New Study: Non-native Plants Reduce Insect Diversity

Acer circinatum (vine maple)

Natives like vine maple (Acer circinatum), trump nonnatives for restoring biodiversity


As if we need further proof
, a new study published recently in Ecology Letters demonstrates that native plants do much better at supporting local insects than nonnative species, and shows that nonnative plants are exacerbating biodiversity loss with their inability to support many insect herbivores.

The authors, Douglas Tallamy (Bringing Nature Home) and Karin Burghhardt, planted test gardens with both native and nonnative tree species and collected data over a three-year period. They measured the insect herbivore species and communities that were using the plants, and compared native trees to nonnative trees of two types: Those with close native relatives in the region and those that had no close native relatives.

They found that nonnative trees with a native relative (in the PNW, think scarlet oak, which is related to Garry oak) host and support fewer species of insects than the native counterpart, and that few of them were unique to that species of tree. The result was even more striking with nonnative trees that had no native relative in the region (such as golden chain tree, a European species).

The study also found that young insects, which are most supportive of an ecosystem, were found on the native trees. Adult insects, on the other hand, may be found on plants, but for various reasons—to rest, to warm themselves, breed, etc.

Essentially, when the diversity of insect herbivores—which are the basis of the food web—plummet, so too do all the species that rely on them for food. If you’re not particularly fond of insects, think of it this way: In spring and early summer, when insect eggs are hatching and larvae are feeding, most birds are wholly dependent on insects to feed to their young, as well as to keep their own strength up. And most other wild species rely on insect herbivores in one way or another.

So, more evidence that natives are the answer for restoring biodiversity, while most nonnatives are problematic. When selecting plant material—even in an urban area—choose plants that help the environment and its community members. Go for the native oaks, pines, maples, willows, etc., with their plethora of insects. There’s almost always a native option!

 

© 2015 Eileen M. Stark

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