Forest fragmentation does not matter to invasions by Hovenia dulcis

Abstract

Testing whether biological invasions can be facilitated by habitat fragmentation can provide important insights for the study of invasion ecology. Hovenia dulcis is considered an aggressive non-native species in subtropical Atlantic forest ecosystems and following the assumptions of invasion ecology we hypothesized it would occur mainly in smaller forest remnants, which are more susceptible to edge effects compared to larger ones. In this study, we verified the relationships between H. dulcis invasion on forest remnants and the current habitat fragmentation and tested whether both occurrence and abundance of this species are driven by landscape and habitat variables. We selected 30 forest fragments in initial, middle or late successional stages and verified the occurrence and abundance of trees and saplings of H. dulcis. We evaluated spatial autocorrelation and the influence of landscape and habitat metrics on occurrence and abundance of such species and the influence of fruiting trees (adults) on the abundance of non-adult individuals. We found that H. dulcis distribution was not related to geographic distance among remnants. The occurrence of adult H. dulcis was directly associated to closed-canopy areas and remnant shape and, contrary our initial hypothesis, not related to remnant size. The occurrence of adult trees increased H. dulcis regeneration leading to higher sapling abundance. High abundance of H. dulcis saplings close to adult trees pointed out the successful colonization of recently invaded Atlantic forest remnants. We showed that this invasive tree species successfully invades closed-canopy forest fragments, which highlight undisturbed subtropical Atlantic forest habitats are as susceptible to biological invasions as disturbed ones.