As scientists everywhere parse the effects of a warming earth on animal and plant life, Richard Primack and his colleagues at Boston University have turned to an unlikely source: Henry David Thoreau’s handwritten notes. From 1851 to 1858, the naturalist carefully noted the flowering dates for hundreds of species of wildflowers, as well as the first leaf-out dates for trees, the stirrings of animals, and the arrival of migratory birds near Concord, Massachusetts.
After poring over Thoreau’s sprawling handwriting and working with botanists to interpret his 19th-century nomenclature, Primack’s team set out in early spring in search of the petals of lady’s slippers, red trillium, and trout lilies. Consistent with the rise in Concord’s average annual temperature of more than two degrees Celsius since the 1850s, Primack found that 43 plants observed by Thoreau today flower approximately 10 days earlier.
Of the species Thoreau described, more than half are either no longer present in Concord or so rare that not enough specimens can be found for statistical comparison. Thoreau’s Concord, a landscape of wet meadows, hayfields, pastures, orchards, and small woodlots, has become mature forest fragments interspersed with suburban housing interlaced with roads that drain commuters into Boston offices.
Changes of this magnitude do not happen overnight, but even when Thoreau lived in his cabin on Walden Pond in 1847, perhaps hearing the first brave chirp of an early spring peeper on a cold April night, he could also hear the cars of a recently built railroad shuffle by, its engine sending out a long trail of coal smoke that at that hour was still invisible.