Exotic vs. native: global and urban investigations of leaf litter decay in streams




Kennedy, Kimberly Theresa May

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Exotic species alter the streamside plant community by changing the resources available to the stream food web, causing cascading changes throughout the entire aquatic ecosystem. To better understand the impacts of exotic litter species on stream communities, investigations were made at global and local levels. A meta-analysis was performed to understand which environmental and litter quality factors impact native and exotic litter decay rates on the global scale. It was found that exotic species are likely to decay faster than native species at larger mesh sizes, and in warm temperature environments because high quality exotic leaves have a lower C:N ratio than native leaves. An urban litter decay experiment in Victoria, B.C. streams contrasting Alnus rubra, Salix sitchensis, Hedera sp., Rubus armeniacus and plastic trash found that trash decays more slowly than leaf litter, but leaf species all decay at the same rate, and stream invertebrates colonize all litter types equally. Significant differences in litter decay rates and invertebrate community alpha and Shannon diversities were also observed across the four different streams. The more that is learned about the impacts of exotic leaf litter, the better we are able to respond to keep streams as healthy and as biodiverse as possible.



Leaf decay, Invasive species, Meta-analysis, Hedera helix, Rubus armeniacus, Salix sitchensis, Alnus rubra, Urban streams, Plastic decay, aquatic invertebrates, C:N, C:P, leaf toughness, leaf mass area, stream temperature