Tree Wound Reactions of Differently Treated Boreholes

Holes from increment borings create wounds that lead to discoloration and may result in a colonization of the wood by fungi. There are various opinions about the damage caused by such borings and about the efficacy of wound dressings. For this reason, 78 differently treated boreholes in large-leaved lime (Jilia platyphyllos Scop.) and small-leaved lime (Tilia cordata Mill.), as well as in horsechestnut (Aesculus hippocastanum L.) and silver birch (Betula pendula Roth), were examined macroscopically and microscopically with regard to the wound reactions nearly 10 years after boring. Obvious differences in wound reactions were observed among the tree species. Both species of lime compartmentalized the wounds very effectively. Horsechestnut, on the other hand, revealed more extensive discoloration. Silver birch had the weakest compartmentalization, with discoloration up to 2 m (6.6 ft) in length. Cambial dieback around all borings, except for those plugged with creosote-impregnated wood dowels, was approximately the same for all species. Fungi occurred only within the discoloration. Cell wall disintegration was rarely observed. Treatment with LacBalsam® or polyurethane had little or no influence on the wound reactions. Boreholes sealed with impregnated wood dowels had far-reaching discoloration and cambial dieback as a result of the toxic effect of creosote.