Soil and litter legacy effects of the Lake Erie invasive flowering rush (Butomus umbellatus)

Background/Question/Methods

 The Great Lakes region has been impacted by the invasion of over 180 different alien species. As these invasives have reduced wetland habitat availability and altered community structure, managers have developed extensive eradication programs. However, even following the removal of dense monocultures, invasives can influence native ecosystems through long-term chemical and biological changes in native soils, known as legacy effects. Our research investigates the potential for these legacy effects following the removal of the understudied emergent Flowering Rush (Butomus umbellatus) in Lake Erie wetlands at Ottawa National Wildlife Refuge.  Our previous work found that cutting can significantly reduce the average leaf area and number of propagules (rhizome buds) produced by each plant, limiting its spread. To examine post eradication challenges, a seed mix comprised of twenty-five native species was sown into flats of soils with different B. umbellatus invasion histories (native dominated soils, and two locations with former B. umbellatus populations of > and < 50% cover).  These flats were then subjected to single and combined treatments of living stands of B. umbellatus vegetative propagules and senesced overwintered litter.  

Results/Conclusions

Preliminary analyses indicate that soil invasion history had no effect on the number of native species present in established mesocosms.  However, trays with added B. umbellatus litter had significantly greater number of species compared to trays with established propagules.  This surprisingly beneficial influence of B. umbellatus litter awaits further support from the results of ongoing analyses of biomass data. Our work looks to better understand the influences of prior invasion by B. umbellatus on native wetland communities to provide managers with improved strategies for wetland restoration.