Arrested development? Investigating the role of bamboo in Araucaria Forest succession in Southern Brazil

Aims Assessing the role of a dominant native bamboo species on tree species diversity and structure in the medium term.Methods Over a 7-year period,we studied the natural regeneration of two dominant forest types in Southern Brazil(Araucaria Forest or AF;Bamboo Forest or BF)after a bamboo(Merostachys skvortzovii Send.)die-off between 2004 and 2006.The study was carried out in the Embrapa Research Station in Cacador,Santa Catarina State,Brazil.Important Findings The die-off provided ideal conditions for the establishment of several species and it kickstarted forest succession dynamics,which in turn affected regeneration diversity.Tree species richness was relatively stable with a transitory increase between 2007 and 2014 in both AF and BF.However,species richness rose in BF because of a relative increase in abundance of some species(especially late and secondary species)while a plunge in some pioneer species drove an increase in diversity.Overall,we found that BF has a lower diversity of recruits and that density declined over time,while AF is more diverse,with a more stable density.In BF,the bamboo die-off created optimal conditions for initial regeneration development(mainly fast-growing pioneer trees),which quickly transited to higher size classes.Yet,after this initial stage of pioneer recruitment,the number of recruits dropped followed by a virtual absence of growth regardless of the species group as a result of a quick bamboo reestablishment.As bamboo recreated a dense understory it reduced species diversity to original levels,suggesting a self-maintaining cycle that halts forest succession.On the other hand,the bamboo die-off had little impact on AF where a slow recruitment process typical of old-growth forests was observed.The results indicate that the die-off event had a temporary effect on species diversity i.e.restricted to forests where bamboos are dominant in a similar process described in other southern South American forests.As the first study to observe the medium-term forest dynamics related to bamboo die-off,we can conclude that when being dominant,native bamboos can hinder forest regeneration,maintaining lower levels of diversity and arresting forest succession that lasts well beyond the short-term,post-die-off effects.Many forest fragments in the region are dominated by bamboos,thus their potential for conservation is at risk and requires appropriate management.