XVI International Botanical Congess

We studied primary plant succession on tropical sand dunes over a 9 year period, by sampling vegetation in permanent quadrats every 6 months. We measured sand movement at monthly intervals. The endemic shrubby legume, Chamaecrista chamaecristoides was the first to colonize mobile areas. As the sand became stabilized, grassy species such as Schizachyrium scoparium arrived and increased their plant cover. Principal component analyses showed a greater increment in grass cover in the dune arms and the inner slope while the dune crest remained relatively mobile and grasses were less abundant. Additional vegetation sampling indicated that plant cover and abundance of C. chamaecristoides was very low in dune grasslands. Thus, the encroachment of these grass species in open dune vegetation can be considered as unfavourable from a conservation viewpoint, since they are slowly replacing the endemic species as mobile areas become lessabundant.