Carol Andrews, Past President of the Wild Ones Arrowhead Chapter in Duluth, Minnesota sent me this story and I couldn’t wait to share it. Researchers participated in a long-term project in the Arboretum at Pennsylvania State University which involved the removal of 18 invasive shrub species in 2009. As they monitored for any re-occurance of non-native species over the next seven years, they found an increase in native plant diversity through the passive regrowth of understory species and some limited regrowth of overstory trees through natural regeneration.*
Because this 42 acre tract of old growth forest known as Hartley Wood was near a municipal park and a large residential area, it had become overrun by non-native species (likely introduced by uncaring shoes, clothing and tires). Non-native invasive shrubs, as we’ve all witnessed, create a dense, greedy understory typically non-usable by native wildlife, while native shrub understory becomes part of a healthy and stable forest ecosystem shared by birds, insects and other forest wildlife.
* Regrowth of native overstory trees was not as observable not only because of length of time for regrowth, but also because of known deer browse. There was also the closed-canopy which limited light conditions during the growing season.
So what does this mean for us?
Regardless whether you’re working in an area which has been disturbed time and again by development or in an area which may be old field or an old growth forest, the findings of this research confirms the need to work in an area small enough and affordable enough to manage from one season to the next. Remove all invasive species all at once, and then plan to continually monitor that area for any regrowth of non-native species.
In a totally disturbed and probably even filled area, developing a native habitat will require a lot of work because you’ll be “starting from scratch” — any native plant seed or root systems will likely have been buried or destroyed. But I’m thinking in an old field area, you might see regrowth of some pre-existing native species. I know we did when we first began eradicating the Wild Parsnip from the old field next to the WILD Center. But we didn’t wait for seven years. After the third season of treatment, we added to the already regenerating native species by seeding the site with prairie species.
In an old growth forest area, I think I’d do the same thing — remove all invasive species all at once from an area the size you can handle successfully, and then plan to continually monitor that area for any regrowth of non-native species. The cited research indicates that native ephemerals, ferns and other typical understory plants should regenerate on their own. If you’re not willing to wait long-term for complete regrowth, you can always supplement with plants purchased through a reputable native plant nursery or your local Wild Ones chapter plant sale.
Read the complete study Invasive shrub removal benefits native plants in an eastern deciduous forest of North America. See also photos.