Effects of disturbance by sand movement and inundation by water on tropical dune vegetation dynamics

Abstract

Sand movement and slack inundation by water act as disturbance agents in dune systems. In this study we focus on these disturbance agents with different intensity and frequency that affect differentially the structure and composition of dune vegetation. Sand movement and slack inundation by water were monitored during 1979 – 1981 and 1991 – 1995. Sand movement reached higher values during the dry months, which coincided with the occurrence of yearly strong northerly winds. Sand movement has decreased over the last 10 years due to an increment in plant cover, particularly Chamaecrista chamaecristoides and Schizachyrium scoparium. Slack inundation was also a common phenomenon at the study site, but its frequency was much less predictable. Pluchea odorata, Panicum maximum, and Schizachyrium scoparium were the first species to recolonize the area after intense inundation. In the absence of inundated periods, slack vegetation increased its species richness and showed a more complex structure with higher shrub and tree cover. Markovian models showed a stable state in which species richness increased. Our study showed that the mosaic pattern of dunes is the result of two types of heterogeneity: spatial heterogeneity due to dune topography, and the asynchronous occurrence of two disturbance regimes that modify succession in a patchy fashion. Key words: tropical dunes, disturbance, heterogeneity, sand movement, inundation, succession.