Long-term effects of large and small herbivores on plant diversity in a salt-marsh system

It is well known that herbivores impact plant communities globally. However, the decade-long effects of herbivores on plant communities remain unclear, due to limited long-term experiments. Using 46-year large herbivore exclosures and 22-year small herbivore exclosures in the salt marsh of the island of Schiermonnikoog, I evaluated the long-term effects of large (cattle) and small herbivores (hares and geese) on plant diversity. I found that long-term management is needed for conserving biodiversity. In addition, using low to moderate densities of large domestic herbivores to conserve plant diversity is sustainable for at least 46 years. However, the effects of large herbivores on biodiversity were more attributed to the non-trophic effects (e.g. trampling, and deposition of urine and dung), particular in the long-term (23 years after). Small wild herbivores (hares and geese) can also slow down plant species decline (for at least 22 years) but only at the early successional stage where their abundance was high. A diverse herbivore community (hares and geese relative to hares alone) had a more positive control of plant communities. On top of that, these ecologically important small herbivores may also have substantial evolutionary effects such as modify local-scale spatial genetic structure of a dominant plant species. Results emphasize the need for the conservation and re-introduction of herbivores, domestic or wild, to sustain long-term grassland plant diversity.