Effect of Density on the Growth of Evergreen Tephrosia candida Shrubs

In tropics and subtropics areas, evergreen shrub species(Tephrosia candida) is good for soil improvement and afforest because of strong biological nitrogen fixation capacity and stress resistance, and then was choose as study object. The effect of density on planting growth was studied by measuring diameter at breast height (DBH), crown width, tree height and clear bole height in young Tephrosia candida stands with different densities (1 tree/m2, 2 trees/m2, 4 trees/m2 ,8 trees/m2) .The results showed that with increasing stand density, the mean DBH and the mean crown width of T. candida stands decreased in the order of 1 tree/m2 stand>2 trees/m2 stand >4 trees/m2 stand >8 trees/m2 stand. The mean tree height was not evidently influenced by the density as DBH, but the heightdiameter ratio increased with the density increment. There were positive linear correlations between clear bole height and stand density as well as between ratios of clear bole height / tree height and the stand density. The mean tree weight of T. candida decreased with increasing stand density, and their relationship could be expressed by the equation y=ax-b (y is mean dry mass, x is density, a is coefficient and b is exponent). The mean dry mass in different organs of single tree decreased with increasing density. With increasing density, the ratio of stem mass to tree mass increased, whereas that of branch mass or leaf mass to tree mass decreased. With increasing stand density, stand biomass and organ biomass increased in T. candida stands. The organ proportion was in the order of stem > roots> branches >leaves> bark in T.candida stand, and stem biomass accounted for 435%-510% of stand biomass, while bark biomass merely accounted for 590%-647% of stand biomass. The proportion in different tree organs was in the order of stem > branches >leaves > roots > bark in T. candida stand with 1 tree/m2, while it was stem> branches> roots> leaves > bark in 2 trees /m2, 4 trees/m2 and 8 trees/m2 stands.