Spatial and temporal variability during primary succession on tropical coastal sand dunes

We studied primary succession on mobile tropical coastal sand dunes over an 8-yr period. Every six months, we monitored changes in species composition and sand movement in permanent quadrats located on the windward slopes. the arms and the crests. Our results indicate that sand movement decreased over time but was significantly higher on the slopes and crests than on the arms. In all cases. there were seasonal fluctuations in sand movement which increased during the period with strong northerly winds and decreased during the rainy season. Sand movement was significantly correlated with species distribution. Plant cover and species richness increased at all three locations. Diversity increased on the slope, decreased on the arms and remained unchanged on the crest. However, the equitability values indicated the dominance of a few species, especially at the end of the study period. Temporal trends and species turnover rates differed among locations. Species turnover occurred first on the arms (1994), then on the crests ( 1998) and lastly on the slopes (at the end of the study period). In all cases the tall grass, Schizachyrium scoparium var. littoralis. became dominant over the endemic legume, Chamaecrista chamaecristoides var. chamaecristoides. Similar to temperate dunes, primary succession on tropical sand dunes was spatially and temporally heterogeneous.