Does growing invasive plants help birds?

This past week I was very excited to pick up a beautiful book, Bird by Bird Gardening by Sally Roth (Rodale, 2006), about designing gardens to attract various families of birds to the garden. And in many ways it is an excellent book, with a wealth of information about the needs of different birds in terms of food, shelter, water, etc., with lists of plants and garden plans for all sorts of lovely birds (she's an American writing for American gardeners but of course a lot of it will apply here in Canada too). It's a beautiful book, lavishly illustrated with full colour photographs, and a wealth of information.

As I read the book more closely, however, I became troubled, as she recommended plants which may be invasive in parts of the US (and Canada too, though I can't fault her for that if she wasn't intending to cover Canada in the book). For example, she suggests

• Berberis spp. (barberries, berbéris) without distinguishing between the native and invasive varieties (B. thunbergii is invasive in the northeastern US, B. vulgaris invasive in many states from coast to coast; they both are listed in the Invasive Exotic Species Ranking for Southern Ontario (PDF))
• Eucalyptus spp. (Australian natives which are invasive in California, especially, but also in the Pacific north west including part of BC)
• Euonymus alatus (winged euonymus, fusain ailé) which is invasive in the northeastern US (and southern Ontario)
• Pyrus calleryana (Callery pear, poirier de Chine) which is invasive in the eastern US

(These are just the most notorious invasives I noticed flipping through the book; I didn't do an exhaustive investigation.)

Now, there are a lot of older wildlife gardening books that recommend various invasives, especially berry plants, but I was very unhappy to see them still being recommended in such a recent book.

I was horrified when I got to a three page essay, "Invasive Implications", on pp. 74-76.

First, she implies that the term "invasive" was created by the USDA and is based on agricultural concerns, and that all non-native plants are invasive. Now, even if invasive plants were only a problem for agriculture, that is still an extremely serious problem since virtually all people in North America are completely dependent on agriculture for our food. To me that would be reason enough to avoid gardening with invasives.

Of course, in reality, there are many ecologists concerned about the impact of invasive species on ecosystems. Invasives are definitely not only a concern for farmers.

Then, she says that invasives mostly affect disturbed areas, and so are not a problem for native plants. Even if invasives only affected disturbed areas, to me that is still a problem, for they are displacing the native plants which would normally colonize disturbed areas. Invasive plants can prevent native plants from returning to disturbed areas, so this habitat is permanently rather than temporarily lost.

(And unfortunately, there are invasive species which invade undisturbed habitat; witness the heartbreaking blanket of garlic mustard (Alliaria petiolata, herbe à l'ail) carpeting the forests in High Park and around the Ontario Science Centre, for example.)

She suggests that invasives are mainly a concern in warm areas (southeast US, California, and Hawaii) or near wetlands. In reality, while invasives may be worse in those areas, that doesn't mean they aren't a serious problem here.

Then she points out that sometimes authorities use environmentally questionable practices (herbicides). There is real debate on if/when pesticides should be used to control invasives, but surely if we don't want the authorities to feel driven to use pesticides we should avoid growing plants that are invasive in the first place! She also describes an instance she witnessed of a birds' nest being destroyed when the plant they were living in was removed. Again, all the more reason to prevent these situations by not growing invasives in our gardens.

Most upsettingly, she writes that since birds use some invasives for shelter or food:

I stick up for many invasives [because] we've destroyed so much bird habitat, so many native plants, and such multitudes of insects, that I believe birds deserve some extra help.

Aargh!

The sad truth is, these invasives she's defending are a leading cause of habitat loss. In particular, the multitudes of insects she mourns depend on a multitude of native plants for food. Most herbivorous insects can only eat certain species; even a closely related non-native plant often supports many fewer insects (in both number of species and number of individuals) compared to its native counterpart. Birds can seek cover and build nests in many locations, and fruit and nectar of many plants are palatable, but without a healthy insect population most birds won't be able to get the nourishment they need.

Invasive plants don't help birds, they harm birds.

If you want to grow plants to help birds, there are many native plants (many listed in Bird by Bird Gardening, and Bringing Nature Home by Doug Tallamy) which provide shelter, berries, and the insects which are such a crucial part of many birds' diets.

For more information about the impact of native vs. non-native plants on wildlife, please read Bringing Nature Home.

Great podcasts by Doug Tallamy on gardening and wildlife

I've already mentioned Doug Tallamy's wonderful book, Bringing Nature Home (Timber Press). I just discovered these fascinating and inspiring podcasts online. Enjoy!

Part 1: the crisis faced by wildlife, making friends with insects. (8:02)

Part 2: how many native vs. non-native plants do you need, which native plants have the most benefit for wildlife. (11:11)

Part 3: how to distinguish native vs. non-native plants, how invasive plants affect the environment, using herbicides to control invasive plants, organic gardening. (9:24)

Part 4: can one garden really make a difference in helping wildlife? How to get started. (9:15)

Part 5: do lawn alternatives help wildlife, what is the most destructive landscaping practice? Current research on the impact of plants on wildlife, especially birds. Effects of native vs. invasive insects. (11:29)

Garden Bloggers' Bloom Day, November 2009

Here in Toronto, there isn't much blooming; in fact, I was surprised to find as many blooms as I did. Interestingly, they're all volunteers except for the chrysanthemums.

Antirrhinum majus (snapdragon, muflier). I'm not sure where these snapdragons blew in from, since we didn't plant them last year either. I'm planning to let them self-sow.

Chrysanthemum sp. (chrysanthème). The mums aren't as pretty as they were last month, but they still have lasted a very long time.

Erigeron annuus (daisy fleabane, vergerette annuelle). I was surprised to see daisy fleabane blooming at this time of year; it mostly blooms in early summer.

Lobularia maritima (alyssum, alysse odorante). I love the way this alyssum volunteers in a crack in the driveway. I may deliberately sow some in cracks next year.

Lobularia maritima (alyssum, alysse odorante). More alyssum. I must plant more of this next year, it has such a long blooming season, smells lovely, and pollinators love it! Stokes has some interesting colours you don't usually see in alyssums.

Petunia. I can't believe this petunia is still blooming, it lost its leaves ages ago and looked so nearly dead my landlords dumped it out of its hanging basket. Here it is sitting in a clump of dried up soil in November, and it's still blooming.

Sutera cordata (bacopa, sutera cordée). This was a pleasant surprise volunteer. I may plant some deliberately next year. It really needs to be started early indoors; this plant didn't bloom until autumn.

Check out what's blooming in gardens around the world this Garden Bloggers' Bloom Day. Thanks to Carol of May Dreams Gardens for hosting!