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.

Ambrosia artemisiifolia: delcious-sounding name for a very annoying plant

Warning: this plant is considered a noxious weed under the Ontario Weed Control Act.

Such a lovely-sounding name for this plant with such pretty, fern-like leaves! (click the photo to get a better look) If only it weren't for the flowers...

In case you haven't recognized this common but easily overlooked plant yet, it's better known as common ragweed (petite herbe à poux). Those boring little green flowers have no interest for animal pollinators, so ragweed instead releases massive amounts of lightweight pollen into the wind, relying on the sheer quanitity of pollen to ensure that some of it will reach a female flower and fertilize it. (Separate male and female flowers are produced on each plant.)

Ragweed grows in the same habitats and blooms around the same time as its showier cousins, the goldenrods (verge d'or, Solidago spp.). Because ragweed is so inconspicuous, goldenrod is often unfairly blamed for ragweed pollen allergies. In fact goldenrod pollen is too heavy to be wind-borned; that's why it has those gorgeous flowers, to attract the insects needed for pollination.

According to Wikipedia, the genus name Ambrosia comes from the same root, άμβροτος, as the ambrosia which is the food of the gods, but this root word actually means "immortal", referring to the difficulty of eradicating this plant. (This species is actually an annual, so not immortal by any means.)

Ragweed is one of the top 10 herbacious plants to feed wild birds, because it produces numerous, oil-rich seeds. However, given how many people are allergic to it, I think it should be kept to wilderness areas far from humanity, certainly not in Toronto gardens.

Amaranthus tuberculatus in bloom

Amaranthus tuberculatus, known in English as "roughfruit amaranth" or "tall waterhemp" (je ne peux pas trouver un nom commun en français), is an annual native to much of eastern and central North America and a few west-coast states. It can reach two metres in height. The spikes of green flowers are not especially showy, but produce abundant seed, making this a useful food source for birds. The glossy foliage is eaten by the larvae of the common sootywing skipper (Pholisora catullus) and some moths.

Top 10 best plants for wild birds and mammals

If, like me, you'd like to encourage wildlife in your garden, check out these lists. According to American Wildlife & Plants by Alexander C. Martin, Herbert S. Zim, and Arnold L. Nelson (New York: Dover, 1961), these are the best plants for feeding birds and mammals in our area (okay, technically, northeast U.S., but I don't think things change that suddenly north of the border). Seeing the wildlife value of a number of less showy herbaceous plants is certainly giving me food for thought in choosing new plants for the garden. The woody plants are all fine ornamentals as well as being valuable sources of food for birds and mammals.

Woody plants

1. oak (Quercus spp.): acorns are one of the most important foods for many mammals and birds. They are one of the blue jay's favourites. White oaks (including Quercus alba, Quercus prinus) produce tastier acorns than black oaks (Quercus velutina). Oak leaves and twigs are used as nesting material.
2. blackberries and kin (Rubus spp.): as well as blackberries, this group includes raspberries, dewberries, cloudberries, and thimbleberries. The delicous fruit are popular, especailly with birds when fresh during the summer, though dried fruit will be eaten in autumn and winter if there's any left. The thorny brambles provide useful cover for birds, rabbits, and others, and are a popular nesting site. Cottontail rabbits eat Rubus stems in the winter.
3. wild cherries (Prunus spp.): the fruit are popular with birds; mammals also eat them, often feeding on the cherries that have fallen to the ground. Deer and rabbits also feed on the twigs, foliage, and bark. The most important cherries in our area are P. virginiana and P. pennsylvanica.
4. pines (Pinus spp.): seeds are eaten by many birds and small mammals; pine needles, bark, and wood are eaten by some animals. Pines with branches near the ground provide cover for wildlife; large pines are favoured nesting sites for mourning doves and migrating robins. In our area the most important is the majestic white pine (Pinus strobus), which is also our provincial tree.
5. dogwood (Cornus spp.): the fruit are an important food in late summer, fall, and into winter.
6. grapes (Vitis spp.): the fruit of grapes appeals to many animals; the dense foliage in summer provides cover and nesting sites. Birds often use the bark of grapevines to build their nests. Our native species are V. aestivalis, V. riparia, and V. vulpina.
7. maples (Acer spp.): maple seeds provide food for birds, squirrels, and chipmunks; animals also eat the buds and flowers. Birds use the leaves and seed stalks to build their nests.
8. beech (Fagus grandifolia): beechnuts are an important food for squirrels and chipmunks, and are also eaten by birds and other mammmals.
9. blueberries and kin (Vaccinium spp.): as well as blueberries, this group includes hillberries, cranberries, and deerberries. The bruit are eaten by many birds and mammals (from mice to bears!), deer and rabbits also feed on the twigs and foliage.
10. birches (Betula spp.): birds feed on the catkins, buds, and seeds; mammals such as deer, hares, porcupines, and beavers eat the bark, twigs, leaves, and wood.

Herbaceous plants

1. ragweeds (Ambrosia artemisiifolia and A. psilostachya): the ragweedsare one of the most important plants for wildlife. In particular, their seeds form a major component of the diet for many songbirds. It's unfortunate that their pollen is so allergenic for humans!
2. bristlegrass (Setaria spp.): although they are not native to our area, the bristlegrasses produce abundant seeds which are a major food source for many birds; some mammals also eat the seeds and leaves.
3. sedges (Carex spp.): many birds eat the seeds; the leaves and roots as well as the seeds are eaten by various mammals. Sedges also provide valuable cover for wildlife.
4. crabgrasses (Digitaria spp.): because crabgrass is common and produces many seeds, it is an important foodsource for many birds. The plants are also eaten by rabbits. D. cognata is native here.
5. pigweeds (Amaranthus spp.): the numerous seeds of the pigweeds remain available in spiked clusters during the winter and sometimes even spring, where they provide an important food source for songbirds when food is scarce. Rabbits and deer feed on the plants. Although a number of pigweeds are alien, A. powellii and A. tuberculatus are native to our area.
6. clovers (Trifolium pratense, T. repens, and T. hybridum): these three widespread aliens provide delicious foliage as well as seeds to many birds and mammals. The first two are somewhat invasive in our area according to Invasive Exotic Species Ranking for Southern Ontario.
7. sheepsorrels and docks (Rumex spp.): the most common of these, R. acetosela, is not native here but because of its abundance the seeds are a common food for ground-feeding birds; the seeds are also eaten by small mammals. Rabbits and deer feed on the plants.
8. dropseed grasses (Sporobolus spp.): the seeds are important for birds who feed on the ground. Small mammals also eat the seeds, and deer browse on the plants.
9. bluegrasses (Poa spp.): birds eat the seeds and rabbits and other mammals graze on the foliage.
10. pokeweed (Phytolacca americana): the fruit are eaten by mourning doves, songbirds, foxes, opossums, raccoons, and mice.

Marsh and aquatic plants

1. smartweeds (Polygonum spp.): the seeds of smartweeds found near and in water are an important food for ducks and songbirds; small mammals also eat these seeds. The most significant are P. persicaria (alien), P. pennsylvanicum (native), P. punctatum (native), and P. lapathifolium (alien).
2. pondweeds (Stuckenia and Potamogeton spp.): these plants dominate lakes and ponds in our area. The seeds and plants are an important food for many birds who live around water. Stuckenia pectinatus is considered the most important species for wildlife.
3. wild rice (Zizania spp.): wild rice seeds are a key component of the diets of waterfowl, marshbirds, shorebirds, and songbirds. Z. aquatica and Z. palustris are native to our area.
4. bulrushes (Scirpus spp.): the seeds are an important food for birds living near water and muskrats; they are also eaten by songbirds.
5. American eelgrass (Vallisneria americana): the foliage, seeds, and roots are all enjoyed by ducks.
6. naiads (Najas flexilis and N. guadalupensis): the stems, leaves, and seeds are favoured by ducks.
7. spikerushes (Eleocharis spp.): waterfowl, marshbirds, and shorebirds eat the seeds; waterfowl also eat the stems and tubers, and rabbits and muskrats eat the plants.
8. bur-reeds (Sparganium spp.): the seeds are eaten by birds living near water, and the whole plant is used by muskrats.
9. wild millets (Echinocloa spp.): the seeds are important for ducks, and are also used by other birds. Rabbits and muskrats eat the plants.
10. duckweed (Lemna minor): although this is a tiny species, its abundance allows it to play an important role in the diet of ducks.

Helianthus annuus 'Velvet Queen': flower

Helianthus annuus, known in English as sunflower and in French as tournesol or grand soleil, is an annual native to the United States. As well as the famous very tall, very large, single yellow variety, there are dwarf varieties, and cultivars in cream, light yellow, orange, and rust. Pollen-less cultivars have been created for use as cutflowers, but for wildlife the pollen-bearing varieties are more appealing, as a source not only of pollon but seeds. The cultivar shown, 'Velvet Queen', is widely advertised with misleadingly red (Photoshopped?) images. It looks more rust-coloured to me.