I've known more than a few wags who have remarked slyly that a weed is simply a plant that you don't want, and while that initially seems generous and open minded with respect to the natural world, it misses the critical role that some plants play in their ecosystem and the role that others don't play. From the perspective of a healthy, diverse, and functioning ecosystem, some plants (weeds) simply don't pull their weight, while others are citizens in good standing. In the first half of Bringing Nature Home, Douglas Tallamy brilliantly argues that plants in good standing are, generally speaking, native to the region, while non-natives tend in almost every case to be either unhelpful or positive threats to the diversity of life. What Tallamy hopes the reader will take home from this is that converting your garden to a native plant preserve is one of the easiest ways a gardener can help recover the ecosystem that is most beneficial to his or her locale.
The key element in the overall picture is the insect population. Gardeners often treat insects as the enemy and in some cases they can be; however, in a well-functioning ecosystem herbivorous insects are a critical link in the food chain linking plants to larger, more charismatic animals, like birds, frogs, rabbits, and turtles. Non-native plants have become best-sellers in nurseries all over the country in large part because they are "insect resistant," meaning, they aren't food for anything in the ecosystem. Planting such species is comparable to laying down astroturf, planting plastic flowers, and erecting artificial trees. They may look nice and be generally whole and intact, but they serve no other purpose but to decorate one's garden. Worse, they have a tendency to spread out of control and take up an enormous amount of space, crowding out ecologically valuable species. Of course, the loss of habitat for insects results in a loss of habitat for larger animals. After reading Tallamy's arguments, one comes to appreciate the beauty of the ragged shape of an insect-eaten leaf. One's heart goes out to noble native plants that has given up some portion of their foliage for the greater good of the ecosystem.
One of the most significant environmental problems we face today is the loss of habitat. Urban sprawl and mono-cultural fence-to-fence agribusiness farming has left less and less room for inhabitants of the natural world and is drastically reducing the size of numerous species' populations. Tallamy argues that urban and suburban gardeners can do quite a lot to mitigate this problem simply by choosing to plant natives in their gardens. One small suburban lot may not seem like a significant contribution to the solution, but if gardening with natives becomes as popular as gardening with non-natives, the problem will be cut in half.
A yet stronger response to the urban-suburban desert-scape that we have created would be to organize whole neighborhood or cities to plant native plants. Recent ecological research shows that the size of a contiguous ecosystem is important to maintaining a native wildlife population. This runs counter to the belief that many small fragments of an ecosystem can effectively support the population. Obviously, fragments suitably close and with no significant barriers can be helpful, but organizing large swaths of natural habitat is preferable. Still, to get to this stage, pioneer native gardeners are critical. Happily, Tallamy provides tips on "making it happen."
The second half of Bringing Nature Home is essentially a reference guide to useful native plants and insects, a.k.a., "bird food." Tallamy also provides a valuable chapter entitled "Answers to Tough Questions," like "If birds eat the berries of alien plants..., why shouldn't I plant those species?" (The short answer is that those berries do not provide adequate nutrients required to make eggs, to feed the parent birds while they are feeding the young, and to feed the young themselves. Too many such plants means there will be fewer insects to provide the nutrition needed for reproduction.)
Finally, there are three excellent indexes listing native plants across the U.S., host plants for specific butterflies, and results from experiments comparing the value of native and non-native plants. Also there are numerous beautiful color photographs and a superb bibliography.
No gardener interested in native plants should be without this book!