It's largely due to the thick canopy. Forests are usually dark because the trees block much of the incoming sunlight. Since rainforests have a much thicker canopy by default, this means that the vast majority of sunlight never reaches the ground. ... read more
So few plants grow on the floor of the tropical rain forest becausesunlight doesn't really reach the ground. The trees and otherfoliage prevent the sun from shining through. read more