Z-tree

from Wikipedia, the free encyclopedia

Z-tree (short version for future tree ) is a forestry term from silviculture . Trees of the future are the core element of single tree-related maintenance measures in forestry . The concept is based on the idea that thick trees can usually be sold more expensive than thinner trees of the same quality.

The main difference to other thinning concepts is the division of all trees in a stand into "Z-trees", "oppressors of the Z-trees" and "indifferent trees". Depending on the tree species, the Z-trees are selected at a very early age (10–40 years). From this point on, all silvicultural measures serve exclusively to maintain and promote these Z-trees and their unhindered crown and trunk growth. Which trees are selected as Z-trees is at the discretion of the farmer and reflects his silvicultural goals. Individual preferences for certain mixed tree species worth preserving (seed-Z-tree), particularly bizarre, attractive trees on hiking trails (forest aesthetics-Z-tree) or trees with woodpecker holes (eco-Z-tree) can easily be integrated into Z-tree concepts.

Sessile oak selected as the Z-tree (right), marked with a small red dot

The rational forest care by means of thinning was originally based on about 50 to 350 value carriers per hectare , depending on the business objective and tree species , which are to be promoted, through selection according to vitality (strength, health), quality (different characteristics on the trunk) and distance (depending on future crown extension).

Z-trees are selected as soon as the desired branch-free stem height (5–10 meters) of a tree is actually free of branches (in the case of dead branch losers), or before the first valuation (in the case of dead branch holders). Sometimes “reserve trees” are eliminated for the Z-tree collective. The selected Z-trees are often given permanent identification in the form of colored markings or ribbons.

Thinning cycle: As soon as the crown branches of the Z-tree and the neighboring tree touch (every 2–7 years), the next thinning (clearance) must take place. This means that all trees that touch the Z-tree in the canopy and begin to harass it are declared to be the “oppressor” and are removed during the thinning. An "adversary" must also be removed if it is in no way inferior to the Z-tree in terms of quality and dimensions. Trees that are indifferent, i.e. neither a “Z-tree” nor a “oppressor”, may not be removed. (Exceptions: fighting bark beetles, clearing back alleys, traffic safety, etc.). It starts with the most harassing “adversary”. The number of oppressors to be removed from each Z-tree and thinning passage (1 to 8 pieces) depends on the stability of the stand and the Z-tree type, since water veins (sticky branches) can form if the trunk previously shaded by neighboring trees is removed from the Sun is irradiated. These secondary branches can partially compensate for the increase in value achieved through greater growth in thickness.

However, it should be noted that, for example, a very thick oak trunk with secondary branches is much more valuable than a knot-free, thin trunk of the same age. When oak and larch are first thinned , these leading branches should be removed at least two years before the first correct intervention in order to ensure the crown extension and the shading of the trunk after the intervention. Too long an impermeable position of the oak exacerbates the problem because it reacts immediately to a lack of light and, in an emergency, even leaves sticky branches in the shade.

The distance between Z-trees is a very structural and stability-defining decision-making criterion and must already correspond to the largest possible crown diameter of the Z-tree at harvest age. This results in tree species-specific minimum Z-tree spacings and maximum Z-tree numbers per hectare. Fears that too many Z-trees could be damaged or die in the course of the stand's life have now proven to be unfounded, but in the past led to the selection of a very high number of Z-trees and reserve Z-trees (200–400 Pieces per hectare, Z-tree spacing 5–7 meters). If the Z-trees were to be freed in an effective manner, this led to very strong thinning interventions with a subsequent high risk of storm damage, or alternatively to the removal of too few attackers per Z-tree, so that this could not be promoted significantly.

More modern Z-tree concepts, which have been further developed from this experience, therefore provide for significantly lower Z-tree numbers of 40–100 (max. 150) pieces per hectare and minimum Z-tree spacings of around 10 meters. This change is difficult for many farmers and requires a considerable amount of self-discipline.

The near-natural permanent forest- like and tiered forest structures favored by many forest administrations and forest owners for several years cannot be realized with high numbers of Z-trees.

literature

Web links

Individual evidence

  1. ↑ Burschel, Peter and Huss, Jürgen: Grundriß des Waldbau. A guide for study and practice. 2nd, revised and expanded edition. Parey, Berlin. 1999. p. 369. ISBN 3-8263-3045-5
  2. ↑ Burschel, Peter and Huss, Jürgen: Grundriß des Waldbau. A guide for study and practice. 2nd, revised and expanded edition. Parey, Berlin. 1999. p. 395. ISBN 3-8263-3045-5