Twenty-third Arboretum Research Symposium Highlights Graduate and Undergraduate Student Fellows

The twenty-third Arboretum Research Symposium was held on February 17 to an appreciative and inquisitive virtual audience. The graduate student presenters were current or former Arboretum Fellows, and an undergraduate presenter was an Arboretum-funded Hilldale Fellow.

Dana Johnson kicked off the annual event by describing her project investigating the effects jumping worms may have on soil structure and mycorrhizal fungi. Preliminary results suggest that pH, moisture, and fungal community composition changed in soil invaded by jumping worms in Gallistel Woods, compared to soil without jumping worms. Dana will continue this research for another year to study longer term impacts.

In Wisconsin and other Midwestern states, managing livestock while also conserving grassland biodiversity is a daunting challenge. Skye Harnsberger’s research investigates how grassland grazing management affects monarchs and other butterfly species. She told the audience that while continuously grazed lands do contain butterfly habitat, rotationally grazed land and ungrazed prairies provide more floral resources throughout the season.

Stormwater is a big issue at the Arboretum. Millions of gallons of stormwater – along with sediments, nutrients, road salt, and other toxins – flow into the Arboretum every year, with consequences for ecosystem health. Nick Hoffman is investigating the legacy of this disturbance by literally digging into decades worth of deposited sediment in Curtis and Coyote ponds to determine the prevalence and concentration of lead contamination. Nick has found that lead concentrations in the pond sediment peaked around 1980, at the same period when airborne lead concentrations were also near their peak. He also found that the difference in lead concentration between the two ponds is likely due to the different sewershed sizes and the amount of impervious surface within each watershed.

The encroachment of invasive shrubs, especially gray dogwood, into prairie ecosystems at the Arboretum is another important factor that can reduce native biodiversity and hinder restoration efforts. Katherine Charton’s research is quantifying how well common shrub management techniques perform over time to impede an invasion and how these techniques affect soil properties. Her early results indicate that while treating cut shrub stems with herbicide was most effective at removing gray dogwood and increasing native understory plants, results were highly variable by site, which indicates the need for more research.

Eliza Soczka, an undergraduate scholar, is piggybacking her study on Katherine’s plots, asking questions about how woody and herbaceous seed deposition affect the establishment and maintenance of a woody invasion. Her research indicated that high shrub cover correlates to more seeds from shrubs in the soil. While birds play a significant role in woody plants seed dispersal, many gray dogwood seeds fall in place, leading to a positive feedback of shrub regeneration and thus the need for continuous management. Her work highlights the need for practitioners to remove invasive woody shrubs before seed set to minimize establishment.

We thank the student presenters for participating in this year’s Research Symposium and the virtual audience for supporting Arboretum research.

—Brad Herrick, ecologist