The Natural Patriot

The creeping dominance of suburbia by non-native ornamental plants is depleting the abundance and diversity of native animals too—but landscaping with native plants can help reverse the trend.  Yes, we can! (OK, I am still in the grips of Obamaphoria)

Non-native plants now dominate the base of the food web in human-inhabited landscapes (which is to say, most landscapes) of North America and many other regions, largely unnoticed as we go about our daily business.  Sure, that Wisteria looks nice.  But does it taste nice–that is, to the creatures that have to make a living on it?  How has this creeping transformation of outdoor space affected the rest of the ecosystem?

I have written before on the interesting work by ecologist Doug Tallamy of the University of Delaware on this topic.  Now a new paper in the journal Conservation Biology has tested his thesis that introducing non-native plants breaks the evolved links in the food chain that support wildlife, and contribute to, well, making our spring (and summer) silent. The authors of the new paper selected six pairs of sites in suburban Pennsylvania, matched by size and approximate plant cover, in each of which one member of the pair was landscaped entirely with native plants and the other with the typical mix of Eurasian grasses, Asian shrubs and native canopy trees.  Total plant cover and diversity were similar between treatments.

The results were dramatic.  The properties landscaped with native plants supported 4 times the caterpillar biomass, 3 times the caterpillar species richness, significantly higher bird abundance and diversity, and 8-fold higher abundance of bird species of “regional conservation concern”, that is, declining or endangered in the local region.  In other words, even on the small scale of most yards or medium to large house lots, providing the right kinds of plants can make a major difference in spport of wildlife and biodiversity.  In fact, the benefits of native vegetation are probably even more pronounced than their results suggest because the authors attempted to choose sites in their study with similar levels of plant diversity, so the non-native sites were more diverse than most suburban yards.

What’s behind these results?  The likely mechanism is that the host specificity (i.e., picky eating habits) of many insects prevents them from thriving on non-native plants–many of which have become popular in the nursery trade precisely because insects don’t like them– and since most birds feed their young on insects, this broken link cascades up the food chain to reduce bird abundance and diversity as well.  The latter point was also supported by the finding that insect-eating birds declined even more than birds with other diets in plots with non-native plants.

Given the unabated breakneck growth of the human population and associated built environment, a critical key to conserving a significant remnant of earth’s biodiversity would seem to lie in actively engineering the human-dominated environment to make it hospitable to other organisms. This paper offers hope that fostering native vegetation can significantly further that goal.  That’s what I’m talking about. More details on the home project as the weather warms up and I can venture outside again . . .

[Source: Karin T. Burghardt, Douglas W. Tallamy, and W. Gregory Shriver. 2009. Impact of Native Plants on Bird and Butterfly Biodiversity in Suburban Landscapes. Conservation Biology 23:219-224.]