The model that best explains tree density was a model with organic matter plus interstitial salinity and interaction, also sig- nificant (p < 0.01). At low salinity values (upper estuary) there is a strong correlation between density and organic matter (i.e. high tree densities associated with higher values of organic matter). At high salinity values (lower estuary) the correlation coefficient is low with almost no difference between tree density at high or low concentrations of organic matter (Fig. 5).