Invasive Glossy Buckthorn (Frangula alnus) Has Weak Impact on Native Understory Plant and Saprophagous Macroarthropod Communities

Glossy buckthorn (Frangula alnus Miller) is an invasive alien plant species (IAPS) rapidly expanding in North America but is largely understudied compared to the common buckthorn (Rhamnus cathartica). Our study investigated the effects of a 27-year-old F. alnus invasion on native understory plant and saprophagous macroarthropod communities in a wet deciduous woodland in Southern Québec, Canada. We hypothesized a decreased taxonomic diversity and a change in community composition of both indicator taxa with increasing F. alnus density. The understory plant and saprophagous macroarthropod communities were characterized, respectively, through vegetation surveys and pitfall trapping across a density gradient of 43 plots invaded by F. alnus. Our results demonstrated that F. alnus did not exert a strong influence on species community composition, although the homogenization of understory plant communities was observed. Despite several decades of F. alnus invasion at our study site, the consequences on the selected indicator taxa were overall relatively small, suggesting that the magnitude of effects is variable. We suggest that further investigation at a larger scale should be performed to evaluate the effect of F. alnus on a broad diversity of indicators and understand any context dependency.