Dendrochronology#Growth rings

As annual ring or tree-ring, formerly wooden ring, the cross-section visible annular grain of the wood a perennial plant, especially a tree is called. Annual rings occur only where it is due to the climatic conditions in a temporary tranquility of the mitotic activity of the cambium. The reasons for this winter may be in season climate or dry seasons in subtropical and tropical regions that can follow even in semi -annual basis ( semi-annual rings). As a false growth rings are referred to considerable fluctuations in the course of wood formation (density fluctuations ) that are not connected to a Kambialruhe.

Periodic development phases

An annual ring reflects the different stages of development reflected in a growing season.

After the rest period in winter (or dry season) are in the mobilization phase nutrients consumed that were created before the rest phase. It follows the growth phase, in the so-called early wood is produced. It forms a much brighter growth zone of relatively loose tissue, which allows the tree to the rapid transport of water and minerals from the root to the crown in order to ensure the foliation and flowering. The cells in the early wood are thin-walled and large lumen. This makes them not very mechanically fixed. In the subsequent deposition phase arise thick-walled small-bore wood cells that form much denser tissue and primarily perform tasks firming. The often darker color of this latewood is caused by the higher proportion of lignin in the cell walls.

Ratio of early wood and late wood

The better the climatic conditions within a growing season, the greater the growth of wood and thus the width of the annual ring.

There are differences in the ratio of early and late wood proportion between deciduous and coniferous trees.

• In conifers subject to the latewood proportion considerably less variability than the earlywood proportion. The latter is higher than under poor growth conditions are favorable. This has as a consequence that fast -grown softwood is softer than slowly grown.
• Deciduous trees always make a little fluctuating amount of earlywood, latewood proportion of this varies.

The enlargement in picture on the right shows three annual rings of a spruce. In the middle obliquely from above downward extending annular seen in the left half of the loose early wood, the right of the denser late wood.

Fluctuations in growth

As climate changes affect not only a single tree, but also on its neighbors, make all trees of a region, a characteristic ring pattern. This allows on the one hand, the climate reconstruction over the centuries and on the other hand, the age of archaeological finds with the help of the grain of wood residues determine ( dendrochronology ).

Age estimation

The age of a tree can be determined with the help of a drill core sampling or by means of a drill resistance Resistograph. Both methods allow the counting of tree rings. In conifers, it is also possible to count the annual shoots of the number of Astquirle of the tribe.

An estimation of age using the tree diameter is speculative, since the increase of genetic factors, the weather, site conditions, and the social position of the individual depends in stock. Some species of oak, willow, poplar and plane may have growth rates of more than 10 mm / year, yew and dwarf trees well below 4 mm / year.