Acacia invasion is facilitated by landscape permeability: The role of habitat degradation and road networks

Context The sandy-savanna ecosystem "Mussununga", a natural ecosystem that occurs as patches throughout the Atlantic Forest domain, is threatened by anthropogenic factors and biological invasions of AustralianAcaciaspecies. Habitat degradation in the Atlantic Forest domain and extensive road networks could facilitateAcaciainvasion into Mussununga. Objectives We investigated whether: (a) landscape permeability (measured by effective conductance) facilitatesAcaciainvasion; (b) forest fragments are barriers, and roads and highways are corridors for invasive spread ofAcacia; and (c) size and shape of Mussununga patches play a role in biological invasion. Methods Acaciainvasion was investigated in 32 Mussununga sites within the Atlantic Forest domain. We tested the effect of a set of landscape permeability scenarios based on circuit analysis and nine other metrics of landscape structure onAcaciaoccurrence using three buffer-zone sizes (0.5, 1, and 2 km). Results The likelihood ofAcaciainvasion significantly increased with landscape permeability. The best-fitting landscape permeability scenario designated road networks as corridors, intact forests and water surfaces as barriers, and degraded habitats as non-barriers. We also found that Mussununga areas within a 0.5 km buffer negatively affected the biological invasion byAcacia. Conclusions Extensive habitat degradation by deforestation and dense road networks facilitateAcaciainvasion into sandy-savanna Mussununga ecosystems. Landscape permeability may be used as a risk-assessment tool for biological invasion byAcaciaspecies. Mussununga patches can be protected fromAcaciainvasion through preserving or restoring forest belts around them and disconnecting them from the road network.