The other day I spent some time poking around the internet looking for information about why on earth the “HarborPark” behind the John Joseph Moakley United States Courthouse seems to be a rugosa rose monoculture. Rugosa roses are hardy, neglectable plants, but they’re hardly the only species that can be ignored, and the Invasive Plant Atlas of New England is a bit nervous about them because they can form dense stands that exclude other plants. They’re not even native; they escaped cultivation in Nantucket in 1899, and have been spreading ever since. Why would “HarborPark’s” designers choose to plant such vast hedges of a plant of questionable provenance in a landscape designed to celebrate the meeting of Boston and the sea?

I found my answer in this commentary by Laurie Olin, one of the landscape architects who designed the “HarborPark.” (I’m not sure who designed the new Frankenword with no space in the center.) I’ll save you the trouble of clicking through to page 22; it reads in part:

“The first plants on our [Laurie Olin and Carol Johnson] list came immediately: bayberry, Rosa rugosa, blueberry, sumac, and pines. As we worked on it we realized that, just as American society has benefited from infusions of immigrants from other parts of the world, our palette of plants has become similarly enriched. Many standard, even favorite, plants in our streets and gardens are hardy immigrants from northern Europe, the Mediterranean, and Asia. Some of these we subsequently included to make another point: that our landscape is a cultural phenomenon built up over decades and centuries, like our cities, our way of life, and our legal system. Purists’ views that demand the use of only native species in an urban region are limiting or worse, and are as fraught with contradictions and distortion as any other doctrinaire form of ‘ethnic’ or ‘original’ purity when dealing with living systems.”

That’s an interesting point of view, and one I would have accepted with an urbane, multicultural, Northeastern-liberal nod of the head if I hadn’t been thinking about Doug Tallamy’s work lately.

Tallamy is a professor of entomology at the University of Delaware. He cares about bugs, especially caterpillars; his book Bringing Nature Home is chock-full of pictures of fuzzy, creepy-crawly goodness. Tallamy gave a talk for Grow Native Cambridge last week, but he didn’t say much about plants. He talked about bugs– and what they eat, what they don’t eat (like rugosa roses), and what eats the caterpillars.

Here’s Tallamy’s grossly oversimplified thesis; caterpillars and insects are at the base of a big fat food chain for our birds, frogs, salamanders, snakes, mice, and larger animals like foxes (about third of their diet is bugs! I guess that’s why the Fantastic Mr. Fox has to drink so much cider.).  If you want birds, you need bugs.

The problem is that modern landscaping doesn’t give the bugs any food. Most plants have natural poisons in them to keep bugs from eating them. Over the past several million years, various insects have evolved to be able to digest the poisons of specific types of plants safely.

When we bring in those “hardy immigrants from northern Europe, the Mediterranean, and Asia,” we’re installing plants that our bugs can’t eat, and won’t be able to eat for millennia. Oak trees support more than 500 types of North American butterflies and moth caterpillars: Phragmites australis reeds, which have been in the U.S. for over 300 years, support just five– although they’re eaten by more than 170 different types of insects in Europe.

Those new inedible lawns and non-native ornamentals are a large part of the reason that many wild bird populations have dropped by more than 50 percent in the last 50 years. Over 40 million acres of the U.S. is now lawn, filled with European grasses that take up room, but don’t contribute to the food chain.

Don’t despair! If you have any space at all in your yard, deck, or window box, you can grow local plants that support local insects, and birds, and frogs, and foxes–without turning your yard into a jungle and scaring the neighbors. Tallamy has lists at his web site, and the New England Wild Flower Society and Grow Native Cambridge are full of ideas. Tallamy referred to growing insect-supporting natives as “citizen conservation.” It’s exciting to think that you can help save the ecosystem in your own back yard.

Now, mind you, I myself am a member of an invasive foreign species. Despite my genealogist Aunt Betsey’s best efforts, my family has yet to discover any Native American ancestry. We’re interlopers, and I’m going to continue to grow exotic plants I like to eat: tomatoes, strawberries, lettuce. But I’m also going to rip out a few aging rhododendrons and replace them with shrubs that can support other life. I can share.

Yes, as Laurie Olin wrote, “our landscape is a cultural phenomenon,” and insistence on “ethnic’ or ‘original’ purity” can be obnoxious when dealing with living systems. But our landscape is not just a cultural phenomenon, even in cities, much as we’d like it to be. It is a living system that can either support local wildlife, or kill it. You can’t just tell a cecropia caterpillars to start eating Chinese food for a change. If cecropia caterpillars can’t find food they can digest, like a black-cherry tree or an alternate-leaf dogwood, they die, and an entire ecology dies with them.

The Moakley Courthouse’s rugosa roses aren’t the worst choice for the site. They do support a certain number of American species though far fewer than in its native ranges. But they take up a huge proportion of the planting area compared to the token natives plunked in side-spaces–and compared to the non-native pines, crabapples, honey locusts and plane trees. Is it really respectful to immigrant cultures to devote half a garden to a single species?

If those ratios were reversed, odds are you’d see butterflies visiting from the Boston Harbor Islands. You might really get a sense of the “living system,” of Boston, where people, and plants, and animals have a place. As it is, what you see is our self-centered neglect of the natural world.