This time of year, the leaves on local trees only hint at autumnal color. To admire early fall foliage, instead of gazing up, I have been looking down.
On Sept. 26, I was in the southern end of Pelham Bay Park in the Bronx. A quick walk from the last stop on the No. 6 train is a meadow dominated by soft-stemmed plants like wildflowers and grasses. This flora is preparing for winter the same way deciduous trees do, with a foliar display.
After weeks of monotonous green, the leaves of common milkweed and Indian hemp have taken on a soft, lemony complexion. This foliage is subdued compared with the exuberantly yellow blossoms of gray goldenrod, now thick with bees, beetles, wasps and flies. Its floral kin, rough and early goldenrods, are here, too. They are older, with wine-stained leaves, and already releasing plumed seeds into the wind.
This annual transformation is largely drive n by the calendar. Plants are ever mindful of seasonal shifts. While we humans were in the throes of summer fun, they anticipated autumn's arrival by measuring the length of darkness.
After the summer solstice, days grew progressively shorter and the nights longer. The attenuation of light cued plants to prepare for senescence. In response, evergreen plants like conifer trees harden off to retain their needlelike leaves through winter. Most trees and other plants in the New York City area lose their leaves for the seasonal slumber. These deciduous species are now ceasing production of chlorophyll.
Most plants make their own food using nothing more than sunshine and air. Chlorophyll is essential in this conversion. This green pigment absorbs and transforms light from the sun, allowing plants to metabolize sugars for sustenance.
Once chlorophyll is gone, the previously hidden yellows and oranges of carotenoid pigments are unmasked. Anthocyanic reds and purp les are made only during the fall season.
Back in the field, these colors pack a visual punch. The burgundy-hued leaves of cinquefoil weave among the matted vegetation underfoot. In thinner soils along the trail are three-foot-high grasses. These culms of little bluestem, all copper and crimson, flex in the breeze. Chalk-white clouds of tall thoroughwort flowers temper the scene.
Encroaching woody plants also contribute. Sweet gum saplings don mahogany and scarlet. Salmon-colored pools of poison ivy creep along the ground.
This phenomenon of foliar color in grasses and wildflowers is largely overlooked, perhaps because it is so intimate. While an 80-foot tree can be admired from a distance, these smaller plants require that you come closer to appreciate them.
Marielle Anzelone - botanist, urban ecologist and founder of NYC Wildflower Week - wrote the weekly Autumn Unfolds series last year for City Room.
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