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he term PHOTOGRAPH BY G M C/ANTHONY BA I LEY refers to the practice of Tdetermining a ’s age from its rings. The science of dendrochronology hinges on the growth rings that produce annually during their growth . The width of a tree ring is

PHOTOGRAPH COURTESY OF Wiki ped i a C o mm ons dependent on a number of factors, including the available moisture

PHOTOGRAPH COURTESY OF Wiki ped i a C o mm ons The Editor’s own crude attempt to date a from precipitation and variations in mature pine tree which he has chopped Dendrochronology: temperature endured by the flora. A dendrochronological drill bit designed to make core samples up for firewood! It appears to be about This scientific field of study concerns for accurate laboratory analysis. 70 old but an expert could date it itself with the interpretation and Frequently used to date timbers in more accurately as each apparent annual timber as a timepiece dating of historic, scientific, cultural ring needs to be interpreted properly ancient wooden structures such as and climatic occurrences and trends. timbered houses, barns and ships Dendrochronology demonstrates the and so much more inherent utility and flexibility of trees when a particular ring was formed. Andrew Ellicott and timber. Tree-ring growth may not always Douglass Dr Nicola Davies explains the science of Dr Henri Grissino-Mayer, Professor be annual. Therefore, the field of The modern of Geography at the University of dendrochronology dictates that a development of analysing tree-ring data Tennessee-Knoxville, says, “Like any particular tree-ring be assigned a dendrochronology other science, dendrochronology specific . For this to be as a science can be has overarching principles. Many successfully carried out a number of credited to the astronomer Andrew of these principles are borrowed principles must be satisfied. Ellicott Douglass, who founded from other sciences. For instance, The first fundamental principle the University of Arizona Tree- the principle of unformitarianism is that the growth rings of the tree ring Research Laboratory in 1937. states that the present is the key to species must be well-defined, i.e. there This laboratory has worldwide the past so with this principle we can must be sufficient contrast between recognition as a foremost authority reconstruct , for example, with the formed early in the growth on dendrochronological techniques tree-ring data.” and the wood formed in the and their application in the fields of latter part of the growth season. This environmental and social science. usually accounts for the lighter and

Birds of a feather flock PHOTOGRAPH COURTESY OF Wiki ped i a C o mm ons together, so do and … darker rings. Second, the rings must apparently have concentric uniformity toward The similarity between the growth the centre or the pith. Third, there rings of trees in the same general must be variations in the annual rings location, as well as those facing the – the principle of sensitivity. In other same climatic conditions, allows words, the tree should be able to dendrochronologists to analyse demonstrate its sensitivity, or response tree-rings and construct extensive to environmental variables, by the going back thousands presence of a range of ring widths. of years. One particular of Since dendrochronology is dependent central Europe goes back some 10,000 on tree-ring patterns, a tree with the An accelerator mass spectrometer years. The Central European study same ring widths throughout would at Lawrence Livermore National analysed oak () trees provide no distinct pattern that could Laboratory used for carbon dating. almost exclusively and was completed be used in crossdating or matching Dendrochronological samples can by the Hohenheim Laboratory. with that of another tree. be used as reference markers to help There is much more to improve the accuracy of carbon dating dendrochronology than counting It’s alive! rings in trees. “We don’t just count Despite the difficulty in absorbing of a tree . The tool is composed tree rings!” states Grissino-Mayer, and employing the rigid methodology of a hollow metallic cylinder, “Statistical orientation is necessary. of dendrochronology, dead trees measuring about 4–5mm, though The centre of a polished slice of a My training as a biogeographer, give up their secrets without much sometimes even up to 160mm. The petrified tree from the late Triassic period biologist and a statistician come resistance – timber obtained from cylinder’s tip is threaded to form an (approximately 230 million years ago) together. We ensure that the tree rings archaeological finds, victims of large auger or cutting tip. A detachable metal found in Arizona. The remains of insects we analyse are precisely dated to the contruction projects, tree stumps and handle is attached perpendicularly to can be detected in an enlarged image exact date without any plus or minus fallen logs. The more intrepid among the cylinder to facilitate the torque to the year. This is the principle of you may have turned your thoughts needed to drill into the tree trunk. crossdating. We will not use tree-ring to vivisection – how are tree rings After extruding the wood, the tree- data unless we are 99.99% confident obtained from living trees? There’s a ring containing sample is taken to a that the tree rings are precisely dated.” tool for that – the . laboratory for analysis. The sample The amateur falls victim to the The increment borer allows has to be sanded smooth to more false premise that he can identify to remove a narrow cylindrical sample accurately reveal the tree rings. ➤

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Dendrochronology websites National Centers for Environmental Information (NOAA) www.ncdc.noaa.gov/data-access/ -data/datasets/tree- ring Nottingham Tree Ring Laboratory www.tree-ringdating.co.uk Oxford Tree Ring Laboratory www.dendrochronology.net University of Arizona Laboratory of Tree Ring Research Above left: A portrait of Mary Queen of Scots, determined to date from the 16th ltrr.arizona.edu century by dendrochronology by an unknown artist. Previously it was thought to be an PHOTOGRAPH s BY G M C/ANTHONY BA I LEY 18th-century copy Vernacular Architecture Group www.vag.org.uk Above right: Little Moreton Hall, Cheshire is mid 16th century, like the portrait to the left. Dendrochronology can be used in buildings like this to determine whether much older timbers have been incorporated in the structure Taking up dendrochronology PHOTOGRAPH COURTESY OF Wiki ped i a C o mm ons Grissino-Mayer provides the following tips to aspiring dendrochronologists, “You have to be a tree person! You need to take biology courses and study botany. Maths is also important for this field as you will be working with Main image: A massive split yew tree () growing very specific software. Hence, it is a in the churchyard of St Mary’s, Buxted, East Sussex. Almost combination of maths and sciences. impossible to accurately date a tree in this condition without You need to read a lot on your a central trunk intact PHOTOGRAPH COURTESY OF own. Visiting a tree-ring laboratory Inset and above: A campaign was mounted to determine and agree the age of this Wiki ped i a C o mm ons can be beneficial. For example, massive yew, which by expert common consent is indeed more than 2000 years old PHOTOGRAPH s COURTESY OF Wiki ped i a C o mm ons you could interact with , St Brothen’s Church, Llanfrothen, Wales On a lighter note – Baumkuchen is a biogeographers, dendroecologists and These rings are then measured using can be applied. Currently, accurate is a Grade 1 listed structure which has traditional German layer cake made from dendroclimatologists who regularly use a microscope and the data stored dendrochronological studies are only had various changes made to it. Tree ring flour, eggs, butter, sugar and vanilla, the tree-ring data.” dating has determined that the trees used name translates as ‘tree cake’ on account in a computer. The data is then facilitated because of tree species like As a woodworking enthusiast, you Whereas tree ring dating in the UK to make the rood screen dated between of the rings in the cake – yummy! compared with other chronologies the (Pinus aristata) can start your first project in this field is most commonly done with oak 1496-1506 from recognised chronology datasets, and oak, whose ages span centuries timbers, in the US the rather raggedy by attempting to date a tree or even the using computer software that matches and sometimes millennia, providing a looking bristlecone pine is the inherent structure of a tree developing limitations, it is safe to say that timber used in your home. If you don’t ring patterns of the sample to a master somewhat continuous pattern against dendrochronologist’s tree of choice from sapwood to heartwood. It is dendochronology has allowed us have access to the wooden slabs or pattern. which other trees may be matched. well-known that sapwood – the outer to leverage trees and timber into cross-sections that you need, you might In the UK, oak is one of the most areas, trees don’t shut down growth to lighter-coloured section of a tree powerful timepieces. It is true that have to obtain an increment borer. Dendrochronology in the UK documented species because of its form an annual ring and without that trunk – is much softer than the inner the field of tree-dating has its fair This tool will also come in handy when Many assumed that dendrochronology widespread use in building timber- we cannot count the tree rings.” and darker-coloured heartwood. As share of critics. However, there is coring live trees. Be sure to seal the would have been hampered in Britain framed structures in the past. However, Additionally, where there is an such, sapwood is more prone to decay extensive and well-documented hole you create to protect the tree from because of the complex climate oak wasn’t the only species used in availability of suitable tree species, precipitated by moisture and insects. research spanning decades to disease. All the information you need experienced there. Science, however, construction; elm (Ulmus procera) the wood needs to be adequately This may result in the absence, or support the principles involved in is readily available, and the results of has silenced the doubters and Grissino- and Western red cedar (Thuja plicata) preserved so that the tree-rings will removal, of sapwood from timber dendrochronology. The enthusiast can your investigation might surprise you. Mayer confirms, “The UK is at the were also utilised. If the only master be easily identifiable; each specimen surfaces used in the construction of access dendrochronology archives and forefront of dendrochronology. Tree- chronology available for a region should have a minimum of 30 rings. timber structures. The removal of the databases for themselves. For example, ring dating is used in its historic and is for the oak species, its use in the In some cases, trees that are cut at a sapwood along with the outer tree-ring the Vernacular Architecture Group Dr Nicola Davies prehistoric structures and musical crossdating and analysis of other young age don’t have enough rings to often makes it impossible to pinpoint maintains a dendrochronological Dr Nicola Davies is instruments. These data can be used to species will certainly be unreliable. facilitate accurate cross-matching. the particular year that tree was felled. database of tree-ring dates for more a psychologist and reconstruct climate and date historic Another requirement and potential Despite the anomalies and than 3,000 buildings in the UK. Freelance writer with structures. The UK has had some of the The limits of hindrance to the application of hundreds of articles top dendrochronology programmes for Despite proving itself an accurate dendrochronology in historical published in 10 countries. Her a long time now.” dating method, dendrochronology studies is that there has to be a fairly research skills make her amenable For accurate dendrochronological does have some limitations. One of the extensive use of timber within the time to a variety of subjects, all with a analyses to be carried out, an existing foremost limitations is that, in some period and geographical region under human interest angle. You can follow master tree-ring pattern has to be parts of the world, the tree species that consideration. Tree-ring analysis of her on Twitter (@healthpsychuk) available for a particular geographical are available don’t demonstrate clear- the timber used in construction is a or sign up to her free blog: http:// region and for the specific tree cut seasonal patterns. Grissino-Mayer major way in which time stamps can healthpsychologyconsultancy. species. This places limitations on explains, “Tree-ring dating doesn’t be identified and applied. This chart underlines some of the difficulties of dating timber from tree rings due to the wordpress.com/ how far into the past tree-ring dating work so well in the tropics. In these Other limitations are linked to the sometimes extreme changes in temperature that can affect each ring

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