Bamboo, fire and flood: regeneration of Bambusa arnhemica (Bambuseae: Poaceae) after mass-flowering and die-off at contrasting sites in monsoonal northern Australia

Bambusa arnhemica F.Muell., a long-lived, gregarious-flowering and semelparous bamboo endemic to north-western Australia, occurs in remarkably disparate but somewhat fire-sheltered flood-prone riparian forest and rocky hillside vine-thickets, but not in adjacent fire-prone savannas. We investigated the response of B. arnhemica seedlings to fire and flood at two contrasting sites over 2.5 years following a mass-flowering and die-off event. Seedlings grew vigorously notwithstanding either prolonged inundation or total loss of above-ground parts to fire within their first year. However, there was no evidence that such disturbance promoted regeneration, and several veins of evidence suggest that B. arnhemica is fire-retardant and refugial rather than fire-promoting. We suggest that creation of canopy gaps by parental death is a more parsimonious and generalisable hypothesis for the evolution of gregarious semelparity in bamboos than the recently advanced bamboo fire-cycle hypothesis. However, both hypotheses are potentially group selectionist, and resolution of dispersal distances and/or the spatial genetics of relatedness are required to resolve the problem.