NATURE’S VIEW
The Understory Sun vs. shade is the variable for forest regeneration and wildlife habitat opportunities By Dave Anderson
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Ahhh summertime…I marvel at the billions of green pennants fluttering overhead in the forested canopy—two dozen shades of green. Tender young leaves of the hardwood canopy cast a seemingly sudden shade on the forest floor that will remain in shadow until autumn when the foliage falls. The summer’s shade-casting foliage is largely uncelebrated, but it is an equally dramatic transition in the woods. A season of filtered sun vs. dappled or deep shade reveals sunlight’s role in heating soils and regenerating seedlings. Sunlight dictates food availability and cover for nesting songbirds and wildlife inhabiting the forest understory. Made in the shade? Meh, not so much in our forests. Dense shade beneath a 100 percent closed canopy of hemlock, pine, or dense hardwoods limits understory growth. At ground level, the forest appears open. Prime real estate for the limited plants that are best adapted to growing in full shade and acidic soil. Canada mayflower (aka false lily of the valley), starflower, and goldthread can often be spotted carpeting the forest floor beneath towering pines—a win by default. Shade-tolerant hardwoods—beech, yellow birch, and sugar and red maple—reproduce from seed in the shade while sun-loving hardwoods—white birch, poplar, pin cherry, ash, and oak species—require full sunlight and warm soil to germinate. Among conifers, white pine and red pine require full sun to regenerate. Red spruce and hemlock can tolerate shade, but they require an opening in the canopy to grow. The more sun-loving trees are short-lived: pin cherry can live up to 40 years, followed by poplar (80 years), white birch (100–120 years), and white pine (perhaps 150 years max). Slower growing 18 | FOREST NOTES Summer 2021
Once hardwood trees are fully leafed-out, nuances of sun versus shade are more apparent. Forest seedling regeneration and wildlife use of habitats for feeding or nesting reveal the influence of full sunlight or a lack thereof.
shade-tolerant trees can live centuries: beech and sugar maple (200-plus years), yellow birch (300-plus years), and hemlock (a whopping 400-plus years). In response to the low-light levels in a hardwood understory, oaks and maples produce larger “shade leaves,” outsized versions of much smaller canopy leaves, to capture more sunlight. Think of how much more energy an array of solar panels can create compared to just one. The same method applies for these larger leaves trying to grow big and strong in a dark forest. In a hemlock forest, the understory is barren, devoid of food for wildlife and cover for birds. Few plants are adapted to live in these harsh acidic soil conditions. Research has shown that people tend to
appreciate an open understory for ease of walking and enhanced peripheral vision compared to a forest with more complexity that also obstructs views. But the latter provides more opportunities for wildlife feeding, nesting, and cover. It is a duality. But this is strictly a human construct— what we the people prefer. A wide field of view through an open understory yields better peripheral vision and provides a comforting sense of security, a throwback to the open Savannah where humans first evolved amid some formidable predators. Conversely, sun-soaked openings ranging from small single-tree gaps to larger apertures quickly fill in with dense new growth. Fruit-bearing shrubs, ferns, wildflowers, and tree seedlings race to claim this valuable space. Foresters seem fond of admiring the strong regeneration of oak and pine seedlings; a new forest emerging in full sun. With the addition of new sunlight, the understory transitions from an assortment of shade-tolerant ferns, witch hazel, striped maple, hemlock, beech, and red maple to a new growth of sweet fern, lowbush blueberry, staghorn sumac, pin cherry, white birch, poplar, and white pine seedlings. Pine, ash, and oak seedlings dominate former skid trails and timber landings surrounded by a matrix of shady closed canopy conditions. It’s no surprise that when people bushwhack, they tend to hike parallel to unmaintained skid trails to avoid the brush—and the ticks!
Wildlife Food and Cover Warm light in forested openings attracts foraging insects drawn to sun-dependent grasses and flowers. In turn, insects attract aerial feeding by foraging songbirds, flycatchers, and bats. Tender leaves and twigs of seedlings and saplings are accessible to
