6 Wood Discoloration

8.2 Tree Wounds and Tree Care 177
the transition of the discolored to the functional phloem (Trockenbrodt and
Liese 1991).
The cambium reacts to the damage at the wound margin with intensified
cell formation (callus) to overwall the opened wood body (Stobbe et al. 2002a).
The wound wood, which is later formed outside the callus, effectively limits
discoloration and decay outward.
8.2.2
Pruning
Forest tress are pruned to produce high-class timber, trees in urban areas are
pruned for safety reasons and along motorways and power-lines for clearance.
Each cut causes a wound, which leads in the exposed wood to discoloration
and decay (Fig. 8.9).
Until the 80s in Germany, the flush cut had been regarded as the correct
method when removing a branch back at the stem. Studies on the pruning
of hardwoods carried out by Shigo and staff (Shigo 1989) caused confusion.
Comparing the effects of different cut locations of a total of 750 pruning
wounds on 115 street and park trees led to the Hamburg Tree Pruning System
(Dujesiefken and Stobbe 2002), which is integrated since 1992 into the
German rules and regulations for tree care methods. The recommendations
Fig.8.9. Discoloration reaching far into
thestemofhorsechestnut9years
after flush cut pruning (a); reduced
discoloration after a branch collar cut
(b) (from Dujesiefken and Stobbe 2002)
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