Trampling enhances the dominance of graminoids over forbs in flooded grassland mesocosms

STRIKER GG, MOLLARD FPO, GRIMOLDI AA, LEÓN RJC, INSAUSTI P

APPLIED VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2011 vol. 14 p. 95 - 106

1402-2001

1. What are the interactive effects of flooding and cattle trampling upon the structural attributes and the floristic composition of a plant community? 2. Do the effects on the plant community persist over an extended recovery period? We assessed the effects of 40-d flooding, trampling and the combination thereof on plant cover and biomass, vertical distribution of foliage and floristic composition in lowland grassland mesocosms. We considered a 120-d recovery period to evaluate the persistence of flooding and trampling effects on the plant community until the end of the growing season. Flooding, with or without trampling, increased the cover and biomass of the graminoid species, especially marsh grasses, which developed a taller canopy. In contrast, most of the forb species were negatively affected. This was drastically enhanced by trampling, as the aerial biomass of the dominant legume L. tenuis decreased by 90%, while the forbs Leontodon taraxacoides, Mentha pulegium and Phyla canescens were not detected on mesocosms subjected to the combination of flooding and trampling. Remarkably, trampling under flooding conditions did not reduce the total aboveground biomass production, as the growth enhancement of graminoids was enough to compensate for the breakdown of the forb species. In contrast, belowground biomass was lower when both disturbances occurred simultaneously. After 120-d of recovery, graminoids continued to be dominant while the remaining forbs (including L. tenuis) recovered only partially and lost species started to reappear, sprouting from reserve organs. Belowground biomass recovered fully at the end of the growing season. The combination of flooding and trampling shifts the community co-dominance of graminoids and forbs towards a persistent dominance of graminoid species until the end of the growing season. When both disturbances are combined, the aboveground production of the grassland is not affected and root biomass is rapidly recovered. However, the loss of the legume L. tenuis deserves attention because this is the unique relevant N-fixing species of the ecosystem, which in turn improves the forage quality for livestock production.