Relationship between light availability, expressed by DIFN, and aboveground biomass of P. serotina, in two classes of propagule pressure, expressed by the number of fruiting P. serotina trees up to 50 m from the plot (open dots and dashed line :≤ 20; solid dots and line: > 20; p < 0.001, R2 = 0.32). Threshold of 20 trees was chosen according to median and mean for all plots (18 and 18.49, respectively). Modification given by class of propagule pressure was statistically significant (p < 0.01). Note log-transformation of the y axis. Shading around regression lines indicate range of model SE.