Henry David Thoreau’s 160-year-old field notes document the changing life in the woods, as a warming climate jumbles the timing of annual springtime schedules.
The leafing out of trees in the spring is one of the most dramatic events of the year in temperate regions of the world—whether New York, England, Japan, or Russia.
New leaves mark the end of winter and the beginning of the growing season.
They mark the awakening of wildlife, the arrival of migratory birds, the emergence of flowers, and the time of year for walks in the park and spring-cleaning.
Although researchers have been interested in the mechanics of leaves for many decades, the natural history of leaf out and leaf drop was largely ignored.
Using Henry David Thoreau’s field notes from Walden Pond in the 1850s, Richard Primack and Amanda Gallinat have shown that leaf emergence times have shifted about 18 days earlier.
Unfortunately, the schedules of the birds and insects that depend on these leaves have not always shifted accordingly, throwing co-evolved schedules out of sync.
Researchers at botanical gardens around the world have joined in monitoring leafing out times to understand this heretofore under-appreciated aspect of natural history, so that scientists can make better predictions about forest ecosystems as the climate changes.