Ancient Forest Society

Why Winter Matters

by Erin Burk

January is often thought of as a quiet month in the forest. Giant sequoias stand dusted with snow and sugar pines have dropped or opened their cones from the summer season. While much of the visible activity of the growing season has passed, winter plays a critical role in the long-term health of these ancient and high-elevation forests. 

In response to cold temperatures and lower light, trees slow their growth and conserve energy. Only physiological processes needed to survive the winter are maintained. Trees conserve and reallocate their resources away from growth processes and toward maintenance, making their survival through the winter possible. In recent years, Ancient Forest Society (AFS) has captured sap flow data showing the substantial decline in giant sequoia water use during the winter months.

Snowfall is especially important for the forests these species call home. A consistent snowpack insulates soils and protects tree roots from extreme temperature fluctuations. Underneath the snowpack, leaf litter decomposes, releasing nutrients into the soil that trees and other plant life will use once the active spring returns. As the snowpack begins to melt, it recharges deeper groundwater reserves and provides a slow and steady release of water that trees rely on. A recent finding from our research indicates that giant sequoias use more of the shallow water stored in soil from winter snowpack in the spring and early summer; once those reserves dry out, the trees begin to draw water from deeper sources. This goes to show that a healthy snowpack in the winter means healthier sequoias though the summer. 

Winter conditions also help regulate forest ecosystems by limiting the spread of certain pests and pathogens. These seasonal checks and balances are particularly important for species already facing pressure from drought, insects, and changing fire regimes. In intact forests, cold winters have long played a role in maintaining this balance. As climate change brings warmer winters and reduced snowpack, many of these processes are being disrupted. Shorter cold periods and declining snowpack can increase stress on trees, making them more vulnerable to drought and insect outbreaks. Protecting these trees means protecting the seasonal patterns they depend on.

Here at AFS, while our field activity diminishes, winter is not an off-season for our staff either. This is our time for processing samples, analyzing data, sharing the results of our critical research, planning upcoming fieldwork, and seeking out new ways to better understand and protect the ancient forest ecosystems that support the iconic species we study. When conditions require, you may even find us tramping a path through the snowy sequoias. And when conditions allow, the AFS team loves taking some time to enjoy the snow at our local ski resorts around Lake Tahoe. During the coldest months, the work—and the forests—remain active.

Thank you for your continued support and for helping us protect ancient forests through every season.

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You can be a part of our inner circle by becoming a member. Ancient trees play a crucial role in the Earth's ecosystem by acting as vital biodiversity hubs, providing habitats for a wide range of species, storing large amounts of carbon, providing critical ecosystem services and enhancing the spiritual and mental well-being of people around the planet. Climate change is rapidly altering the conditions which sustain ancient trees and forests, creating unprecedented threats to their survival. Our goal is to provide scientific insights that can help land managers address these threats. We also aim to inspire people to join in the fight to protect these amazing forests through outreach and education.

By becoming a member you can invest in these valued forests and join us in our mission to study and protect old trees and ancient forests. Your monthly donation will help us achieve these important goals.