Continuous growth of the giant grass Zizaniopsis bonariensis in subtropical wetlands

1. Zizaniopsis bonariensis (giant grass) is an emergent macrophyte species endemic to subtropical wetlands in Brazil, Argentina, Paraguay and Uruguay. In this study, we show the effects of its continuous clonal reproduction and its 'phalanx' growth strategy in the Taim Wetland (southern Brazil). 2. The continuous clonal growth of this 3-m high grass gave rise to the emergence of 11.7 new shoots m-2 per month and a high total above ground production (2870 g dry weight m-2 year-1). The biomass of the new shoots emerging every month formed a wave of growth, moderated by only weak seasonal variation. 3. We show its phalanx growth strategy by analysing the variations in population density and shoot height within a transect through the stand canopy. The inverse relation between density and height from the border to the interior indicates self-regulation of biomass. 4. The plants modified their environment, enhancing resistance to drought within the stand and thus facilitating their dominance. This positive feedback suggests that the dominance of the plant might constitute an alternative state in subtropical wetlands