When the light pours through trees it causes a dappling of highlights and shadows on the scene and can create an interesting effect. In the movie business the grip guys use gobos with patterns cut in them and hold them up between the light source and the scene. They also will move them, so in film it appears as if the wind is blowing the foliage. They call them Cucoloris, Kookaloris, or even cookies and are used frequently.
In photography we really don’t use them often, even though the same technique the grip guys use could be set up in the studio easily. More often, we run into it when shooting beneath tree cover. The “cucoloris effect” is best used to create a dance of positive and negative shadow in your image, integrate them into your composition. They can be tricky to expose properly, best to use standard metering and adjust as needed with exposure compensation.
As I researched this post I realized the phenomenon is not spoken of in photography much at all, but it plays such a large part of the relationship between light and shadow. Embrace the Cucoloris, seek it out and use it to build complexity to your images.