Woundwood

Overgrowth by wound wood

Woundwood occurs when there are major external injuries to the tree . It overwhelms injuries, stumps or tissue areas damaged by overuse.

After an injury, callus cells initially develop from the surviving cambium of the wound edges . The wound wood differentiates from this tissue through cell division. There is no connection with the underlying, now dead wood of the wound surface. The wound wood initially differs greatly from normal wood. Libriform fibers , which serve to strengthen the wood, recede in favor of parenchymatic cells. In the vicinity of the wound edges there is still a short-cell zone, but the longer the distance from the wound the wood becomes more and more long-celled, until finally secondary wood arises from the primary wound wood, in which the newly formed cells assume the normal form. The wound wood cannot cause gravitropic trunk curvatures, as presumably when differentiating from the callus to the primary wound wood, the position in the gravity field must first be redefined.

Woundwood formation when pruning

The formation of the wound wood depends on the location, type and shape of the injury. The callus collar, which encloses a dead branch stump, must not be confused with the trunk collar. It only arises after the branch dies. If the wound wood in the area of ​​the knot closes the wound evenly round from the wound edges, no further cambium of the trunk collar was injured. The more oval the branch wound closes after a branch, the more cambium of the trunk collar was injured.

If a branch receives too little light in the long term and therefore the flow of sap is too low, the tree actively repels this branch by slowly forming a farewell collar with a predetermined breaking point at which the branch ultimately breaks off due to mechanical action. The farewell collar immediately changes to the formation of wound wood, which enables the knot to close quickly.

Woundwood formation in other injuries

In the case of mechanical injuries on the trunk or branch surface, the formation of the wound wood behaves differently than with correct pruning. The callus cells form at the edges of the still living cambium. The cambium is mainly supplied with energy by the sieve elements of the bark. If the sieve cells die, the cambium below usually also dies. The surviving bast supplies the cambium with enough energy that the cambium forms evenly undifferentiated callus tissue from the wound edges. More rapid differentiation or stronger wound wood growth can usually be observed from the wound edges that run vertically to the direction of growth. In this way the tree tries to compensate for the loss of its dead pathways. In this way, wounds on the tree surface are more pointed elliptical.

Individual evidence

1. ↑ This is how Shigo called this form of woundwood in 'The New Tree Biology'