Arboriculture & Urban Forestry 38(6): November 2012 Arboriculture & Urban Forestry 2012. 38(6): 277–286 277 An Evaluation of Internal Defects and Their Effect on Trunk Surface Temperature in Casuarina equisetifolia L. (Casuarinaceae) Daniel C. Burcham, Eng-Choon Leong, Yok-King Fong, and Puay-Yok Tan Abstract. Tree risk assessment is important when communities choose to cultivate trees near people and property, and many tools may be used to enhance these assessments. The effectiveness of determining internal tree stem condition by measuring trunk surface temperatures with infrared cameras was assessed in this study. The trunk surface temperature of 48 Casuarina equisetifolia was evaluated; the trees were felled and dissected to quantify internal stem defects; and a mixed-methods approach was employed to determine the presence of defects. In total, 27% of trees were decayed, 62% discolored, 6% cavitated by termite infestations, and 2% undamaged. Qualitative visual evaluation of the infrared images revealed the close association of external stem features, opposed to internal defects, with surface temperature distributions. External features, such as cankers, detached bark, and mechanical damage, were associated with temperature anomalies. The trees’ internal condition accounted for a small percentage of the variability in evaluated temperature measurements (r2 = 0.001- 0.096). Overall, no clear relationship was found between the extent of internal defects and surface temperature distributions. These results are practically im- portant for the arboricultural professional community because they show the technique does not provide accurate results about the internal condition of trees. Key Words. Casuarina equisetifolia; Diagnostic Device; Infrared Camera; Internal Defect; Singapore; Temperature; Thermal. In managing urban forests, arborists strive to maximize the en- vironmental, social, and economic benefits of trees while mini- mizing costs to society. These costs may include direct financial resources used to plant and maintain trees as well as indirect socioeconomic costs resulting from undesirable conflicts with trees, such as root growth into sewer pipes, drains, and pavement. The costs of structural tree failures, in particular, represent an important challenge toward mitigating damage to property and injury to people. In general, trees naturally adapt to external forces experienced cumulatively on-site with various anatomi- cal features, including reaction (i.e., tension and compression) wood (Fisher and Stevenson 1981), buttress roots (Setten 1953), mass damping of flexible branches (James et al. 2006), and wood material property optimization (Wiemann and Williamson 1989; Dahle and Grabosky 2010). However, trees fail when loaded by an external force exceeding the structural capacity of their mate- rial components; these critical forces are commonly generated by intense weather events, including wind, rain, ice, and snow. Structural defects can render trees less resilient against ex- ternal forces, and those trees containing defects in an urban setting may become hazardous (Harris et al. 2003). Structural defects in the stem and branches commonly include cracks, lightning scars, included bark, cankers, cavities, and decayed wood; these defects can substantially reduce the load-bearing capacity of the natural structure. Consequently, arborists regu- larly conduct tree risk assessments to evaluate the condition of individual trees, search for the existence of structural de- fects, and, if necessary, perform corrective work to preserve their long-term condition (Smiley et al. 2000). The ultimate objective of a tree risk assessment is to recognize and remedy hazardous specimens before failure and damage occurs; this process requires that arborists successfully recognize and iden- tify many different structural defects (Matheny and Clark 1994). Frequently, arborists use visual tree inspection frameworks to guide the tree risk assessment process (Matheny and Clark 1994; Mattheck and Breloer 1994; Ellison 2005). These frameworks ensure a consistent, systematic approach toward visually observ- ing a tree’s general and local condition for possible defects. De- spite these professional best practices, wood decay, in contrast with many other defects, can remain obscure during an inspec- tion in the absence of external symptoms. Symptoms indicative of wood decay, such as fruiting bodies, cracks, fiber buckling, and crown dieback, may not be visible until the advanced stages of infection (Schwarze et al. 2004). A complete review of the epi- demiology, diagnosis, and assessment of wood decay in trees can be found elsewhere (Rayner and Boddy 1988; Schwarze 2008). In some cases, visual symptoms can point to the probable existence of wood decay, but they may not permit accurate es- timates of an infection’s extent or severity. The supplemental use of advanced tree diagnostic devices has received consider- able research attention in order to enhance wood decay assess- ment. The devices enhance visual tree inspections by employing optical, acoustic, electrical, mechanical, or biochemical mea- surement techniques to distinguish material property changes ©2012 International Society of Arboriculture
November 2012
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