Pervasive Effects of Roadside Plant Invasions on Native Vegetation in Tropical Forests and Savannas

Abstract

Aims

Edge effects and biological invasions are among the major threats in protected areas. Invasive plant species are often found alongside roads in protected areas, facilitated by local edge effects. Although structurally distinct, both forests and savannas seem to be under strong invasion along roadsides. In this study, we investigated how edge effects of roads facilitate plant invasions in protected areas of forest and savanna, and how they affect native vegetation.

Location

Protected areas of forest (Parque Estadual do Morro do Diabo, Reserva Biológica Municipal da Serra do Japi, and Parque Estadual Porto Ferreira) and savanna (Estação Ecológica de Santa Bárbara, Estação Ecológica de Itirapina, and Parque Estadual Juquery) in southeastern Brazil.

Methods

We conducted replicated multistrata surveys in 180 plots and 60 patches (groups of plots), distributed across protected areas of forest and savanna, in two treatments: edge of the road and core (50 m from the road). We analyzed diversity metrics—species richness, abundance, and evenness—at two spatial scales (plots and patches), along with β-diversity.

Results

We found facilitative effects of road edges for invasive plant species in both vegetation types and at both spatial scales. Savannas, however, also have considerable invasion even in core areas. The abundance of invasive species was related to an increase in native species evenness, a decrease in native species abundance, and changes in relative abundances of dominant native species.

Conclusions

We recommend prioritizing non-invaded forest and savanna edges for invasive species prevention and early detection, and continued management of invaded areas, as they still support valuable native diversity. Finally, new roads in protected areas should be avoided, or if unavoidable, carefully planned and closely monitored.