Los Amigos;plants;Monocots;bamboo;vegetation;dynamics;large spatial scales;ecology;paleontology
Monodominant bamboo forests cover vast areas in the south-western Amazonian basin, and were poorly known until the last decade. Such a lowly diversified vegetation contrasts within a land primarily known for its great biological diversity. Various hypotheses suggesting anthropogenic or climatic origins have been put forward to account for this vegetation whose dynamics remain largely unclear. I investigated the origins of these vegetal formations by combining paleobotanical, and historical approaches (public records, diachronic remote sensing). The geographical and environmental context surrounding these formations was studied using a Geographic Information System (GIS). The taxonomic diversity of the encountered bamboos is also described, and temporary plots allowed a three-year monitoring of Guadua weberbaueri (Pilg.) patches vegetative dynamics. Finally, we monitor monocarpic flowering and regeneration events observed in the field. I demonstrate that bamboo was still present 45 790 yrs. BP and that may correspond to topographic elevations within the Amazonian basin. The botanical inventory reveals important diversity of bamboos (Poaceae: Bambusoideae: Bambuseae) belonging to three genera (Guadua Kunth, Elytrostachys McClure, Merostachys Sprengel), with taxons (Guadua sp., Elytrostachys cf. typical) not yet check listed for this part of the Amazonian basin. Moreover G. weberbaueri shows a noticeable vegetative stability in opposition to that predicted by several published hypotheses. This taxon also shows a synchronised flowering common to all patches of a same area with rhythm into several days unknown at time. Finally, mapping the soil occupation reveals a density of the rhizomes red higher than what let suppose the distribution of the culms. All these data permit an assessment of the dynamics of these bamboo monodominant forests, maybe present in south-western Amazonia since long time (geological scale ?). And we predict for the future the maintenance of this vegetation in stable or more humid conditions, when drier ones may reduce areas covered with these bamboo forests. More generally, our results permit to better understand biodiversity in the Amazonian forest.