On average, only 5% of sunlight penetrates a hemlock forest canopy and is available to plants on the forest floor.
(only 5% of sunlight; penetrates; a hemlock forest canopy) (only 5% of sunlight; is; available to plants on the forest floor)
only 5% of sunlight only 5% of sunlight
penetrates is
a hemlock forest canopy
available to plants on the forest floor