When inaction is not an option. Disturbance maintains grassland biodiversity in the face of widespread invasion by exotic forage grasses.

CECILIA DENISSE MOLINA; SILVOSO, M. C.; CAMPANA, M. SOFÍA; GRAFF, PAMELA; TOGNETTI, P.; CHANETON, E.J.

FOZ DO IGUASSU

Congreso; SER 2017. World Conference on Ecological Restoration; 2017

Temperate grasslands have been prone to invasion by alien plant species. Removal of livestock grazing has been advocated to enhance restoration of native plant communities. Paradoxically, long-term protection of grassland has compounded this pattern by favoring dominance by highly competitive grass species. Here we evaluate mowing as a management tool to prevent exotic grass invasion, and for restoring native grass assemblages after removal of livestock grazing. We further compared composition and diversity of ungrazed mowed grassland to that of seasonally grazed grassland. The study was conducted in the Flooding Pampa, Buenos Aires, Argentina. In 2004, we established 6 grazing exclosures, which were became heavily dominated by the pasture grass Festuca arundinacea. In 2014, we started a mowing treatment applied three times per year in each of 6 plots, adjacent to unmowed plots. For two years, relative cover and biomass of native and exotic species were monitored in ungrazed, mowed and grazed grassland. The proportional contribution of native species to total richness was equal across treatments. However, relative native biomass was 60% and 19% greater in grazed and mowed grassland, compared to fenced grassland, respectively. Grazing and mowing increased community evenness (27%, and 15%, respectively), relative to exclosures. This reflected the larger contribution of native grasses under grazing (30%) and mowing (4%). Our results show that, at present, domestic grazing is a valid option for precluding widespread dominance by exotic grasses and for biodiversity conservation. A mowing regimen might be useful to recover native grass communities only in the longer term