Your lawn is an 'ecological dead zone.' The case for replacing it with native plants

Fall is the time to plant shrubs and perennials for next year, and as people are planning, an entomologist wants them to think about their yard as a habitat.

Doug Tallamy is a professor in the Department of Entomology and Wildlife Ecology at the University of Delaware and the author of four books about nature. His most recent book is The Nature of Oaks: The Rich Ecology of Our Most Essential Native Trees. He’s started a sort of movement to convince people to give up some of their grassy lawn and instead plant native trees, shrubs, and plants.

The Allegheny Front’s Kara Holsopple spoke with him about it.

Kara Holsopple: Why should people choose native plants instead of a lawn?

Doug Tallamy: There are many reasons. We’ve got to start right at the beginning. We humans are part of nature. We depend on the life support systems that nature delivers us every day, but the way we landscape excludes nature and pretends that we are separate from nature. Lawn doesn’t do any of the things that we need every landscape to do, and there are four of them I always talk about: sequester carbon, manage the watershed, support a food web and support pollinators.

Lawn is the worst plant choice for all of this, and we’ve got over 40 million acres of lawn. We have this notion that what’s happening in parks and preserves is good enough. Well, it’s obviously not good enough because we just lost three billion breeding birds in North America. We’ve got global insect decline. The UN says we’re going to lose a million species in the next 20 years. That’s not working. So we now need to do conservation outside of parks and preserves. That means our private property, and lawn is the lowest hanging fruit that’s out there because it’s an ecological dead zone.

Holsopple: In your book, Nature’s Best Hope, you introduce the concept of the Homegrown National Park. What is that and what does it look like?

Tallamy: If we have 40 million acres, and that’s a 2005 statistic, so, you know, we have more than that now, what if we cut that area in half and replanted it in productive plants to produce those ecosystem services, to regenerate biodiversity instead of destroy it? That would give us 20 million acres to put towards conservation where there’s now lawn.

So I start adding up how big is 20 million acres? And I added up all the major national parks in the country. It’s bigger than all of them combined, including Denali, which is huge. And I said, ‘Well, gee, we’re doing this at home. Let’s call this Homegrown National Park.’ So it looks like that oak tree that’s in your front yard. It looks like plantings under that tree, like groundcover, wild ginger, mayapple, spring ephemerals. [It’s] any productive, native plant that is not lawn.

Holsopple: You talked about ecological services. Can you just say a little bit more about what those are? 

Tallamy: These are all the things that keep us alive on planet Earth. How about oxygen? Pretty important. Plants make oxygen. How about clean water? Plants capture the water as it falls from the sky. They slow its journey to the sea where it becomes too salty to use. They allow it to infiltrate into the soil, which keeps it clean. They prevent floods.

You don’t have the flowering plants unless you have the pollinators that allow them to reproduce. So this is a feedback loop. You need the plants to have the pollinators so that you have the plants. But if you don’t have the plants, the pollinators have specialized on, you don’t have the pollinators.

Native plants also support the food web. This is the one everybody skips. That chickadee that wants to breed in your yard requires 6,000 to 9,000 caterpillars just to get their babies to the point where they leave the nest. They continue to feed them caterpillars for another 21 days. You’re talking about tens of thousands of caterpillars to make one clutch of a tiny bird and think of all the birds out there. Those insects come from native plants, not from the non-native plants that our insects are unable to eat because they don’t have the adaptations to eat them.

Why do we need these things? Because insects are the little things that run the world. And why do we need birds? Why do we need the other animals? They’re the things that run the ecosystems that produce these ecosystem services. Every time we lose a species from our ecosystem, it’s more unstable and less productive.

When you look at your yard and you’ve got one-thousandth of the number of species in your yard that you had before it was your yard, that’s ecosystem destruction. And, you know, if you’re the only person that does, that’s OK. But when we do it over half the country, it’s not OK.

This notion that we’re separate from nature is what’s killing us. We are totally dependent on nature. We have to learn to live together because we need ecosystem services everywhere, not just in parks and preserves. And we all have this notion that nature is there for entertainment, but that’s it. That’s killing us.

Holsopple: I know that there is some pushback in the ecology world about this intense focus on native plants. Does it have to be all or nothing? Does it have to be all native plants? What about other plants that are non-native, that are in the same family as native plants or behave like native plants? 

Tallamy: We have been studying that issue for the last 15 years. So why native plants? Because our insects are adapted to eating native plants. I use the monarch [butterfly] as an example. It’s a host plant specialist on milkweed. You can have all the crepe myrtle, you can have all the buckthorn, all the multiflora rose and all the burning bush and porcelain berry and all these things that have escaped and displaced our native plants in our natural areas. And you won’t make a single monarch.

That’s true for 90 percent of the insects that eat plants. The ecologists giving pushback against native plants are not entomologists. They’re botanists who don’t look beyond the plant. They’re not looking at the food web. They think if a plant makes a berry, that’s good enough. We need plants that make the insects and the berries, not just the berries.

Birds don’t reproduce on berries, they reproduce on insects. Ninety-six percent of birds are rearing young on insects. I talk about birds because they’re the charismatic megafauna these days. It’s not that they’re the only things that eat insects. Insects are a critical component of the food web, even aquatic food webs.

What about non-natives that act like natives? We did a common garden experiment looking at congeners, so things like Norway maple versus red Maple, Norway maple is in the maple family. It’s “Acer,” in the same genus. Does that support as much as our native maples? We did that with generic comparisons and on average, even among congeners, closely related individuals, it reduced insect use by, what was it, 65 percent? Yeah.

So it’s not as bad as when they’re not related because then it reduces it by 78 percent or something. So some insects eat some non-natives, but it’s not nearly what we need to have viable food webs.

And my question is, what is the benefit? Our major invasive woody plants are all ornamentals that have escaped from us bringing them in. And along with that, we brought a whole bunch of diseases that have devastated our forests. The cost is extraordinary compared to the benefit of being able to use a Chinese plant. There are some exceptions like willows. The species reduction, when you use weeping willow versus the native willow, is not that much, and crabapples are pretty much the same thing.

Anything that hybridizes with the native easily means it is closely related. Insects interact with plants through chemistry, and if the chemistry is so similar that they don’t recognize it, they’ll use it. But most don’t do that. Those are exceptions. I always hear about those exceptions, but we can’t landscape based on exceptions because that means the general rule is it won’t work.

Holsopple: We always have the peony example among our staff. A lot of us have gardens and we think about planting native plants. And last year, one of us said, well, what about if I just want a couple of peonies in my garden? Can I have a couple of peonies and, you know, and the rest native plants? 

Tallamy: Yes, you can. You know, one of the most important studies we’ve done was done by my grad student, Desirée Narango in Washington, D.C., looking at what kind of landscape do you need to sustain a chickadee population and what kind of landscape will not sustain a chickadee population.

So it was a four-year study, NSF funded, published in Proceedings of National Academy of Sciences. Chickadees forage on woody plants, so that’s what she looked at. She found that when you exceed 30 percent of the plant biomass in your yard as being woody non-natives, that’s when the chickadee population becomes unsustainable. That’s when birth rates do not equal death rates. So it gets smaller every year. But it does suggest there’s an area for compromise.

You can have your ginkgo, you can have your peonies, you can have these other things, as long as they don’t exceed 30 percent of the plant biomass. And there’s nothing that beats oaks in 84 percent of the counties of North America. So if you have, you know, one or more oaks in your yard, you can have your peonies. It’s OK.

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