Flood disturbance and the coexistence of species in a lowland podocarp forest, south Westland, New Zealand

Age and size structures, and tree locations were used to identify cohorts of trees that were initiated by flood events. This, along with information on species microsite preferences and spatial patterning, was used to reconstruct the patterns of establishment of the four dominant canopy trees (Dacrycardpus dacrydioides, Dacrydium cupressinum, Prumnopitys ferruginea, Weinmannia racemosa) in response to flood disturbance. The four species coexisted by partitioning establishment site with respect to the amount of overhead cover and the type of forest floor microsite. D. dacrydioides and D. cupressinum established in large gaps but colonized contrasting microsites; D. dacrydioides established mostly on mineral soil while D. cupressinum established on elevated microsites. W. racemosa and P. ferruginea both established on elevated microsites beneath largely intact canopies. However, W. racemosa colonized canopy gaps while P. ferruginea established mostly under closed cover. Disturbance was critical to the maintenance of species diversity because it was the source of much of the environmental variation to which species responded differentially. -from Author