Coexistence of Juncus articulatus L. and Glyceria australis C. E. Hubb. in a temporary shallow wetland in Australia.

Abstract

Juncus articulatus, a species introduced to Australia, is codominant over large areas of Mother of Ducks Lagoon but is rare in other lagoons. It occurs widely within the lagoon but is concentrated in lower, wetter areas that are more disturbed by birds and cattle. This suggests that J. articulatus may be separated over elevation (and therefore water regime) and disturbance gradients from the native grass Glyceria australis, the dominant species in the lagoon. This paper compares the growth and interaction of G. australis and J. articulatus under different water regimes. The species responded differently to water regime both in monoculture and in mixture. Above ground production of J. articulatus was greatest under fluctuating water levels, least under a damp water regime and intermediate under flooded conditions. G. australis production was greatest under the damp, least under the flooded and intermediate under the fluctuating water regime. The outcome of interaction is dependent on water regime and time. After one year J. articulatus was the superior competitor under all water regimes. At the end of two years J. articulatus was still the superior competitor under fluctuating and flooded water regimes but not under the damp regime. The change in outcome after two years was due to the competitive superiority of G. australis during the second year under all water regimes. The relative importance and the management implications for the invasive potential of J. articulatus are assessed in shallow Australian wetlands with fluctuating water regimes.