Effect of stand age and stand density on building material property of Pinus tabulaeformis
[Objective]To explore the influence and correlation between the age,density and interactive effect of building timber of Pinus tabulaeformis on wood property,and provide theoretical reference and technical guidance for the precise cultivation of building timber of P.tabulaeformis.[Method]A cross-comparison experiment was carried out on 3 kinds of densities of P.tabulaeformis plantation in Liangzi,a state-owned loess plantation in Pingquan city,Hebei province.The effects of different densities of 3 kinds of forest ages(21-30 a),near-mature forest(31-40 a)and mature forest(41-60 a)were analyzed.[Result]1)There was no significant difference in wood properties of low density trees of different ages.At medium density,the total dry density and basic density of near-mature forest were 0.497 and 0.435 g/cm3,respectively,which were higher than that of middle-aged forest but had no significant difference,and higher than that of mature forest by 15.58%and 8.75%(P＜0.05).The toughness,shearing strength and Compressive strength parallel to grain were 56.268 kJ/m2,9.136 MPa and 45.671 MPa,respectively,which were 37.02%,9.73%and 19.00%higher than that of middle-aged forest(P＜0.05)and 45.94%,13.75%and 10.74%higher than that of mature forest(P＜0.05).Under high density,the index of near-mature forest was significantly better than that of middle-aged forest and mature forest.2)The air-dry density,total dry density and basic density were 0.509,0.503 and 0.412 g/cm3,respectively,which were higher than those of medium density stands(1 350-1 800 plants/hm2).It was 11.14%,17.25%,9.57%higher than high density stand(1 800-2 400 plants/hm2)(P＜0.05).The flexural modulus,toughness and shearing strength were 7 398.879 MPa,49.220 kJ/m2 and 10.866 MPa,respectively,which were 10.45%,19.85%and 30.51%higher than those of medium density stands(P＜0.05).It was 27.81%,93.68%and 21.87%higher than high density stand(P＜0.05).The index of near,mature low density stand and medium density stand is significantly better than that of high density stand.3)The interaction effect of forest age and density had significant effects on the shrinkage,toughness,shearing strength,hardness and compressive strength parallel to grain(P＜0.01),and tangential compression perpendicular to grain had significant effects(P＜0.05).4)Under medium and high density,the comprehensive strength of middle aged forest wood was lower than 110MPa,which belonged to low strength wood.The comprehensive strength of other medium,near and mature forest wood under various densities was between 111-170 MPa,which belonged to medium strength wood.The strength quality coefficient of medium,near and mature forest at all densities was greater than 215.6 MPa,which belonged to high grade.Compared with the main building wood species,P.tabulaeformis belongs to the middle strength(Class II).5)The correlation analysis showed that the air-dry density had the greatest influence on flexural elastic modulus(r=0.80)and toughness(r=0.83),which was a significant positive correlation.[Conclusion]The physical and mechanical properties of P.tabulaeformis first increase and then decrease with the increase of forest age,and then decrease with the increase of density,and the density of forest age has an interactive effect on shrinkage,toughness,hardness and other indicators.The factors affecting forest age and density should be comprehensively considered in cultivating building timber forest.P.tabulaeformis is a medium strength and high grade timber.Compared with the main building wood species such as P.koraiensis and P.asperata,it belongs to the list of medium strength(Class II),and can be used as building wood for processing and utilization.
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