Invader removal restructures multitrophic communities and triggers secondary invasion

Efforts to restore ecosystems invaded by non-native plants often aim to
reverse invasion impacts, yet removal can trigger new community shifts
across trophic levels. We examined how removal of Rhamnus cathartica
(common buckthorn) influenced plants, arthropods, pollinators and rodents
in a post-industrial forest preserve in western New York, USA. Across 18
plots representing restored, buckthorn tree, and buckthorn shrub stands,
we quantified vegetation structure, leaf litter biomass and faunal
abundance. Buckthorn removal promoted a tenfold increase in herbaceous
cover and species richness, yielding more diverse and structurally complex
understories. These changes coincided with higher arthropod and pollinator
abundance, but also a three- to fivefold increase in the invasive ant
Myrmica rubra (European fire ant). Contrary to expectations, M. rubra
flourished in restored plots, responding to thicker and more stable leaf
litter rather than canopy shade. Pollinator abundance declined with
increasing M. rubra density, suggesting interference or avoidance effects,
whereas detritivores and rodents responded primarily to vegetation and
litter structure. Our single-site design isolates general
mechanisms—litter-mediated ant responses and structure-driven pollinator
and arthropod gains—that are testable across temperate forests. The
results indicate that R. cathartica removal reshaped multitrophic
community structure – enhancing plant and arthropod recovery but
simultaneously facilitated a secondary invasion. Restoration success may
therefore depend on eliminating the initial invader while recognizing that
restoration itself can act as an invasion-promoting disturbance.