Duluth WRS Seminar

Emerald Ash Borer Effects on Stream Ecosystems


Courtney Larson
Environmental Protection Agency, Duluth

September 21, 2020


Emerald ash borer (EAB) has killed millions of ash trees since its introduction, propelling this invader to the forefront of natural resources concerns. Despite the prominence of this destructive forest invader, information about impacts of widespread ash mortality on terrestrial-aquatic linkages is scarce. Mortality of ash trees along stream corridors can result in canopy gaps, which increases light available to riparian plant communities and potentially affects organic matter subsidies into streams. The aim of these studies was to determine how forest disturbance due to an invasive insect affects organic matter subsidies and macroinvertebrate and microbial communities in streams. In 2016, we identified EAB-related canopy gaps in six headwater streams of Michigan and characterized the coarse woody debris, leaf litter, and their associated bacterial communities (terrestrial and aquatic), along with macroinvertebrate communities upstream, downstream, and at the center of one EAB-related canopy gap per stream. In a subsequent study, we quantified decomposition and macroinvertebrate and bacterial colonization of leaf packs upstream, downstream, and at the center of a canopy gap from EAB-related ash mortality. Overall, our survey revealed EAB invasion negatively impacted stream ecosystems through indirect routes downstream of canopy gaps, yet leaf litter subsidies were resilient to the disturbance. There was no gap effect on leaf litter decomposition rates; yet macroinvertebrate diversity was significantly higher in gap leaf packs, compared to upstream and downstream reaches, implying recovery from gap conditions. Our findings suggest a structural and functional shift in macroinvertebrate communities in response to EAB by indirect routes of leaf litter subsidies and light availability. These results provide an important connection between the indirect impacts of invasive species on altered leaf litter dynamics and habitat in riparian zones that further the field of stream ecology.

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Meeting ID: 956 8739 9002
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