Riparian forest invasion by a terrestrial shrub (Lonicera maackii) impacts aquatic biota and organic matter processing in headwater streams

Lonicera maackii, a highly invasive species of riparian habitats, has the potential to substantially alter aquatic ecosystems. We investigated effects of this terrestrial invader on aquatic biota and ecosystem processes in three 3rd order headwater streams in southwestern Ohio. We assessed (1) in situ leaf breakdown and (2) aquatic macroinvertebrate colonization of leaf packs containing senesced foliage from either a) invasive (L. maackii), b) native (Fraxinus spp. and Platanus occidentalis), and c) a native-invasive species mix. Leaf breakdown rates and macroinvertebrate density, richness, and functional feeding group (FFG) relative abundances were measured for leaf packs deployed in the autumn of 2009. Invasive leaf breakdown rates were up to 4x faster than native leaves (F = 20.46, df = 2, P < 0.001), resulting in significantly less organic matter remaining compared to the other leaf pack types throughout the study (Friedman's test = 8.00, P < 0.05). The gathering-collector FFG, represented by Chironomidae and Hydropsychidae, dominated the macroinvertebrate community in the invasive and mixed species leaf packs (F = 73, df = 4, P < 0.01) in all streams but were only dominant in native packs in one stream (F = 41.91, df = 4, P < 0.05). In summary, L. maackii leaf breakdown was significantly faster than native leaves in headwater streams, and colonization of macroinvertebrates was variable depending on leaf pack species composition. These results support the hypothesis that L. maackii can have direct and significant impacts on aquatic ecosystems by influencing organic matter availability and macroinvertebrate community dynamics.