Salinity levels fluctuate because heavy rains dilute the salt, while storms bring new seawater in. Evaporation and opening of the gate increase salinity. The gambasien can't tolerate high salinity and die or immediately leave the area around the sluice gate when it is opened. This left much of the land exposed and quickly led to erosion. It was favoured as it is very fast growing, evergreen and highly salttolerant.
Sparse vegetation grows underneath because of the high acidity of the needles.
It is also shallow-rooted and is easily toppled in high winds. Now a replanting scheme is in hand to replace the casuarina forest by native and endemic species. Also widely used in replanting scheme after the cedar blight. Despite the name Spanish Rock, the inscription is thought to be from a Portuguese shipwreck. Due to erosional processes and vandalism a bronze cast was made from a mold of the inscription in 1940.