Ever wonder whether it really makes a difference whether or not you plant native species? Do native plants do a better job of hosting local insect communities than their non-native counterparts? Now a University of Delaware study shows that not only are natives much better at sustaining local insects, planting non-natives actually compounds the problem of declining species diversity because non-natives support fewer herbivore species across our landscapes.

A yellow swallowtail enjoying a purple coneflower at the Children’s Garden at Suffolk County Farm, part of the National Pollinator Garden Network’s Million Pollinator Garden Challenge. Photo by Mary Howe.

The research was conducted by Karin Burghardt and Doug Tallamy, who is professor of entomology at University of Delaware and author of the bestselling book, Bringing Nature Home. Together they published their findings in a recent issue of Ecology Letters: http://onlinelibrary.wiley.com/doi/10.1111/ele.12492/abstract To conduct their study, they planted imitation yards with different common garden selections of both native and non-native tree species, and then collected data over a three-year period, measuring the herbivore communities and species found on those plants.

Tallamy said that finding young herbivores on a plant is a good indication of how that plant is supporting the local ecosystem, as opposed to finding adult insects, which could be on a plant for a number of reasons, such as resting or looking for a mate. “The relationship between the adult and food is far weaker than the relationship between immatures and food, so when you find adults on the non-natives, it doesn’t mean that much. When you find immatures, that’s what you should be measuring,” Tallamy said. “Those are the plants that are creating those immatures, and so we do get significant differences between the immatures that are using native plants versus the immatures using non-natives.”

He also stressed that that native plants always do the best job per tree of supporting herbivore communities when compared to their non-native counterparts. This study expands the understanding of that fact by looking at whether that lower per tree diversity is magnified further by non-natives hosting more similar communities across trees species and locations.

Burghardt said the goal of the research was to understand how the composition of the plants that homeowners plant in their yards affects herbivore communities. “What the gardens we constructed for the study are trying to replicate are landscaping decisions that people might make if they wanted to support native insect communities that in turn support much of the diversity around us.”

Learn more about how what you plant affects biodiversity at the Long Island Native Plant Initiative’s biennial Native Plant Conference on Saturday, October 24, at Farmingdale State College. LINPI’s Registration Flyer includes a symposium agenda and list of speakers.

Robin Simmen is Community Horticulture Specialist for CCE Suffolk. She can be reached at rls63@cornell.edu or at 631-727-7850 x215.