Dating of events from tree growth and wood structure

Fundamentals of Tree-Ring Research | James H Speer -

dating of events from tree growth and wood structure

An overview of the main technologies used to date historic structures and their Whilst earlier types of wooden joints may be copied in later buildings and In a ' poor' growing season the trees all respond so that only a very narrow growth ring is formed. . carbon dioxide from the air and so may be used to date this event. Tree - Tree structure and growth: In the section Ecological and evolutionary The bark and the wood together constitute the secondary plant body of the tree. used to provide information on past climates as well as to date events of the past. Fundamentals of Tree-Ring Research By James H. Speer Fundamentals of Republic and is one of the most difficult pieces of wood that I have ever tried to date. .. 72 CHAPTER 4: GROWTH AND STRUCTURE OF WOOD. EVENT.

Evolutionary history of plants - Wikipedia

With fewer rings the pattern might have repeat matches at different points in the time scale and so give rise to multiple possible dates. This has implications for some vernacular structures in which rapidly grown, wide-ringed oaks, 30 to 40 years old, were used. In such instances it might be possible to date the wall plate which often contains far more rings.

In practice it is found that or growth rings are most likely to provide a unique match. However, because of the local ecological, non-climatic effects on the tree ring, it is not possible to guarantee that any particular specimen will give a date. In order to have greater certainty it is important to obtain several samples, in the form of cores drilled from the timber, and to construct a 'site chronology' for the building. The number of cores required will depend upon the complexity of the structure, but some ten cores per building phase is preferred.

dating of events from tree growth and wood structure

These are normally taken by the dendrochronologist in co-operation with the historian and the position of the cores is carefully marked on the building plan for future analysis of the results. The core leaves a small hole in the timber of about 15mm in diameter which may be plugged with a timber dowel. Although this method is capable of dating to the individual year, in practice several factors conspire to reduce the precision in dating the construction, sometimes drastically, and it is important to be aware of the limitations.

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Whilst in the middle ages it was the practice to use the timber 'green' - usually within a year of the felling date - in more recent times the timber is usually allowed to dry out, sometimes for decades, before use.

Furthermore, carpenters, aware of the effects of insect attacks, would deliberately remove the sapwood and even some heartwood. The number of sapwood rings may vary between 15 and 50 years, depending on the position in and the age of the tree. Thus the year of the last ring dated could be misleading to the construction date and be underestimated by an unknown number, possibly 60 years.

Sapwood may be found on at least some of the timbers in the dendrochronological survey and the site master chronology will lead to a more reliable date than an individual core. The range of radiocarbon dating reaches back to 60, years. For the last few thousand years it can have a precision of a few decades and may, in certain circumstances, be comparable with tree-ring dates.

The laboratory at Cambridge here in England was among the first six to be set up anywhere in the world. There are now several radiocarbon dating laboratories in Britain including those at Belfast, Cambridge, East Kilbride, Oxford and Swansea, as well as a commercial unit near Harwell. Radiocarbon dating is based on the element carbon, the basis of all life on earth.

The atoms of this element are of three different types or 'isotopes'. They are identical chemically but have slightly different physical properties, particularly in mass. The isotopes are respectively 12, 13 and 14 times as heavy as the common hydrogen atom the base unit by which the weight of other elements is measured.

The isotopes C and C are stable and make up the bulk of the element, but the C isotope, which is mildly radioactive, is extremely rare. The instability of radiocarbon results in half of it disappearing in 5, years its 'half-life'.

This instability is the basis of the dating method. All creatures have the same concentration of radiocarbon in their cells while they remain alive. This level is maintained constant by a sequence of events affecting the food web. It starts with photosynthesis in green leaves of plants, whereby atmospheric water vapour and carbon dioxide, containing the radiocarbon, are combined in the presence of sunlight to produce sugar.

The plant biological process converts this to the myriad of substances required for life. These substances are shared via the food network to all animals including man. For our purposes it may be assumed that the amount of radiocarbon in the atmosphere is constant over time. Once the creature dies the food chain is broken and the concentration of radiocarbon in the cells falls away. By measuring the residual C concentration in the material the date of its death may be calculated.

In the case of tree-rings the food chain is effectively broken at the end of the growing season and the radiocarbon concentration immediately begins to fall.

Dating Technology and Historic Buildings

Thus, in principle, the age of each growth ring may be measured. In practice, the measurements may resolve differences of about 20 or 30 years. Samples from a building for radiocarbon dating should be taken with care and due regard to provenance. For timber specimens, samples should be obtained as near to the bark as possible, as for dendrochronology.

Samples such as leather, cloth, food residues or straw represent a year's growth and so a point in time. Thatch, whether straw or rush, will date the last repair and not necessarily the construction date. When slaked and used as mortar between layers of bricks it dries by absorption of contemporary carbon dioxide from the air and so may be used to date this event. Upon resolution of the technical problems the method was used for dating pottery and burnt flints from archaeological sites with a precision of about per cent.

Subsequently it has been used in the investigation of recent geological formations reaching back to half a million years. In its most common form it may shed light on the age of fired clay and quartz based materials but approaching the present no closer than about a thousand years. A modern variant on the technique is able to date far more recent fired clay material.

TL depends upon minute levels of background radiation in the clay matrix, a tiny fraction of which is absorbed and stored as a charge at imperfections in the crystal lattice of quartz inclusions.

The firing of pottery removes the inherited geological TL and sets the dating clock to zero. Superimposed upon the red-hot glow, a tiny flash of light is produced as the stored energy is released hence 'thermoluminescence' and the flash is recorded by computer. The quantity of light produced is proportional to the length of time since it was last fired.

dating of events from tree growth and wood structure

Such methods are grouped under the term standardization in the dendrochronological literature, and they are intended to minimize changes in growth rate that are not common to all trees. For climatological reconstruction, the final tree-ring chronology is statistically calibrated against instrumental records of climate, such as precipitation and temperature, to identify the main climatic signals present in the tree-ring record. The relationship between tree growth and climate is then extrapolated back into the past, and climatic changes are estimated from the tree-ring chronology itself.

Because of the long life of many tree species, dendrochronological records tell of climate conditions occurring each year over hundreds, sometime thousands, of years, whereas instrumental weather records are commonly limited to the last decades, and seldom exceed one hundred years.

Tree-ring chronologies have been developed from a number of species in all continents where trees exist. In the western United Statesmost tree-ring records are derived from conifers, because they are very common, reach old ages, and, as softwoods, they are easier to sample than hardwoods. However, not all trees are equally suitable for dendrochronological studies.

In temperate, high-latitude and high-elevation climates, wood growth is usually constrained to the warm season, and tree rings are easily recognizable. Cross-dating is easier when year-to-year variability of tree growth is higher, because this causes a greater number and degree of pattern differences in tree-ring series.

When ring widths are less variable, common, climatically influenced patterns are more difficult to discern. Site conditions are therefore very important in dendrochronological studies because they affect tree-ring variability, which is an expression of the sensitivity of tree growth to climate.

To date, tree-ring studies of tropical trees have been limited by the fact that wood growth layers are not visually identifiable, especially in species found at low elevations.

Anatomical features and the lack of pronounced seasons allow wood growth in tropical lowlands to occur throughout or erratically during the year, making the identification of synchronous growth patterns among trees a difficult task. Even outside the tropics it is not always possible to reliably cross-date tree-ring patterns among individuals of the same species and site.

A notable example is the world's tallest tree, the California coast redwood Sequoia sempervirenswhose rings are not uniform around the stem. This causes different radii from the same tree to include a widely different number of rings, which prevents the development of a reliable tree-ring chronology. Such ring discontinuities are species specific and apparently unrelated to climate.

  • Understanding the Old Wood Effect
  • Dendrochronology
  • Dating in Archaeology

Franco Biondi Baillie, M. Tree-ring Dating and Archaeology. University of Chicago Press, Tree Rings and Climate.

Evolutionary history of plants

Time, Trees, and Prehistory: University of Utah Press, Basics and Applications of Dendrochronology. An Introduction to Tree-ring Dating. University of Arizona Press,