Dendroarchaeology

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Pinus ponderosa stump section timeline 1937. Ponderosa pine stump section showing tree growth rings and fire scars from 1255-1930. Deming Creek. Bly, Oregon. (34049124174).jpg
Pinus ponderosa stump section timeline

Dendroarchaeology is a term used for the study of vegetation remains, old buildings, artifacts, furniture, art and musical instruments using the techniques of dendrochronology (tree-ring dating). It refers to dendrochronological research of wood from the past regardless of its current physical context (in or above the soil). This form of dating is the most accurate and precise absolute dating method available to archaeologists, as the last ring that grew is the first year the tree could have been incorporated into an archaeological structure. [1]

Contents

Tree-ring dating is useful in that it can contribute to chronometric, environmental, and behavioral archaeological research. [2]

The utility of tree-ring dating in an environmental sense is the most applicable of the three in today's world. Tree rings can be used to reconstruct numerous environmental variables such as temperature, precipitation, stream flow, drought society, fire frequency and intensity, insect infestation, atmospheric circulation patterns, among others. [2]

History

At the beginning of the twentieth century, astronomer Andrew Ellicott Douglass first applied tree ring dating to prehistoric North American artifacts.  Through applying dendrochronology (tree-ring dating), Douglass hoped for more expansive climate studies. Douglass theorized organic materials (trees and plant remains) could assist in visualizing past climates. Despite Dr. Douglass’s contributions, archaeology as a discipline did not begin applying tree-ring dating until 1970s with Dr. Edward Cook and Dr. Gordon Jacoby. [3] In 1929, American Southwestern archaeologists had charted a non continuous historic and prehistoric chronologies for the Chaco Canyon Region. [4] Tree ring laboratory scientists from Columbia University were some of the first to apply tree-ring dating to the colonial period, specifically architectural timbers in the eastern United States. For agencies like the National Park Service and other historical societies, Dr. Jacoby and Cook began dating historic structures in the lower Hudson River Valley, New Jersey and Eastern Pennsylvania. This was difficult at the time due to a lack of sufficiently long master dating chronology and access to suitable structures. Not until 1998 was a Boston area master dating chronology developed. Today, the effectiveness of tree ring laboratory archaeological dating chronologies covers most of the area that was settled by the first European colonists. The numbers of these are in the hundreds and include historically significant structures such as Independence Hall and the Tuckahoe estate. [5]

Methodology

There are two types of dates that can be assigned to tree specimens: cutting dates, and noncutting dates. Which date is assigned to a specimen is dependent on whether or not there is evidence that the last ring present on the specimen was the last ring the tree grew before it died. [2]

Cutting dates can be used for crossdated tree specimens that "possess evidence that the last ring present on the specimen was the last ring grown by the tree before it died." [2]

Noncutting dates are used for crossdated tree specimens "if there is no evidence indicating that the last ring present on the specimen is the last one grown before the tree died." [2] Patterns of tree growth will be similar between trees of the same species, growing in the same climate. These matching patterns align growth rings in different trees formed in the same year. Once aligned, knowing the precise calendar year of any individual tree-ring is the same as knowing the calendar year of all the rings. The goal of a dendroarchaeologist is to determine the year when the last ring was formed. Crossdating, the skill of finding matching ring-width patterns between tree-ring samples, is used to assign the precise calendar year to every ring. This is affected by the climate that the timber was in. It is also important to have enough rings to actually confirm a date. Once the rings are dates, the chronology is measured. The last step is to compare the rings with that of ring-width patterns in sampled timbers and a master dating chronology. [6]

For trees to be useful in archaeological analysis, they must "produce annual growth rings that are uniform around the tree stem", they must "live for decades and, preferably, centuries" and they "must have been used extensively by humans either for habitation or fuel." [2] One of the problems with this evaluation is that it is possible under certain conditions for a tree to miss a growth-ring or produce two growth rings in a season. During extreme drought there can be insufficient growth of xylem to form a noticeable ring. Alternatively, if a defoliating agent (e.g. drought, late frost, or insect damage) can arrest the growth of a tree early in a year, after which there is a secondary growth period of new foliage causing two rings to form. [7] Another difficulty in the use of tree-ring dating as applied to archaeology is the variety and condition of wood used in construction of archaeological sites. Many such samples are encountered wet. Heartwood can normally retain much of its substance and can be dried out and polished for analysis. On the other hand, ancient wet sapwood samples seldom survive drying out. As a result, the sapwood should either be measured wet and then allowed to dry, or it should be frozen or kept wet. [7]

In North America, "millennial-length chronologies have been developed for two species of bristlecone pine (Pinus longaeva in the Great Basin and Pinus aristata in the Rocky Mountains), bald cypress (Taxodium distichum), coast redwood (Sequoia sempervirens), Douglas-fir (Pseudotsuga menziesii), eastern cedar (Juniperus virginiana), juniper (Juniperus sp.), Larch (Larix sp.), lodgepole pine (Pinus contorta), limber pine (Pinus flexilis), mountain hemlock (Tsuga mertensiana), ponderosa pine (Pinus ponderosa), and giant sequoia (Sequoiadendron giganteum) (Jacoby, 2000a).” [2]

“In the southern hemisphere, successful crossdating has been achieved on alerce (Fitroya cupressoides) and pehuen (Araucaria araucana), also known as 'Chilean pine' or the 'monkey puzzle tree,' specimens in South America, kauri (Agathis australis) specimens in New Zealand, clanwilliam cedar (Widdringtonia cedarbergensis) specimens in Australia and Tasmania, and huon pine (Lagarostrobus franklinii) in Tasmania (Jacoby, 2000al; Norton, 1990).” [2]

Application

The main application of tree research laboratory science or dendroarchaeology is to produce records of past climates that might be unavailable otherwise. Timber remains give insight into what little remains of our national forests prior to colonial settlement. This also benefits the sciences of paleoclimatology. [8]

Dendrochronological dating is potentially applicable wherever trees were growing, except in tropical regions. For use in absolute dating of archaeological sites, it is partially limited by the availability of a master reference chronology for the region concerned. If there is a gap in the chronology (e.g. the inability to use a chronology constructed from pine samples in the British Isle prior to the 17th century due to the lack of use of pine in architecture then) then absolute dating cannot be applied. [7] Additionally, non-climatic influences can also affect the tree-ring pattern of timber samples. Even if a reference chronology is available, care must be taken to identify aberrations in the ring pattern to determine if the sample is usable for dating. [9]

Dendroarchaeology has been used extensively in the dating of historical buildings. After cross-matching the chronology from the building with the chronology of living trees, it is immediately possible to figure out the dates at which the historic timbers used in construction were felled. Archaeologists at Chaco Canyon, New Mexico used tree-ring dating and found structure remains originated fifty miles south from the Zuni Mountains. [10] Similarly, if an extended chronology is available, then dating of samples from buildings of known or unknown date is possible. However, a limiting aspect of this application becomes apparent when dating medieval buildings. In such buildings, many timber samples lack completeness out to the underbark surface which can make the task of determining the felling year much more difficult. [11]

The application of dendroarchaeology in uncovering past trade patterns also becomes possible as chronology records for timber around the world become more complete and accessible. Patterns from individual samples will match much more closely with their native chronologies than with their regional chronology. For example, strong cross dating is found between Irish and English chronologies, but individual ring patterns tend to match better against their local chronologies. Hence, this strong geographical component of tree ring chronologies can be used to source timber samples at archaeological sites to uncover trade routes required for the site construction. [11]

Dendrochronology can also be used in concert with radiocarbon dating to allow for more accurate date measurements using radiocarbon dating on archaeological sites. It is known that the concentration of carbon-14 in the atmosphere is not constant. By performing radiocarbon dating on timber samples in a known chronology, radiocarbon dates can be plotted against real time generating a calibration curve that can be used for future radiocarbon samples. [7]

While dendrochronology is often considered as an absolute dating method, it can also be used as a powerful tool in the relative dating of an archaeological site. Timber samples may be able to be compared with others on the site to help construct a timeline of events for that particular site. Such samples can also be used to settle issues in constructing a chronological typology for artifacts found on site. The important point is that such within-site analysis can be done whether or not a chronology is available to date the whole assemblage. [7]

Archaeological Dendroclimatology

Dr. A.E. Douglass primary goal for early dendrochronology applications was understanding prehistoric climates. Today, many archaeologists utilize tree-ring dating for insights on past environmental conditions. Tree ring patterns can reflect past earthquakes, volcanic activity, fires, and insect infestations. [4] Dendroclimatology is a sub-discipline of dendrochronology and dendroarchaeology that utilizes research methods for climate analysis. Dendroclimatology research has charted humidity changes in the American southwest since 1600. [12]

See also

Related Research Articles

Radiocarbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.

<span class="mw-page-title-main">Dendrochronology</span> Method of dating based on the analysis of patterns of tree rings

Dendrochronology is the scientific method of dating tree rings to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmospheric conditions during different periods in history from wood. Dendrochronology derives from Ancient Greek dendron, meaning "tree", khronos, meaning "time", and -logia, "the study of".

<span class="mw-page-title-main">Chronology</span> Science of arranging events in order of occurrence

Chronology is the science of arranging events in their order of occurrence in time. Consider, for example, the use of a timeline or sequence of events. It is also "the determination of the actual temporal sequence of past events".

<span class="mw-page-title-main">Bristlecone pine</span> Three species of pine trees native to the Western United States

The term bristlecone pine covers three species of pine tree. All three species are long-lived and highly resilient to harsh weather and bad soils. One of the three species, Pinus longaeva, is among the longest-lived life forms on Earth. The oldest of this species is more than 4,800 years old, making it the oldest known individual of any species.

Archaeological science, also known as archaeometry, consists of the application of scientific techniques to the analysis of archaeological materials and sites. It is related to methodologies of archaeology. Martinón-Torres and Killick distinguish ‘scientific archaeology’ from ‘archaeological science’. Martinón-Torres and Killick claim that ‘archaeological science’ has promoted the development of high-level theory in archaeology. However, Smith rejects both concepts of archaeological science because neither emphasize falsification or a search for causality.

<span class="mw-page-title-main">Varve</span> Annual layer of sediment or sedimentary rock

A varve is an annual layer of sediment or sedimentary rock.

Before Present (BP) years, also known as "time before present" or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because the "present" time changes, standard practice is to use 1 January 1950 as the commencement date (epoch) of the age scale. The abbreviation "BP" has been interpreted retrospectively as "Before Physics", which refers to the time before nuclear weapons testing artificially altered the proportion of the carbon isotopes in the atmosphere, which scientists must now account for.

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 (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. By combining multiple tree-ring studies, scientists have estimated past regional and global climates.

Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be temporally fixed or floating.

<span class="mw-page-title-main">Egyptian chronology</span>

The majority of Egyptologists agree on the outline and many details of the chronology of Ancient Egypt. This scholarly consensus is the so-called Conventional Egyptian chronology, which places the beginning of the Old Kingdom in the 27th century BC, the beginning of the Middle Kingdom in the 21st century BC and the beginning of the New Kingdom in the mid-16th century BC.

Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy. Absolute dating provides a numerical age or range, in contrast with relative dating, which places events in order without any measure of the age between events.

The old wood effect or old wood problem is a pitfall encountered in the archaeological technique of radiocarbon dating. A sample will provide misleading or confusing results if materials of different ages are deposited in the same context.

Florence May Hawley Ellis was one of the first anthropologists to work extensively on dendrochronology, or tree-ring dating. She conducted archaeological and ethnographic research in the Southwestern United States; and undertook some of the first dendrochronological research in eastern North America in the mid 20th century, examining samples from a number of archaeological sites. She was also highly regarded as a passionate teacher who pushed her students toward greatness by encouraging them to think for themselves and work hard for what they wanted to achieve. Although faced with many challenges in her career, and discriminated against for being a woman, she persevered in her research and became a great influence both for her students and for other women in her field.

<span class="mw-page-title-main">Divergence problem</span>

The divergence problem is an anomaly from the field of dendroclimatology, the study of past climate through observations of old trees, primarily the properties of their annual growth rings. It is the disagreement between instrumental temperatures and the temperatures reconstructed from latewood densities or, in some cases, from the widths of tree rings in far northern forests.

<span class="mw-page-title-main">Chronology of the ancient Near East</span> Chronology article

The chronology of the ancient Near East is a framework of dates for various events, rulers and dynasties. Historical inscriptions and texts customarily record events in terms of a succession of officials or rulers: "in the year X of king Y". Comparing many records pieces together a relative chronology relating dates in cities over a wide area.

The Hallstatt plateau is a term used in archaeology that refers to a consistently flat area on graphs that plot radiocarbon dating against calendar dates. Radiocarbon dates of around 2450 BP always calibrate to c. 800–400 BC, no matter the measurement precision. The carbon 14 dating method is hampered by this large plateau on the calibration curve in a critical period of human technological development. Just before and after the plateau, calibration is accurate; during the plateau only techniques like wiggle matching can yield useful calendar dates. The plateau is named after the Hallstatt culture period in central Europe with which it coincides.

<span class="mw-page-title-main">A. E. Douglass</span> American astronomer

A. E. Douglass was an American astronomer. He discovered a correlation between tree rings and the sunspot cycle, and founded the discipline of dendrochronology, which is a method of dating wood by analyzing the growth ring pattern. He started his discoveries in this field in 1894 when he was working at the Lowell Observatory. During this time he was an assistant to Percival Lowell, but fell out with him when his experiments made him doubt the existence of artificial "canals" on Mars and visible cusps on Venus.

Radiocarbon dating measurements produce ages in "radiocarbon years", which must be converted to calendar ages by a process called calibration. Calibration is needed because the atmospheric 14
C
:12
C
ratio, which is a key element in calculating radiocarbon ages, has not been constant historically.

Fire history, the ecological science of the study of the history of wildfires, is a subdiscipline of fire ecology. Patterns of forest fires in historical and prehistorical time provide information relevant to the pattern of vegetation in modern landscapes. It provides an estimate of the historical range of variability of a natural disturbance regime, and can be used to identify the processes affecting the occurrence of fire. Fire history reconstructions are achieved by compiling atlases of past fires, using the tree ring record from fire scars and tree ages, and the charcoal record from soils and sediments.

Elizabeth K. Ralph (1921–1993) was a pioneer in the development and application of radiocarbon dating techniques to archeology, as well as a long-time member of the U.S. women’s field hockey team. In the Radiocarbon Laboratory at the University of Pennsylvania, and later in the Museum Applied Science Center for Archaeology (MASCA) in the Penn Museum, Ralph developed methods for dendrochronology, or tree-ring dating, and thermoluminescence for dating ceramics. She also improved instruments for the measurement of magnetic intensity, including cesium magnetometers, which located landscape anomalies that could signal the presence of archaeological sites. In the 1960s, she used these instruments to help locate the Archaic Greek site of Sybaris in southern Italy. She went on to analyze and date materials from dozens of archaeological sites in several countries. She published her research in journals including Science and Nature, and with her colleague H.N. Michael, published a textbook entitled Dating Techniques for the Archaeologist, which appeared from MIT Press in 1971. From 1962 to 1982 she served as Associate Director of MASCA lab, which she helped to establish with support from the National Science Foundation.

References

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  3. "Dendrochronology: What Tree Rings Tell Us About Past and Present | EnvironmentalScience.org". www.environmentalscience.org. Retrieved 2022-09-20.
  4. 1 2 Roosevelt, Mailing Address: 26260 N. AZ Hwy 188 Lot 2; Us, AZ 85545 Phone: 928 467-2241 Contact. "Dendrochronology - Tonto National Monument (U.S. National Park Service)". www.nps.gov. Retrieved 2022-09-22.
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  6. "Scientific Application". Columbia University. 2012. Retrieved April 12, 2012.
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  8. "Scientific Application". Columbia University. 2012. Retrieved April 12, 2012.
  9. Aitken, M.J. (1990). Science-based Dating in Archaeology. New York: Longman Inc. pp. 37–47. ISBN   0-582-05498-2.
  10. "Unexpected Wood Source for Chaco Canyon Great Houses". University of Arizona News. 2015-12-07. Retrieved 2022-09-22.
  11. 1 2 Gӧksu, H.Y. (1991). Scientific Dating Methods. Luxembourg: Kluwer Academic Publishers. pp. 199–200. ISBN   0-7923-1461-1.
  12. Sheppard, Paul R. (May 2010). "Dendroclimatology: Extracting climate from Trees" (PDF). Wiley Interdisciplinary Reviews: Climate Change. 1 (3): 343–352. doi:10.1002/wcc.42. S2CID   129124697.