Gap disturbance triggers the recolonization of the clonal plant Ambrosia tenuifolia in a flooding grassland of Argentina

PEDRO INSAUSTI; AGUSTIN GRIMOLDI,

AUSTRAL ECOLOGY

Blackwell

Año: 2006 vol. 31 p. 828 - 836

1442-9985

Abstract Flooding provokes the death of many dicotyledonous species in grazed grasslands of the FloodingPampa in Argentina, including the clonal plantAmbrosia tenuifolia,which produce the opening of numerous gaps.The objective of this study was to investigate the recolonization of grassland byA. tenuifoliaafter this speciesdisappeared due to the occurrence of prolonged flooding events. To this end, responses of seed germination toenvironmental factors associated with gaps, such as light quality and temperature regime, conditions related toseedling survival, and clonal growth of ramets outside the gaps were studied in two different experiments in thefield. Environmental factors related to gaps promoted the recruitment of new genets. The combined effect ofalternating temperatures and the high red : far-red ratio set off germination from the soil seed bank; germinationalso was enhanced when signals were generated artificially under the intact canopy in the field. Higher resourceavailabilities and maximum seedling survival were recorded in canopy gaps, which were the focus of invasion.Grassland recolonization outside the gaps continued rapidly by clonal growth, from small gaps and large ones,even within the dense surrounding canopy. This provoked an intense competition with the other species. Gapopening by disturbances, seed germination in gaps and clonal growth were decisive for the recolonization ofA. tenuifoliapopulations. This sequence of events triggered the recolonization of the plant community by thisspecies, in sites where it had been eliminated by prolonged flooding. This process represents one of the mostsignificant fluctuations in the vegetation dynamics of the Flooding Pampa Grasslands.Key words:clonal growth, Flooding Pampa Grasslands, gap disturbance, germination, recolonizationFlooding provokes the death of many dicotyledonous species in grazed grasslands of the FloodingPampa in Argentina, including the clonal plantAmbrosia tenuifolia,which produce the opening of numerous gaps.The objective of this study was to investigate the recolonization of grassland byA. tenuifoliaafter this speciesdisappeared due to the occurrence of prolonged flooding events. To this end, responses of seed germination toenvironmental factors associated with gaps, such as light quality and temperature regime, conditions related toseedling survival, and clonal growth of ramets outside the gaps were studied in two different experiments in thefield. Environmental factors related to gaps promoted the recruitment of new genets. The combined effect ofalternating temperatures and the high red : far-red ratio set off germination from the soil seed bank; germinationalso was enhanced when signals were generated artificially under the intact canopy in the field. Higher resourceavailabilities and maximum seedling survival were recorded in canopy gaps, which were the focus of invasion.Grassland recolonization outside the gaps continued rapidly by clonal growth, from small gaps and large ones,even within the dense surrounding canopy. This provoked an intense competition with the other species. Gapopening by disturbances, seed germination in gaps and clonal growth were decisive for the recolonization ofA. tenuifoliapopulations. This sequence of events triggered the recolonization of the plant community by thisspecies, in sites where it had been eliminated by prolonged flooding. This process represents one of the mostsignificant fluctuations in the vegetation dynamics of the Flooding Pampa Grasslands.Key words:clonal growth, Flooding Pampa Grasslands, gap disturbance, germination, recolonization