Eugene Weekly : Gardening : 11.11.10


A Call to Action 
We can help restore wildlife diversity in our yards
By Rachel Foster

Osoberry. Photo by Hendricks Park staff

Once in a while, something you’ve known for a long time suddenly hits home with a force you never felt before. I was loading up some plants at Doak Creek Native Plant Nursery when the nursery’s proprietor, Cynthia Lafferty, handed me something she wanted me to read. It was the cover story in a trade publication from Fourth Corner Nurseries in Bellingham, Wash., entitled Gardening for Life. The article was written by Dr. Douglas Tallamy, a professor of entomology and wildlife ecology at the University of Delaware.

Lafferty had been shocked by some statistics cited in Tallamy’s article, and so was I.  Fifty-four percent of the land area of lower 48 states is now in towns and suburbs. We’ve connected them with four million miles of roads, the paved surface of which, Tallamy says, is “nearly five times the size of New Jersey.” Forty-one percent of the remaining land is under some form of agriculture. (That number that is actually shrinking, as suburban sprawl continues at the rate of more than two million acres a year.) Add up those numbers. That means we have taken over 95 percent of nature and made it unnatural. Ninety-five percent

Much of the land that’s left is in small fragments and is impacted by humans to some degree, including some of the paltry 2.6 percent of the lower 48 that’s in designated wilderness. Fragmented land is especially prone to degradation and loss of species as creatures become more vulnerable to unfamiliar predators and alien plants move in. Alien plants have invaded 100 million acres of land across the U.S., an area that is expected to double in the next five years. Alien plants too often out-compete natives, forming monocultures that don’t provide what local wildlife needs to survive.

If you believe that biodiversity matters, these are shocking numbers. Species have been shown to disappear, over time, in direct proportion to habitat loss. No wonder a third or more of birds native to the U.S. are in rapid decline. At this point, a major loss of biodiversity is already under way, especially in the densely developed  Eastern states. Tallamy says 40 percent of Delaware’s plant species are rare or extinct, and 41 percent of its forest birds no longer nest in the state. What Tallamy wants us to understand, though, is that gardeners are in a position to make a real difference. There is ample evidence that wildlife can coexist with humans, if humans are willing to manage their environment to accommodate wildlife. 

The entire food chain rests on the photosynthetic ability of plants. Animals either eat plants, or they eat other animals that do. The largest group of animals that convert plant food into animal food is insects. And insects sustain much of the rest of the food chain, including 96 percent of terrestrial birds. So many animals depend on insects for food that “removing insects from an ecosystem spells its doom,” Tallamy says. Human-dominated landscapes could support far more insects, and more biodiversity, than they do at present. Look at our 40 million acres of mown grass. All the lawns that represents, and most of the plants around them, contribute very little in the way of habitat for insects.  

What we need are native plants, and lots of them. Tallamy’s research shows that native trees and other plants support 29 times more biodiversity than non-native ornamentals do. That’s not because those ornamentals are inherently less useful to animals: where those plants are native, they support animal life as well as our own native plants do here. The point is that, with a few exceptions called generalists, the insects within a given ecosystem depend for food on the species with which they evolved. Even the generalists can utilize a greater variety of native plants than non-native. This story is laid out persuasively in Bringing Nature Home, a book authored by Tallamy and published by Timber Press. 

Loss of biodiversity through habitat destruction may be as great a threat to humanity as global climate change, and we are not doing a great job of minimizing either. Unlike with climate change, however, the results of individual human efforts to help preserve biodiversity in gardens are readily observable. Native plant gardeners report more insect visitors, more birds, more salamanders, lizards and frogs. Yes, some of  their plants get eaten, but that’s the point.  

The article by Douglas Tallamy, Gardening for Life, is available on line. Go to and click on “About Native Gardening.”

Rachel Foster of Eugene is a garden writer and consultant. She can be reached at rfoster@efn.