Mangrove-saltmarsh dynamics on a bay-head delta in the Hawkesbury River estuary, New South Wales, Australia

Mangroves of the species Avicennia marina and Aegiceras corniculatum occupy a range of intertidal environments in the Hawkesbury River estuary, New South Wales, Australia. Over the previous four decades, these species have, in a number of locations, encroached upon upper-intertidal saltmarsh environments. The authors have investigated the upper stratigraphy of saltmarsh plains to determine whether evidence can be found of prior occupation of these sites by mangroves. On the prograding bayhead deltas, mangrove root systems were found preserved at approximately 0.3 m beneath the current saltmarsh surface indicating that vegetation progression has occurred from mangrove to saltmarsh with the accretion of the flat. The mangrove roots dated from 500 to 1700 years before present, indicating that the current landward transgression of mangroves is contrary to the longer-term successional trend in these environments.