It'd block the sun that a good beard could block if a good beard could block sun*
Sci is at Neurotic Physiology today, looking a study oh how much UV radiation protection you really get from a beard. But of course, you can't just use dudes with beards for this. No. No, you need a series of manikin heards with fake facial hair in your garden. For science, you know? Head over and check it out.
*How much wood could a woodchuck chuck?