The progression of a mangrove forest over a newly formed delta in the Umhlatuze Estuary, South Africa

Different age groups were recognised in a mangrove forest that progressed over a delta forming after the construction of a harbour in the Umhlatuze Estuary, South Africa in 1976. The rate of progress was high during the first period, varying from 20 to 55ha year(-1) until 1982, Thereafter there was a small decrease in the total area, whereas the rate has been 5.4ha year(-1) over the last 13 years. Diameter at breast height (dbh) and densities of trees and seedlings were investigated in the field in the different age groups recognised from the aerial photo record covering the area. The youngest stands (1-6 years old trees) had a significantly lower mean dbh compared to the older stands (>6 years). The difference was also clear when it came to stem densities, where significantly higher densities were found in the youngest stands. The mean density of live seedlings was high in the youngest stands, being significantly lower in the older stands. When it came to the mean density of dead seedlings, the number from the youngest stand was lower than the ones obtained for older groups. The oldest group had however a very low density. It is suggested that the mangrove progression has slowed down, thus indicating that the system is settling down.