under similar climatic conditions. Following these tree-ring patterns from living trees back through time, chronologies can be built up, both for entire regions, and for sub-regions of the world. Thus wood from ancient structures can be matched to known chronologies (a technique called cross-dating) and the age of the wood determined precisely. Cross-dating was originally done by visual inspection, until computers were harnessed to do the statistical 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. This process is 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. Fully anchored chronologies which extend back more than 11,000 years exist for river oak trees from South Germany (from the Main
Main river
Main rivers are a statutory type of watercourse in England and Wales, usually larger streams and rivers, but also include some smaller watercourses. A main river is defined as a watercourse marked as such on a main river map, and can include any structure or appliance for controlling or regulating...

 and Rhine rivers) and pine from Northern Ireland. Furthermore, the mutual consistency of these two independent dendrochronological sequences has been confirmed by comparing their radiocarbon and dendrochronological ages.
Another fully anchored chronology which extends back 8500 years exists for the bristlecone pine in the Southwest US
Southwestern United States
The Southwestern United States is a region defined in different ways by different sources. Broad definitions include nearly a quarter of the United States, including Arizona, California, Colorado, Nevada, New Mexico, Oklahoma, Texas and Utah...

 (White Mountains
White Mountains (California)
The White Mountains of California are a triangular fault block mountain range facing the Sierra Nevada across the upper Owens Valley. They extend for approximately as a greatly elevated plateau about wide on the south, narrowing to a point at the north, with elevations generally increasing...

 of California).
In 2004 a new calibration curve INTCAL04 was internationally ratified for calibrated dates back to 26,000 Before Present
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...

 (BP) based on an agreed worldwide data set of trees and marine sediments.
The part of the new calibration curves that relies on tree-ring evidence (IntCal04) dates back to 12,410 calendar (cal) yr B.P. Beyond that and back to 14,700 cal yr B.P., IntCal04 is mainly constructed from 14C dates of foraminiferas from Venezuela.s Cariaco basin that are corrected for a constant reservoir age of 405 years.

Sampling and dating


Timber core samples measure the width of annual growth rings. By taking samples from different sites and different strata within a particular region, researchers can build a comprehensive historical sequence that becomes a part of the scientific record; for example, ancient timbers found in buildings can be dated to give an indication of when the source tree was alive and growing, setting an upper limit on the age of the wood. Some genera of trees are more suitable than others for this type of analysis. Likewise, in areas where trees grew in marginal conditions such as aridity or semi-aridity, the techniques of dendrochronology are more consistent than in humid areas. These tools have been important in archaeological dating of timbers of the cliff dwellings of Native Americans
Native Americans in the United States
Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...

 in the arid Southwest.

A benefit of dendrochronology is that it makes available specimens of once-living material accurately dated to a specific year to be used as a calibration
Calibration
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....

 and check of radiocarbon dating
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

, through the estimation of a date range formed through the interception of radiocarbon (B.P.
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...

, or 'B'efore 'P'resent, where present equals 1950-01-01) and calendar years. The bristlecone pine
Bristlecone pine
The bristlecone pines are a small group of pine trees that are thought to reach an age far greater than that of any other single living organism known, up to nearly 5,000 years....

, being exceptionally long-lived and slow growing, has been used for this purpose, with still-living and dead specimens providing tree ring patterns going back thousands of years. In some regions dating sequences of more than 10,000 years are available.

The dendrochronologist faces many obstacles, however, including some species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...

 which inhabit tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

s and extend their galleries into the wood, thus destroying ring structure.

Similar seasonal patterns also occur in ice core
Ice core
An ice core is a core sample that is typically removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice...

s and in varve
Varve
A varve is an annual layer of sediment or sedimentary rock.The word 'varve' is derived from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as Hvarfig lera on the first map produced by the Geological Survey of Sweden in...

s (layers of sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 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. Some columnar cactus
Cactus
A cactus is a member of the plant family Cactaceae. Their distinctive appearance is a result of adaptations to conserve water in dry and/or hot environments. In most species, the stem has evolved to become photosynthetic and succulent, while the leaves have evolved into spines...

 also exhibit similar seasonal patterns in the isotopes of carbon and oxygen in their spines (acanthochronology
Acanthochronology
Acanthochronology is the interdisciplinary study of cactus spines or Euphorbia thorns grown in time ordered sequence . Physical, morphological or chemical characteristics and information about the relative order or absolute age of the spines or thorns is used to study past climate or plant...

). 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 and paleoclimatologists.

While archaeologists can use the technique to date the piece of wood and when it was felled, it may be difficult to definitively determine the age of a building or structure that the wood is in. 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.

Applications


European chronologies derived from wooden structures found it difficult to bridge the gap in the 14th century when there was a building hiatus which coincided with the Black Death
Black Death
The Black Death was one of the most devastating pandemics in human history, peaking in Europe between 1348 and 1350. Of several competing theories, the dominant explanation for the Black Death is the plague theory, which attributes the outbreak to the bacterium Yersinia pestis. Thought to have...

. Other plagues which were less well recorded also appear in the record.

In areas where the climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 is reasonably predictable, trees develop annual rings of different properties depending on weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

, rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

, temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

, soil pH
Soil pH
The soil pH is a measure of the acidity or basicity in soils. pH is defined as the negative logarithm of the activity of hydrogen ions in solution. It ranges from 0 to 14, with 7 being neutral. A pH below 7 is acidic and above 7 is basic. Soil pH is considered a master variable in soils as it...

, plant nutrition
Plant nutrition
'Plant Nutrition is the study of the chemical elements that are necessary for growth. In 1972, E. Epstein defined 2 criteria for an element to be essential for plant growth:# in its absence the plant is unable to complete a normal life cycle or...

, CO2 concentration, etc. in different years. These variations may be used to infer past climate variations.

Given a sample of wood, the variation of the tree ring growths provides not only a match by year, it can also match location because the climate across a continent is not consistent. 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.

Dendrochronology has become important to art historians in the dating of panel painting
Panel painting
A panel painting is a painting made on a flat panel made of wood, either a single piece, or a number of pieces joined together. Until canvas became the more popular support medium in the 16th century, it was the normal form of support for a painting not on a wall or vellum, which was used for...

s, and can also provide information as to the source of the panel - many Early Netherlandish painting
Early Netherlandish painting
Early Netherlandish painting refers to the work of artists active in the Low Countries during the 15th- and early 16th-century Northern renaissance, especially in the flourishing Burgundian cities of Bruges and Ghent...

s have turned out to be painted on panels of "Baltic oak" shipped from the Vistula
Vistula
The Vistula is the longest and the most important river in Poland, at 1,047 km in length. The watershed area of the Vistula is , of which lies within Poland ....

 region via ports of the Hanseatic League
Hanseatic League
The Hanseatic League was an economic alliance of trading cities and their merchant guilds that dominated trade along the coast of Northern Europe...

. Since panels of seasoned wood were used, an uncertain number of years has to be allowed for seasoning. Panels were trimmed of the outer rings, and often each panel only uses a small part of the radius
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...

 of the trunk, so dating studies usually result in a "terminus post quem
Terminus post quem
Terminus post quem and terminus ante quem specify approximate dates for events...

" (earliest possible) date, and a tentative date for the actual arrival of a seasoned raw panel using assumptions as to these factors.

See also

  • Baumkuchen
    Baumkuchen
    Baumkuchen is a kind of layered cake. It is a traditional dessert in many countries throughout Europe and is also a popular snack and dessert in Japan...

    , cake that resembles growth rings
  • Dendroclimatology
    Dendroclimatology
    Dendroclimatology is the science of determining past climates from trees . Tree rings are wider when conditions favor growth, narrower when times are difficult. Other properties of the annual rings, such as maximum latewood density have been shown to be better proxies than simple ring width...

  • Dendroarchaeology
    Dendroarchaeology
    Dendroarchaeology is a term used for the study of vegetation remains, old buildings, artifacts, furniture, art and musical instruments using the techniques of dendrochronology . It refers to dendrochronological research of wood from the past regardless of its current physical context ....

  • Dendrology
    Dendrology
    Dendrology or xylology is the science and study of wooded plants . There is no sharp boundary between plant taxonomy and dendrology. However, woody plants not only belong to many different plant families, but these families may be made up of both woody and non-woody members. Some families include...

  • Paleoclimatology
    Paleoclimatology
    Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...

  • Post excavation
    Post excavation
    In archaeology once the archaeological record of given site has been excavated, or collected from surface surveys, it is necessary to gain as much data as possible and organize it into a coherent body of information. This process is known as post-excavation analysis, and is normally the most...

  • Varve
    Varve
    A varve is an annual layer of sediment or sedimentary rock.The word 'varve' is derived from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as Hvarfig lera on the first map produced by the Geological Survey of Sweden in...

  • Timeline of dendrochronology timestamp events
    Timeline of dendrochronology timestamp events
    -Timeline from all sub-regions:-Cliff-dwellings, etc, the Americas:*for the Americas, see also: Timeline of Chacoan history...

  • sclerochronology
    Sclerochronology
    The term sclerochronology dates from the early 1970s, and was coined in 1974 following pioneering work on nuclear test atolls by Knutson and Buddemeier. Sclerochronology is the study of physical and chemical variations in the accretionary hard tissues of invertebrates and coralline red algae, and...

  • acanthochronology
    Acanthochronology
    Acanthochronology is the interdisciplinary study of cactus spines or Euphorbia thorns grown in time ordered sequence . Physical, morphological or chemical characteristics and information about the relative order or absolute age of the spines or thorns is used to study past climate or plant...

  • herbchronology
    Herbchronology
    Herbchronology is the analysis of annual growth rings in the secondary root xylem of perennial herbaceous plants. While leaves and stems of perennial herbs die down at the end of the growing season the root often persists for many years or even the entire life...


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