Density effect, self‐thinning and size distribution in Pinus densiflora Sieb. et Zucc. stands

Abstract

The competition‐density (C‐D) effect for given times and self‐thinning over time in even‐aged, natural, pure stands of Pinus densiflora Sieb. et Zucc. were analyzed with the reciprocal equation of the C‐D effect in self‐thinning stands, and the equation describing the time‐trajectory of mean stem volume and stand density. The C‐D effect and self‐thinning were consistently well explained by the two equations. Differences in mean stem volume and in stand density among the stands tended to merge with increasing stand age. The self‐thinning line with a slope of approximately –3/2 was reached by the higher density stand prior to the medium and lower density stands. The skewness of tree height distribution showed positive values, which means that the distribution is more or less L‐shaped, and in addition the skewness decreased with increasing mean tree height, which indicates that smaller trees died as the stands grew. This trend is consistent with the asymmetric (one‐sided) competition hypothesis that self‐thinning is driven by competition for light. The tree height distribution was analyzed using the Weibull distribution. The location parameter hmin of the Weibull distribution increased with increasing stand age, and the scale parameter a tended to increase slightly with increasing stand age. The range of the shape parameter b of the Weibull distribution corresponded to that of the skewness.