Basically, the book explains that 95 percent of native plant and animal species in North America are on course to become extinct within our lifetimes - but that we can prevent these extinctions by planting native plants. This is not what originally brought me to native plant gardening - I was just looking for plants that would survive without me needing to water them. But it is what should have brought me to native plant gardening, and what should bring other people to native plant gardening too - if only more people knew about it. The book persuasively argues that even though "some species such as the cougar, gray wolf, and ivory-billed woodpecker are just too reclusive to become our fellows" (page 37), the vast majority of plants and animals could survive very well in urban and suburban areas, coexisting peacefully with humans and even improving humans' experience of their homes, if humans simply bothered to plant native plants instead of non-native ones and allowed insects, birds, reptiles, amphibians, and so on to live in our yards. If all of us planted native plant gardens, we could rebuild functioning ecosystems on close to half the land in the lower 48 states.
Here are some of the major points the book makes (although it gives far more details to back up each point than I have time to include here):
- The consensus among landscape ecologists is that humans have already "taken and modified for our own use between 95 and 97 percent of all the land in the lower 48 states," leaving only about 3 to 5 percent of the land as relatively undisturbed habitat for plants and animals: "The 2002 USDA Census of Agriculture tells us that 41.4 percent of our land is in agriculture, which means that we have converted 53.6 to 55.6 percent of the land to cities and suburbia. As far as our wildlife is concerned, we have shrunk the continental United States to 1/20 its original size. And because our refuges and woodlots are not contiguous habitats, but survive as scattered islands from coast to coast, the effective size of undisturbed land in the United States is far smaller than those statistics indicate. When extinction adjusts the number of species to the land area that remains for the plants, mammals, reptiles, birds, and invertebrates of North America (something that will happen within most of our lifetimes), we will have lost 95 percent of the species that greeted the Pilgrims." (page 36)
- Dividing a piece of undisturbed land by placing even a narrow barrier through the middle of it, such as a single street with houses and lawns on each side of it, drastically reduces the number of plants and animals that can survive on either side of the barrier. For example, when the Panama Canal was built in 1914, a patch of forest that had previously stood atop a small mountain was transformed into Barro Colorado Island, separated from the nearest shore by less than a mile in most places. "Even though the island spreads over 3700 acres, a sizable chunk of real estate compared to most of the habitat islands we have created in North America, it is too small to sustain the populations of many of its original inhabitants. Sixty-five species of birds have disappeared from the island since 1914, and many others are on the brink of extinction. In all the years since Barro Colorado Island was cut off from the mainland, the extinction debt has been only partially paid. No one knows how long it will take before the island community reaches its final equilibrium number of species balanced between extinction and immigration. What is clear, however, is that the number of species that can be sustained on the island is a fraction of what existed on that same acreage at the beginning of the 20th century." Similarly, "Ashdown Forest in Sussex, England, the inspirational setting of A. A. Milne's Winnie-the-Pooh, has become entirely isolated by development. Since the 1920s, when Milne was writing his famous children's stories, the forest has lost 47 plant species." (pages 30-31)
- Even the "undisturbed" areas are increasingly disturbed - if not directly disturbed by people, then disturbed by invasive alien plants and animals that were introduced to this continent by people. "Even our most pristine national parks are under attack. The Great Smoky Mountains National Park, for example, has been invaded by over 300 species of alien plants." (page 85) There is no way to be certain which non-native plants will become invasive, especially because there is often a significant lag time between when non-native plants are introduced and when their populations suddenly explode to invasive levels, so the only way to be sure of preventing further plant invasions is to stop growing non-native plants. (Some non-native plants are, however, at lower risk of invasiveness than others, and websites such as the Hawaiian Ecosystems at Risk Weed Risk Assessment Page attempt to assess these risks. Personally, I Google the name of any non-native plant species I plant with the word "invasive" appended to the end of it and examine the results to determine how safe I think the plant is. I do plant some non-native plants - mainly food plants such as pumpkins, thyme, and rosemary.)
- Even if every non-native plant you ever buy does remain safely non-invasive, buying imported non-native plants still increases the risk of introducing invasive alien pests that destroy our ecosystems - such as chestnut blight, which rendered the American chestnut tree functionally extinct (i.e., too rare to contribute to the function of the ecosystem), or sudden oak death, which is now threatening to cause the extinction of our native oak trees. It is impossible to be certain that all invasive alien insects, insect eggs, and other tiny pests or diseased are removed from imported plants when they are brought into this country.
- Insects need native plants to survive. "Since the 1960s, an extensive body of theory developed by experts on interactions between plants and insects predicts that most [plant-eating] insect species should be able to eat only vegetation from plants with which they share an evolutionary history. Up to 90 percent of all [plant-eating] insects are considered specialists because they have evolved in concert with only a few plant lineages." (page 52) Tallamy conducted his own research on this: "One of the first things I did was compare the diversity and biomass of the insects that were developing on the four most common woody natives in our yard (black oak, black cherry, black walnut, and fox grape) with the insect diversity and biomass on our five most alien plants (autumn olive, mile-a-minute weed, oriental bittersweet, multiflora rose, and Japanese honeysuckle). Following standard protocol for sampling diversity, I found that native plants produced over 4 times more herbivore biomass than did alien species and supported 3.2 times as many herbivore species. When I compared natives and aliens in terms of their production of Lepidoptera (moths and butterflies) and sawfly caterpillars - the largest diet component of insectivorous birds - I found that the native plants in the study supported a whopping 35 times more caterpillar biomass than the aliens. We know that most bird populations are limited by the amount of food they can find, so if there is 35 times less food available for birds in habitats that comprise primarily alien plants, there will be 35 times less bird biomass in those habitats as well. No wonder our birds are struggling." (pages 59-61) In addition to finding zero insect specialists on the alien plants, Tallamy found that even insect generalists - the approximately 10% of plant-eating insect species that can eat a wide variety of plant species - did not do as well on non-native plants; the native plants produced twice as much insect generalist biomass as the non-native plants did.
- No, really: Insects do need native plants to survive. Even if a non-native plant species was introduced to the United States centuries ago, this is not long enough for insects to evolve to be able to eat it, so the non-native plant species still does not function as part of the ecosystem. For example, Tallamy points out that the common reed (Phragmites australis) was introduced to the United States more than 300 years ago. In its native land, it supports 170 insect species. In the United States, it supports only 5 insect species. Similarly, the paper bark tea tree (Melaleuca quinquenervia), which was introduced to the United States 120 years ago, supports 409 insect species in its native land but only 8 insect species in the United States. (page 285)
- No, really! It's true that nectar-drinking insects can drink the nectar of many non-native plants, which is why many people who want to attract butterflies to their yard plant non-native plants such as "butterfly bushes" (Buddleia davidii). But "not one species of butterfly in North America can use buddleias as larval host plants" (page 95). Butterfly populations are limited by the ability of the caterpillars to survive, so planting non-native "butterfly bushes" does nothing to prevent the butterflies' populations from declining and soon becoming extinct.
- Birds need insects to survive. "If you count all of the terrestrial bird species in North America that rely on insects and other arthropods (typically, the spiders that eat insects) to feed their young, you would find that figure to be about 96 percent - in other words, nearly all of them." (page 21) "For those who would like birds in their future, the statistics are truly frightening. Neotropical migrants, such as wood thrushes, warblers, catbirds, hawks, wrens, vireos, flycatchers, kingbirds, nightjars, swallows, tanagers, orioles - species that fly thousands of miles to Central or South America to spend the winter - have declined an average of 1 percent per year since 1966. Add up those percentages, and you're looking at nearly a 50 percent reduction in population sizes for many of our bird species within the space of 50 years. . . . Conservation ecologists such as Cagan Sekercioglu of Stanford University believe that one fourth of all bird species worldwide] will be functionally extinct (that is, so rare that they no longer contribute to the function of ecosystems) within a century." (page 30) Already, the majority of birds now seen in many American neighborhoods are invasive species from Europe such as sparrows and starlings, rather than the much broader diversity of native birds that ought to be here.
- Many other animals also need insects to survive. Virtually every meat-eating animal species on Earth relies on insects or the species that eat them for food. "And no wonder! Insects are unusually nutritious. Pound for pound, most insect species contain more protein than beef, and their bodies are extremely high in valuable energy." (page 21) For example, consider the common garden "problem" of aphids. "Throughout the world, simply because they are so common and so numerous, tiny aphids play an enormously important role in transferring the sun's energy from plants to larger animals. Anthony Frederick George Dixon, the famed British entomologist who dedicated his life to the study of aphids, once estimated that a single acre can support 2 billion aphids on vegetation and another 260 million below ground on plant roots. . . . One acre of alfalfa can indefinitely support aphids at a biomass equivalent to that of an elephant, whereas an elephant would eat all of the alfalfa in that acre in a matter of hours. Aphids usually exploit plants with few measurable effects on those plants, particularly when the plants are not water stressed." (pages 186-188)
- People need functioning ecosystems to survive, too. "If New York City were an isolated entity without connections to other parts of the country, it would collapse - in less than a week. Manhattan Island is an ecological sink; it requires the influx of great quantities of ecological resources that are generated in healthy ecosystems elsewhere (ecological sources) to sustain life. Manhattan Island does not have enough of its own water or food to support more than a few thousand people . . . The water that quenches the thirst of millions of New Yorkers comes entirely from an ecosystem that remains functional: the forested Catskill Mountains north of the city. The oxygen that New Yorkers breathe is generated by the vast forests of the Amazon and by populations of phytoplankton in the sea. The fish that are served in exclusive West Side restaurants come from oceans all over the world. The beef comes from rangelands across the continent, and the grain from fragile topsoils laid down during the last glaciation in the Midwest. Every natural resource required to keep New Yorkers alive comes from ecosystems that have not yet collapsed. If urban and suburban sprawl destroys the hydrology of the Catskills, New Yorkers will suffer. If we continue to employ the farming methods that lose tons of topsoil per acre every year, New Yorkers will be breadless. If we continue to overharvest the world's great fisheries, New Yorkers will lose fish as a source f protein. If we convert the rest of the world to an artificial habitat fit for humans but nothing else, New Yorkers, as well as the rest of us, are doomed." (pages 46-47)
Once this summer, she found a California whipsnake in my front porch flower garden and called me outside to look at it. We looked up pictures of local snakes on the Internet to find out what it was, and learned that it is rare to see California whipsnakes as low in the valley as where we are. We also learned that they are not poisonous and pose no danger to humans. We were delighted to see the snake in our yard, and hoped that it would continue to live here so that Susan could greet it regularly in the evenings and develop a name for it. But a few weeks later, one of our neighbors in the other half of the duplex mentioned to Susan that she had seen a gigantic snake in her yard and was terrified that it was poisonous, and when her neighbor on the other side of her heard her screaming at her kids to stay away from it, that neighbor came over and chopped the snake's head off. The snake we saw is very likely the same one whose head the neighbor chopped off.
Humans need to stop assuming that animals pose a threat to us and start bothering to research whether they actually do. Chopping the head off a random snake just in case it might might be poisonous makes no more sense than spraying a random plant with herbicide just in case it might be poison oak. If you don't know whether something is poisonous, don't touch it. Take a picture of it, and do some Googling until you find out what it is. You'll be surprised how much fun it is to get to know your non-human neighbors.
As I mentioned in my last post, our local ecosystem is not particularly healthy, despite the fact that we live in a rural area. The orchards and rice fields across the street from us do not contain native plants, and therefore do little to support the native insect population. The crop duster airplanes make things even worse. As a result, the only butterfly species I've seen all summer is a white one that I suspect is the non-native small cabbage white butterfly, which (being non-native itself) does not require native plants to survive. Even so, there are some native insects that benefit from my native plant garden. The milkweed beetles are in full force on my native milkweed right now, and would be unable to survive on any plant other than milkweed. Last spring, native leafcutter bees cut patterns into the leaves of my Western redbud, and both they and the native carpenter bees regularly visited my native annual wildflowers. Bluets and dancers (two kinds of damselflies) have been flitting around the yard all summer, eating other insects, and the other day I saw a dragonfly land on my coffeeberry - probably to eat the ants and aphids on it, since the coffeberry is currently covered with both. I was inside at the time, looking out the window at it, so the dragonfly was not scared by my proximity and remained on the coffeeberry for a good five minutes.
I did not know the names of many of these insects when I first saw them. One at a time, I used the Internet to identify milkweed beetles, carpenter bees, and several species of damselfly. I used it to identify the leafcutter bees when I saw them visiting my Clarkia flowers, and then I used it again to figure out that the holes in my redbud leaves had been made by the leafcutter bees. I did not need to find out what species any of these insects were, but it is surprisingly entertaining to find out what sorts of creatures one lives among. And after reading this book, I realize that many of them would not be here without the native plants - and that without them, the birds here would have an even harder time finding food for their young. And that the more other people plant native plants in their own yards, the more we can prevent the impending extinctions of 95 percent of the native plant and animal species of North America within our lifetimes - which is not just an aesthetic improvement, although it's certainly that too, but also essential to make our ecosystems strong enough to keep supporting us humans in our current numbers as well.
Here are some excerpts from other people's reviews of the same book:
"So the message is loud and clear: gardeners could slow the rate of extinction by planting natives in their yards. In the northeast, a patch of violets will feed fritillary caterpillars. A patch of phlox could support eight species of butterflies. The buttonbush shrub, which has little white flowers, feeds 18 species of butterflies and moths; and blueberry bushes, which support 288 species of moths and butterflies, thrive in big pots on a terrace. (Appropriate species for other regions are listed by local native plant societies.)
"You don’t have to cut down the lilacs, but they are doing nothing for the insects and birds. 'It's as if they were plastic," Mr. Tallamy said. "They’re not hurting anything, except that they're taking space away from something that could be productive." (from "To Feed the Birds, First Feed the Bugs" by Anne Raver, The New York Times, March 6, 2008)
"In all honesty until reading Bringing Nature Home: How You Can Sustain Wildlife with Native Plants by entomologist Douglas W. Tallamy I think I was rather avoiding the subject of native plant rearing. In asking myself why? I had to admit that I associated the largely misunderstood concept of native plant selection as a choice that would entail having to 'give something up.' After all, the name of my blog is Plant Whatever Brings You Joy, right? Once into Doug's book, however, I realized how myopic that thought was, and my world expanded into a much deeper understanding of the importance of maintaining native plants in our environment." (from Plant Whatever Brings You Joy)
"And though human beings like to believe they can proliferate in isolation from other species, it's not possible. Our race would exist a few short years without a sustaining ecosystem to support it. Dire though the consequences of a bug-less world would be, Tallamy argues that it's quite feasible to rehabilitate lost populations of insects and animals. The effort is not just imperative: it's appealing.
"Highways, high rises and parking lots are some of the major causes of habitat fragmentation and the resulting loss of biodiversity. Another--which many of us enjoy--is the great expanse of sterility known as the suburban yard. The suburban aesthetic is playing a huge role in the destruction of native plants and animals nationwide. There is exactly a 1:1 correlation between the amount of habitat and the species that can exist in that habitat: meaning, if we destroy 80% of a habitat--places where species can nest, feed, and move freely--we will lose 80% of the biodiversity in that space. And even though most Americans favor green around their homes, most of what we're growing is not feasible eating or housing for the bugs that feed our favorite animals, which are disappearing at alarming rates." (from "Bringing Nature Home: Fostering Biodiversity in Your Own Backyard" by Isabel Cowles, The Huffington Post, April 30, 2010)
"This book makes the best argument I have ever read about the absolute importance of the use of native plants in our gardens, and should be required reading for every landowner." (from Doug Tallamy: Ecosystem Gardening Hero by Carole Brown)
Also see three posts about this book at the Garden Rant blog: Doug Tallamy Wants YOU . . . to Plant Natives,", "The Best Possible Case for Native Plants," and "Doug Tallamy Answers Your Questions."