Arboriculture & Urban Forestry 36(3): March 2010 Arboriculture & Urban Forestry 2010. 36(2): 81–85 81 Evaluation of Compressive Strength of Decayed Wood in Magnolia obovata Kahoru Matsumoto, Futoshi Ishiguri, Kazuya Iizuka, Shinso Yokota, Naoto Habu, and Nobuo Yoshizawa Abstract. To obtain the basic information needed to estimate the degree of decay from compressive strength measured using a Fractometer (CS), relationships between CS and the contents of chemical components were analyzed for Magnolia wood decayed by three types fungi (brown rot, white rot, and soft rot fungi) at various decay levels. Weight loss ratio was significantly, negatively correlated with CS in woods decayed by brown rot and white rot fungi. In addition, a relatively high correlation coefficient was recognized between CS and holocellulose or α-cellulose content, except for wood decayed by soft rot fungus. The results obtained showed that Fractometer can detect the decrease of CS at relatively early stage of decay. Key Words. Compressive Strength; Core Sample; Decay Degree; Fractometer; Wood Decay. In standing trees, many nondestructive and semi-destructive testing methods using various instruments have been applied to identify the degree of decay within the tree trunk (Bethge et al. 1996; Johnstone et al. 2007). The Fractometer, which can mea- sure compressive and bending strength using core samples (5 mm in diameter) obtained from the trunk, is an instrument used for semi-destructive tests in standing trees (Mattheck and Bre- loer 1994; Mattheck et al. 1995; Bethge et al. 1996; Matheny et al. 1999). Mattheck and Breloer (1994) used a Fractometer to measure the fracture moment in the bending strength (load was applied to tangential surface of core samples), of core samples collected from many tree species growing in Europe. They clas- sified the fracture moment in the bending strength obtained for each species into three categories, green, yellow, and red, to determine the degree of decay in standing trees. In addition, Schwarze et al. (1995) observed anatomical and physical chang- es of wood decayed by different fungi and used a Fractometer to measure the bending strength of core samples (load was ap- plied to tangential surface of core samples), one of the physi- cal properties of decayed wood. They concluded that, in order to evaluate the safety of standing trees, more data are needed so that the relationship between anatomical changes and changes in physical properties measured by Fractometer in decayed wood can be determined. However, it is very difficult to collect decayed wood samples from standing trees because the decayed part is frequently present in the central position. Therefore, only a few reports concerning the relationship between the degree of decay and bending strength measured by Fractometer are available. On the other hand, in small wood specimens with any defects such as knots, the relationship between the degree of decay and the reduction of mechanical strength has been researched using wood samples decayed in a laboratory (Mizumoto 1966; Fukuda and Haraguchi 1979; Doi and Nishimoto 1986; Curling et al. 2002). To determine the degree of decay in standing trees more accurately, the relationship between the degree of decay and the compressive strength parallel to grain of wood as measured by Fractometer should be examined for a large number of specimens decayed in a laboratory, and the obtained data should be classi- fied according to the level of decay and mechanical properties. The object of the present study was to obtain basic informa- tion in order to clarify the degree of decay based on compressive strength parallel to grain as measured by Fractometer. Wood core samples were decayed by brown rot, white rot, and soft rot fungi in a laboratory. In the present study, these fungi were defined as follows (Schwarze et al. 2000): brown rot fungi could degrade cel- lulose and hemicellulose, white rot fungi could degrade cellulose, hemicelluloses, and lignin, and soft rot fungi could degrade cellu- lose, hemicelluloses, and slightly lignin. After a certain period of decay, the compressive strength parallel to grain of each decayed core sample was measured by Fractometer. In addition, the con- tents of the chemical components (holocellulose, Klason lignin, and α-cellulose) in the decayed woods were determined. The relationships between the compressive strength and the contents of chemical components at various decay levels were analyzed for examining the urban tree diagnosis by using the Fractometer. MATERIALS AND METHODS Increment cores 5 mm in diameter were collected from sap- wood of 14-year-old Magnolia obovata Thunb. (17 cm) di- ameter at breast height] using a nonsterilized increment borer (Haglöf, Sweden). Sever damages of increment cores were checked by naked eyes and intact increment cores were select- ed for the following experiment. Thus, increment cores used in the present study microchecks leading to increase of varia- tion of compressive strength measured by Fractometer. Figure 1 shows the schematic diagrams of the experiments. The incre- ment cores were cut into about 3 cm lengths for the decay test. ©2010 International Society of Arboriculture
March 2010
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