Inundation duration and vertical vegetation zonation: a preliminary description of the vegetation and structuring factors in borokotóh (hummock igapó), an overlooked, high-diversity, Amazonian vegetation association

Abstract

Here we present data on a study of the species composition and structure of borokotoh, a habitat associated with central Amazonian seasonally black-water flooded forests. Borokotoh appears never to have been specifically studied before, being mentioned only once or twice in the literature (and then not under this name). This is the first report on the phytosociology of this vegetation association. Borokotoh is, on average, only some 20 m wide, but very species rich (107 species in 60 genera from 34 families in one 0.25-ha plot). It consists of a series of rounded hummocks of fine-grained mud, each 6–12 m in length and 2–3 m in height, separated by narrow sloughs. Hummocks are seasonally inundated almost to their flat tops, which remained dry in the years of the survey. Species are strongly stratified within the borokotoh, with over 78% of identified species being recorded in just one of the three hummock sub-divisions: top, side or in between-hummock slough. This specificity, almost certainly linked to inundation duration and waterlogging tolerance, may explain the high species diversity recorded. The study is significant in demonstrating that undescribed habitats still exist in Amazonia, and that biodiversity there may be structured in ways that are highly localized and habitat-specific. There is clearly a need for more detailed work on borokotoh and similar vegetation associations where high biodiversity may be associated with very specific local features.