"Native plants in a Forest understory contribute to the health and stability of woodland ecosystems".............."It is a fact that native shrubs don't reach the same density in the understory as invasive, non-native shrubs do, having dire implications for bird, mammal, insect and forest amphibian communities"............"In eastern deciduous forests of North America, invasive, non-native shrubs are increasing in richness and abundance at the expense of native species".......... "Using an non-native shrub removal experiment over a 7 year span starting in 2009, Penn State Researchers have provided us with insight into the effect of repeated removal of a suite of 18 invasive shrub species dominated by border privet"............... "In a region in Pennsylvania known as Hartley Wood, non-natives were removed from five 20-m-diameter treatment plots"............. By 2016, there was an increase in native plant diversity, understory species abundance, and overstory tree species regeneration for individuals under a meter in height"..........."For plants 1 to 4 m in height, the non-native removal treatment has a positive effect on understory woody species, but did not result in the regeneration of native overstory trees"............. "A lack of overstory tree regeneration to greater heights is not surprising, given the time frame and the closed-canopy conditions, as well as other factors such as white-tailed deer over-browsing"................While this research is both relevant and illuminating, the question I pose is what is the cost, feasibility and reality of this type removal paradigm actually being implemented over large tracts of our species-compromised open space?

https://phys.org/news/2019-05-native-regenerate-invasive-shrubs.html

Native forest plants rebound when invasive shrubs are removed

by Pennsylvania State University

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.

Seven years of invasive shrub removal from the Hartley Wood in The Arboretum at Penn State promoted plant diversity and facilitated passive natural regeneration of native canopy tree seedlings, understory woody species and woodland herbaceous species. Among them (top left to right) Indianpipe, mayapple and hepatica, (bottom left to right) spotted geranium, waxflower shinleaf and mapleleaf viburnum. Credit: Erynn Maynard-Bean

"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.

Non-Native Asian Kudzu on floor and climbing and 
"drowning" the Georgia Forest

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, where the mostly oak, hickory and maple trees escaped the loggers' blades. A massive white oak that died there in 2000 was determined to have germinated around 1673. But likely because of its proximity to many landscaped homes, the Hartley Wood has been beset by an invasion of exotic plants, and Arboretum managers hope to eliminate them.

Significantly, Maynard-Bean noted, the research demonstrates that sampling the abundance of invasive shrubs and native plants in a forest can minimize 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."

Non-Native Asian Honeysucke(behind the man)
invading and taking over large expanses
of the northeastern forest understory

This research has allowed the native forest plant community to respond to invasive removal over nearly a decade, and highlights the capacity for that system to rebound, pointed out Kaye, whose research group in the College of Agricultural Sciences has been studying the impacts of woody shrub invasion on eastern forest dynamics for even longer.

The findings of the study, published recently in Invasive Plant Science and Management, are important, Kaye explained, because invasive shrubs are increasing in abundance at the expense of native species across eastern deciduous forests of North America. Interest in invasive shrub removal to restore native habitat is growing but forest managers are not sure about how much natural regeneration of native plants they can expect.

"A lot of people think that when you remove invasive shrubs you have to plant natives, and that is obviously helpful but difficult to afford on a large scale," Maynard-Bean said. "But there are native plants in the forest that are mixed with the invasives, and if you maintain the removal, the natives will come back in and take over."

The research is relevant because eastern deciduous forests are becoming more fragmented as urban and suburban areas extend into forests, and associated edges and open spaces have allowed invasive shrubs to make inroads. That does not bode well for wildlife, Maynard-Bean said.

"Native plants in the understory contribute to the health and stability of the forest ecosystem," she said. "Native shrubs don't reach the same density in the understory as invasive shrubs do, and that has implications for bird, insect and even forest amphibian communities."

more information: Erynn Maynard-Bean et al, Invasive shrub removal benefits native plants in an eastern deciduous forest of North America, Invasive Plant Science and Management (2019). DOI: 10.1017/inp.2018.35