Abstract:

The physical and mechanical properties of wood were analyzed for 4 Larix species (Larix kaempferi, L. gmelinii, L. olgensis, and L. principis-rupprechtii) and 3 hybrids (L. kaempferi×L. gmelinii, L. kaempferi×L. principis-rupprechtii, and L. kaempferi×L. olgensis), and the differences were evaluated comprehensively using the membership function based on Fuzzy mathematics. The results showed that the timber of Larix spp. had significant heartwood ratio and great air-dried density as 0.634 g·cm^-3 in average. The dry shrinkage of the wood was relatively high with average radial and tangential shrinkage as 4.52% and 8.93%, respectively. However, the wettability of the wood was poor, showing the average contact angle in radial and tangential directions as 57.70° and 59.14°, respectively, which indicated the favorable natural decay resistance to water. The timber also showed fine mechanical properties with average modulus of elasticity (MOE), modulus of rapture (MOR), tensile strength parallel to grain, crushing strength, and cleavage strength as 15.36 GPa, 120.07 MPa, 134.25 MPa, 46.30 kJ·m^-2, and 9.93 N·mm^-1, respectively. Significant differences were found among species or hybrids in the properties of tree height, heartwood width, average ring width, wood radial contact angle, dry shrinkage, radial air-dried shrinkage, tangential-to-radial dry shrinkage ratio, MOE, and MOR. Generally, the 3 hybrids showed great improvement in growth and timber properties when compared with the male parents. As a result, the comprehensive evaluation based on the properties above indicated that the female parent of L. kaempferi and the 3 hybrids were more suitable to be selected as structural or non-structural timber tree species than the 3 native male parents.

Key words: Larix spp., species, hybrid, physical and mechanical properties, comprehensive evaluation