Tree species-dependent effects of urbanization and plant invasion on deadwood biota and decomposition rates

Human activities are swiftly reshaping ecosystems, and the simultaneous rise of urbanization and plant invasions has become a significant challenge that jeopardizes both global biodiversity and ecosystem function. Deadwood is an important provider of biodiversity and carbon storage, yet it remains unknown how urbanization and plant invasion affect wood-inhabiting taxa and decomposition rates, separately and interactively. Here we conducted a two-year wood decomposition experiment using Acer saccharum and Pinus strobus at 19 paired invaded and uninvaded plots along an urbanization gradient in Toronto, Canada. We assessed the individual and combined effects of urbanization and plant invasion by Vincetoxicum rossicum on the community composition and diversity of bacteria, fungi and insects, as well as on wood decomposition rates, which are partly driven by these taxa. Our results show that urbanization had individual effects on the diversity of all three taxa and on the composition of bacterial and fungal communities. Plant invasion individually affected fungal and insect diversity. Interactive effects of urbanization and plant invasion occurred only for fungal diversity in Pinus strobus. Wood decomposition rates varied by tree species, with urbanization accelerating the rates for Pinus strobus but not Acer saccharum. Fungi were the only taxon that significantly influenced wood decomposition. Our findings together indicate that urbanization and plant invasion lead to changes in deadwood-inhabiting communities and decomposition processes, yet their interactive effects are of minor importance. They also show that these effects differ between tree species. Hence, integrating the combined effects of various anthropogenic drivers and different tree species is crucial for developing effective strategies to restore and sustain biodiversity and ecosystem functioning in urban landscapes.