On a February day, it may seem as if all the trees and shrubs — except for the evergreens or conifers — are leafless. But a walk in the neighborhood, or a local natural area, will reveal that’s not true.

In my front yard, the brown leaves of witch hazel hang on even as the buds are preparing to open into blooms. At Lakewood Forest Preserve near Wauconda, a shingle oak tree stands in the parkway holding all of its brown and curled leaves on a foggy February day.

This phenomenon, called marcescence, adds a unique dimension to the winter landscape, and gives me something to ponder while taking a walk on a cold, gloomy day.

I knew that northern pin oaks hold their brown leaves throughout winter, but during a recent walk, we discovered so many more signs of marcescence. Brown leaves attached to huge white oaks danced in the wind. The long, brownish-yellow leaves of the sumac were complemented by the persistent red berries on this native shrub growing along the trail. Some dogwood, species, also held steadfastly onto their leaves.

We also noticed a 3-foot-tall shagbark hickory that was holding onto its leaves, which can occur in younger trees. My sister’s Japanese maple is awash with brown curly leaves, even in February. She says that’s not normal for this species, and perhaps it isn’t for sumacs and dogwoods, but it certainly is for the oaks, witch hazels and beeches.

When deciduous trees’ leaves turn green in spring, water and nutrients flow through their vascular systems, which can be related to human blood vessels. In fall, the flow stops, the leaves begin to die and an abscission layer forms at the end of each leaf stalk.

The layer keeps the leaves from being able to hold onto the stalk, and they fall to the forest floor, adding nutrients, and stopping the tree’s growth until spring.

But in marcescent trees, the abscission layer doesn’t form until spring and that’s when their leaves finally fall to the ground.

Scientists aren’t sure why certain tree species hold their leaves until spring.

It could be a way to protect the forming leaf buds from drying up in winter, or a way to add more nutrients to the soil in spring when the leaves decompose beneath the tree. Leaves dropped in autumn by other deciduous trees may get washed away by winter precipitation before they can decay and add nutrients to the forest floor. But that doesn’t explain why other tree species, like ashes and walnuts, drop all their leaves in autumn.

Some scientists speculate that the remaining leaves on trees in winter trap snow, which provides more water in spring.

Another theory suggests the marcescent trees keep deer and other critters away that might eat the buds hidden by the leaves.

It also might be quite noisy as mammals press against the crunchy leaves looking for food. So perhaps they have learned to stay away from such trees in winter to avoid being heard by potential predators.

Wandering along the trail at Lakewood, we noticed some trees had lost some of their leaves, but not all of them. An oak had a large crown of leaves attached, but the rest of its branches were bare. It was as if these plants had made individual decisions on the best way to survive winter and get a headstart in spring.

We realized that like everything else in nature, the falling of leaves is more complicated than we imagined.

With that realization comes a sense of wonder, knowing each species evolves differently to find the best ways to ensure its survival.

Sheryl DeVore has worked as a full-time and freelance reporter, editor and photographer for the Chicago Tribune and its subsidiaries. She’s the author of several books on nature and the environment. Send story ideas and thoughts to sheryldevorewriter@gmail.com.