Invasive European Bird Cherry Affects Terrestrially-Derived Prey Abundance for Juvenile Coho Salmon

Invasive species are a concern worldwide as they can displace native species and disrupt ecological processes. European bird cherry (Prunus padus) (EBC) is an invasive, ornamental tree that is rapidly spreading and possibly displacing native riparian trees along streams in parts of urban Alaska. To assess whether riparian EBC is affecting terrestrial-sourced invertebrate prey resources for stream salmonids, we sampled terrestrial invertebrates on riparian foliage, their infall into streams, and consumption by juvenile coho salmon in two Anchorage, Alaska streams, Campbell and Chester creeks. Results from the 2009 and 2010 field seasons showed that EBC foliage supported lower biomass of terrestrial invertebrates than native riparian deciduous tree species, and contributed less biomass of terrestrial invertebrates to streams compared to mixed native vegetation; however, no differences were detected in terrestrial invertebrate prey mass consumed by juvenile coho salmon. Terrestrial invertebrate community structure differed between EBC and native species (alder, birch, and spruce), but diets of fish captured associated with patches of EBC vs. native plants did not differ. These data suggest that while EBC is affecting the availability and composition of terrestrial invertebrate communities, we were unable to detect that EBC affected terrestrial invertebrate prey biomass consumed by juvenile coho salmon. Collectively, these results are providing clues about the extent to which invasive plant species in riparian zones can affect native species and ecological processes in stream ecosystems of Alaska.