From Tree Hugger to Bug Hugger

Is your sleep disturbed by worries about disappearing spotted owls and snail darters? Maybe the objects of your concern are too grand. What you should really be worrying about is bugs: native bugs and the native plants that sustain them. That is the argument advanced by professor of entomology Douglas Tallamy in his recent book, Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens.(1) He says that we are starving our insects by replacing the native plants that they eat with exotic plants that they can't even recognize as food.

Native sweetbay magnolia. Native insect? Click to enlarge.

Starving the bugs sounds like a great idea, right? Maybe not. Tallamy presents insects as unloved heroes that transform the stored energy in plants into food (themselves) for the next level up in the food chain. In order to transform themselves into bird food, for example, insects must have food of their own to eat. But we are depriving them of food by replacing the native landscape with foreign plants. The vast majority of our insects are dietary specialists; the only foods they are capable of eating are members of the native plant community with which they have co-evolved over millions of years. Those are the foods to which their anatomy and physiology are adapted. They have as much success eating foreign plants as we would have if we tried to adopt the koala bear's diet of eucalyptus leaves. Without native plants, the insects have nothing they can eat, and they perish. With the insects gone, all of the food chain above insects will collapse.

American elm 1267 Park Avenue

The differences between the numbers of insects that can eat native versus foreign plants can be startling. Native oaks can provide food for over 500 different native insect species. Eucalyptus, an exotic, is eaten by only one native insect species. Native plants in Pennsylvania were found to support 35 times more caterpillar biomass, the preferred source of protein for most bird nestlings, than alien plants supported.

Native northern red oak, New Jersey state tree, West 8th St

How big a problem can this insect starvation be? Biodiversity depends on space. The more space, the larger the number of species that can be supported. The relationship is linear.(2) Only 3-5% of the lower 48 states remains undisturbed habitat for plants and animals. The rest has been paved, farmed, taken over by noxious foreign weeds like kudzu and Japanese honeysuckle, or transformed into suburban gardens dominated by exotic shrubs and vast lawns of non-native grasses. Tallamy points out that suburban lawns cover about 62,000 square miles of this country, an area more than eight times the size of New Jersey that is devoted to alien grasses.(3) Worse, 43,000 square miles of blacktop has been spread over the landscape, equal to five and a half New Jerseys. If we have eliminated much of the native vegetation from 95-97% of the American landscape, we can expect to lose 95-97% per cent of our native flora and fauna over time, as extinction adjusts the number of species to the land area that remains. Tallamy cites the toll of habitat destruction on Delaware, where he teaches. As of 2002, Delaware had lost 78% of its freshwater mussel species, 34% of its dragonflies, 20% of its fish species, and 31% of its reptiles and amphibians. Forty per cent of all native plant species in Delaware are threatened or already lost.

American holly East 9th Street

At this dismal point in his book Tallamy offers a ray of hope: suburban gardeners to the rescue! If suburbanites, who control a large swath of the landscape, were to plant native plants on their properties, the countryside could still support a diverse flora and fauna. Mix some American elms in with all those Zelkovas. Make your lawn smaller, and plant a meadow. Tear out some of your English ivy and Japanese pachysandra and plant mayapples. I repent ever having written that foreign, kousa dogwoods have the advantage of not being attacked by the borers that plague native flowering dogwoods (a good example of just what Tallamy is talking about). How petty of me ever to have planted exotic hollies instead of American hollies because of the Americans' problems with leaf miners! I'm going to be beating myself up for years over this. But as part of my rehabilitation program, I will spread the word about Tallamy's book, essential reading for anyone who plants.

Native black walnut leaf nibbled by, no doubt, native insects

(1) Tallamy, DW. Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens. Timber Press, 2007.

(2) Tallamy cites the work of Michael Rosenzweig at the University of Arizona to support his claim that species diversity decreases in proportion to the loss of available space. His very cursory discussion of this important underpinning for his argument is, for me, the weakest part of his book. I would like to have seen Rosenzweig's data and analysis described in detail.

(3) If you would object that Kentucky bluegrass is a native, you would be mistaken. Its seeds were imported by European settlers in the digestive tracts and droppings of cattle.

Copyright Gregory Palermo

Sweetbay magnolia

I have fragrant roses in my garden, but I can never detect their scent unless I put my nose right down into a bloom. The difficulty isn't an insensitive sense of smell. It is, rather, that I have a sweetbay magnolia in bloom at the same time. The fragrance of the magnolia is so potent that it overwhelms the scent of the roses.

Sweetbay magnolia (Magnolia virginiana) blooms over about six weeks from May into early July. Its flowers are small and never make a big visual impact. They bloom a few at a time, each flower lasting only a few days. Their fragrance is huge. To my nose their scent is rose-like, but much more intense.

There is a very handsome sweetbay magnolia in front of 500 Stelle Avenue.

The flowers are followed by shiny, bright red, clustered fruits(1) that ripen in August and September. The fruit is a favorite food of catbirds and mockingbirds. The photograph below shows unripe fruits on July 1.

Sweetbay magnolias are closely enough related to southern magnolias to have been hybridized with them. Unlike southern magnolias, sweetbays are mostly deciduous in this climate. Sweetbay flowers are much smaller and much more fragrant than southern magnolia flowers. Sweetbay leaves are duller and have a silvery gray underside that displays itself very attractively in a breeze.

Another feature that helps with identification is the rather smooth, light gray bark.

Sweetbays grow into large trees in the southern United States. In New Jersey a height of 25 to 30 feet is typical.

I have grown one of the hybrids of sweetbay and southern magnolias, 'Timeless Beauty'. The flowers of the hybrid resembled southern magnolia flowers. The foliage was less attractive than that of either southern or sweetbay magnolia. Worse, the hybrid's foliage suffered winter burn in winters that left pure southern magnolias unscathed. All in all, a disappointing plant.

Sweetbay magnolias are underutilized. Any garden can benefit from having their fragrance for six weeks in late spring and early summer. Very adaptable plants, they are tolerant of both wet soil and shade. A peculiarity of sweetbay magnolias is that they make a dense network of roots just beneath the soil surface. Mulch your beds heavily and the roots will grow right into the mulch. When the mulch dwindles with time, you are left with "aerial" roots. A drawback to this beautiful New Jersey native is that deer eat the leaves and stems.

Sweetbays were the first magnolias imported into Europe from the Americas. The genus was named by Linnaeus after Pierre Magnol, pioneering botanist and physician to the court of Louis XIV.

(1) The fruits are aggregates of follicles.

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Copyright Gregory Palermo

Southern magnolia

Do you have doubts about climate change? New Jersey gardeners don't. As warming winters have threatened to make New Jersey into a southern state, its gardeners have started planting southern magnolias (Magnolia grandiflora) everywhere. In the 1980s, the only southern magnolias I knew of in Plainfield were at the former Memorial Funeral Home on East Seventh Street. Now East Seventh Street has seven southern magnolias within a length of just 300 feet. 1330 East Seventh Street at the corner of Coolidge Street is southern magnolia central.

Many varieties of southern magnolia are cold-hardy in New Jersey. The best known is 'Edith Bogue', named for Miss Edith Bogue of Montclair, NJ, in whose garden it first attracted notice. My experience with 'Edith Bogue' is that it is a rapidly growing, beautiful plant that has stayed green in winters that have browned my Nellie R. Stevens hollies and blackened my aucubas.

Some southern magnolia varieties that can be purchased at area nurseries aren't as cold-hardy. A particularly beautiful and tempting one is 'Little Gem'. It is a small tree with smaller leaves than those of most southern magnolias. Unfortunately, even rather mild winters can cause serious leaf burn. An example at 828 Arlington Avenue is pictured below after the winter of 2006-2007, not a very hard winter.

The tree is in much better condition this winter, which has been very mild so far, but this 'Little Gem' would probably be happier in Virginia.

Some of the varieties of southern magnolia that thrive in New Jersey have leaves with brownish, felt-like undersides.(1) A very handsome example is at 911 Woodland Avenue.

The Woodland Avenue tree shows a feature that is common in southern magnolias, the tendency to grow in a Christmas tree shape. European gardeners often take advantage of that tendency by treating southern magnolias as topiary specimens. Most southern magnolias that I have seen in European gardens have been formally pruned to form perfect cones. An exotic look that is well suited to an exotic plant; in Europe, southern magnolias are imports. I rarely see formally pruned southern magnolias in the United States, where the species is native. That sort of formal pruning is extremely high-maintenance gardening, by the way. It's very different from pruning a yew into a cone. Yews, with tiny leaves, can be shaped with shears. One can't prune southern magnolias with shears because their leaves are too large; the leaf fragments would be grotesque. Each stem must be cut individually with hand clippers.

Southern magnolias are capable of reaching great size in our climate. The grandest southern magnolia I have seen in the vicinity is at 221 East Westfield Avenue in Roselle Park. Twenty-five years ago, before the lower branches were removed, the house behind the tree was essentially invisible.

Magnolias are primitive trees. How primitive? Magnolias evolved more than 50 million years ago, before pollinators like bees and butterflies existed. Beetles are their pollinators.(2) The huge, white, lemon-scented blooms of southern magnolias might be the epitome of romance, but their intended audience is beetles, not you.

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A close relative of southern magnolia, but even more fragrant, is sweetbay magnolia (Magnolia virginiana). I have some sweetbay magnolias in my garden, but I would be grateful to hear of any examples of this species that can be seen from the street.

(1) There is apparently some correlation between brown leaf undersides and cold-hardiness (Manual of Woody Landscape Plants, Michael Dirr. Stipes Publishing Company 1998, p. 598). That correlation doesn't work for 'Little Gem', however.

(2) Magnolias, J.M. Gardiner. Globe Pequot Press 1989, p. 14.

Copyright Gregory Palermo