The lowbush blueberry will begin its growing seasons a full month earlier than it did in Thoreau’s time. That shift might not matter, if a blueberry were just a blueberry. But like every species of plant, a blueberry is one piece of a complex ecosystem, one that can be thrown out of balance when a single element, like the timing of spring leaf-out, begins to fluctuate.
increase in spring temperatures predicted from 2014 to 2100
days earlier leaf-out than in Thoreau’s time by 2100
plant species lost from the Concord landscape since Thoreau
That, according to Richard Primack, a College of Arts & Sciences biology professor, is exactly what is happening in the woods of Concord, Mass. Primack and graduate students Caroline Polgar (GRS’13) and Amanda Gallinat (GRS’17) have been tracking the changing leaf-out times of trees and shrubs at Walden Pond, starting with dates first noted by Henry David Thoreau in the 1850s. The team has determined that contemporary leaf-out dates are on average 18 days earlier than they were when Thoreau made his observations.
At Bostonia’s request, Primack’s team pushed their data one step further to predict leaf-out times for one particularly sensitive species, the lowbush blueberry (Vaccinium angustifolium), through the end of the 21st century. The lowbush blueberry’s projected leaf-out date at the end of this century is April 7, about 20 days earlier than this year’s.
While no one knows the specific impacts of the blueberry’s earlier leaf-out on other plants and animals, Primack says there will be consequences. That’s because some of the plants and animals whose life cycles have been interwoven for centuries do not respond to warming temperatures in the same way that others do, essentially throwing the ecosystem out of whack. Insects and plants are responding to warming temperatures similarly (ticks, for example, are emerging earlier to feed on white-footed mice and suburban hikers), but songbirds are not. This disconnect could spell trouble for songbirds if they miss the abundance of insects that accompanies the peak of spring leaf-out. Warmer springs also mean earlier flowering times. Gallinat warns that if species like the lowbush blueberry flower early in response to warmer temperatures, but the insects that help pollinate them don’t have the same response, the reproductive capacity of the lowbush blueberry could suffer. And so could populations of its pollinators, including honeybees, bumblebees, and other insects.