At this time of year, when it’s still frigid at night but daytime temperatures are starting to warm, it may look like trees are just sitting there doing nothing. But, inside their cells, changes are happening and sap is starting to flow, explains Anne T. and Robert M. Bass Professor of Natural Sciences Nathaniel T. Wheelwright.

Enjoy this latest Nature Moments video, and if you want to make your own natural history observations, The Naturalist’s Notebook by Wheelwright and Bernd Heinrich (Storey Publishing, 2017) provides guidance and a systematic format, with 100 percent of royalties going to conservation and environmental education.

Check out more Nature Moments.