Arboriculture & Urban Forestry 42(3): May 2016 1 summarizes the nondestructive evaluation meth- ods used for tree assessment in this experiment. The experiment was also carried out in situ on 24 different decay-damaged Japanese cedar trees (Group G, planted along both sides of the trail) in the Tower Area of the Xitou Nature Education Area. These trees were investigated in 2014, when the trees were about 60-years- old with diameters at breast height of 28.3–83.1 cm. Tree trunk deterioration was detected by stress wave tomography (using the same method previously described). After the stress wave velocity tomography information (2D image) of each cross section provided by the tomo- gram was tabulated, the sampling core method was conducted using an increment corer to understand the wood deterioration (with or without decay damage) by the visual method. RESULTS Seven categories of tree defects and appearance were inspected by the visual tree inspection form (see APPENDIX). The seven main defects were decayed wood, cracks, root problems, weak branch unions, cankers, poor tree architecture (trunk and branch), and dead trees, First, the Japanese cedar trees were tops, or branches. inspected visually, focusing on different decay-damaged trees. The evaluated parameters of different nonde- structive techniques, including the average lateral 205 impact vibration performance, drilling resistance value, green crushing strength, and air-dried wood density were 284.6 m Hz, 18.5%, 186.2 kgf/ cm2 , and 500.4 kg/m3 , respectively (Table 2). The transversal stress wave velocity, lateral impact vibration performance, drilling resistance value, green crushing strength, and air-dried wood den- sity of a normal undamaged tree stem serve as the index of diagnosis or standard reference value. The average minimum and maximum V values were 1,159–1,488 m/sec and 1,721–2,080 m/sec, respectively, for the 89 undamaged Japanese cedar trees planted in four different areas (Table 3). The mean V value of the tomogram was 1,440–1,772 m/sec. In the undamaged trees group, the aver- age V valves (minimum, maximum, and mean) of the larger diameter class were higher than those of the smaller diameter class (Table 3). This result shows that different diameter classes affected the transversal acoustic velocity of the tomogram. The average minimum and maximum V values were 1,159 m/sec and 2,062 m/sec, for the 24 decay-damaged Japanese cedar trees, respec- tively (Table 4). The mean V of the tomogram was 1,610 m/sec. The average minimum V value of the trunks in the decay-damaged trees (Table 4) was clearly lower than that of the undamaged trees (Table 3). The minimum V values (1,354 m/ sec) can be considered as the threshold values of diagnosis by stress wave velocity tomogram. Table 1. Assessment of standard values (reference) in sound trees by different nondestructive techniques for tree hazard assessment. Item 1 2 3 4 5 6 7 Methods Visual tree inspection Acoustic device 2D tomogram Lateral impact vibration Drilling resistance method Increment borer Fractometer X-ray wood density profile Evaluated parameter Tree inspection form Transversal acoustic velocity (m/sec) Diameter × frequency (m • Hz) Drilling resistance value (%) Visual observation of core Crushing strength (green, kgf/cm2 Density (air dried, g/cm3 ) Table 2. Average measurements of sound trees by different nondestructive techniques. No. Japanese cedar (in this study) Norfolk island pine (Lin et al. 2015) Hoop pine (Lin et al. 2016) DF (m Hz) 284.6 (28.7) 381.3 (17.8) 327.6 (13.2) R (%) 18.5 (7.0) 32.4 (5.6) 39.7 (8.4) C (kgf/cm2 186.2 (28.4) 248.9 (31.4) 256.8 (31.4) ) ) D (kg/m3 500.4 (93.0) 533.4 (29.2) 578.0 (46.2) Notes: DF = lateral impact vibration performance; R = drilling resistance value; C = crushing strength; D = air-dried density; parentheses ( ) indicate standard deviation. ) ©2016 International Society of Arboriculture
May 2016
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