The floor of an undisturbed tropical rain forest usually lacks much vegetation. explain why?

Question

environmental science

Answer 1

no sun falls trough upper layers of vegetation

since primary rain forests consist of tall trees, their branches abubdant with bromeliae and lianas.

those sick undergrowth jungles of east asia are secondary grown in the previously inhabited and agriculcured land, and there has not yet been time for really big trees to grow