Abstract: The competition density (C-D) effect for Populus deltoides stands was analyzed using the reciprocal equation of the C-D effect, i.e. 1/w=Aρ+B, where w and ρ respectively represent mean stem volume and density. The C-D curve, which is given by the reciprocal equation on logarithmic coordinates, shifted upward with the progress of time. The relationship between biological time τ and physical time t followed a hyperbolic curve. The coefficients Aand Bincluded in the reciprocal equation were calculated at each growth stage. With increasing τ, the coefficient Aincreased abruptly up to a maximum value, whereas the coefficient Bdecreased exponentially and tended to close to zero. The λ(t) decreased with increasing stand age.