On any late spring morning, if we forgot to turn off the outside lights the night before, the porch wall’s gray wood will be covered with hundreds of resting moths. The first time this happened I counted 25 species, although I could only name one, the rosy maple moth (Dryocampa rubricunda), easily keyed out from its striking pink and yellow wings.
Each unknown moth species represented a strand in the garden food web, no doubt some more familiar in their summer or autumn larval stages, the leaf chewing caterpillars, exemplars of what bird food looks like. For example, the caterpillar stage of the rosy maple moth, the green-striped maple worm, is a favorite food of blue jays.
This abundance of lepidopteran life is due, in part, to the presence of four groups of native trees in and around Marjorie’s Garden. According to entomologist Douglas Tallamy, author of Bringing Nature Home, How Native Plants Sustain Wildlife in Our Gardens (Timber Press, 2007), native birches, the subject of this essay, rank fourth among native woody plants in their ability to support butterflies and moth species. Oaks lead the list, attracting 517 lepidopteran species, followed by willows (456 lepidopteran species ), cherries (448 lepidopteran species), and birches (413 lepidopteran species). All four of these tree groups grow in Marjorie’s Garden, including three species of native birch, as well as red maples, the host plant for the rosy maple moth and over 200 other lepidopterans.
Each native birch species is a major link in the garden food web, hosting a wide variety of insect and bird life. Thus a garden that grows one or more of the three birch species discussed below will sustain a much greater biodiversity than a garden without native birches.
Paper Birch (Betula papyrifera)
The lane from the main highway meets the drive into our garden via a long curve lined with paper birches, also called paperbark birches. The white bark of these trees, particularly in winter sunlight reflected from a snowy landscape, always brings to mind a passage from Donald Culross Peattie (A Natural History of Trees of Eastern and Central North America, Houghton Mifflin Company, 1948):
“For the Birch, where it is found near habitations, is usually spared [from harvest] for its beauty. As a result it is now one of the best-loved trees of the New England Landscape, and when we remember a scene there, we see birches in it – gleaming white trunks, houses, and churches painted a cold, clean white, and pure country snow stretching white over dale and hill.”
In and around Marjorie’s Garden, paper birches keep company with the dark conifers, black spruce, white pine, and arborvitae. Being light tolerant, the birches quickly filled canopy gaps left by wind-thrown spruces and now rise to 50 feet in height. Younger seedlings and saplings wearing the red-brown bark that marks the first decade of growth are abundant along the edges of the drive and in clearcut areas around the vegetable garden.
In spring, each male catkin on a mature paper birch produces over five million pollen grains, some of which are captured on the silken strands of the cross orb-weaver spider (Araneus diadematus). The young of this spider are pollen feeders, eating the pollen, web and all.
In addition to the hoards of arthropods feeding on paper birch leaves, the tree is also a favorite of the yellow-bellied sapsucker, a woodpecker that drills holes in regular horizontal rows high in the tree, then returns to the pitted area at intervals to lick up the leaking sap and any insects attracted by it. Ruby-throated hummingbirds may take advantage of the sapsucker’s efforts.
Common seed foragers on the catkins of paper birch include chickadees, redpolls, pine siskins, and fox sparrows. Philadelphia vireos and black-throated green warblers use birch-bark strips for next construction. And in winter, the buds of paper birch are eaten by grouse.
Gray Birch (Betula populifolia)
Gray birch is often mistaken for a poplar, hence the specific epithet, populifolia, and the alternate common name of poplar-leaved birch. It is the smallest of the native birches, never exceeding 30 feet in height and typically smaller. Its bark is gray and does not peel and thus it has been overlooked as a garden tree in spite of the introduction of a much whiter-barked cultivar, ‘Whitespire’, in 1993.
As a landscape plant, ‘Whitespire’ can offer a welcome alternative in size and bark texture to the too frequently used paper birch. Its tolerance for many stresses, including soil compaction and drought, makes it suitable for difficult sites where other trees would fail. Still, ‘Whitespire’ will be scarce in gardens as long as ornamental attributes are the only criteria.
When I see the tattered leaves of a gray birch in autumn, I know that it is a host plant for some of those moth species drawn to the porch light. “Moth-eaten”, we call it. Gray birch is also a larval host for several species of butterfly, including Eastern and Canadian tiger swallowtails, white admiral, mourning cloak, Compton tortoiseshell, and dreamy duskywing. Juncos, blue jays, titmice, chickadees, waxwings, and other birds eat its flower buds and seeds.
Yellow Birch (Betula alleghaniensis)
Of all New England’s native birches, I am fondest of the yellow birch for the warm honey-gold color of its exfoliating bark and its rich golden yellow fall foliage. And I have a history with this tree. While teaching woody ornamentals as part of the Horticulture Program at University of Maine, Orono, I would take my students on a campus tour that included a yellow birch. We would take cuttings of new growth to smell and taste the wintergreen essence of crushed wood. I smile now at the memory of campus pedestrians gawking at a group of students sniffing twigs with such enthusiasm.
In Marjorie’s Garden we have two old yellow birches, each at least 70 feet tall with broad canopies, just across the drive from the back steps, both leaning toward the house. An arborist friend strongly recommended cutting them down but settled instead for reducing the sail on each tree. Meanwhile, seedlings of these venerable trees are scattered in canopy gaps throughout the nearby woods as well as along the edges of the garden, a promise of yellow birch in this place well beyond our time here.
The yellow birch is a larval host for the banded purple and white admiral butterflies, as well as many moth species. Songbirds, including redpolls, pine siskins, and chickadees eat its seeds. The tree is a favorite nesting site for red-shouldered hawks and ruffed grouse feed on the seeds, catkins, and buds in winter. Red squirrels cut and store the mature catkins, eat the seeds, and feed on the sap.