The influence of nutrient enrichment upon mangrove seedling establishment and growth in the Hawkesbury River Estuary, New South Wales, Australia

The hypothesis that mangrove exclusion from saltmarsh is attributable to nutrient deficiency is experimentally tested on the Hawkesbury River estuary. Survivorship and growth of seedlings of the grey mangrove Avicennia marina were followed for a sixteen month period, in an experiment in which half of all seedlings were treated with a slow-releasing source of phosphorus, nitrogen and potassium. While fertilisation substantially increased growth rate, this occurred in the second summer of growth and fertilisation did not improve the low survivorship of A. Marina at the mangrove-saltmarsh boundary. Fertilisation has no influence on the root/shoot ratio where measured. It is postulated that factors other than nutrient deficiency are primarily responsible for determining the upslope distribution of mangroves in temperate Australian estuaries.