The effects of tree cover and soil nutrient addition on native herbaceous richness in a neotropical savanna

Exotic grasses and high‐nutrient availability are common factors that may limit recovery of herbaceous diversity in derived savannas, while tree encroachment is a threat to diversity in old‐growth savannas. To understand the impacts of these factors on herbaceous communities, we studied the effect of nutrient addition, and the resulting increase in the exotic grass, Melinis minutiflora, at a savanna‐forest boundary in the Brazilian Cerrado. We inventoried richness of reproductive herbs, tree basal area and cover of the exotic grass, Melinis minutiflora, in each plot. Nutrient addition caused a large increase in Melinis and a large decrease in richness of flowering plants. Unexpectedly, structural equation model analysis suggests that the decline in herbaceous richness was a direct result of nutrient addition, rather than an indirect effect caused by the increase in Melinis. Tree density had a strong negative effect on both Melinis cover and herbaceous richness. Our results reveal that high‐nutrient availability imposes a barrier to the restoration of a diverse, native herbaceous layer in anthropogenic savannas, while tree encroachment is a threat to diversity in old‐growth savannas. Abstract in Portuguese is available with online material.