Remaining eucalypt trees may hamper woody plant regeneration in a neotropical savanna

Abstract

When an area previously used for agricultural or sylvicultural purposes is abandoned, it may undergo natural regeneration. However, the outcome of such regeneration depends on a number of factors, including the presence of non-native invasive plants, and, when production forests such as eucalypt plantations are considered, remaining non-native trees may also affect the natural regeneration possibilities. We studied how remaining eucalypt trees affect woody species regeneration and invasive grasses in an abandoned Eucalyptus grandis plantation in a regenerating Brazilian savanna site. We sampled the woody vegetation and invasive grasses in 30 8 × 8-m plots and surveyed the eucalypt trees within these plots and in 3 m-wide strips around them. Eucalypts negatively affected the cover of the C4 invasive African grass Melinis minutiflora and the total abundance and basal area of native woody plants in general and of two dominant species, suggesting an overall negative effect on native plant regeneration notwithstanding the also negative effects on African grasses. Conversely, they had no effect on species richness, species diversity nor mean height of woody plant communities nor on the abundance of three other dominant native woody species. Interestingly, a low eucalypt abundance had small effects on native woody species but much stronger effects on the cover of M. minutiflora, possibly due to shading. Thus, our results indicate that remaining eucalypt trees may hamper the natural regeneration of native woody plants, but also suggest that maintaining a low density of eucalypt trees may be a cost-effective strategy, given the high costs associated with the complete removal of remaining trees and the difficulties in controlling invasions by African grasses.