Feb 18 2009
If you attended the 2008 Master Gardener Mini-College, perhaps you heard Doug Tallamy speak about the importance of native plants to the conservation of bird and insect species. A seminal paper, which provides data in support of Tallamy’s arguments, was recently published in Conservation Biology (Burghardt, Tallamy and Shriver. 2009. Impact of native plants on bird and butterfly biodiversity in suburban landscapes. Conserv Biol. 1:219-24).
Burghardt and colleagues measured the diversity of birds and caterpillars (which are, of course, the larval or juvenille form of butterflies) in 12 suburban yards in Pennsylvania. Six yards were landscaped almost exclusively with native plants (43% native and 6% exotic plant cover), and the other six were landscaped with exotic shrubs and groundcovers (although, native trees were present on these properties; 18% native and 26% exotic plant cover).
The abundance of caterpillars (the larvae of butterflies and moths) was 4 times greater on the ‘native sites’, relative to the ‘exotic’ sites. In addition, the number of different species represented by these caterpillars was 3 times greater on the ‘native’ sites, relative to the ‘exotic’ sites. Approximately 19 species of bird were found at the native sites, compared to 11 species at the ‘exotic’ sites. Mean abundance of birds at the ‘native’ sites was 17, compared to 11 birds at the ‘exotic’ sites.
Why do yards landscaped with native plants contain a greater abundance and diversity of birds and butterfly larvae? Burghardt and colleagues hypothesize that greater food availability for caterpillars at ‘native’ sites creates greater food availability for birds at such sites. Because many plant feeding insects can not feed exotic plants, and because many birds rely upon insect protein (rather than seed protein) to rear their young, planting native plants seems to cascade up the food chain – fostering an increase in abundance and diversity of plant feeding insects, which in turn fosters an increase in abundance and diversity of insect-feeding birds.
What does this mean for the home gardener? A yard landscaped with native plants can be beautiful, may reduce your fertilizer and water use (if you zone your plants accordingly, and if the natives are adapted to your soils), and can help to conserve biodiversity in your area.