Questions: 1. Does flood pulsing drive metacommunity dynamics and provide insurance against catastrophic flooding in desert southwestern riparian ecosystems? 2. Do upland and wetland species in the floodplain differ in their dynamics?

Location: Southwestern USA.

Methods: We sampled vegetation and propagule banks in four communities along a floodplain hydrogradient. Plant species were classified as wetland or upland and community wetland indicator scores were calculated. ANOVA tested for differences between data categories amongst communities (extant vegetation and propagule banks) and soil depths. Sørensen's similarity coefficient was calculated to determine compositional similarity between vegetation and propagule banks.

Results: Community propagule banks had high similarity indicating broad dispersal by flood waters. Wetland propagules were present in soils from channel bars to floodplain edges, despite declines in wetland vegetation with distance from channel. Wetland communities in propagule banks were dissimilar from those in vegetation except on channel bars. Upland species (vegetation and propagule banks) increased with distance from channel. Propagules of upland species were most abundant in the litter, and were compositionally similar to upland species in most communities.

Conclusions: Flood pulsing is one mechanism that drives spatiotemporal metacommunity dynamics in dynamic desert riparian ecosystems. The homogenized regional propagule bank created by flood pulsing provides wetland species with a mechanism to escape local extinction by allowing for recolonization after flooding creates suitable establishment conditions. Upland species are able to germinate from in-situ sources after small-scale flooding or rainfall moistens soil. In fluctuating environments, these dynamics sustain biodiversity in the face of ongoing environmental change.

Nomenclature: Kearney & Peebles (1960).