was almost entirely due to an increase in grass biomass; in the process forbs were overtopped and shaded out such that a significant decline in species richness was recorded. In contrast, herbivore exclusion did not significantly impact nitrogen mineralization, perhaps due to the short period of herbivore exclusion (3 years in 2005). However, the moist riparian and wetland zones supported a high nitrogen mineralization rate, while the potential denitrification rate was also significantly higher

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... than other topographic positions. Thus, it is clear that large herbivores are essential agents for disturbance in the riparian zone, acting to maintain species richness by keeping grass biomass low.