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26. Spring Tensions
- West Virginia University Press
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189 26 Spring Tensions T hat first waft of warm air, the pale green brush to a hillside, the first warbler singing in a treetop — all excite our senses and push aside the day’s problems. It is fitting that the opening movement of Aaron Copland’s “Appalachian Spring” captures the timid, cautious mood of the first few days of resurrection. Then comes the onrush. From a biological point of view, things change faster in spring than at any other time. Along Pine Cabin Run, phoebes flick their tails, hickory leaves unsheathe, and creek chubs vie for headwater pools. With a big shudder, my living neighbors shake off winter and begin anew. But spring emergence is fraught with tension. Timing is everything. The first warm sunshine of February rekindles the flow of sap on the south side of trees, and leaves soon begin to unfurl. In a locally predictable sequence, the leaves of various tree species emerge over the span of a couple of months. The timing of leaf-out appears to vary from year to year — late April one year, early May the next — but our printed calendar offers only weak relevance. The immediate stimulus for leaf emergence is actually the cumulative thermal sum, or the amount of ambient heat available in the spring after a requisite cold period. When we relate the timing of leaf-out to thermal sums rather than to the days of the month, we find it consistent over the years. (When I speculate with my neighbors up the hollow about whether spring has come early or late, I know I’m applying the wrong yardstick, but I enjoy the rite just the same.) 190 Most of the plants of the forest floor respond acutely to lessening sunshine as trees leaf out. The seasonal light hitting the forest floor runs out of synchrony with the temperature cycle. Ground cover plants receive strong sunshine or warm weather, but not at the same time. The woodland herbs of early spring display their flowers during the brief window of time between the first prolonged period warm enough for pollinators and the closing of the canopy. The heydays of herbaceous wildflowers end as the canopy closes above. Early-blooming, ephemeral herbs of the Appalachian forest include spring beauty, round-lobed hepatica, cut-leaf toothwort, squirrel corn, Dutchman’s breeches, rue anemone, and bloodroot. Many of these early-spring bloomers have white, bowl-shaped, sun-following flowers with reflective petals, and fuzzy pollen-producing and seed-bearing organs. These flowers stay warmer than the surrounding air because they reflect visible light and other forms of radiation onto the flower’s sexual organs. Such tiny parabolic solar ovens speed the development of pollen, seeds, and fruits, and aid the survival and reproduction of visiting insects by providing them with a warm microenvironment. These wildflowers need the full energy of bright sunshine to grow and bloom, and so retreat as the canopy thickens. Some of the extremely early bloomers actually produce their own heat. With short bursts of intense metabolism, the eastern skunk cabbage warms its flowers to as much as 31 degrees Fahrenheit above the ambient temperature, allowing them to melt their way through ice and snow. Because skunk cabbage plants generate heat, they get a jump on flowering and seed production. The spike of flowers inside the skunk cabbage’s hood is warm to the touch, and the hood, which resembles styrofoam, insulates the flower spike. The warmth inside the flower and the plant’s characteristic smell of feces and decaying flesh lure insect pollinators. The heat may help to volatilize the odorous molecules. After pollination, the plant maintains a tropical climate for embryonic development. The temperature of a skunk cabbage’s flower spike varies little because a built-in thermostat helps regulate the plant’s metabolic rate, and thereby its body temperature. In fact, the metabolic rates Hollows, Peepers, and Highlanders [3.90.255.22] Project MUSE (2024-03-29 10:26 GMT) 191 of skunk cabbage’s flower spike and warm-blooded animals of similar weight are about equal, suggesting that both plants and vertebrates independently evolved the ability to generate heat via the common route of elevating their metabolic rates. The sequence of wildflower bloom in West Virginia from late winter through mid-spring, goes something like this: skunk cabbage, blood root, spring beauty, hepatica, Dutchman’s breeches, squirrel corn, violets, star chickweed, trilliums, crested dwarf iris, columbine, and fire pinks. Our...