Assistant Professor California State University, Bakersfield, United States
Abstract: Introductions of invasive plant species to riparian zones can impact nearby freshwater ecosystems by altering the composition of leaf litter available to freshwaters that serve as critical habitat and food resource for aquatic biota. The deciduous Tree of Heaven (Ailanthus altissima; [TOH]) is an invasive species that impacts terrestrial ecosystems; however, little research has focused on potential impacts on freshwater ecosystems. This study aims to understand if TOH leaf litter 1) decomposes at different rates compared to native species’ leaf litter, and 2) supports a unique macroinvertebrate community compared to native species’ leaf litter. Tree of Heaven leaves are compared to two local California, USA species, the Frémont's cottonwood (Populus fremontii) and London Planetree (Plantanus acerifolia). These two species will serve as fast (cottonwood) and slow (planetree) leaf breakdown comparison points for TOH. Leaf packs contained 3 g of invasive, native, or mix of all leaf types (n = 35 leaf packs/treatment/habitat). Leaf packs were anchored in a perennial pond and a headwater stream site and harvested every 3-5 weeks. Macroinvertebrates that colonized leaf packs were identified to Family level and sorted by functional feeding group. The remaining leaf litter was dried and weighed to identify the decomposition rates across leaf pack treatments, plant species, and habitats. We expect that TOH leaf litter will 1) decompose the fastest, with this pattern more pronounced in the stream site, and 2) support greater macroinvertebrate abundance dominated by Collector-gatherers and Shredders linked with the rapid fragmentation of TOH expected in the stream site compared to the pond site. Preliminary results suggest that invasive leaf pack breakdown was up to 2 × faster compared to native leaf breakdown across habitats with mixed leaf packs at intermediate breakdown rates. Aquatic macroinvertebrate communities were unique between freshwater habitats (P < 0.05). The macroinvertebrate community was dominated by detritivores (~90%) across habitats. Chironomidae and Ephydridae the dominant taxa (~20% to 80%) in the pond habitat with Philopotamidae and Chironomidae the dominant taxa at the stream site (~30% to 50%). These preliminary results suggest that leaf litter from an invasive species may be a short-term resource for aquatic macroinvertebrates. Considering that freshwater ecosystems are under immense pressure due to anthropogenic activities, increasing our understanding how invasive species affects our freshwater ecosystems can help improve our efforts to protect them.
