Though not exactly the same, crepuscular rays (also known as god rays) come close to what you are asking for.
a streak of light that seems to radiate from the sun shortly before or after sunset when sunlight shines through a break in the clouds or a notch in the horizon line and illuminates atmospheric haze or dust particles
It's often used as a special effect in games.
Wikipedia includes a list of alternative names, some of which are more idiomatic than the latin derived crepuscular:
- Backstays of the sun – a nautical term, from the fact that backstays that brace the mast of a sailing ship converge in a similar way
- Cloud breaks
- Jacob's Ladder
- Ropes of Maui – (originally. taura a Maui) from the Maori tale of Maui Potiki restraining the sun with ropes to make the days longer
- Shafts of light
- Sun drawing water – from the ancient Greek belief that sunbeams drew water into the sky (an early description of evaporation)
- Volumetric lighting (used by the computer graphics industry)
- God rays (used by the computer graphics industry)
- Fingers of God
(Some links and references in the article.)
As you mention, a singular shaft of light, whether separated from the rest of the sunlight by clouds, annulus (man-made or natural) or through the canopy of a forest is more properly called a sunbeam (Merriam-Webster).
a ray of sunlight
As Andrew Leach mentions and fully explains in his answer, there is precedent for calling this a sheaf or sheafs (or sheaves).
a. Physics and Math. A bundle of rays, lines, etc. all passing through a given point.
But this has two drawbacks with regards to your question.
- It is a fairly technical definition and not commonly understood in every day English.
- You would still have to specify what makes up the sheaf; it cannot be used as a single word in the sense you want.
Walking through the forest, I was awestruck by the beauty of a sheaf.
Walking through the forest, I was awestruck by a beautiful sheaf of sunlight.
There does not appear to be an exact word for sunlight filtered specifically through foliage.