growth and wood characteristics of acacia mangium grown in kerala

4.4.6. Mechanical propertiesTable 20 shows the variation of MOR, MOE and MCS with tree height. As canbe seen from the table, within tree variation of MOR ranges from 77-130N/mm 2 . whereas MOE ranges from 7- 13 kN/mm 2 . MCS has a range of 26-64N/mm 2 . All these values are for the material tested at 8% MC. The meanvalue of wood density at test condition was around 600 kg/m 3 .Table 21 shows the variation of mechanical properties between trees whensamples tested at a mean moisture content of 8% and density around 540kg/m 3 . The mean value of MOR, 99 N/mm 2 obtained at 8% MC, whencorrected for air-dry moisture content (12%), by applying the formula suggestedby Sekhar and Rajput (1968). MOR will be around 66 N/mm 2 .Similarly the mean MOE value after applying the correction will be 6.1kN/mm 2 and MCS 30.4 N/mm 2 . Wang et al(1989) reported MOR value of74.5 N/mm 2 and 9.9 kN/mm 2 MOE for mangium trees of lower age (lowerthan 12 years). For 12-year-old trees, Razali and Hamami (1993) reported amean MCS 43.4 N/mm2. All the values of mechanical properties obtained inthe present study are in a lower range as compared to teak as well as rubberwood; may be due to a lower age of 8 years.The average values of the mechanical properties reported for teak wood inair-dried condition is 96 N/mm 2 for MOR. 12 kN/mm2 for MOE and 53N/mm 2 for MCS (Nazma et al., 1981).The strength values of rubber wood at 12% MC, as reported by Gnanaharanand Dhamodaran (1993) are in a much higher range; the average values are98.4 N/mm 2 . 15.7 kN/mm 2 and 52.7 N/mm 2 for MOR, MOE and MCSrespectively. The comparison shows that mechanical properties of lower agedAcacia mangium are inferior to that of rubber wood of age around 35 years.However, Mohd. Zin et al(l99 1) indicated that the strength properties of A.mangium are not seriously affected by tree age.4.4.7. Sawn timber recoveryIt can seen from Table 22 that the sawn timber recovery varies from 16 to80.5%. The pooled mean sawn timber recovery is around 45%. Chan (1983)reported a low recovery rate of 37-40°/o for the sawn timber of A. mangiumThe low recovery rate obtained in the present study may be due to thepresence of comparatively large soft core portion and heart rot. According toPeh and Khoo (1984). no problems were associated with the sawing of thewood.42