Trunk diameter
The trunk diameter or trunk circumference is a tree-based measure of the age of a tree and the amount of wood it contains . More specifically, one speaks of breast height diameter ( BHD ) or chest height circumference ( BHU ).
About the measurements used
The chest height diameter / chest height circumference is determined in Central Europe at a height of 130 centimeters above the ground. In other regions other heights are used (USA: 4.5 feet , which corresponds to about 137 cm, also in Japan to 137 cm; in other countries with non-metric measurements often also 5 feet, about 150 cm). The measuring height is derived from the fact that the fathoms of the circumference were originally measured here in arm spans .
Deviating from this, the diameter or circumference at a height of 1 meter is also used in nature conservation, and also in tree nurseries, since the roots of young trees hardly play a role.
In wood processing, you can then determine the diameter directly on the cut tree ( round wood ). Since many tree species but abholzig are therefore decrease over the entire length to diameter is measured here on Zopfende of lumber, so the former top end of the log. In the case of timber with strong trunk thickness fluctuations, the smallest diameter of the round timber must be determined before sawing sawn timber in order not to produce rejects. This is less of a role for industrial wood, here one often uses the mean value of the plait and root end or empirical values of the deforestation of a tree species. Between the site of the cut and the sawmill or other wood processing , depending on the further use, the measurement with bark is switched to without ( round timber diameter with bark or without bark ), in the case of timber with worthless sapwood sometimes even without it.
Measurement
The circumference and diameter can easily be converted into one another using the factor π .
A simple tape measure is used as a measuring instrument for the circumference , and usually a clip for the diameter . Diameter measuring tapes can also be used, which determine the diameter indirectly via the ratio to the circumference. The measurement with the clip ( clip ) is carried out twice crosswise (offset by 90 °) and a mean value is determined from the two measurements. In the case of a strongly oval tree cross-section, the clumps of the narrowest and widest point are averaged. If there are branches, bumps or growths at chest level, measurements are taken above and below them and the mean value is calculated. If there is any doubt, experience has shown that measurements are made several times and a mean value is calculated for particularly large trees.
In the case of trees on the slope , the chest height of 1.3 meters is determined in the forestry on the upper side of the slope ( A in the graphic), since the uneven and strongly deformed trunk foot is not used in the wood industry (i.e. in the sawmill). In the case of particularly thick trees, however, the measurement on the top of the slope gives a higher measurement point. The actual growth in thickness of the tree, especially with a tapering trunk (woody), is shown reduced. In order to achieve comparable values, it is therefore necessary to measure thick trees that are not intended for timber use in the middle of the trunk axis ( B in the graphic). The approach on the ground should correspond as much as possible to the assumed germination point, so any humus layers or embankments should be taken into account. This is the method used to carry out the measurements for the “German Tree Archive”, but at a height of 1 meter instead of 1.3 meters.
use
The diameter of the chest height is determined in forest inventory for the determination of the wood mass in particular. The more suitable diameter in the middle of the trunk of a tree could only be determined with great effort, so that one is usually content with an easy measurement at chest height. At this height, the influence of the roots on the diameter of most trees no longer exists and the diameter values show close statistical relationships to other characteristic values of a stand (e.g. base area, height or volume). There are suitable volume tables to determine the stock volume.
For changing the measurement from diameter with bark (forest wood) to diameter without bark (timber) there are also table values depending on the type of wood and also for regional site characteristics. Likewise, from the diameter without bark to cubic meters of usable effective mass or weight using tables, depending on the length of the piece.
The age of a tree is also estimated with the trunk diameter or circumference. This method is based on empirical values and is only halfway reliable with older trees, since the growth in thickness of a tree depends on numerous factors. The age of the living tree can only be determined precisely with an elaborate core drilling and a possible counting of the annual rings , which one tries to avoid because of the inevitable damage to the plant. Even if the core is already rotten and the tree is hollow, this option has its limits. Therefore, estimating trees that are not used for forestry, especially trees that are worth protecting, is widespread. Since hardly any data are available for particularly old trees, the estimate remains extremely unreliable and is only possible in the range of a century, often not even that (problem of "1000-year-old" trees ).
literature
- Horst Kramer , Alparslan Akça: Guide to forest measurement . 3rd expanded edition, Sauerländer, Frankfurt am Main, 1995, ISBN 3-7939-0830-5
Web links
Individual evidence
- ↑ Bernd Ullrich, Stefan Kühn, Uwe Kühn: Our 500 oldest trees: Exclusively from the German Tree Archives . BLV Buchverlag GmbH & Co. KG, Munich 2009, ISBN 978-3-8354-0376-5 , p. 12 .
- ↑ see for example conversion factors forest wood and residual wood . Swiss Community of Interested Parties for Industrial Wood - suggested guide values (pdf, holz-bois.ch, accessed November 11, 2014).