| The effects of site conditions, stand density and mixed conditions on variation of growth, wood property and wood chemical component of Betula platyphylla naturally growing was studied in this paper. The proper method of cultivation birch as pulp timber was systematically analyzed and the results are as follows:1. In different sites (slope positions, flat land, meadow), birches on downhill had the best growth, their average height(16.63 m), DBH(15.17 cm) and ring width(2.80 mm) higher than those of uphill[3.31%,5.81%,12.60%(p<0.05)] and meadow[25.69%(p<0.05),28.53% (p<0.05),16.77%(p<0.05)].2. Impact of sites on wood basic density, fiber length and ratio of fiber length to width of birch show significant differences(p<0.05). Wood basic density on uphill higher than that of flat land(0.466 g/cm3) and meadow(0.453 g/cm3) with rate 10.09% and 13.25%. Fiber length of birch on downhill had the maximum fiber length(1.168 mm) and ratio of fiber length to width(55.15). The wood chemical compositions of birch on middle slope suitable for papermaking. The contents of holocellulose(83.36%) and pulp yield(51.18%) of birch on middle slope had maximum values.3. There are three different stand densities including 1650 strain/hm2,825 strain/hm2 and 500 strain/hm2. The average DBH and ring width of birch had the significant values (p<0.05) and the height had no significant differences among the three stand densities(p>0.05). The average DBH(12.53 cm) and ring width(2.96 mm) of stands with low density(500 strain/hm2) had maximum values.4. The stands with high density(1650 strain/hm2) is favorable to papermaking. The average wood basic density(0.523 g/cm3), fiber length(1.183 mm),fiber width(21.7μm), content of holocellulose(83.05%), pulp yield(52.77%) of birch had maximum values and the content of benzene-ethanol extractive(2.15%) had the minimum value. The wood chemical compositions of birch is favorable to papermaking.5. Birches in the birch and mixed larch forests had a poor growth in water-wet site and had a better growth in the other sites. In the same site. The average height(13.87 m), DBH(12.33 cm) and ring width(2.65 mm) respectively higher than those of pure birth(13.23 m,11.7 cm,2.49 mm). The differences was no significant(p>0.05).6. Effect of water-wet site and other site on wood properties of birches were no significant differences(p>0.05). In the same sit, mean and subordinate function value of chemical composition of birch in larch-birch forest was lower than those in birch pure forest. So the wood property of birch in larch-birch forest had no significantly improvement. The studies show that the birch with the stand density of 1650 strain/hm2 in a middle-aged plantation on middle slope is favorable to papermaking. The birches with a better growth and higher wood basic density which of the fiber traits and the wood chemical compositions was favorable to papermaking.
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