LEBEN, CURT. 1985. Sap pressure may affect decay in wounded trees. Am. Nurserymen 161(7): 59-63.
When a tree trunk is wounded, two things happen. First, if the wound is not too large and the tree is growing vigorously, the wood will heal over with callus tissue. Second, the wood within the trunk directly above and below the wound will become discolored in a more-or-less cone shape. The extent of this discoloration is very important because decay proceeds only in discolored wood. This article describes results of my recent work, which has led to a new explanation of some of the conditions that limit discolored columns in functioning (sap-containing) wood vessels. If the explanation, which is stated below, continues to hold true after more experimentation, we should be better able to shape our tree-care practices to reduce losses from decay. I have proposed a new explanation why discolored wood columns are likely to be shorter when wound healing is good than when healing is poor. This explanation, called the hydrostatic explanation, is based on the sap pressure within the tree at the time of wounding and probably for an undetermined amount of time afterward. If sap pressure is negative when wounds are made, many types of microorganisms in the air and from the bark may be drawn or grow into cavitating vessels. Decay organisms may or may not be present. On the other hand, if wounds are made in spring when sap pressure is positive, cut vessels continue to function close to the wound, thus limiting the amount of wood in which decay organisms can grow.
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