To Remove or Not to Remove, That is the Question

I often get asked, is it worth the time, effort, and money to remove invasive plants. Now we have a study that shows it just might be. Researcher Erynn Maynard-Bean, Penn State University, tried to answer that question in a section of woods belonging to Penn State and managed as part of the arboretum known as Hartley Woods. She found that after seven years of invasive shrub removal natural regeneration of native plants exceeded the abundance measured in unmanaged forest understories with low levels of shrub invasion. This research highlights the capacity for that system to rebound following invasive plant removal.

By Jeff Mulhollem

May 14, 2019

UNIVERSITY PARK, Pa. — Removing invasive shrubs to restore native forest habitat brings

a surprising result, according to Penn State researchers, who say desired native understory plants display an unexpected ability and vigor to recolonize open spots.

"The regeneration of native plants that we saw where invasive shrubs had been removed exceeds what we expected from looking at uninvaded parts of the forest," said researcher Erynn Maynard-Bean, who recently earned her doctoral degree in ecology.

"We believe that's because invasive shrubs take up residence in the best spots in the forest. They are most successful where there are the most resources — sunlight, soil nutrients and water. Then, when invasive shrubs are removed, the growth of native plants in those locations beats expectations."

She drew that conclusion after participating in a long-term project in the Arboretum at Penn State, which involved repeated removals of a suite of 18 invasive shrub species and closely monitoring the growth of native plants. That removal experiment was initiated by Margot Kaye, associate professor of forest ecology. In the experiment, after invasives were removed over seven years, plant diversity, native understory species abundance and overstory tree species regeneration, increased.

The study took place in a woodlot known as the Hartley Wood, a unique old-growth tract of about 42 acres adjacent to what is now a municipal park in State College, PA, where the mostly oak, hickory and maple trees escaped the loggers' blades.

Significantly, Maynard-Bean noted, the research demonstrates that simply assessing the abundance of invasive shrubs and native plants in a forest can minimize the perceived negative impacts that invasive shrubs have on native plant numbers.

"We found that seven years of invasive shrub removal boosted natural regeneration of native plants that exceeded the abundance measured in unmanaged forest understories with low levels of shrub invasion," she said. "In this study, in which invasive shrubs have been prominent in the understory for more than 20 years, an ambient sampling approach underestimates the effect of invasive shrubs and the benefits of their removal."

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