Further evidence on the value of planting native plants

by Irene Shonle, Gilpin County

If you didn’t see it, the Smithsonian Magazine recently highlighted a study which was just published in the Proceedings of the National Academy of Sciences last month (Oct 2018) (http://www.pnas.org/content/115/45/11549).

The Smithsonian’s headline was catchy: Ecologists have this simple request to homeowners: plant native. In it, they summarized the results of a newly released survey of Carolina chickadee populations in the Washington, D.C., metro area which shows that only when an area (a backyard, park, etc), has a proportion of at least 70% native species, will a native bird such as the chickadee be able to survive.

I didn't have a picture of a chickadee, but here are Pine Grosbeaks and finches as some other examples of native birds

 This is because nonnative plants lack an evolutionary history with native fauna and support insect communities that are less abundant and diverse. Given that 96% of all bird species require soft-bodied insects such as caterpillars in order to rear a clutch of young (6,000-9,000 of them!), this lack of insects can spell doom for birds. 

Hummingbird moth caterpillar on native fireweed

According to the study, “most insectivorous birds are absent or declining in urban areas, yet no study has tested whether nonnative plants impact bird populations via food limitation. We monitored reproduction and survival of Carolina chickadees within residential yards and found that when nonnative plants increased, both insect availability and chickadee population growth declined.”  This meant that Carolina chickadees (Poecile carolinensis) had to switch diets to less preferred prey and produce fewer young, or forgo reproduction in nonnative sites altogether. The findings can be extrapolated to habitats beyond the mid-Atlantic U.S. “The general trend will almost certainly hold true, no matter where you are”.

The lead author, Desirée Narango, is quoted in the Smithsonian article: “There has been a lot of press lately about drastic insect declines and insectivorous bird declines. We hear a lot in conservation that things are in trouble, and they are. So I think this study is a nice example of something that we can actually do at home to make some positive ecological change.”

Native plant garden at Chatfield Botanic Garden

The researcher’s article ends with a recommendation that, to promote sustainable food webs, urban planners and private landowners should prioritize native plant species.  I love that this is something that we can all do, in our back yards, to help.  How often can you do that?  Get out there and plant some native plants! 

Goldenrod makes an excellent habitat plant