Figure 2 . Estimated size-frequency distributions of BCI forest under different bin-widths of size classes. To verify the effect of growth rate variance, size classes were bound with the estimated mean diameter increments of the corresponding sizes, in approximately 5-years (blue dots) and 1-month (red dots). This way of data grouping is different with the linear- or log-even size classes, which were used previously and would lead to a decreasing exponent with the magnitude increase of bin-width due to statistical bias(White et al. 2008).