A Macroscopic and Microscopic Study of Compartmentalization and Wound Closure after Mechanical Wounding of Black Walnut Trees
Keywords:Juglans nigra, wound response, discoloration, compartmentalization, anatomy, pathology
Compartmentalization is a concept developed to explain tree response to injury. To study this concept, uniform mechanical wounds were made in fifty black walnut trees. Each tree was wounded at two different heights, 0.5 and 1.4 m, and at two different times, fall (November 1975) and spring (March 1976). The amount of wound closure was noted after one complete growing season, as were several macro- and microscopic characteristics of compartmentalization. Wound closure and compartmentalization were separate responses. Most of the wounds were closed after a single season's growth.
The eight trees with one or more open wounds were among the smallest and slowest growing trees in the study. This suggests a positive relationship between growth rate and wound closure, but statistically the relationship was not significant. Wood discoloration was the most prominent wound-related defect. Greater volumes of discolored wood were associated with fall wounds than with spring wounds. Similarly, fall and spring upper wounds were associated with larger volumes of discolored wood than their lower counterparts. Prior fertilizer treatments had no effect on wound closure or compartmentalization. The compartmentalization of wound-affected wood in black walnut agrees with the generalized model of compartmentalization of decay in trees (CODIT). The outer tangential and lateral compartment walls are the strongest, and the inner tangential and top and bottom compartment walls are the weakest and most easily overcome by invading microorganisms. The initial wood discoloration process did not appear to be associated with microorganism activity. Effective compartmentalization was positively correlated with growth rate. Some results of this study suggest that the relative ability to compartmentalize is under genetic control.
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