Dendroarcheology
Dendroarcheologie is a subfield of dendrochronology. This method dating wood, which is based on measuring the widths rings. It is most often used for this method of dating archaeological finds of wood and wooden elements of historical buildings, especially roofs, but also for example to determine the age of wooden art objects.
For dendrochronological dating is a critical input parameter tree ring width. Ring width is usually measured on the cross section. If it is not possible to cut the measurements performed, it is possible to ring width measured on a radial cut. For dating archaeological wood or subfossil tribes sample is usually taken in the form of a cross-notch given item. For dating functional design elements buildings are samples collected in the form of bores through Presslerova přírůstového auger. When dendrochronological dating of wooden art objects and musical instruments is destructive interference in the subject dated almost always undesirable. For this reason, measuring the widths of annual rings is carried out directly on the dating subject or a photo letokruhového profile.
Measurement annual ring widths is performed using a special measuring table, which is associated with the computer. Measuring table is equipped with a sliding screw mechanism and impulsmetrem, which chronicles the interval shift countertops and thus the width of tree rings. The last part of the measuring apparatus is mounted on a tripod stereolupa crosshair. Another possible way to measure the width of tree rings is the use of hand-held magnifying light.
The measured ring width appears on your computer in the form of tree ring curves that are synchronized with each other. The degree of similarity between the curves letokruhovými is assessed using correlation coefficient and called. Coefficient of concurrency. These calculations are used to facilitate optical comparison of the two curves, which is decisive for the final dating. From the well Syncable curves created called. Average curve that highlights common extremes associated with climate change and override all other oscillations caused by other factors. The average curve is then compared with the selected standard chronology for the area of trees and timber.
Dendrochronological dating is mainly limited number of measurable growth rings, species and the existence of the standard chronology. In order to sample dendrochronologically date must contain at least 40 to 50 measurable rings. From the point of view dendrochronological are the most suitable trees for dating hardwoods with ring-porous wood structure (eg. Oak, ash, elm) and softwoods. Wood with wood scattered porous structure (eg. Linden, maple, beech) are very difficult dendrochronologically datable. Unfortunately, this group of woods used to be and is often used for making objects of art, mostly sculptures.
The standard chronology form for each tree species separately by continuous overlapping tree-ring sequences from present to past. At present, the Czech Republic compiled a standard chronology for oak, fir, pine and spruce. For other tree species dating in exceptional cases to use other standard chronologies (eg. For Dating elm can be used oak standard chronology). In the event that the subject was dated on our territory previously imported from another territory, it is necessary to use a standard chronology dating created on the territory of origin.
Accurate determination of AD felled tree can be done only when the last preserved tree rings formed before skácením (ie. Podkorní annual rings). If not preserved podkorní annual rings (wood be machined) can not estimate how much growth rings missing. For trees without a clearly differentiated nucleus and sapwood (fir, spruce) can usually only define a year, after which the tree was felled. When dating such a sample has to be noted that the tree was felled sometime after that has been found dating. In case that it is oak specimen having a boundary sapwood can be missing rings calculate with a certain tolerance. For our area, and following the age of the tree and the site contains oak wood 5-25 annual rings of sapwood.
Year, when there was a tree felling, however, may not match exactly the year in which the tree was used to produce a dated object. It is necessary to add a certain time required e.g. for drying wood. A special case is secondarily used wood, which is not too common, but it is always necessary to count with this possibility.