SNOW: WINTER’S GIFT TO THE FOREST

The first big snow has arrived at the Harvard Forest, and with it, an insulating blanket that ecologists are learning is key to the forest’s productivity.

Pam Templer, associate professor and director of the PhD program in biogeosciences at Boston University, studies the effects of climate change, particularly in the winter months, on nutrient cycling, productivity, and health of northern forest ecosystems.

 In experiments at the Hubbard Brook Experimental Forest in New Hampshire and the Harvard Forest in Petersham, MA, she and her team dug into the science of winter – literally. In snow removal experiments, the team shoveled off the snow from several plots to determine the effects on trees of reduced snowfall. It was a way to explore how the forest could be affected by reduced snow levels already occurring, and expected to intensify in a warming climate.

Winter, Templer and her team are finding, is a critical time in northern woods. “Traditionally, people thought of winter as a time when everything goes dead,” Templer said in an interview. But nothing is going dead, it is going dormant. Evergreens on a warm day photosynthesize and take up nitrogen. And below the frost line, microbes in the soil are not dead, or even dormant; they just keep cranking along and doing what they do.

Enter the importance of snow. It insulates the soil, so it does not freeze as deeply, and that, the team learned, has implications for the function of trees and forest ecosystems, not only in winter, but also in the next year’s growth.

“In areas that traditionally got snow, trees adapted to that insulating layer on the ground,” Templer said. “You get cold days that are below freezing, but the soil is still above freezing. The snow insulates the soil and the roots.” But without snow, the abundance and diversity of insects in the soil goes down, and trees come spring don’t take up as much nutrients or water in the beginning of the growing season, Templer found.

That lead to increased nitrogen run off, Templer found, and while the trees seem to repair themselves and catch up in their productivity, “if this happened year in and year out, we don’t know what would happen.”

Red oaks, which are more deeply rooted, seem less affected. But maples, with their shallow root system, showed distinct damage.

Based on sap flow, Templer’s team could tell both species were taking up less carbon in the beginning of the growing season – simultaneously reducing the forest’s reduction of the C02 in the atmosphere causing global climate change.

What is the future of winter? At Hubbard Brook, already there are 20 fewer days in winter with snow on the ground, temperatures in winter are up 2.5 degrees in the long term average, and snow pack has shrunk by ten inches, Templer said.

That’s easy right now, amid this first gift of snow, a perfecting blanket of white settled in a quiet, bright beauty here at the Harvard Forest. Let it snow, let it snow. It’s what the forest needs. Not only now, but in the future.