Studies on the Density Effects of Chinese Fir Stands

There are three parts in this research, including the effects of different planting density, different thinning intensity and planting density thinning on the growth of Chinese fir stand. (1)Planting density experiment consist of five density treatments:A(1 666 trees·hm-2), B(3 333 trees·hm-2),C(5 000 trees·hm-2), D(6 666 trees·hm-2) and E(10 000 tress·hm-2). The result of experiment shows that the dominant height, average height and diameter at breast height (DBH)of stands increases with the increase of stand age, and decreases with the increase of stand density. The dominant height after age 9, average height after age 6 and DBH after age 5 have evident differences among different stand densities. Stand volume increase with the increase of stand age, and it reaches evident difference from age 5 to 7 among different densities, but it only has remarkable differences between A and E or D from age 8 to 18. The tree height under first branch increases with the increase of stand density and trees age, the difference among C,D and E are not obvious after age 12. The crown diameter decreases with the increase of stand density, and increases with the increase of trees age, the differences among different stand densities decreases after age 9 10. (2)The primary planting density for the thinning test of planting density is same as the planting density experiment, thinning methods are that C is reduced to D and D is reduced to E after thinning. The results shows that at same site index class, comparing the unthinned stand with the thinned stand which keeps the same density with the unthinned stand after thinned, their average height and dominant height has no evident difference, but the standing tree volume of thinned stand is lower than that of unthinnned stand, the total volume (standing tree volume + thinned tree volume) of thinned stand is higher than that of unthinned stand, the ratio of total volume of thinned stand with high primary density to unthinned stand is higher than that of thinned stand with low primary density to unthinned stand. At the same primary density, the ratio of volume thinned stand to unthinned stand at the high site index class is higher than that at the low site index class.