Beautification of parks and roadsides is something heritage planners have to consider, but the actual decisions tend to get handed to a landscape architect. We were involved a few years ago in an urban park revitalization project with one of the most celebrated landscape architects in America. He proposed to make the park a kind of botanical history museum containing specimens of tree species that had been brought to the city from overseas over a period of three centuries. At the time, everyone agreed : What a wonderful idea – connecting horticulture with history!
If anybody on the planning team had read Douglas W. Tallamy’s book Bringing Nature Home: How You Can Sustain Wildlife with Native Plants there’d have been a howl of protest. Tallamy cites several hair-raising examples of widespread environmental destruction wrought by alien organisms and invasive plants that were brought from overseas to beautify America. Two of the best known are the chestnut blight, called the single worst environmental disaster in North American history, and the wooly adelgid, an alien insect that’s at this very moment busily wiping out old-growth stands of hemlock forest. Tallamy’s central point is that we owe it to the environment to plant only native species, which provide food for our increasingly beleagered wildlife and avoid apocalyptic risks to the ecosystem.
And just what is a “native species” anyway? Apparently there are lots of exotics that, after living on this continent for a few hundred years, are generally considered “naturalized.” Not so, says Tallamy. He defines native as having the ability to support a large number of insect and animal species. Non-native extends even to other parts of the continent: a Douglas fir from the Pacific Northwest is worthless to species living in the eastern states.
A fascinating point Tallamy makes is that most plants have developed chemical defenses to make their leaves unpalatable to most insects, but each species of caterpillar has evolved specialized abilities get past certain kinds of defenses and feed on leaves that are inedible to others. Our North American caterpillars have not developed the ability to eat leaves of most alien plants. But why all the fuss about caterpillars? We’ve all been raised believing a caterpillar in the garden is a pest. Nurseries have, in fact, convinced people to buy exotic plants because they’re immune to the depredations of caterpillars and other insects. In fact, the caterpillar is a most generous beast. It provides food for most birds, especially during critical nesting periods, and forms the base of a food pyramid that’s critical to the whole ecosystem. A yard full of foreign nursery stock may look green and natural, but it might as well be paved with asphalt if you’re a caterpillar, or an animal that’s looking to feed on one
The real point of this book is that landscaping badly needs to be rethought. We need to realize that what we’ve thought of as simply nice patches of green lawn and pretty flowers are actually deadly in terms of the effect on biodiversity. As Tallamy puts it, landscaping should be about our taking steps to slow the rate of extinction. Planners are in a great position to carry this message forward and set good examples. As we develop byway beautification plans or park management plans or anything that involves plantings in a developed area, we have a responsibility to urge that non-native species be eliminated and replaced with true native species.