An Evaluation of Internal Defects and Their Effect on Trunk Surface Temperature in Casuarina equisetifolia L. (Casuarinaceae)

Each cross section was photographed in a 1 m × 1 m frame for visual reference. Among the sampled trees, sections were excised containing: (a) termite-induced cavitations with irregular, smooth-walled voids; (b) decay with irregular color changes, host reaction zones, and dark fungal interaction lines; (c) discoloration with irregular wood color changes and dark fungal interaction lines; and (d) no measurable defects with substantially healthy tissue.

The relative amount of cross-sectional area occupied by a defect (relative defect CSA), represented as a percentage, was determined by dividing the surface area of the defect by that of the entire stem. In order to determine cross-sectional area, the perimeter of the stem and defect(s) were manually transferred onto a clear PVC transparency sheet, digitized, and analyzed using image processing software.

As shown in this diagram, temperature data was extracted from each tree using two separate methods. First, temperatures within vertically adjacent rectangular transects (a) were extracted for analysis. Second, temperature values were extracted along five lines equidistantly spaced across the stem breadth (b) and averaged into one linear trend line. Temperature values were then compared with the quality of internal stem tissue immediately beneath the area from which they were extracted.

For each specimen, the relationship between vertical temperature changes and internal stem condition was summarized in a dual y-axis coordinate plane containing the trunk surface temperature (°C), extracted from five parallel vertical lines, and relative defect CSA (%) as a function of stem height (cm). As seen in the example from specimen J, the difference between the surface temperature (point “A”) and its trend line (point “B”) was assessed at the position containing the largest internal defect.

Qualitative IR image evaluation showed a consistent relationship between external stem features and temperature anomalies, particularly those caused by (a) detached bark, (b) termite nests, (c) branch wounds (arrows) and marking tape used to identify sampled specimens (black box), and (d) irregular stem geometry. Atmospheric conditions contributed to surface temperature anomalies, particularly for trees (e) growing in relatively exposed locations receiving direct, unfiltered solar radiation (black box). In contrast, specimens (f) growing in dense forested areas with low sunlight infiltration presented relatively homogenous surface temperature distributions.

The two histograms, representing surface temperature distributions extracted from the trunk surface of trees “I” and “N,” do not exhibit strong visual similarity, in spite of comparable internal cavity sizes.