Secondary dune succession on Inhaca Island,Mozambique

Old field succession was studied on coastal dunes supporting tropical evergreen forest on Inhaca Island, Mozambique. Plots of 10×10 m were sited in three early successional stages and in relatively undisturbed forest. Woody species increased in number during succession; leptophylls were most frequent in younger vegetation, whereas microphylls and mesophylls were most frequent in forest. Grasses, shrubs and forbs dominated initially following abandonment, and shrubs persisted as dominants in the three early successional stages. The initial floristic composition model was generally supported by the pattern of species sequences, with many forest species entering early in the succession. Of the few species conforming to the relay floristic model, many were grasses and forbs of the forest understorey. Similarity between plots of equivalent vegetation age indicated that, at least in early succession, there was linearity in the successional pathway; there was no evidence for divergence or multiple pathways. In early succession, no accumulation was detected in either soil organic matter or extractable nutrients, thus providing little support for the facilitation model of succession. It is stressed that the findings are probably scale-dependent.